Chemistry 9701 · AS & A Level · The Periodic Table: chemical periodicity

The Periodic Table: chemical periodicity — practice question

Although the exact size of an atom cannot be measured directly, the separation between the nuclei of two atoms can be measured. For example, the ‘covalent radius’ of the Cl atom is taken to be half the distance between the nuclei in a $\text{Cl}_2$ molecule. In a similar way, the ‘metallic radius’ is half the distance between two metal atoms in the crystal lattice of a metal. These two kinds of radius are generally referred to as ‘atomic radii’. The table below gives the atomic radii obtained for the period three elements of the Periodic Table, Na to Cl.
(a(i))

Explain qualitatively this variation in atomic radius.

(a(ii))[4]

Suggest why the same kind of measurement cannot be used for argon, Ar.

(b(i))

Use the Data Booklet to fill in the table below with the radii of the cations and anions formed by some period three elements: $\text{Na}^+$, $\text{Mg}^{2+}$, $\text{Al}^{3+}$, $\text{P}^{3-}$, $\text{S}^{2-}$, $\text{Cl}^-$.

(b(ii))

Explain the size differences between the cations and the corresponding atoms.

(b(iii))[5]

Explain the size differences between the anions and the corresponding atoms.

(c(i))

Write an equation for the reaction of each of these oxides with water: $\text{Na}_2\text{O}$ and $\text{SO}_2$.

(c(ii))

What pH does the resulting solution have in each case?

(c(iii))[5]

Write an equation for the reaction that takes place between the products of your reactions in (i).

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