Relatively atomic mass formula. How to calculate atomic mass. The isotopic component of a substance affects the relative atomic weight accuracy value

02.11.2019

Dimensioning

Dimensions show the geometric dimensions of objects, the distances and angles between them, the coordinates of individual points. AutoCAD uses 11 types of dimensions, which can be divided into three main types: linear (Fig. 6.8-6.10), radial (Fig. 6.11) and angular (Fig. 6.12). Linear dimensions are divided into horizontal, vertical and parallel, rotated, ordinate, basic and dimensional chains. Below are simple examples of their application.

Rice. 6.8. Horizontal, vertical and parallel dimensions

Rice. 6.9. Basic dimensions

Rice. 6.10. Dimensional chains

Rice. 6.11. Radial dimensions

Rice. 6.12. Angle dimensions

Dimensioning commands are found in the Dimension dropdown menu.
For convenience, you can use the icons on the toolbar of the same name (Fig. 6.13).

Rice. 6.13. Dropdown Menu and Dimension Toolbar

Dimensional images include the following components:

dimension line - a line with arrows at the ends, made parallel to the corresponding measurement. As a rule, dimension lines are placed between extension lines. If there is not enough space on a short dimension line, dimension arrows or text are placed outside, depending on the dimension style settings. For angular dimensions, the dimension line is an arc;
dimensional arrows - arrows, serifs or an arbitrary marker, defined as a block, to indicate the ends of the dimension line;
extension lines are drawn from the object to the dimension line. They can be built perpendicular to it or be inclined. Formed only for linear and angular dimensions (used if the dimension line is outside the object being measured);
dimension text - a text string containing the dimension value and other information (for example, diameter, radius, tolerance). This is an optional element, that is, its output to the picture can be suppressed. It is possible to accept the size automatically calculated by AutoCAD or replace it with other text. If you accept the default text, you can automatically add tolerances to it and enter a prefix and suffix;
callouts are used if the dimension text cannot be placed next to the object;
center marker - a small cross that marks the center of a circle or arc;
axial lines - lines with a break (dash-dotted), intersecting in the center of a circle or arc and dividing it into quadrants.

All lines, arrows, arcs and text elements that make up a dimension will be treated as a single dimension primitive if the associative dimensioning mode is set. Associative dimensions change as the elements being dimensioned change.

Linear dimensions

AutoCAD provides several types of linear dimensioning, which differ in the angle at which the dimension line is drawn.
The DIMLINEAR command allows you to create horizontal, vertical, or rotated dimensions. The command is called from the Dimension > Linear drop-down menu or by clicking on the Linear Dimension icon on the Dimension toolbar.
DIMLINEAR command prompts:
: -press the Enter key to specify an object
Select object to dimension: - select an object to dimension
Specify dimension line location or
: - specify the position of the dimension line

DIMLINEAR command keys:

Mtext - allows you to edit dimension text in the multiline text editor. You can completely change the text or save the measured value using the angle brackets o and optionally add any text before and after the brackets
Text - allows you to edit dimension text. This prompts you to:

Enter dimension text<измеренное значение>: - enter the required text string

Angle - allows you to set the rotation angle of the dimension text. This prompts you to:

Specify angle of dimension text:- specify the rotation angle of the dimension text

Horizontal - determines the horizontal orientation of the size, measures the distance between two points along the X axis;
Vertical - determines the vertical orientation of the size, measures the distance between two points along the Y axis;
Rotated - rotates dimension and extension lines, measures the distance between two points along a given direction in the current UCS. This prompts you to:
<0>: - specify the angle of rotation of the dimension line

Example 6.1. Setting a horizontal dimension

Put down the horizontal size of the rectangle (Fig. 6.14).
Run the DIMLINEAR command by calling it from the Dimension > Linear dropdown menu or by clicking on the Linear Dimension icon on the Dimension toolbar.
Respond to requests:
_DIMLINEAR
Specify first extension line origin or : - specify point 1
Specify second extension line origin:- specify point 2
Specify dimension line location or :- specify point 3
Dimension text = 80

Rice. 6.15. Vertical Dimension

Example 6.3. Setting a rotated dimension

Set the size at a given angle (Fig. 6.16).
Run the DIMLINEAR command by calling it from the drop down menu Dimension >
Respond to requests:
_DIMLINEAR
Specify first extension line origin or : - indicate the beginning of the first extension line
Specify second extension line origin:- indicate the beginning of the second extension line
Dimension text = measured value

