Question

1. explain how atoms can share electrons and form covalent bonds. 2. explain how water disassociates ions. 3. explain how the siassociation of an acid and a base changes pH.

Answer 1

1. Covalent bonds will be formed when an atom does not have complete octet i.e. required electron count in its valence shell. Covalent bonds are formed by sharing of electrons between two atoms, to complete its octet. In covalent bond, both atoms share there valence electron to form covalent bond.

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This is ex. of formation of H₂ molecule. Since H atom has only one valence electron so two hydrogen atoms combine and form covalent bond by sharing.

2. H₂O it has a bent structure. It will dissociates in two ions, one will be positive and other negative. Since oxygen is more electronegative, it will form negative ion and one of the two hydrogen will form positive ion.

H₂O H⁺ + OH^-

this is the equation of dissociation of water.

3. According to Arrhenius concept, Acid is a species which dissociate to give H⁺ ions, and Base is dissociate to give OH^-  ions.

So when an acid dissociate, there will be increase of protons and thus it increase acidity of the solution. on the other hand if a base is dissociates, there will be increase of Hydroxide ions, hence it will increase basicity of the solution.

eg. HCl(aq)⟶H+(aq)+Cl−(aq) hence HCl is an acid

NaOH(s)Na⁺(aq) + OH^-(aq) hence NaOH is an base