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Atomic Mass

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  • Last Updated : 02 Sep, 2022
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The atomic mass of an element is the average mass of the atoms in an element, calculated in Atomic Mass Units (amu) or Daltons. Unified atomic mass units are used to measure the atomic mass of elements. In terms of weight, one unified atomic mass unit is equal to one-twelfth of the mass of a Carbon-12 atom when it is at rest. The atomic mass of a given element is almost equal to its mass number since protons and neutrons make up almost all of the mass of the given atom. The atomic mass is also used in the classification of different isotopes of the same element, e.g. in the case of isotopes of hydrogen, Carbon, neon, etc.

Atomic Mass

 

What is Atomic Mass?

Atomic mass of an element is defined as the total mass of one atom of that element. The average mass of an element’s atoms expressed in atomic mass units is known as its atomic mass (amu, also known as daltons, D). The atomic number can also be called by the terms atomic weight.

The mass of each isotope is multiplied by its abundance to produce the relative atomic mass, which is a weighted average of all the isotopes of that element. For example, one Carbon atom has just six protons and typically six neutrons in its nucleus, thus its atomic mass should be roughly 12 amu. 

Atomic mass units were created based on the masses of protons and neutrons. This is much simpler than stating that a proton or neutron weighs 1/167000000000000000000000th of a gram. Perhaps smaller than electrons, protons have a mass that is 1,836 times more than that of an electron.

List of Atomic Mass of First 30 Elements

Here is the table showing the first 30 elements of the periodic table with their atomic masses and atomic number:

Atomic Number

Elements

Symbol

Atomic Mass (in amu)

1

Hydrogen

H

1.008

2

Helium

He

4.0026

3

Lithium

Li

6.94

4

Beryllium

Be

9.0122

5

Boron

10.81

6

Carbon

C

12.011

7

Nitrogen

N

14.007

8

Oxygen

O

15.999

9

Fluorine

F

18.998

10

Neon

Ne

20.18

11

Sodium

Na

22.99

12

Magnesium

Mg

24.305

13

Aluminium

Al

26.982

14

Silicon

Si

28.085

15

Phosphorus

P

30.974

16

Sulfur

S

32.06

17

Chlorine

Cl

35.45

18

Argon

Ar

39.948

19

Potassium

K

39.098

20

Calcium

Ca

40.078

21

Scandium

Sc

44.956

22

Titanium

Ti

47.867

23

Vanadium

V

50.942

24

Chromium

Cr

51.996

25

Manganese

Mn

54.938

26

Iron

Fe

55.845

27

Cobalt

Co

58.933

28

Nickel

Ni

58.693

29

Copper

Cu

63.546

30

Zinc

Zn

65.38

Atomic Number

An element’s atomic number is determined by how many protons are found in one of its atoms. Each atom in an element has precisely the same number of protons. For instance, the atomic number of carbon is “6” since all carbon atoms have six protons.

Regardless of the presence of neutrons, elements are classified according to the number of protons in their nuclei. Uncharged subatomic particles known as neutrons are stable when contained in an atomic nucleus. Except for hydrogen, all other elements’ atoms have neutrons in the nucleus. Hence, 

Atomic Number = Number of Protons in an atom

Mass Number

The total number of protons and neutrons in an atom’s nucleus is known as the mass number. Consequently, an atom of carbon will have an exact mass of 12 if its nucleus contains 6 protons and 6 neutrons. 

The difference between the mass number and the atomic mass of an element is that a mass number is a whole number obtained by the addition of a number of protons and neutrons. While the atomic mass or atomic weight is the average number of protons and neutrons in an element for all of its isotopes.

The formula below can be used to determine the mass number of an atom of a specific element when looking at the periodic table of elements:

Mass Number = Number of Protons + Number of Neutrons

How to calculate the Atomic Mass?

Here are three ways to determine the Atomic Mass, depending on the given conditions:

  • By looking up to the atomic mass on the periodic table- In the periodic table digit of an atomic mass is usually marked under the representation of an element. Like Hydrogen 1u, Helium 3u.
  • Adding the Mass of Protons and Neutrons – The total number of protons and neutrons in an atomic nucleus gives the mass number.
  • Weighted Average for All Atoms of an Element – The weighted average of each element’s isotopes, grounded in nature by their abundance, is the atomic weight of that element. These recommendations can be used to calculate the atomic mass of the component. A list of isotopes with natural abundance and mass is given a percentage or decimal value. Each isotope’s abundance is multiplied by its mass. Divide the solution by 100 and add the findings if isotope abundance is present.

Molecular Mass

The atomic masses of the constituent atoms that make up a compound are added to determine its molecular mass.

The mass a molecule carries is known as its molecular mass, additionally known as molecular weight. It can be computed by summing the masses of all the atoms in the molecule and multiplying the result by the number of the element’s atoms. One oxygen atom and two hydrogen atoms, for instance, make up water. A water molecule’s mass is determined by multiplying its average hydrogen atomic mass by two and adding its average oxygen atomic mass. The atoms that make up the molecule are what define an element’s molecular mass.

FAQs based on Atomic Mass of Elements 

Question 1: What is atomic mass?

Answer:

The mass of a single atom in a chemical element is known as its atomic mass. It involves the masses of protons, neutrons, and electrons, the three atomic subatomic particles.

Question 2: What is the significance of atomic mass?

Answers:

The fundamental physical property of matter is mass. The atomic mass refers to the mass of an atom or a molecule. The atomic mass is used to determine the average mass of atoms and molecules as well as to solve stoichiometry problems.

Question 3: What is one amu?

Answer:

1 a.m.u is defined as the average of the rest mass of proton and neutron, and is equal to 1.67377 × 10-27 kg.

Question 4: Why was carbon-12 selected as the reference element for calculating atomic mass?

Answer:

Because it is the only atom with the same whole-number mass as the amu scale, carbon-12 is utilised in amu.

Question 5: What is an atom consist of?

Answer:

The three main types of particles that make up an atom are protons, electrons, and neutrons.

Question 6: What is the atomic mass number?

Answer:

The total number of protons and neutrons (together known as nucleons) in an atomic nucleus is the mass number.

Question 7: What is the atomic mass of Sodium?

Answer:

Atomic mass of Sodium is 23u (22.990u).

Question 8: Which element has the tiniest particle, which may or may not have its own existence but is always engaged in a chemical reaction?

Answer:

An atom is the tiniest particle of an element that may or may not have its own existence but is always involved in a chemical reaction.


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