Example 6.4. Parallel Dimensioning

Set the size parallel to the measured line of the object (Fig. 6.17).
Run the DIMALIGNED command by calling it from the Dimension > Aligned dropdown menu or by clicking on the Aligned Dimension icon on the Dimension toolbar. Respond to requests:
_DIMALIGNED
Specify first extension line origin or : - specify the beginning of the second extension line
Dimension text = measured value
Specify a second extension line origin or : - indicate the beginning of the next extension line
Dimension text = measured value
Specify a second extension line origin or : - specify point 1
Specify second extension line origin:- specify point 2
Specify dimension line location or :- specify point 5
Dimension text = 120
Run the DIMBASELINE command by calling it from the Dimension > Baseline dropdown menu or by clicking on the Baseline Dimension icon on the Dimension toolbar. Respond to requests:
_DIMBASELINE
Specify a second extension line origin or : - specify point 4
Dimension text = 270
Specify a second extension line origin or : - specify the beginning of the second extension line

Specify a second extension line origin or : - indicate the beginning of the next extension line
Dimension text = measured value
Specify a second extension line origin or : - specify point 1
Specify second extension line origin:- specify point 2
Specify dimension line location or :- specify point 4
Dimension text = 100
Run the DIMCONTINUE command by calling it from the Dimension > Continue dropdown menu or by clicking the Continue Dimension icon on the Dimension toolbar.
Respond to requests:
_DIMCONTINUE
Specify a second extension line origin or : - press the Enter key
Select continued dimension: - press the Enter key to end the command

Rice. 6.19. Setting a consistent dimensional chain

Radial Dimensions

The DIMDIAMETER command plots the diameter of a circle or arc. The command is called from the dropdown menu Dimension > Diameter or by clicking the Diameter Dimension icon on the Dimension toolbar.
DIMDIAMETER command prompts:
Select arc or circle: - select arc or circle
Dimension text = measured value
Specify dimension line location or :- specify the position of the dimension line
When setting a diameter dimension, the default text starts with the sign 0. The command keys allow you to change the dimension text and the angle of the dimension text. Center marks and centerlines automatically appear at the center of an arc or circle when dimensioned outside, and are not applied when dimensioned inside a circle or arc, or when center marks are disabled. It is possible to force the placement of the dimension text and the leader line inside the circle or arc.

Example 6.7. Setting the diameter

Put down two options for the diametrical size on the circle (Fig. 6.20).
Run the DIMDIAMETER command by calling it from the Dimension > Diameter dropdown menu or by clicking the Diameter Dimension icon on the Dimension toolbar. Respond to requests:
_DIMDIAMETER
Select arc or circle: - select point 1 lying on the circle
Dimension text = 180
Specify dimension line location or :

Rice. 6.20. Setting the diameter

The DIMRADIUS command, which allows you to plot the radius of a circle or arc, is called from the Dimension > Radius drop-down menu or by clicking the Radius Dimension icon on the Dimension toolbar.
DIMRADIUS queries are similar to those of the DIMDIAMETER command. By default, when setting the radius, the text starts with the character R .

Example 6.8. Setting the radius

Put down two options for the radial dimension on the arc (Fig. 6.21). Run the DIMRADIUS command by calling it from the Dimension > Radius dropdown menu or by clicking on the Radius Dimension icon on the Dimension toolbar. Respond to requests:
_DIMRADIUS
Select arc or circle: - select point 1 lying on the arc
Dimension text = 90
Specify dimension line location or :- specify the location of the dimension line

Rice. 6.21. Setting the radius

Angle dimensions

The DIMANGULAR command allows you to enter an angular dimension. It is called from the Dimension > Angular dropdown menu or by clicking on the Angular Dimension icon on the Dimension toolbar.
DIMANGULAR command requests:
Select arc, circle, line, or : - select an arc, circle, segment
Select second line: - if the first indication was a segment, you should specify a second segment that is not parallel to the first
Specify dimension arc line location or :
Dimension text = measured value
If the Enter key is pressed in response to the first prompt, then the angular dimension is built from three points and the DIMANGULAR command issues the following prompts:
Specify angle vertex: -select the vertex of the corner
Specify first angle endpoint: - Specify the first endpoint of the angle
Specify second angle endpoint:- specify the second end point of the corner
- specify the location of the dimension line
Dimension text = measured value
When setting an angular dimension, the default text ends with a degree sign °. The command keys allow you to change the dimension text and its angle. When an angle is formed by two non-parallel lines, the dimension arc subtends the angle between them. If, in this case, the arc does not intersect both or one of the dimensioned lines, AutoCAD draws one or two extension lines until it intersects with the dimension arc. The contracted angle is always less than 180°.

