SSLC Chemistry, Chapter 1 - Periodic Table and Electronic Configuration

 

Write the subshell electronic configuration of the following elements?

1. Helium
2. Potassium
3. Magnesium
4. Iron
5. Copper
6. Chromium
7. Fluorine
8. Sulphur

(Atomic number of He-2, K – 19, Mg- 12, Fe- 26, Cu- 29,

Cr- 24, F- 9, S- 16)

Answers:

1.      

Peculiarity of the subshell electronic configuration of chromium and copper

In the electronic configuration of chromium and copper, the outermost s orbit has one electron only. Why?

The d subshell can accommodate a maximum of 10 electrons. The completely filled configuration (d¹⁰) or the half filled configuration (d⁵) of this subshell is more stable than the others. So the d⁴ s²  configuration of chromium is changed to d⁵ s¹ and the d⁹ s² of copper is changed to d¹⁰ s¹ .

Electronic configuration and block

The block to which an element belongs will be the same as the subshell to which the last electron is added.

In the periodic table the first two groups belong to s block, the groups from 13 to 18 belong to the p block and the groups from 3 to 12 belong to the d block. The elements at the bottom of the periodic table in two separate rows (lanthanones and actinones) belong to f block.

From the following electronic configuration identify the block of each element.

Answer:

Complete the table.

Answer:

Subshell electronic configuration and group number.

Group number of s block elements

                For s block elements the number of electrons in the outermost subshell will be the group number.

Characteristics of p block elements

Metals, non-metals, metalloids and all the noble gases are in this block.

Elements in the solid, liquid and the gaseous state at room temperature are seen in this block.

p block elements usually show higher ionisation energy than s block elements.

The element having the highest electronegativity (fluorine) is in this block.

There are electropositive and electronegative elements in this block (eg: Boron, Aluminium etc. are electropositive elements, Oxygen, Chlorine etc. are electronegative elements).

Group number of d block elements                               

 The group number of d block elements will be same as the sum of electrons in the outermost s subshell and the number of electrons in the preceding d subshell.

Characteristics of d block elements

d block elements are found in groups 3 to 12 of the periodic table.

d block elements are known as transition elements.

d block elements are metals.

The last electron is filled in the d subshell of the  penultimate shell.

They show variable oxidation state.

They form coloured compounds.

Transition elements

Transition elements (d block elements) show similarities in properties not only in groups but also in periods. Why?

The outermost subshell electronic configuration of the transition elements are generally the same in a group and also along a period, therefore they show similarities in properties not only in groups but also in periods.

Transition elements show variable oxidation states. Why?

In the case of transition elements the difference in energy between the outermost s subshell and the penultimate d subshell is very small. Hence under suitable conditions the electrons in d subshell also take part in chemical reactions. Hence transition elements show variable oxidation states.

Most of the coloured salts are compounds of transition elements. Why?

Most of the coloured salts are compounds of transition elements. The colour is due to the presence of transition metal ions present in these compounds.

Transition metal compounds and colours

Copper sulphate – blue

Cobalt nitrate – red brown

Potassium permanganate – dark purple

Ferrous sulphate – green

Potassium dichromate – orange

Cobalt chloride – sky blue

Inner transition elements

f block elements

The f block elements are the elements coming after lanthanum(6^th period) and actinium(7^th period) and are placed in two rows at the bottom of the periodic table.

The elements in first row are called lanthanoids and those in the second row are called actinoids.

Characteristics f block elements

These elements show variable oxidation states

Most of the actinoids are radioactive and are artificial elements.

f block elements Uranium, Thorium, and Plutonium are used as fuels in nuclear reactors.

Many of f block elements are used as catalyst in the petroleum industry.

Let's assess Questions and Answers

Ans:

 Wrong electronic configurations are a, c, and d

Ans:

a) 2d and 3f are not possible.

b) Second shell has no d subshell and third shell has no f subshell

Extended activities Questions and Answers

Answers:

a) Halogens

b) -1

c) Flourine

d) Flourine

e) Some examples of compounds of halogens and s block elements : NaF, NaCl, KF, KCl, MgF₂ , MgCl₂, CaF₂