Chemistry
'Valency' is also the number of electrons - donated or accepted by an atom so as to achieve stable electronic configuration of the nearest noble gas'. With reference to this definition -
(a) State what is meant by 'stable electronic configuration'.
(b) State why the valency of -
(i) sodium, magnesium & aluminium is: +1, +2 & +3 respectively.
(ii) chlorine, oxygen & nitrogen is: -1, -2 & -3 respectively.
Atomic Structure
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Answer
(a) Stable electronic configuration — The atom's outermost shell needs 2 electrons for stability (duplet rule) if it has only one shell. If it has multiple shells, it requires 8 electrons (octet rule) in the outermost shell for stability.
(b) (i) The atoms of sodium, magnesium and aluminium donate 1, 2 and 3 electrons, respectively, in order to achieve a stable electronic configuration of 8 electrons (octet rule) in the outermost shell. Hence, their valencies are +1, +2 & +3.
(ii) The atoms of chlorine, oxygen and nitrogen accept 1, 2 and 3 electrons, respectively, in order to achieve a stable electronic configuration of 8 electrons (octet rule) in the outermost shell. Hence, their valencies are -1, -2 & -3.
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Related Questions
Draw the atomic diagrams of the following elements showing the distribution of - protons, neutrons & the electrons in the various shells of the atoms.
(a) Carbon - 126C
(b) Oxygen - 168O
(c) Phosphorus - 3115P
(d) Argon - 4018Ar
(e) Calcium - 4020Ca
[The upper number represents the - mass number & the lower number the - atomic number e.g. calcium - mass number = 40, atomic number = 20]
'Valency' is the number of hydrogen atoms which can combine with [or displace] one atom of the element [or radical] forming a compound. With reference to the above definition of valency, state the valency of chlorine in hydrogen chloride, giving reasons.
With reference to formation of compounds from atoms by electron transfer - electrovalency, state the basic steps in the conversion of sodium & chlorine atoms to sodium & chloride ions leading to the formation of the compound - sodium chloride.
[electronic configuration of: Na = 2,8,1 & Cl = 2,8,7]
Match the statements in List I with the correct answer from List II.
List I List II 1. Mass number of an atom is the number of protons and A: Electron 2. The sub-atomic particle with a negligible mass. B: Argon 3. An atom having stable electronic configuration. C: Nitrogen 4. A molecule formed by sharing of electrons [covalency]. D: Sodium 5. A metallic atom having unstable electronic configuration. E: Neutrons