Example 6.9. Setting an angular dimension

Put down two options for the angular size (Fig. 6.22). Run the DIMANGULAR command by calling it from the Dimension > Angular dropdown menu or by clicking on the Angular Dimension icon on the Dimension toolbar. Respond to requests:
_DIMANGULAR
Select arc, circle, line, or : - specify point 1
Select second line: - select point 2
Specify dimension arc line location or :- specify the location of the dimension line
Dimension text = 125

Rice. 6.22. Setting an angular dimension

Ordinate dimensions

Ordinal dimensions define the distance along the coordinate axis from the base point to the object being measured (for example, to a hole in a part). The use of such dimensions prevents cumulative errors, since the position of objects is measured from a single base point.
An ordinate dimension consists of an x or y coordinate value and a callout. The X ordinate dimension expresses the distance from the origin of coordinates to the object along the X axis, and the Y ordinate dimension expresses the distance along the Y axis, respectively. If a point is specified, AutoCAD automatically determines which axis to put the ordinate dimension on. This method is called automatic ordinate dimensioning.
The text of an ordinate dimension is positioned along the leader, regardless of the text orientation set by the current dimension style. The command keys allow you to change the dimension text and its angle.
A line leader or each segment of a polyline leader is drawn perpendicular to one of the coordinate axes, so it is advisable to turn on the ORTHO mode.
The DIMORDINATE command allows you to set ordinate dimensions. It is called from the Dimension > Ordinate drop-down menu or by clicking on the Ordinate Dimension icon on the Dimension toolbar.
DIMORDINATE command prompts:
Specify feature location: - specify the position of the element
Specify leader endpoint or :- specify the end point of the callout or the coordinate that needs to be changed; as a result, the orientation of callouts and dimension text will change
Dimension text = measured value
Callouts and explanatory inscriptions
The QLEADER command for drawing a leader is called from the Dimension > Leader drop-down menu or by clicking on the Quick Leader icon on the Dimension toolbar.
QLEADER command prompts:
Specify first leader point, or : - Specify the first point of the leader.

Specify next point: - specify the next leader point
Specify text width<0>: - specify text width
: - enter the first line of text explanation
- enter the next line of explanation text
Enter next line of annotation text:-press the Enter key to end the command
A callout is a line that connects an explanatory inscription in the figure with the object to which it refers. Callouts and explanatory inscriptions are associative, that is, when editing one of these objects, the other one also changes accordingly.
A leader, consisting of straight or spline segments, can be started from any point and from any object in the drawing. All callout properties, its color, lineweight, scale, arrow type, size, etc. are determined by setting the current dimension style for the first dimension arrow.
To connect the explanatory inscription and the callout, a short segment is used, which is called a shelf. Shelves are placed if the deviation from the horizontal position exceeds 15 °. To specify the exact start point of the callout, use object snaps.
Explanatory inscriptions can be multi-line texts, tolerance frames for shape and location of surfaces, or occurrences of blocks. They are either built from scratch or copied from existing explanations.
Texts of explanatory inscriptions are entered line by line at the command line or in the Text Formatting dialog box if Enter was entered at the prompt Enter first line of annotation text : - enter the first line of text explanation
The explanation, leader line and arrow options, as well as the way text is positioned relative to the leader, can be set in the Leader Settings dialog box:

on the Annotation tab shown in fig. 6.23, the type of explanation is set, for which the callout is built. As explanations, multiline text, copies of objects, shape and location tolerance frames, blocks can be used. The Copy an Object option allows you to use an existing object as an explanation without creating a new one. Here you can also specify multiline text modes and set up reuse of the annotation for subsequent callouts;
on the Leader Line & Arrow tab shown in fig. 6.24, the type of leader line is indicated: broken line Straight or spline Spline. In the Arrowhead area, you can select the type of arrow from the drop-down list, and in the Angle Constraints area, set the angle constraints for the callout segments. To ensure that callouts are quickly drawn, you can in the area Number of Points or by clicking on the Quick Dimension icon on the Dimension toolbar
QDIM command prompts:

Select geometry to dimension: - select objects for dimensioning
Select geometry to dimension: - press the Enter key when you have finished selecting objects
: - specify the location of the dimension line
The QDIM command asks only for the contours to be dimensioned, and requires you to select the type of dimensions to be dimensioned by setting the appropriate key.
Example 6.10. Fast dimensioning
Put down the dimensions on the part (Fig. 6.26). Run the QDIM command by calling it from the Dimension > QDIM drop - down menu or by clicking on the Quick Dimension icon on the Dimension toolbar . Respond to requests:
_QDIM
Select geometry to dimension: - select point 1
Select geometry to dimension: - specify point 2
Select geometry to dimension: - specify point 3
Select geometry to dimension: - press the Enter key when you have finished selecting objects
Specify dimension line position, or
: - specify point 4
Rice. 6.26. Fast dimensioning

Answer: Theory: The size on the drawing shows the dimensions of the part or circuit: length, width, circle radius, hole diameter, wire pitch, etc. Dimensions in AutoCAD are needed in order to indicate to the installer, locksmith, or any other person who will manufacture the product according to your drawing - what size this or that element of the drawing should be made, what tolerances to take. In addition, the dimensions on the drawing in AutoCAD or Compass are a tribute to the Soviet era, in which it was customary to indicate the dimensions of parts according to certain rules. These rules are called the Unified System for Design Documentation (ESKD). And to put it simply, the dimensions are nothing more than arrows with numbers. All of you must have seen them at some point.

