Types of Solids

Types of Solids

Molecular solids result due to weak intermolecular forces that attract the individual molecules to each other. These solids require relatively little energy to become liquids (or gases) and have the lowest melting points of all solids.

Research the properties of the carbon tetrahalides (CX4). Provide the state, electronic shape, and melting point for each.

Table 1 Trends in the properties of the carbon tetrahalides

Formula / State at SATP / Electronic Shape / mp (oC)
CF4
CCl4
CBr4
CI4

1.  Explain the trend in melting points for the carbon tetrahalides.

Ionic solids arise from the crystal lattice arrangement of positive and negative ions that exert electrostatic attractions toward oppositely charged ions – ionic bonds.

Ionic compounds tend to have much higher melting points due to the strength of the ionic bonds, but this can vary.

Table 2 The chlorides of alkaline earth metals

Ionic compound / mp (oC)
magnesium chloride
calcium chloride
strontium chloride
barium chloride

Research the melting points for the compounds formed by alkaline earth metals with chloride. What is the trend that arises for the melting point of chloride compounds in this group?

2.  Predict the melting point for radium chloride.

Metallic solids are held together by an arrangement of metal atoms sharing the electrons of their valence level. The positive nuclei of each metal atom are attracted to the loosely held valence electrons through metallic bonding. View images at http://www.ausetute.com.au/metallic.html.

Depending on the attraction of the nuclei to the valence electrons, the strength of metallic bonds will vary, resulting in a wide array of melting points for these solids.

Research the alkali metals to observe one of the trends noted in the periodic table.

Table 3 Melting points of alkali metals

Alkali metal / First ionization energy (kJ/mol) / mp
(oC) / 3.  Explain the trend in the melting point for the alkali metals.
lithium
sodium
potassium
rubidium
cesium

4.  The only metal to exist in the liquid state, mercury has one of the broadest temperature ranges as a liquid of any metal. Yet, mercury is unreactive. Research why mercury forms weak metallic bonds.

Covalent network solids are the final type of solid using strong covalent bonds to hold the atoms together in large structures (sometimes referred to as macromolecules). The strength of these bonds creates the most stable solids with the highest melting points.

The two allotropes of carbon, diamond and graphite, fit into this category. Research the properties of these allotropes.

Allotrope / VSEPR shape around carbon / Hybridization of carbon / Hardness
(Moh’s scale)
diamond
graphite

Table 4 The allotropes of carbon

5.  Explain the difference(s) in the intramolecular force within diamond and graphite.

6.  Quartz also falls into this category of solids. Research the structure (formula, hybridization, bonding) and properties (hardness, mp, solubility) of this covalent network.