Question

What type of solid will each of the following substances form? a. diamond b. \(\mathrm{PH}_{3}\) c. \(\mathrm{H}_{2}\) d. \(\mathrm{Mg}\) e. \(\mathrm{KCl}\) f. quartz g. \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) h. \(\mathrm{SF}_{2}\) i. Ar j. \(\mathrm{Cu}\) k. \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\)

Short answer

a. Diamond forms a covalent solid. b. PH3 forms a molecular solid. c. H2 forms a molecular solid. d. Mg forms a metallic solid. e. KCl forms an ionic solid. f. Quartz forms a covalent solid. g. NH4NO3 forms an ionic solid. h. SF2 forms a molecular solid. i. Ar forms a molecular solid. j. Cu forms a metallic solid. k. C6H12O6 forms a molecular solid.

Step-by-step solution

a. Diamond

Diamond is a covalent solid, as it consists of carbon atoms covalently bonded together in a tetrahedral arrangement.

b. PH3

PH3 (phosphine) is a molecular solid, as it is formed by discrete molecules of phosphorous and hydrogen that are held together by weak van der Waals forces.

c. H2

H2 (hydrogen) is a molecular solid, as it consists of discrete H2 molecules held together by weak van der Waals forces.

d. Mg

Mg (magnesium) is a metallic solid, as it consists of a regular arrangement of magnesium atoms, where the electrons are delocalized and form a "sea of electrons" that holds the metal lattice together.

e. KCl

KCl (potassium chloride) is an ionic solid, as it consists of potassium (K+) and chloride (Cl-) ions held together by electrostatic ionic bonds.

f. Quartz

Quartz is a covalent solid, as it consists of silicon and oxygen atoms covalently bonded together in a tetrahedral network.

g. NH4NO3

NH4NO3 (ammonium nitrate) is an ionic solid, as it consists of ammonium (NH4+) and nitrate (NO3-) ions held together by electrostatic ionic bonds.

h. SF2

SF2 (sulfur difluoride) is a molecular solid, as it consists of discrete SF2 molecules held together by weak van der Waals forces.

i. Ar

Ar (argon) forms a molecular solid, as it consists of discrete argon atoms held together by weak van der Waals forces, also known as an "argon lattice" when in solid form.

j. Cu

Cu (copper) is a metallic solid, as it consists of a regular arrangement of copper atoms, with the electrons being delocalized forming a "sea of electrons" that holds the metal lattice together.

k. C6H12O6

C6H12O6 (glucose) is a molecular solid, as it consists of discrete glucose molecules held together by weak van der Waals forces.

Key concepts

Covalent Solids

Covalent solids are structures where atoms are bonded together by covalent bonds in a continuous network. These bonds form a solid that is generally hard and has a high melting point.
A famous example of a covalent solid is diamond. Diamond comprises carbon atoms connected by covalent bonds in a tetrahedral arrangement. This structure gives diamond its renowned hardness.
Quartz is another covalent solid, made up of silicon and oxygen atoms bonded together. This interconnection forms a well-organized lattice that makes quartz very strong.
Covalent solids do not conduct electricity because there are no free electrons or ions to carry the electric charge.

Molecular Solids

Molecular solids are composed of individual molecules held together by weak forces such as van der Waals forces or hydrogen bonds. These forces are much weaker than covalent or ionic bonds, which results in solids that often have low melting points and are typically soft.
Examples of molecular solids include substances like \(\mathrm{PH}_{3}\) (phosphine), \(\mathrm{H}_{2}\) (hydrogen), and \(\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}\) (glucose).
In these solids, the molecules retain their integrity, meaning they do not break apart into atoms or ions like in other solids. Instead, they are packed in a regular arrangement, forming a solid at low temperatures. A unique feature of molecular solids is that they are often poor conductors of electricity due to the lack of charged particles.

Metallic Solids

Metallic solids are characterized by a lattice of metal atoms with delocalized electrons. This "sea of electrons" allows metals to be both conductive and malleable. The electrons can move freely through the solid, which explains the excellent electrical and thermal conductivity of metals.
Examples of metallic solids are elements like \(\mathrm{Mg}\) (magnesium) and \(\mathrm{Cu}\) (copper). These solids are usually shiny and can be deformed without breaking due to the nature of metallic bonding.
The malleability and ductility of metals come from the ability of atoms to slide over each other while maintaining their metallic bonds, thanks to the mobile electrons.

Ionic Solids

Ionic solids consist of positive and negative ions held together by strong electrostatic forces, called ionic bonds. This bond typically leads to hard, brittle materials with high melting and boiling points.
Common examples include \(\mathrm{KCl}\) (potassium chloride) and \(\mathrm{NH}_{4}\mathrm{NO}_{3}\) (ammonium nitrate). These solids have a crystal lattice structure, where each ion is surrounded by ions of the opposite charge, creating a stable and rigid framework.
Ionic solids do not conduct electricity in their solid form because the ions are fixed in place. However, when melted or dissolved in water, the ions are free to move, allowing them to conduct electricity.