Practice: Now we will practice the techniques for specifying dimensions on a drawing in AutoCAD. Since almost all parts of the drawing represent some kind of geometric figure, you first need to figure out for yourself how to set dimensions in AutoCAD for such simple shapes as a rectangle, a circle, 2 parallel lines, an angle. To apply dimensions in AutoCAD, there is a special item in the top menu, namely the "Dimensions" item.

If you look at this paragraph, you will see that there are different types of dimensions: linear, parallel, angular, radius, and others. All of them, in fact, are a line with an arrow pointer, as well as a numerical designation of the size above the arrow or inside the arrow (you can change it yourself). But the appearance of the arrow will change depending on which geometric shape you set the size of. Consider the main types dimensions on the drawing.

Linear dimension in drawing (straight line dimension)

In order to dimension in AutoCAD near a straight line, choose :Dimensions-Linear. I prepared a segment in advance, the size of which I want to specify. After the linear dimension is selected, you need to left-click on the left and right ends of the segment once. A preview of the size will appear, which now needs to be raised to the height you want to make the leader line with the size. The size index can be omitted, but in ESKD it is customary to designate the size above the part. We left-click on the part of the screen where you want to place the dimension line, and our size is ready! Now you can not only put dimensions in autocad for a simple line, but also to indicate almost all overall dimensions of parts. To apply the size of the part in AutoCAD, we do exactly the same thing, but now we mark the start and end points of the part, not the lines, with the mouse. There are 2 small remarks here. half of the detail. In this case, we mark the second point with the mouse not at the end of the part, but where you want to end the dimension line. If you have already drawn a dimension line and want to move it, this is easily done using the blue squares that appear when you select a part dimension with the right mouse button. The second important note. How to resize in autocad? AutoCAD set the size (number) automatically. You can change this number in the size properties. To do this, do the following: 1. Select the dimension line with the left mouse button. 2. Right-click on the line with the size to call the menu Properties. I have Properties appeared as a window in the upper right corner of the screen.

3. Scroll down the field with the properties, and find the item there Text, which has a field Text string. That's what we need to resize in autocad. We write in it the value we need. Now the size above the dimension line has changed.

In the same menu, you can set various size properties in AutoCAD, such as font, size, alignment, color, arrow type, and more. I will not describe all the properties in detail here. Who needs it - see the menu Properties at the size. Circle size in AutoCAD (radius or diameter). In fact, this is the same size, since the radius is half the diameter. Set the size of a pre-prepared circle in AutoCAD. Choose: Dimensions-radius mustache (or Dimensions-Diameter). Select with the left mouse button 2 points on the circle in the case of a diameter, or the center of the circle + one of the points on the circle in the case of a radius. It turns out one of the options:

The size (number) above the line changes in the same way as in the case of a linear size: PropertiesText - Text string. Parallel dimension in AutoCAD. Now let's try to set a parallel dimension - a dimension between two parallel lines in the drawing. For a change, I drew a rectangle, and I want to set the size between its two parallel sides. In the top menu of AutoCAD, select: Dimensions-Parallel.

With the left mouse button, select 2 lines of the rectangle in turn. We get the size between two parallel sides:

In principle, the example is not very successful, since a linear size could be dispensed with here. But if you need to put a size in AutoCAD between two parallel lines that are not connected to each other in any way, then in this case the parallel size will be simply irreplaceable. How to change the number 40, we already know (read above) Angular dimension in AutoCAD The penultimate example for today is the designation of the angular dimension. Let's say we have a triangle, and we need to specify in degrees the value of one of its angles. Choose: Dimensions-Angular. Then, with the left mouse button, select two adjacent sides of the triangle, between which you need to set the size of the corner. Click Enter, and our angular size is ready! On the drawing it looks like this:

I talked about the most common types of dimensions in AutoCAD, and how they can be put on the drawing. Other types of sizes are less commonly used. When you choose a size from the menu Dimensions, AutoCAD offers tooltips on a blue background for reading, looking at which you can quickly figure out what to select and where to click to specify the size of the element. Multileader in AutoCAD: But what about the leader dimensions common in drawings, with the help of which extension dimensions are placed where another type of size does not fit, or where there is simply no place to specify it?

This is done like this: Dimensions-Multileader, put the left mouse button on the place where the size arrow will point, and drag the multileader to the place on the screen where I have a shelf and it says "Leader". AutoCAD will immediately prompt you to enter your multileader text.

To measure the mass of an atom, the relative atomic mass is used, which is expressed in atomic mass units (a.m.u.). The relative molecular mass is the sum of the relative atomic masses of substances.

