Question

Question #825b1

Answer 1

1) To attain stability.
2) To complete valence shell.
3) To lower their energy.
4) To acquire the noble gas electronic configuration.

Explanation:

Stable atoms cannot react because their valence shell E.C( electronic configuration) is complete.
Non-stable atoms react because they have to complete their valence shell, e.g.,
Na is metal and Cl is non-metal. Metal atom tends to lose electrons and non-metal atoms tends to gain electrons to acquire electronic
configuration of nearest noble gas. Since Na atom has one electron in the outer most shell. It losses one electron to form `Na^+` ion. Since Cl atom has seven electrons in outermost shell, it needs one electron to complete octet. So it gains one electron to form `Cl^-` ion.

The stable atoms or particles which has their complete valence shell electronic configuration are called noble gases. You have noticed that each period on the periodic table starts with alkali metal (except period 1 that starts with hydrogen) and ends at a noble gas.
The noble gases have `ns^2np^6` electronic configuration in the outer moct shell. These elements are sometimes called inert gases. This is because they do not participate in chemical reactions. Electronic configurations of first three noble gases are shown below:
He= `1s^2`
Ne= `1s^2,2s^2,2p^6`
Ar= `1s^2,2s^2,2p^6,3s^2,3p^6`

But, these elements have completely filled outer most `s` and `p` sub-shells. Helium contains two electrons and remaining noble gases contain 8 electrons in the valence shell, because of these configuration noble gases are stable and not active.

In 1916, a chemist G.N.Lewis used this fact to explain why atoms undergo chemical reactions. He called his explanations as Octet rule.
An octet is a set of eight. In forming compounds, atoms tend to gain electronic configuration of a noble gas. Remember that each noble gas (except He) has eight electrons in the valence shell. Thus the octet rule takes its name from this fact noble gases.

The tendency of atoms to acquire eight electron configuration in their valence shell, when bonding, is called octet rule.

Helium has two electrons in its valence shell and is also chemically inert. Some elements that are close to He on the periodic table tend to achieve two electron configuration in their valence shell. For example hydrogen, lithium and beryllium e.t.c., tend to achieve two electron configuration in the valence shell.

The tendency of some atoms to acquire two electron configuration in their valence shell, when bonding, is called duplet rule.