Atomic Mass of Elements

Dhristi JEE 2022-24

In this article, we will learn about the following things: the atomic mass of elements in detail, what is the atomic mass of all elements, and what is the atomic number and atomic mass of elements.

The atomic mass of a solitary atom is its absolute mass and is regularly expressed in atomic mass units or amu. For example, a normal carbon atom with six neutrons and six protons is denoted as carbon-12. It has an atomic mass equal to 12 amu. The atomic mass number is usually rounded off to the nearest whole number.

Since an element's isotopes have distinctive atomic masses, researchers may likewise decide the general atomic mass—once in a while called the atomic weight—for an element. The general atomic mass is the normal of the atomic masses of the apparent multitude of various isotopes in an example. Every isotope's contribution to the normal is controlled by how huge a fraction of the example it makes up. The overall atomic masses that are given in periodic tables like the one for hydrogen are determined for the naturally occurring isotopes of each element, weighted by the weight of those particular isotopes on earth.

The Periodic Table

In 1869, when Dimitri Mendeleev put together the first periodic table, the elements in the table were arranged in the order of increasing atomic mass. This approach is because the nucleus of the atom was yet to be discovered, and the chemists at the time had no understanding of the internal structure of atoms. Until the discovery of the structure of the atom, it was not known that the properties of the elements were governed by the atomic number.

Atomic Number

The atomic number gives a number of how many protons are inside the nucleus of the atom. Elements are identified based on the number of protons in the nucleus regardless of the number of neutrons present. Neutrons are uncharged subatomic particles which are stable when bound in an atomic nucleus. Atoms of all elements have neutrons in the nucleus except hydrogen.

The atomic number is important because the number of protons determines the number of electrons that surround the nucleus. The number of electrons in an element considerably determines the chemical behavior of the element. 

When observing the periodic table, one can see that elements are arranged on the basis of increasing atomic numbers. Elements that have similar qualities fall into the same column or group. For example, the elements in Group 1A are mostly soft metals that are highly reactive with water. Similarly, the elements in Group 8A are unreactive gaseous at room temperature. In the same group, a periodic repetition of properties can be seen in the elements with increasing mass.

Atomic Number of Elements from 1 to 30

Let us take a look at what is the atomic mass of elements from 1 to 30. Given below is the atomic mass of elements list.

Atomic Number

Element

Atomic Mass

1

Hydrogen

1.008

2

Helium

4.0026

3

Lithium

6.94

4

Beryllium

9.0122

5

Boron

10.81

6

Carbon

12.011

7

Nitrogen

14.007

8

Oxygen

15.999

9

Fluorine

18.998

10

Neon

20.18

11

Sodium

22.99

12

Magnesium

24.305

13

Aluminium

26.982

14

Silicon

28.085

15

Phosphorus

30.974

16

Sulfur

32.06

17

Chlorine

35.45

18

Argon

39.948

19

Potassium

39.098

20

Calcium

40.078

21

Scandium

44.956

22

Titanium

47.867

23

Vanadium

50.942

24

Chromium

51.996

25

Manganese

54.938

26

Iron

55.845

27

Cobalt

58.933

28

Nickel

58.693

29

Copper

63.546

30

Zinc

65.38

This was the atomic mass of the first 30 elements. Let us now learn the difference between atomic number and atomic mass of elements.

Isotopes

Before going into atomic mass, it is essential to learn about isotopes. Atoms of the same element that have a different number of neutrons are called isotopes. The isotope of a given element is defined by adding the number of protons and neutrons in its nucleus. An element (which has the same atomic number) can have multiple isotopes with different numbers of neutrons. The most common examples are the isotopes of carbon, 12C, and 13C which possess 6 and 7 neutrons, respectively. Isotopes vary in their abundance in nature depending on the source of the materials.

Atomic Mass

The atomic mass is the average mass of the atoms of an element measured in the atomic mass unit (amu) or Daltons, D. The atomic mass is determined by averaging the weight of all the isotopes of the element. The averaging procedure also involves taking into consideration the abundance of each isotope and multiplying it with the mass of each. 

Consider the gas neon, which has three isotopes: 

  1. neon-20: It is made up of ten protons and ten neutrons. The atomic mass unit of the gas is 19.992, and the abundance of the gas is 90.48%. 

  2. neon-21: It is made up of ten protons and eleven neutrons. The atomic mass unit of the gas is 20.994, and the abundance of the gas is 0.27%. 

  3. neon-22: It is made up of ten protons and twelve neutrons. The atomic mass unit of the gas is 21.991, and the abundance of the gas is 9.25%. 