Concepts

To understand what relative atomic mass is in chemistry, it should be understood that the absolute mass of an atom is too small to be expressed in grams, and even more so in kilograms. Therefore, in modern chemistry, 1/12 of the mass of carbon is taken as an atomic mass unit (amu). The relative atomic mass is equal to the ratio of the absolute mass to 1/12 of the absolute mass of carbon. In other words, the relative mass reflects how many times the mass of an atom of a particular substance exceeds 1/12 of the mass of a carbon atom. For example, the relative mass of nitrogen is 14, i.e. the nitrogen atom contains 14 a. e. m. or 14 times more than 1/12 of a carbon atom.

Rice. 1. Atoms and molecules.

Among all the elements, hydrogen is the lightest, its mass is 1 unit. The heaviest atoms have a mass of 300 amu. eat.

Molecular weight - a value showing how many times the mass of a molecule exceeds 1/12 of the mass of carbon. Also expressed in a. e. m. The mass of a molecule is made up of the mass of atoms, therefore, to calculate the relative molecular mass, it is necessary to add the masses of the atoms of a substance. For example, the relative molecular weight of water is 18. This value is the sum of the relative atomic masses of two hydrogen atoms (2) and one oxygen atom (16).

Rice. 2. Carbon in the periodic table.

As you can see, these two concepts have several common characteristics:

the relative atomic and molecular masses of a substance are dimensionless quantities;
relative atomic mass is denoted A r , molecular mass - M r ;
the unit of measurement is the same in both cases - a. eat.

The molar and molecular masses coincide numerically, but differ in dimension. Molar mass is the ratio of the mass of a substance to the number of moles. It reflects the mass of one mole, which is equal to Avogadro's number, i.e. 6.02 ⋅ 10 23 . For example, 1 mol of water weighs 18 g / mol, and M r (H 2 O) \u003d 18 a. e.m. (18 times heavier than one atomic mass unit).

How to calculate

To express the relative atomic mass mathematically, one should determine that 1/2 part of carbon or one atomic mass unit is equal to 1.66⋅10 −24 g. Therefore, the formula for the relative atomic mass is as follows:

A r (X) = m a (X) / 1.66⋅10 −24 ,

where m a is the absolute atomic mass of the substance.

The relative atomic mass of chemical elements is indicated in the periodic table of Mendeleev, so it does not need to be calculated independently when solving problems. Relative atomic masses are usually rounded to integers. The exception is chlorine. The mass of its atoms is 35.5.

It should be noted that when calculating the relative atomic mass of elements that have isotopes, their average value is taken into account. The atomic mass in this case is calculated as follows:

A r = ΣA r,i n i ,

where A r,i is the relative atomic mass of isotopes, n i is the content of isotopes in natural mixtures.

For example, oxygen has three isotopes - 16 O, 17 O, 18 O. Their relative mass is 15.995, 16.999, 17.999, and their content in natural mixtures is 99.759%, 0.037%, 0.204%, respectively. Dividing the percentages by 100 and substituting the values, we get:

A r = 15.995 ∙ 0.99759 + 16.999 ∙ 0.00037 + 17.999 ∙ 0.00204 = 15.999 amu

Referring to the periodic table, it is easy to find this value in an oxygen cell.

Rice. 3. Periodic table.

Relative molecular weight - the sum of the masses of the atoms of a substance:

Symbol indices are taken into account when determining the relative molecular weight value. For example, the calculation of the mass of H 2 CO 3 is as follows:

M r \u003d 1 ∙ 2 + 12 + 16 ∙ 3 \u003d 62 a. eat.

Knowing the relative molecular weight, one can calculate the relative density of one gas from the second, i.e. determine how many times one gaseous substance is heavier than the second. For this, the equation D (y) x \u003d M r (x) / M r (y) is used.

What have we learned?

From the 8th grade lesson, we learned about the relative atomic and molecular mass. The unit of relative atomic mass is 1/12 of the mass of carbon, equal to 1.66⋅10 −24 g. To calculate the mass, it is necessary to divide the absolute atomic mass of a substance by the atomic mass unit (a.m.u.). The value of the relative atomic mass is indicated in the periodic system of Mendeleev in each cell of the element. The molecular weight of a substance is the sum of the relative atomic masses of the elements.

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Currently, the atomic mass unit is taken equal to 1/12 of the mass of a neutral atom of the most common carbon isotope 12 C, so the atomic mass of this isotope is, by definition, exactly 12. The difference between the atomic mass of an isotope and its mass number is called the mass excess (usually expressed in MeV ). It can be both positive and negative; the reason for its occurrence is the nonlinear dependence of the binding energy of nuclei on the number of protons and neutrons, as well as the difference in the masses of the proton and neutron.

