What is Relative Atomic Mass and Molecular Mass?

Since the actual mass of atoms is very small, it would be very troublesome to calculate them by their actual mass, for example, the actual mass of a hydrogen atom is kilograms, (limited to the format, 10 (-27) represents scientific notation, meaning the power of 10 to the 27th power, the same below), and the mass of an oxygen atom is kilograms. The mass of one carbon-12 atom is kilograms. So when we calculate the mass of a water molecule, it is extremely inconvenient to calculate (a water molecule is made up of two hydrogen atoms and one oxygen atom).

This is even more cumbersome when calculating the mass of other, more complex molecules. Therefore, it is internationally stipulated that the relative atomic mass and relative molecular mass are used to express the mass relationship between atoms and molecules. Internationally, the mass of a carbon-12 atom is divided into 12 equal parts, (there are several kinds of carbon atoms, among which there is a carbon atom that contains 6 protons and 6 neutrons in its nucleus, which adds up to 12, so it is called carbon-12.)

Of course, there are others such as carbon-14, which contains 6 neutrons and 8 protons, which add up to 14. The reason why carbon-12 is chosen instead of carbon-14 is that when carbon-12 atoms are selected as the standard, the relative atomic masses of other atoms are close to integers, which is easy to remember and use). The quality of that every bit is:

Kilogram. The result of comparing the actual mass of some other atom with this number is called the relative atomic mass of that atom. For example, the relative atomic mass of an oxygen atom is calculated as:

Approx.), i.e., the relative atomic mass of the oxygen atom is about 16, and we use 16 in our calculations. It's much simpler that way.

The relative atomic masses of other atoms are also calculated in the same way.

The relative atomic mass has a unit, and its unit is "1", but it is often omitted.

A molecule is made up of atoms, and the relative molecular mass of each atom that makes up the molecule (multiplied by the number of atoms in the molecule) is added to give the relative molecular mass. The unit is also "1".

From the above discussion, it can be seen that neither the relative atomic mass nor the relative molecular mass is the actual mass of the atom and the molecule itself, but a relative numerical value. But with them, we can save a lot of computational headaches.

The relative atomic mass is the relative mass based on the atomic mass of carbon-12, that is, the molecular mass obtained by dividing the actual atomic mass by the atomic mass of carbon-12.

To learn chemistry well, you should pay attention to the following points.

1. Chemical test operation process and precautions, as well as various instruments. Exams are coming.

2. The periodic table of elements is commonly used to remember.

3. Chemical reaction equation This is easy to understand as long as you pay attention to life Many people find it difficult to memorize the equation In fact, you don't need to memorize it You just need to combine it with real life to know what he generates when he reacts In addition to the equilibrium on both sides of the equation, the law of the immortality of matter can be written out and then balanced by yourself.

I didn't spend time memorizing equations when I studied chemistry before, and it was all about understanding, otherwise how would I remember so many equations, especially if I didn't learn them, I had to rely on the above methods to write them.

In the past, chemistry was very good, but now I can't use it at all if I don't have chemistry-related majors in college, but it's good to learn it, I feel that there is a problem with Chinese education, and there is no need to learn knowledge like this, which is not necessary for life, so it is so difficult to learn, and it makes students have a heavy burden, and it should be used as an elective course for interested students to choose.

One-twelfth of a carbon atom is called a relative mass. The relative mass of an atom is the relative atomic mass and can be found in the periodic table. The relative mass of a molecule is the relative molecular mass, which can be obtained by adding up the relative atomic masses of the atoms in the molecule.

The comparison of 1 12 of the carbon atom with other atoms is the atomic mass.

1. The definitions are different. Relative atomic mass refers to the ratio of the average atomic mass of any atom to the 1 12 atomic mass of a carbon-12 atomic mass based on 1 12, which is called the relative atomic mass of the atom, and the relative molecular mass refers to the sum of the relative atomic masses of each atom in the chemical formula.

2. The description object is different. The object described by relative atomic mass is a single atom, whereas the object described by relative molecular mass is a molecule consisting of two or more atoms.

3. The calculation method is different. Relative atomic mass = number of protons + number of neutrons, while relative molecular mass = sum of the relative molecular masses of the individual atoms in the molecule.