To determine the atomic mass of neon, the average of the isotopes need to be extracted: 

0.9048 × 19.992 = 18.09 amu

0.0027 × 20.994 = 0.057 amu

0.0925 × 21.991 = 2.03 amu 

The average atomic mass is thus: 20.18 amu

The atomic mass of elements directly relates to the concept of “mole” which is an important way of measuring the amount of substance. The relation between the atomic mass and the number of moles is that, when measured, the amu directly gives a measure in grams of the element present in one mole. 

For example, iron has an atomic mass of 55.847 amu. Therefore, one mole of iron has a weight of 55.847 grams. The same concept is also used to determine the molar quantities of ionic molecules and compounds. For example, one mole of sodium chloride (NaCl) has a molecular mass of 58.44 amu (Na: 22.989 amu Cl: 35.453 amu) which gives the molar weight of salt as 58.44 grams. Similarly, the molecular mass of water is 18.02 amu which gives a molar mass of 18.02 grams.

Difference Between the Atomic Number and the Atomic Mass of Elements

Let us now learn about the difference between the atomic number of elements and their atomic mass.

Atomic Mass

Atomic Number

Atomic mass is related to the number of neutrons and protons which are present in the nucleus of an element.

Atomic number refers to the number of protons that are present in the nucleus of an element.

It refers to the average weight of a particular element.

It refers to the total number of nucleons that are present in the atom’s nucleus.

Atomic mass is denoted by the letter A

The letter Z is used for representing the atomic number.

Atomic mass cannot be used for defining the type of element.

Atomic numbers usually help to classify and identify an element.

Atomic mass is also used in the classification of different isotopes of the same element

Only isotopes of an element share the same atomic number.

Atomic mass is always measured using the atomic mass unit (amu).

The atomic number is simply a digit which is used for placing the elements in the periodic table.

FAQs on Atomic Mass of Elements

1. What is the Atomic Mass of the First 20 Elements?

Given below is the atomic mass number of the first 20 elements.

 

Atomic Number

Element

Atomic Mass

1

Hydrogen

1.008

2

Helium

4.0026

3

Lithium

6.94

4

Beryllium

9.0122

5

Boron

10.81

6

Carbon

12.011

7

Nitrogen

14.007

8

Oxygen

15.999

9

Fluorine

18.998

10

Neon

20.18

11

Sodium

22.99

12

Magnesium

24.305

13

Aluminium

26.982

14

Silicon

28.085

15

Phosphorus

30.974

16

Sulfur

32.06

17

Chlorine

35.45

18

Argon

39.948

19

Potassium

39.098

20

Calcium

40.078

21

Scandium

44.956

22

Titanium

47.867

23

Vanadium

50.942

24

Chromium

51.996

25

Manganese

54.938

26

Iron

55.845

27

Cobalt

58.933

28

Nickel

58.693

29

Copper

63.546

30

Zinc

65.38

2. What is the Definition of Atomic Number?

Indeed, even the proton number is known as the atomic number. A chemical element's atomic no. is characterized as the whole of protons present in the nucleus of that atom of the element. Since neutrons convey no net electrical charge it is the charge number of the nucleus. 

 

Atomic mass and atomic number may have similarities, however, they are accustomed to uncovering various qualities of elements. As indicated by the definitions given, atomic mass which is additionally called atomic weight is the deliberate complete mass of an element's atom. Though, atomic number is only the absolute number of neutrons and protons in the nucleus of an atom.

3. Define Atomic Mass and Give Examples.

Atoms are the essential units of matter. They are the littlest segments of a chemical element, which is a substance that can't be separated into easier material. Atoms have explicit properties that will decide their chemical and physical nature. One of these properties is their atomic mass. This video will talk about our atomic mass and its function in science. 

 

Atomic mass is generally equal to the aggregate of the individual particle masses of an atom. Atoms have three essential segments: protons (emphatically charged particles), neutrons (non-charged particles), and electrons (adversely charged particles). 

 

Protons and neutrons are the bigger particles and are found in the nucleus, which is the centre of the atom. Atomic mass is commonly determined by including the number of protons and neutrons together, overlooking the electrons on account of their little size. Daltons are the standard units utilized for estimating atomic mass. 

4. Why should one refer to Vedantu?

All the reading materials at Vedantu are curated by the subject-matter experts who have years of experience in the respective field. The content is well - researched and compiled into easy readable format for the benefit of students. Students can refer to these resources with ease and learn things at their own pace. Most importantly all the content on Vedantu is provided for free and it can be easily downloaded into PDF from both the website and mobile application of Vedantu. 


5. How can I download reading material from Vedantu?

Accessing material from Vedantu is extremely easy and student-friendly. Students have to simply visit the website of  Vedantu and create an account. Once you have created the account you can simply explore the subjects and chapters that you are looking for. Click on the download button available on the website on Vedantu to download the reading material in PDF format. You can also access all the resources by downloading the Vedantu app from playstore. 



Comment