The dependence of the atomic mass of the isotope on the mass number is as follows: the excess mass is positive for hydrogen-1, with increasing mass number it decreases and becomes negative until a minimum is reached for iron-56, then it begins to grow and increases to positive values for heavy nuclides. This corresponds to the fact that the fission of nuclei heavier than iron releases energy, while the fission of light nuclei requires energy. On the contrary, the fusion of nuclei lighter than iron releases energy, while the fusion of elements heavier than iron requires additional energy.

Story

Until the 1960s, atomic mass was determined so that the nuclide oxygen-16 had an atomic mass of 16 (oxygen scale). However, the ratio of oxygen-17 to oxygen-18 in natural oxygen, which was also used in atomic mass calculations, resulted in two different tables of atomic masses. Chemists used a scale based on the fact that a natural mixture of oxygen isotopes should have an atomic mass of 16, while physicists assigned the same number of 16 to the atomic mass of the most abundant oxygen isotope (having eight protons and eight neutrons).

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See what "Atomic mass" is in other dictionaries:

The mass of an atom, expressed in atomic mass units. The atomic mass is less than the sum of the masses of the particles that make up the atom (protons, neutrons, electrons) by an amount determined by the energy of their interaction (see, for example, Mass Defect) ... Big Encyclopedic Dictionary

Atomic mass is the mass of an atom of a chemical element, expressed in atomic mass units (a.m.u.). For 1 amu 1/12 of the mass of a carbon isotope with an atomic mass of 12 is adopted. 1 amu = 1.6605655 10 27 kg. Atomic mass is made up of the masses of all protons and... Nuclear power terms

atomic mass- is the mass of the element's atoms, expressed in atomic mass units. The mass of that amount of an element that contains the same number of atoms as 12 g of the 12C isotope. General chemistry: textbook / A. V. Zholnin ... Chemical terms

ATOMIC MASS is a dimensionless quantity. A. m. atom mass chem. element, expressed in atomic units (see) ... Great Polytechnic Encyclopedia

- (obsolete term atomic weight), the relative value of the mass of an atom, expressed in atomic mass units (amu). A. m. is less than the sum of the masses of the constituent atom h q per mass defect. A. m. was taken by D. I. Mendeleev for the main. characteristic of the element at ... ... Physical Encyclopedia

atomic mass- — [Ya.N. Luginsky, M.S. Fezi Zhilinskaya, Yu.S. Kabirov. English-Russian Dictionary of Electrical Engineering and Power Industry, Moscow, 1999] Electrical engineering topics, basic concepts EN atomic weight ... Technical Translator's Handbook

The mass of an atom, expressed in atomic mass units. For the atomic mass of a chemical element consisting of a mixture of isotopes, take the average value of the atomic mass of isotopes, taking into account their percentage (this value is given in the periodic ... ... encyclopedic Dictionary

The concept of this quantity underwent long-term changes in accordance with the change in the idea of atoms. According to Dalton's theory (1803), all atoms of the same chemical element are identical and its atomic mass is a number equal to ... ... Collier Encyclopedia

atomic mass- santykinė atominė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Cheminio elemento vidutinės masės ir nuklido ¹²C atomo masės 1/12 dalies dalmuo. atitikmenys: engl. atomic mass; atomic weight; relative atomic mass vok. Atomasse …

atomic mass- santykinė atominė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Vidutinės elemento atomų masės ir 1/12 nuklido ¹²C atomo masės dalmuo. atitikmenys: engl. atomic mass; atomic weight; relative atomic mass vok. Atomasse, f;… … Penkiakalbis aiskinamasis metrologijos terminų žodynas

The masses of atoms and molecules are very small, so it is convenient to choose the mass of one of the atoms as a unit of measurement and express the masses of the remaining atoms relative to it. This is exactly what the founder of the atomic theory Dalton did, who compiled a table of atomic masses, taking the mass of a hydrogen atom as a unit.

Until 1961, in physics, 1/16 of the mass of an oxygen atom 16O was taken as an atomic mass unit (abbreviated a.m.u.), and in chemistry, 1/16 of the average atomic mass of natural oxygen, which is a mixture of three isotopes. The chemical mass unit was 0.03% larger than the physical one.

At present, a unified measurement system has been adopted in physics and chemistry. 1/12 of the mass of the 12C carbon atom was chosen as the standard unit of atomic mass.

1 amu \u003d 1/12 m (12 C) \u003d 1.66057 × 10-27 kg \u003d 1.66057 × 10-24 g.

When calculating the relative atomic mass, the abundance of isotopes of elements in the earth's crust is taken into account. For example, chlorine has two isotopes 35Cl (75.5%) and 37Cl (24.5%). The relative atomic mass of chlorine is:

Ar(Cl) = (0.755xm(35Cl) + 0.245xm(37Cl)) / (1/12xm(12C) = 35.5.

