Valency climbs 1-2-3-4, then falls 3-2-1-0
Valency of Elements
Class 9Class 10NEETFoundation
Items to Memorize
- Group 1 (H, Na, K) — valency 1
- Group 2 (Mg, Ca) — valency 2
- Group 13 (Al) — valency 3
- Group 14 (C, Si) — valency 4
- Group 15 (N, P) — valency 3
- Group 16 (O, S) — valency 2
- Group 17 (F, Cl) — valency 1
- Group 18 (He, Ne, Ar) — valency 0
Mnemonic Tricks
How It Maps
| Cue | Maps To |
|---|---|
| Group 1 | Valency 1 |
| Group 2 | Valency 2 |
| Group 13 | Valency 3 |
| Group 14 | Valency 4 |
| Group 15 | Valency 3 |
| Group 16 | Valency 2 |
| Group 17 | Valency 1 |
| Group 18 | Valency 0 |
Why It Sticks
Reading across the main groups, valency rises 1-2-3-4 up to the carbon group, then falls 3-2-1-0. It rises while atoms lose electrons and falls once they start gaining them. Picture a mountain: up to 4, back down to 0.
'-ous' is the lower valency, '-ic' is the higher valency
How It Maps
| Cue | Maps To |
|---|---|
| Ferrous | Iron, valency 2 (lower) |
| Ferric | Iron, valency 3 (higher) |
| Cuprous | Copper, valency 1 (lower) |
| Cupric | Copper, valency 2 (higher) |
Why It Sticks
For metals with two valencies, the name ending '-ous' is always the lower valency and '-ic' is the higher one. Ferrous iron is Fe(2), ferric iron is Fe(3); cuprous copper is Cu(1), cupric copper is Cu(2).
Frequently Asked Questions
What is valency?
Valency is the combining capacity of an element — the number of electrons an atom loses, gains or shares to form a compound. Hydrogen has valency 1 and oxygen has valency 2, which is why water is H2O.
What is the easiest trick to find valency from the periodic table?
For main-group elements, valency follows the group: groups 1, 2, 13, 14 have valency 1, 2, 3, 4; groups 15, 16, 17 have valency 3, 2, 1 (that is 8 minus the last digit); group 18 has valency 0.
What are the valencies of common elements?
Hydrogen 1, Sodium 1, Potassium 1, Chlorine 1; Magnesium 2, Calcium 2, Oxygen 2; Aluminium 3, Nitrogen 3; Carbon 4. These cover most Class 9 and Class 10 chemical formulas.
How do you use valency to write a chemical formula?
Use the criss-cross method: write both symbols with their valencies, then swap the valency numbers so they become the subscripts. For example, Ca (2) and Cl (1) give CaCl2.
What is the difference between ferrous and ferric?
Both are iron. Ferrous is iron with valency 2 (Fe2+) and ferric is iron with valency 3 (Fe3+). The '-ous' ending is always the lower valency and '-ic' the higher.