Relative atomic mass(ar) is a way to calculate the atomic mass, which refers to the ratio of the true mass of any atom to the mass of a carbon-12 atom of 1 12 using 1 12 as the standard, which is called the relative atomic mass of the atom. Atomic weight.

As a unit of mass, the symbol u, it is defined as 1 12 of the atomic mass of carbon.

Relative molecular weight(Relative molecular mass) refers to the sum of the relative atomic masses (Ar) of each atom in the chemical formula, represented by the symbol MR, and the unit is 1.

So the difference between the two is that in one molecule of a compound, the latter is the sum of the former.

1. The definitions are different.

Relative atomic mass: refers to the ratio of the average atomic mass of any atom to the 1 12 atomic mass of a carbon-12 atom using 1 12 of the atomic mass of a carbon-12 as the standard, which is called the relative atomic mass of the atom.

The atomic weight is a unit of mass, the symbol u, which is defined as 12 12 of the atomic mass of carbon.

Relative molecular mass (relativemolecularmass): refers to the sum of the relative atomic masses (Ar) of each leaky atom in the chemical formula, denoted by the symbol MR, and the unit is 1.

It can be understood that the relative molecular mass is the sum of the relative molecular mass of each atom in the molecule, that is, the difference between the relative molecular mass and the relative molecular mass is the difference between the whole and the parts.

2. The description object is different.

The object described by relative atomic mass is a single atom, including a single metal atom and a single non-metal atom.

Relative molecular mass describes an object that is a molecule made up of two or more atoms.

It can be a combination of non-metallic and non-metallic atoms, a combination of metallic and non-metallic atoms, or a combination of metallic and metallic atoms.

3. The calculation method is different.

Relative atomic mass = number of protons + number of neutrons.

Relative molecular mass = sum of the relative molecular masses of the individual atoms in the molecule.

Relative atomic mass = mass of a certain atom (1 12) = mass of the nucleus + mass of electrons outside the nucleus [(1 12]mc= mass of protons + mass of neutrons (1 12) mc = number of protons + number of neutrons. ”

Relative atomic mass is a way to calculate the mass of an atom, because the actual mass of atoms is very small, it would be very troublesome if people used their actual mass to calculate, for example, the actual mass of a hydrogen atom is kilograms, and the mass of an oxygen atom is kilograms. The mass of one carbon-12 atom is kilograms.

The relative atomic mass is the ratio of the atomic mass of an element to the mass of a carbon-12 atom.

The relative atomic mass of common atoms is something to keep in mind, for example, the relative atomic mass of h is 1, and the relative atomic mass of o is 16.

Relative atomic Mass = Atomic Mass of a carbon atom (1 12), e.g. the atomic mass of h is , the atomic mass of c is , then the relative atomic mass of h is , note that there is no decimal in the relative atomic mass, only an integer.

The mass fraction of common elements in chemistry is shown in the table below

The international basic unit of relative atomic mass is 1. The concept of relative atomic reifite mega is based on the mass of a carbon atom (a carbon atom with 6 protons and 6 neutrons in the nucleus, i.e., c-12) 1 12 (approximate as a standard, the ratio of the mass of other atoms to its ratio is the relative atomic mass of such atoms).

Relative atomic mass is not measured in our stupid unit of mass. Rather, it is the atomic mass compared with the carbon atom.

Relative atomic mass refers to the ratio of the true mass of any atom to the mass of a carbon-12 atom of 1 12 based on the ratio of 1 12 of the atomic mass of a carbon-12 atom to the relative atomic mass of the atom. Just like the hydrogen atom, the relative atomic mass is 1. That is to say, the mass of the Chunsun hydrogen atom is equivalent to the mass of a carbon atom 1 12.

The relative atomic masses of common elements are as follows: Hydrogen H: 1, Oxygen O:

16, C: 12, N: 14, Na:

23, Mg: 24, Fe: 56, Si:

28, phosphorus p: 31, potassium k: 39, zinc zn:

65, manganese Mn: 55, bromine br: 80, iodine I:

127, barium ba: 137 etc. 4.