From the definition of relative atomic mass it follows that the average absolute mass of an atom is equal to the relative atomic mass times the amu:

m(Cl) = 35.5 × 1.66057 × 10-24 = 5.89 × 10-23 g.

Examples of problem solving

Relative atomic and molecular masses

This calculator is designed to calculate the atomic mass of elements.

Atomic mass(also called relative atomic mass) Is the value of the mass of one atom of a substance. Relative atomic mass is expressed in units of atomic mass. Relative atomic mass distinctive(True) weight atom. At the same time, the actual mass of an atom is too small and therefore unsuitable for practical use.

The atomic mass of a substance affects the amount protons and neutrons in the nucleus of an atom.

The mass of the electrons is ignored as it is very small.

To determine the atomic mass of a substance, you must enter the following information:

Number of protons- how many protons are in the nucleus of a substance;
Number of neutrons How many neutrons are in the nucleus of matter.

Based on these data, the calculator will calculate the atomic mass of the substance, expressed in units of atomic mass.

Table of chemical elements and their atomic mass

hydrogen	H	1,0079	nickel	There is no	58,70
helium	is he	4,0026	baker	Cu	63,546
lithium	Li	6941	zinc	Zn	65,38
beryllium	be	9,01218	Gaul	Georgia	69,72
Bor	AT	10,81	Germany	G.E.	72,59
carbon	With	12,011	arsenic	as	74,9216
nitrogen	N	14,0067	selenium	are	78,96
oxygen	about	15,9994	Bromine	bromine	79904
fluoride	F	18,99840	krypton	Cr	83,80
neon	not	20,179	rubidium	Rb	85,4678
sodium	on the	22,98977	strontium	erased	87,62
magnesium	mg	24,305	yttrium	Y	88,9059
aluminum	Al	26,98154	zirconium	Zr	91,22
niobium	Nb	92,9064	Nobel	not	255
molybdenum	Mo	95,94	Lawrence	lr	256
technetium	Ts	98,9062	Kurchatovy	ka	261
ruthenium	Ru	101,07	*	*	*
rhodium	rhesus	102.9055	*	*	*
palladium	Pd	106,4	*	*	*
silver	Ag	107 868	*	*	*
silicone	you	28,086	cadmium	CD	112,40
phosphorus	P	30,97376	India		114,82
sulfur		32,06	tin	sn	118,69
chlorine	Cl	35,453	antimony	Sb	121,75
argon	Arkansas	39,948	tellurium	these	127,60
potassium	To	39,098	iodine	I	126,904
calcium	California	40,08	xenon	Xe	131,30
scandium	South Carolina	44,9559	cesium	Cs	132.9054
Titanium	these	47,90	barium	ba	137,34
vanadium		50,9414	lanthanum	la	138.9055
chromium	Cr	51,996	cerium	Ce	140,12
manganese	Minnesota	54,9380	Praseodym	Pr	140.9077
iron	Fe	55,847	I do not	Nd	144,24
cobalt	Co.	58,9332	promethium	evenings
Samaria	sm	150,4	bismuth	would	208.9804
europium	European Union	151,96	Polonium	after	209
gadolinium	G-d	157,25	ASTAT	in	210
terbium	Tb	158.9254	radon	Rn	222
dysprosium	du	$ 16,50	France	fr	223
Holmium	hey	164.9304	radius	R	226.0254
erbium	Er	167,26	actinium	alternating current	227
thulium	Tm	168.9342	thorium	th	232.0381
ytterbium	Yb	173,04	protactinium	Pennsylvania	231.0359
Lutetia	Lu	174,97	Uranus	U	238,029
hafnium	high frequency	178,49	neptunium	Np	237.0482
tantalum	This	180.9479	plutonium	Pu	244
tungsten	W	183,85	America	Am	243
rhenium	re	186,207	curie	cm	247
osmium	OS	190,2	Berkeley	B.K.	247
iridium	infrared	192,22	California	compare	251
platinum	Pt	195,09	Einstein	es	254
gold	Au	196.9665	fermi	fm	257
mercury	mercury	200,59	Mendelevy	Maryland	258
thallium	Tl	204,37	*	*	*
Lead	Pb	207,2	*	*	*

Relative atomic mass of an element

Task status:

Determine the mass of the oxygen molecule.

task number. 4.1.2 from the "Collection of problems of preparation for the upcoming exams in physics of USPTU"

information:

Decision:

Consider a molecular oxygen molecule $\nu$ (arbitrary number).

Recall that the oxygen formula is O2.

To find the mass (\m) of a given amount of oxygen, the molecular weight of oxygen $M$ is multiplied by the number of moles $\nu$.

Using the periodic table, it is easy to establish that the molar mass of oxygen is \ (M \) 32 g / mol or 0.032 kg / mol.

