# Chapter 24 – Atomic number

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Right from a young age, we are told that all of the matter that we see and perceive around us can actually be expressed in terms of a certain parameter that we begin to refer to as elements. Gradually, when we are taught about the periodic table we notice that all of the elements in there are actually placed in a rather specific arrangement. Now, this brings to mind two questions that we need to address. Firstly, what distinguishes one element from the remaining many that we come across on a daily basis? Secondly, what is the factor that rules this particular arrangement of a periodic table? The answer to both of these questions, however, is one- Atomic Number.

Much like our roll numbers in a classroom, every element of the periodic table has a unique atomic number that differentiates it from its counterparts. The modern periodic table arranges its constituent elements in an increasing manner of their atomic numbers, and consequently in an increasing manner of their mass numbers as well. But before we attempt to understand any of these, we must make out what the term atomic number and mass number mean in the first place.

#### Introduction to Atomic Number and Mass Number

We are all aware of the fact that the building blocks of an element comprise electrons, protons, and neutrons. Among these, electrons and protons are considered to be the charged particles in matter whereas neutrons are neutral in nature.  While the number of electrons that exist in the outermost shell of an element gives us an idea about its valency, the number of neutrons and protons that it holds helps us define its atomic number and mass number

Because the entities of protons, neutrons, and electrons are regarded as whole objects, we always obtain atomic numbers and mass numbers in whole numbers as well. The sum total that is constituted by the mass number and atomic number for an atom is representative of the overall count of its subatomic particles.

#### Understanding Atomic Number

By definition, the total number of protons that are present in the nucleus of an atom is collectively referred to as its atomic number. The letter “Z” of the English alphabet is used to denote atomic numbers in general. In the case of any particular element, since all of its atoms possess the same number of protons, all of them end up having the same atomic number as well.

Since atoms of different elements contain varying counts of protons, all of them have different atomic numbers. For instance, in the case of Nitrogen, all of its atoms have 7 protons in its nucleus and so it has an atomic number of 7. Likewise, Oxygen has an atomic number of 8, because its nucleus comprises 8 protons.

#### Understanding Mass Number

Mass Number of an element refers to the sum total of the protons and neutrons that reside in its nucleus. The letter “A” of the English alphabet is used to represent mass numbers in general. Let us take Oxygen as our example. It consists of 8 protons and 8 neutrons in its nucleus. As a result, its mass number is 16. Considering the fact that both protons and neutrons exist in the nucleus of an atom, together they are called nucleons. Hence, mass number is alternatively addressed as nucleons number as well.

#### Isotopes and Isobars

It is often the case that while the atoms of an element contain a fixed number of protons, the number of neutrons occasionally vary. This, in turn, results in the phenomenon of isotopes and isobars that directly have an influence on the structure of an atom. While isotopes refer to variants of the same element that have different mass numbers, isobars refer to those cases when atoms of two separate elements end up having the same number of nucleons. For example, Carbon-12 and Carbon-14 are isotopes of one another, for Carbon-12 has 6 protons and 6 neutrons whereas Carbon-14 has 6 protons and 8 neutrons. On the other hand, Carbon-14 and Nitrogen are isobars because both of them have the same count of nucleons, that is 14.

#### Why are atomic numbers important?

• They help us distinguish one element from another.
• As they dictate the arrangement of elements in the modern periodic table, knowledge of atomic numbers enables us to read and understand the periodic table in a better manner.
• Atomic numbers lead and guide our discovery of the entire spectrum of properties that is native to any particular element.

#### Atomic numbers and protons

Irrespective of the number of protons and electrons that constitute an atom, the atomic number is always determined by its count of protons, without any dispute whatsoever. Even though a large number of elements consist of the same number of protons and neutrons, you must not ever make use of the count of neutrons to calculate the atomic number.

This rule is maintained with the vision of avoiding misunderstandings in the domain of isotopes. For example, Carbon-12 has 6 protons and 6 neutrons, and Carbon-14 has 6 atoms and 8 neutrons. Although both of them have different mass numbers of 12 and 14 respectively, both of them have the same atomic number, i.e., 6. This is because either of them has 6 protons each.

#### FAQs

What is meant by atomic number?

The total number of protons in the nucleus of an atomic number is its atomic number. It is denoted as “Z”.

What is atomic number and mass number?

An element’s atomic number refers to the total number of protons in the nucleus of its atom whereas Mass number of the same element refers to the total count of protons as well as neutrons that exist in its atom’s nucleus.

How do you find the atomic number?

Atomic number is determined by reading the count of protons that the nucleus of an atom holds.

What is the difference between atomic mass and atomic number?

While atomic number refers to the total count of protons of an atom’s nucleus, atomic mass refers to the complete mass of an atom that is determined by carrying out a weighted average of all the isotopes of that element.

What is another name for ‘atomic symbol’?

Atomic number is another name for atomic symbol.

Often understanding the concepts of atomic number and mass number requires adopting an immersive and highly interactive approach. With the help of MSVgo’s comprehensive video library, students not only gain an intuitive understanding of the various concepts that abound in these topics but also develop the ability of applying them to a practical setting. Consequently, this greatly advances their learning curve.

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