Valency is the combining capacity of an element — the number of electrons an atom needs to gain, lose, or share to achieve a stable configuration. Here are the key valencies you need for CBSE exams.
Potassium Valency: 1 (loses 1 electron to form K⁺).
Lead Valency: 2 or 4 (variable).
Bromide Ion Valency: 1 (gains 1 electron).
Variable Valency: Common in transition metals (Fe, Cu, Pb, Cr).
| Element | Symbol | Valency |
|---|---|---|
| Potassium | K | 1 |
| Lead | Pb | 2 or 4 (Variable) |
| Bromine (Bromide ion) | Br / Br⁻ | 1 |
| Sodium | Na | 1 |
| Calcium | Ca | 2 |
| Aluminium | Al | 3 |
| Nitrogen | N | 3 or 5 |
| Oxygen | O | 2 |
| Chlorine | Cl | 1 |
Lead (Pb) is a transition element that can form two stable compounds:
Bromine (Br) has 7 electrons in its outermost shell. It gains 1 electron to become the stable Bromide ion (Br⁻), giving it a valency of 1.
The valency of potassium (K) is 1. It loses its single outermost electron to form the K⁺ ion.
Lead has variable valency — it can be 2 (Plumbous/Pb²⁺) or 4 (Plumbic/Pb⁴⁺).
The bromide ion (Br⁻) has a valency of 1, as bromine gains 1 electron to complete its outermost shell.
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