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Atomic Mass

  • Last Updated : 12 Oct, 2021

Atoms, which are the smallest units of matter, make up a chemical element. Every solid, liquid, gas, and plasma is made up of atoms, whether neutral or ionized. With a diameter of about 100 picometers, atoms are very small. Because atoms are far too small to be examined, researchers must utilize a large number of them to study their structure and behaviour. Based on the findings of this research, we can attempt to construct a hypothetical model of an atom that behaves similarly to the real thing.

Covalent (chemical) bonds are used to join one or more atoms to build molecules. Atoms are depicted as a circle with a nucleus in the centre (containing protons and neutrons), surrounded by one or more concentric circles symbolizing the atom’s “shells” or “levels” in which the electrons surrounding the nucleus are situated, with markings denoting the electron at each level. The smallest unit of a chemical that can yet be categorized as the same substance is called a molecule. It is made up of chemically bonded atoms that are two or more in number.

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What is the size of an Atom?

An atom is extremely little, far smaller than our imagination can comprehend. A layer of an atom the thickness of a thin sheet of paper is formed when more than millions of atoms are packed together. It’s impossible to measure the size of an isolated atom since it’s difficult to discern the positions of electrons surrounding the nucleus.



However, the size of an atom can be approximated if the distance between neighbouring atoms is equal to half the radius of an atom. An atom’s radius is commonly measured in nanometres.

1 m = 109 nm

What are Atoms made of?

An atom is made up of three particles: neutrons, protons, and electrons, with the exception of hydrogen, which has no neutrons.

  • The nucleus of every atom is surrounded by one or more electrons.
  • Protons and neutrons together referred to as nucleons, are usually found in equal numbers in the nucleus.
  • Protons are positively charged, whereas electrons are negatively charged and neutrons are neutrally charged.

Atomic Mass

An atom can’t be seen or isolated because it’s so small. As a result, determining the true mass of a single atom is challenging. Avogadro’s solution, on the other hand, was finally successful in fixing the problem. In a similar temperature and pressure setting, he combined equal amounts of two different gases. He weighed them after that. Surprisingly, their single-molecule mass ratio was equal to the mass ratio of their masses. The true masses of the atoms could not be determined, but their relative masses could. If the atomic mass of hydrogen is 1, the relative atomic mass of oxygen is 16.

The entire mass of one atom of a specific element is defined as the atomic mass of that element. The unified atomic mass unit, abbreviated as ‘u,’ is the unit’s name.

Initially, scientists determined all elements’ atomic masses by comparing them to hydrogen’s mass, which was considered to be one. The problem was that when atomic masses were estimated this way, most of the elements’ atomic masses were fractional. As a result, carbon is employed to determine atomic masses as a benchmark.

It has the mass of 1/2 of a carbon-12 atom in its ground state. The mass of an atom can be calculated using the sum of the masses of protons and neutrons, which is almost equal to the atomic mass. This tiny change is due to a loss of binding energy mass.



1 amu = 1.66 ×10−24 g

where amu is the Atomic Mass Unit.

Atomic masses of the first 20 Elements of the Periodic table are:

Atomic

Number

Element Name

Element Atomic Mass(u)

Atomic Mass (Round off)

1

Hydrogen (H)

1.008u

1

2

Helium (He)

4.002u

4

3

Lithium (Li)  

6.94u

7



4

Beryllium (Be) 

9.012u

9

5

Boron (B) 

10.81u

11

6

Carbon (C) 

12.011u

12

7

Nitrogen (N) 

14.007u

14

8

Oxygen (O) 

15.999u

16

9

Fluorine (F) 

18.998u

19

10

Neon (Ne) 

20.180u

20

11

Sodium Na) 



22.990u

23

12

Magnesium (Mg) 

24.305u

24

13

Aluminium (Al) 

26.982u

27

14

Silicon (Si) 

28.085u

28

15

Phosphorus (P) 

30.974u

31

16

Sulfur (S) 

32.06u

32

17

Chlorine (Cl) 

35.45u

35

18

Argon (Ar) 

39.95u

40

19

Potassium (K) 

39.098u

39

20

Calcium (Ca) 

40.078u

40

When the atomic weight of an atom is divided by the unified atomic weight (Daltons), the result is a dimensionless number. The atomic masses of elements range from 1.008 amu for hydrogen to 250 amu for extremely high-atomic-number elements. The mass of a molecule can be calculated using the average atomic mass of each atom in the molecule.

How to Calculate Atomic Mass?

There are three ways to calculate the atomic mass-



  • By referring to the periodic table

 In the periodic tables digit of an atomic mass is usually marked under the representation of an element. Like Hydrogen 1u, Helium 3u.

Periodic Table

  • Addition Of Mass Of Protons and Neutrons

The total number of protons and neutrons in an atomic nucleus gives the mass number.

  • All Atoms of an Element – Weighted Average

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 element. 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.

Sample Questions

Question 1: What is an atom consist of?

Answer:

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

Question 2: 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 3: 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 4: What is the simple definition of 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 5: What is the atomic mass of Sodium?

Answer:

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

Question 6: 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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