Hemant Kumar

You need not go to either francium or Moscovium.

First, clear your objective toward study; I mean you are to pass the class then till calcium is more than enough. If you want to score higher than, also you are to remember till calcium and some other like( copper iron zinc manganese tin-lead silver-gold), and all inert gas also

Below is also an important one:

aka boron – Scandium.

Aka aluminium - Gallium.

Aka Silicon-Germanium.

Now you have mastered in 10th!

First, you need to understand what is a reaction, what happens in it. In reaction, an atom exchanges electron with another atom. 

There are two types of reactions: Ionic and Covalent.

Ionic reaction: In this reaction, an atom exchanges electrons completely. It means if an atom has an extra electron in the outermost shell, it gives its electron to another unstable atom.

(Note:- in an ionic bond, the reaction occurs between the metal and non-metal.)

What is a Stable/ Unstable Atom?

Stable means: 

1. Atom desperately wants or give an electron for being stable.
2. Atom wants to achieve INERT GAS configuration. If you know what inert gas configuration is, it is good; otherwise, don't bother about inert gas configuration.

Covalent reaction: in covalent bond/reaction, atom share/partially exchange electron to another Unstable atom. Partly exchange means, atom give its extra electron to another atom for some time and take it back. This process continues, and both the atoms achieve a stable state. 

(NOTE:- in Covalent bond, reaction take place between non-metal and non-metal.)

Bond and reaction both are the same things.

Metal:- It can give electron.

Non-metal:- It can receive electron.

By nature, only 3 electrons can be exchanged between atoms completely. So what happens to those who are to exchange 4 electrons? So here, covalent comes in role. It doesn't mean that all who have four extra electrons in their outermost shell make a covalent bond.

Covalent bond Examples:-

• O2, N2, O3, C3H5, C2H2, NH3
• O:- oxygen(non-metal)
• N:- Nitrogen(non-metal)
• C:- Carbon(non-metal)
• H:- Hydrogen(non-metal)

Carbon has six atomic number and 4 electrons in its outermost shell. To make itself a stable carbon atom, it has to give 4 electrons to another atom or take 4 electrons from another atom. As I have taught you already, 4 electrons can be exchanged. So carbon exchanges electrons partially, and hence, uses a covalent bond.