Class 8 - Language of Chemistry

Language of Chemistry

1. THE LANGUAGE OF CHEMISTRY - Valency and variable valency

2. N JNKN ,N KNKNKN KNKN KJNIJHNM KNJKN KNJKNJK KNJKNJK VALENCY Definition : The combining capacity of an element or of a radical to form molecules is known as valency. Valency can be even zero (e.g. inert gases)

3. S.No . Name of the element Symbol Valency 1. Hydrogen H 1 2. Helium He 3. Carbon C 4 4. Nitrogen N 3 5. Oxygen O 2 6. Fluorine F 1 7. Neon Ne 8. Sodium Na 1 9. Magnesium Mg 2 10. Aluminium Al 3 11. Argon Ar VALENCIES OF SOME ELEMENTS

4. VALENCIES OF SOME RADICALS NAME OF THE RADICAL SYMBOL VALENCY Sodium Na + 1 Potassium K + 1 Ammonium NH 4 + 1 Magnesium Mg 2+ 2 Calcium Ca 2+ 2 Zinc Zn 2+ 2 Aluminium Al 3+ 3 Hydroxide OH - 1 Chloride Cl - 1 Carbonate CO 3 2- 2 Sulphate SO 4 2- 2 Nitride N 3- 3 Phosphate PO 4 3- 3

5. N JNKN ,N KNKNKN KNKN KJNIJHNM KNJKN KNJKNJK KNJKNJK VARIABLE VALENCY Definition : Elements showing more than one valency is known as variable valency . E.g. Iron exhibit the valencies 2 and 3 Copper exhibit the valencies 1 and 2

6. N JNKN ,N KNKNKN KNKN KJNIJHNM KNJKN KNJKNJK KNJKNJK HOW TO DENOTE VARIABLE VALENCY ? For lower valency , the suffix ‘ ous ’ should be added to the name of the element E.g. Iron is named as ‘Ferrous’ when it exhibits the valency 2. (lower valency )

7. N JNKN ,N KNKNKN KNKN KJNIJHNM KNJKN KNJKNJK KNJKNJK HOW TO DENOTE VARIABLE VALENCY ? For higher valency , the suffix ‘ ic ’ should be added to the name of the element Eg : Iron is named as ‘Ferric’ when it exhibits the valency 3. (higher valency )

8. N JNKN ,N KNKNKN KNKN KJNIJHNM KNJKN KNJKNJK KNJKNJK HOW TO DENOTE VARIABLE VALENCY ? Instead of using suffixes, roman numerals can also be used. The valency is represented in roman numerals enclosed in brackets Eg : ‘Ferrous’ is represented as Iron(II) and ‘Ferric’ as Iron(III)

9. VALENCIES OF SOME RADICALS NAME OF THE ELEMENT SYMBOL LOWER VALENCY STATE HIGHER VALENCY STATE Copper Cu Cu + or Cu(I) Copper(I) / Cuprous Cu 2+ or Cu(II) Copper(II) / Cupric Silver Ag Ag + or Ag(I) Silver(I)/ Argentous Ag 2+ or Ag(II) Silver(II)/ Argentic Iron Fe Fe 2+ or Fe(II) Iron(II)/Ferrous Fe 3+ or Fe(III) Iron(III)/Ferric Lead Pb Pb 2+ or Pb (II) Lead(II)/ Plumbous Pb 4+ or Pb (IV) Lead(IV)/ Plumbic

10. Significance of molecular formulae Chemical equations UPCOMING TOPICS …