In one mole, the number of avogadro molecules \ (N_A \) and v \ (\ nu \) mol - v \ (\ nu \) is sometimes greater, i.e.

To find the mass of one molecule \ (m_0 \), the total mass \ (m \) must be divided by the number of molecules \ (N \).

\[(m_0)=\frac(m)(N)\]

\[(m_0)=\frac((\nu\cdot M))((\nu\cdot(N_A)))\]

\((M_0)=\frac(M)(((N_A)))\]

Avogadro's number (N_A1) is a tabular value equal to 6.022 1023 mol-1.

We perform calculations:

\[(M_0) = \frac ((0.032)) ((6.022\cdot ((10) * (23)))) = 5.3\cdot (10^(-26)) \; = 5.3 kg\cdot(10^(-23))\; r\]

Answer: 5.3 10-23

If you don't understand the solution, and if you have any questions or find a bug, you can leave a comment below.

Atoms are very small and very small. If we express the mass of an atom of a chemical element in grams, then this will be a number for which the comma is more than twenty zeros.

Therefore, measuring the mass of atoms in grams is inappropriate.

However, if we take a very small mass per unit, all other small masses can be expressed as a ratio between that unit. 1/12 of the mass of a carbon atom is chosen as the unit for measuring the mass of an atom.

It is called 1/12 of the mass of a carbon atom. atomic mass(Ae.

Atomic mass formula

Relative atomic mass the value is equal to the ratio of the actual mass of an atom of a particular chemical element to 1/12 of the actual mass of a carbon atom. This is an infinite quantity, since the two masses are separated.

Ar = math. / (1/12) mug.

However, absolute atomic mass is equal to the relative value and has the measurement unit amu.

This means that the relative atomic mass indicates how many times the mass of a given atom is greater than 1/12 of a carbon atom. If an Ar atom = 12, then its mass is 12 times greater than 1/12 of the mass of a carbon atom, or, in other words, 12 atomic mass units.

It can only be for carbon (C). On the hydrogen atom (H) Ar = 1. This means that its mass is equal to the mass of 1/12 parts of the mass of the carbon atom. For oxygen (O), the relative atomic mass is 16 amu. This means that an oxygen atom is 16 times larger than 1/12 of a carbon atom, it has 16 atomic mass units.

The lightest element is hydrogen. Its mass is about 1 amu. On the heaviest atoms, the mass approaches 300 amu.

Usually, for each chemical element, its value is the absolute mass of atoms, expressed as a.

For example.

The value of atomic mass units is recorded in the periodic table.

Concept used for molecules relative molecular weight (g). Relative molecular weight indicates how many times the mass of a molecule is greater than 1/12 of the mass of a carbon atom. However, since the mass of a molecule is equal to the sum of the masses of its atomic atoms, the relative molecular mass can be found simply by adding the relative masses of those atoms.

For example, a water molecule (H2O) contains two hydrogen atoms with Ar = 1 and one oxygen atom with Ar = 16. Therefore, gentleman (H2O) = 18.

Many substances have a non-molecular structure, such as metals. In this case, their relative molecular weight is equal to their relative atomic weight.

Chemistry is called a significant amount mass fraction of a chemical element in a molecule or substance.

It shows how much relative molecular weight belongs to this element. For example, in water, hydrogen has 2 parts (as both atoms) and oxygen 16. This means that when hydrogen is mixed with 1 kg and 8 kg of oxygen weight, they react without leaving any residue. The mass fraction of hydrogen is 2/18 = 1/9, and the oxygen content is 16/18 = 8/9.

microbalance otherwise support, atomic equilibrium(English microbial or English nanotubes) is a term referring to:

a large group of analytical instruments, the accuracy of which measures mass from one to several hundred micrograms;
a special high-precision instrument that allows you to measure the mass of objects up to 0.1 ng (nanovesy).

description

One of the first references to the microglobuk is from 1910, when William Ramsay was informed of how much it had evolved, allowing weights in the 0.1mm3 body range to 10-9g (1ng) to be determined.

Nowadays, the term "microbial" is more commonly used to refer to devices that measure and determine changes in mass in the microgram (10-6 grams) range. Microbiologists have entered the practice of modern research and industrial laboratories and have been produced in different versions with different sensitivities and corresponding costs.

At the same time, a measurement technique is being developed in the area of nanograms.

chemistry. how to find relative atomic mass?

When we talk about measuring mass at the nanogram level, which is important for measuring the mass of atoms, molecules or clusters, we first consider mass spectrometry.

In this case, it should be borne in mind that the measurement of mass using this method implies the need to convert weighing objects into ions, which is sometimes very undesirable. This is not necessary when using another practically important and widely used device for accurate measurement of bulk quartz microbes, the mechanism of action of which is described in the corresponding article.