Question

Classify each of the following solids as molecular, ionic, metallic, or covalent.

(a) ${\mathbf{\text{BaCl}}}_{\mathbf{\text{2}}}$

(b) SiC

(c) CO

(d) Co

Short answer

a) Ionic

b) Covalent

c) Molecular

d) Metallic

Step-by-step solution

Subpart (a) Barium Chloride.

Barium chloride is a compound formed because of the large difference between the electronegativities of the two atoms.

${\text{Cl}}^{-}{\text{- - Ba}}^{2+}{\text{- Cl}}^{-}$

This difference in electronegativities makes the compound ionic.

These ions are usually hard and charged spheres occupying different positions on the crystal lattice.

Subpart (b) Silicon Carbide.

The bonding between silicon and carbon atoms is covalent

$$\begin{gathered} |||| \\ -\mathrm{Si}-\mathrm{C}-\mathrm{Si}-\mathrm{C} \\ |||| \\ -\mathrm{Si}-\mathrm{C}-\mathrm{Si}-\mathrm{C} \\ |||| \\ -\mathrm{Si}-\mathrm{C}-\mathrm{Si}-\mathrm{C} \end{gathered}$$.

As carbon valency is 4, it needs four more electrons to complete its octet.

Similar is the rule for silicon atom that is present just below carbon, in the periodic table.

Both of the atoms coordinate covalently (shares electrons) to form silicon carbide, as shown above.

Subpart (c) Carbon Monoxide.

The intermolecular forces that hold carbon monoxide areVan der Waals forces. This force is quite weaker than ionic, metallic, and covalent bonding because of which molecular crystals have low melting points,which makes them soft.

Carbon monoxide is a molecular crystal where the molecules are packed together without overlapping.

Subpart (d) Cobalt.

In metals, there is little tendency for ionic bonding because whether in the main group or transition metals, present in the periodic table, only a small difference in electronegativity is found.

And because of the nearly-filled subshells, they do not have much tendency to form covalent bonds.

The German physicist Paul Drude, viewed the solid metal as the arrangement of positively charged ions in the crystal lattice.

There is a sea of mobile electrons found around the fixed ions. Metal is electrically neutral as the density of electrons is similar to that of positively charged ions.

These interactions between stable ions of cobalt that keep the metal together, and strong is metallic bonding.