What is Inside an Atom – Explanation

Key Concepts

• Mass number
• Atomic model
• Electric Charge
• Isotopes and isobars
• Valence shell and electrons

Introduction: 

What is inside the atom? 

Atom is the smallest particle of an element that cannot be further divided into simpler substances or smaller particles. All atoms are made of three different sub-atomic particles, electrons, protons, and neutrons. All these sub-atomic particles have an electric charge except for neutrons. Now in this topic, we are going to learn some important terms like mass number, atomic number, electric charge, nucleus, isotopes, isobars, etc. 

Explanation: 

Mass number: 

The sum of number of protons and neutrons in an atom is called the mass number. Mass of the atom will be at the center of the nucleus, and it occupies the whole atom. For example, when we lift a heavy stone or rock, it means that we are lifting the protons and neutrons in the stone that we weigh. Mass of protons and neutrons is 1800 times more than the electrons. Mass number of the element differs from atom to atom. Mass number is represented with ‘A’ and is written at the top left of the symbol .

Atomic number: 

The total number of protons present inside the nucleus, or the number of electrons present outside of the nucleus in an atom is called the atomic number. The atomic number is different for each element. For example, the atom of the element manganese has 25 protons, so the atomic number is 25. Atomic number is represented with ‘Z’ and is written at the bottom left of the symbol.  

Finding the number of neutrons 

n= A – Z 

Where n= number of neutrons 

              A= mass number 

              Z= atomic number 

Electric charge:  

There are two different kinds of charges: positive and negative. Positive charge is for proton, and negative charge is for electron. Like charges (same charge) repeal each other and unlike charges attract each other. Each proton has the electric charge of ‘+1’, and each electron has the electric charge of ‘-1’. Atom has an equal number of protons and electrons, which gives the neutral or uncharged atom upon adding. 

Nucleus: 

Protons and neutrons combine and are arranged in the nucleus. The nucleus is much smaller than an atom and very dense. Nuclei of an atom consist of positively charged particles and electrically negative charged particles; this all together forms an atom.  

The proton with positive charge and electron with negative charge are held with strong attractive forces. These protons or neutrons, which are held in the nucleus of an atom, cannot easily enter the nucleus or leave the nucleus. 

It would take 10,000 nuclei lined up side by side to stretch across the diameter of a typical atom. For example, an atom of gold has an atomic number 79, this means that it has 79 protons and its charge is +79 

Isotopes and isobars:  

The atoms with the same atomic number but a different mass number are called isotopes. In other words, it is evident that the difference between the isotopes is due to the presence of different numbers of neutrons present in the nucleus.  

For example: Hydrogen atom has only one proton, one electron but no neutrons. 

                          Hydrogen atom has 3 isotopes; they are protium, deuterium, tritium. 

                          Protium: 1 proton, 0 neutron. 

                          Deuterium: 1 proton, 1 neutron 

                          Tritium: 1 proton, 2 neutrons 

The atoms with the same mass number with identical atomic number are called isobars.  

For example:     ⁴⁰ Ar_18, ⁴⁰ Ca₂₀   

Valence shell and valence electrons: 

The outermost shell or orbit of an element is called the valence shell. We can also call it an ultimate shell. The number of electrons present in the valence shell is called valence electrons. 

The number of electrons lost or gained from the element or atom to attain stability is called valency. 

For example: In the calcium atom, 

Electronic configuration: 1s²2s²2p⁶3s²3p⁶4s² 

Valence shell: 4s² 

Valence electrons: 2 

Valence: 2 

Summary:

1. Atom is the smallest particle of an element that cannot be further divided into simpler substances or small particles and have the properties of an element.
2. All atoms are made of three different sub-atomic particles; electrons, protons and neutrons.
3. The sum of number of protons and neutrons in an atom is called the mass number.
4. The total number of protons present inside the nucleus, or the number of electrons present outside of the nucleus in an atom is called the atomic number.
5. Each proton has the electric charge of ‘+1’, and each electron has the electric charge of ‘-1’.

6. Nuclei of an atom consist of positively charged particles and electrically negative charged particles; this all together forms an atom.
7. The atoms with the same atomic number but a different mass number are called isotopes.
8. The atoms with the same mass number with identical atomic number are called isobars.
9. The outermost shell or orbit of an element is called the valence shell. 10. The number of electrons present in the valence shell is called valence electrons.
10. The number of electrons lost or gained from the element or atom to attain stability is called valency.