Question

Compare the electron configurations of the elements belong to second and third periods.Please refer to Table 2.​

Answer 1

Answer:

The elements in Group 2 (beryllium, magnesium, calcium, strontium, barium, and radium) are called the alkaline earth metals (Figure below). These elements have two valence electrons, both of which reside in the outermost s sublevel. The general electron configuration of all alkaline earth metals is ns2.

Answer 2

Valency:

• Valency is the combining capacity of an atom.
• Metals donate electrons and form positive ion.
• Non Metals donate electrons and form negative ions.

In Modern Periodic table,

There are 7 rows called periods.

and there are 18 columns called groups.

The valency of elements is got by its Electronic Configuration.

★ The first shell or K shell contains 2 electrons

★ The second shell or L shell contains 8 electrons and

★ The third shell or M shell has 8 electrons

and so on.

Note: This rule is applicable only upto 20th element (Calcium)

The valency across Second and third period of the periodic table increases from 1 to 4 and then decreases from 4 to 0

Noble gases are elements which have completely filled electrons in its outermost shell. So, their valency is 0.

Kindly see the attached table from website.

$\boxed {\begin{array}{|c|c|c|c|cccc|}\cline {1-8}\sf Element & \sf Symbol & \sf Valency & \sf{Atomic\:Number} & & \sf{Electron} & \sf Configuration & \\ \cline {5-8} &&&&\bf K&\bf L &\bf M&\bf N \\ \cline {1-8}\rm Hydrogen &\sf H & 1 & 1 & 1 &&& \\ \cline {1-8}\rm Helium &\sf He & 0 & 2 & 2 &&& \\ \cline {1-8}\rm Lithium &\sf Li & 1& 3 &2 &1 && \\ \cline {1-8}\rm Beryllium &\sf Be & 2 & 4 & 2 & 2 && \\ \cline {1-8}\rm Boron &\sf B & 3 & 5 & 2 & 3 && \\ \cline {1-8}\rm Carbon & \sf C & 4 & 6 & 2 & 4 && \\ \cline {1-8}\rm Nitrogen &\sf N & 3 & 7 & 2 & 5 && \\ \cline {1-8}\rm Oxygen &\sf O & 2 & 8 & 2 & 6 && \\ \cline {1-8}\rm Fluorine &\sf F & 1 & 9 & 2 & 7 && \\ \cline {1-8}\rm Neon & \sf Ne & 0 & 10 & 2 & 8 && \\ \cline {1-8}\rm Sodium &\sf Na & 1 & 11 & 2 & 8 & 1 &\\ \cline {1-8}\rm Magnesium &\sf Mg & 2 & 12 & 2 & 8 & 2 & \\ \cline {1-8}\rm Aluminium &\sf Al & 3 & 13 & 2 & 8 & 3 & \\ \cline{1-8}\rm Silicon &\sf Si & 4 & 14 & 2 & 8 & 4 & \\ \cline {1-8}\rm Phosphorus &\sf P & 3 & 15 & 2 & 8 & 7 & \\ \cline {1-8}\rm Sulphur &\sf S & 2 & 16 & 2 & 8 & 8 & \\ \cline{1-8}\rm Chlorine &\sf Cl & 1 & 17 & 2 & 8 & 8 &1 \\ \cline {1-8}\rm Argon &\sf Ar & 0 & 18 & 2 & 8 & 8 & 2 \\ \cline {1-8}\rm Potassium &\sf K & 1 & 19 & 2 & 8 & 8 &3 \\ \cline {1-8}\rm Calcium &\sf Ca & 2 & 20 & 2 & 8 & 8 & 4 \\ \cline{1-8} \end {array}}$