Practice

• Look at the basic empirical formula
• If simply an atom (i.e., U), it is an atomic solid
• Label the position it is in on the periodic table
• If in the metallic properties section (roughly from 1A to 4A and everything in between), it is also a metallic solid

• Composed of cations and anions (i.e., Na⁺ and OH^–)
• Considered an ionic solid (i.e., NaOH)
• See what type of intermolecular forces
• Weak intermolecular forces and consists of one giant molecule
• It is a molecular solid (i.e., CO₂)
• Covalent bonding
• Consists of silicon or carbon
• Possibly a network solid (i.e., SiO₂)

Sample Problem

What type of solid is NaOH?

• Not an atom therefore it cannot be an atomic solid nor a metallic solid
• No silicon or carbon
• Neither is it one giant molecule or does it contain Hydrogen, dipole-dipole, or London dispersion forces.
• It is however composed of Na+ and OH- ions
• Therefore it must be an ionic solid.

Classification Table

Additional Practice

(highlight text next to/after question for answer)

What type of solid will each of the following substances form?

CO₂      Molecular. One giant molecule with discrete molecular units.
SiO₂     Covalent Network. Silicon is a component of covalent network solids.
Si         Atomic. Simply an atom.
Ru        Atomic, Metallic. Atom with metallic character
I₂         Molecular. One giant molecule with discrete molecular units.    
KBr       Ionic. K⁺ cation with a Br^– anion.
NaOH    Ionic. Na⁺ cation and OH^–  anion
U          Atomic, Metallic. An atom and metal.
CaCO₃   Ionic. Ca²⁺ cation and CO₃^2- anion

Conceptual

How do the physical properties of ionic solids differ from the properties of molecular solids?
Answer: Ionic Solids are harder and have a higher melting and boiling point. This is mainly due to the stronger bonds that ionic solids exhibit.

Why do ionic solids have higher melting point than molecular solids?
Answer: Ionic solids have strong intermolecular forces (dipole-dipole) than molecular solids (London Dispersion). Therefore, greater forces are required to overcome the change. Ionic solids also have a higher melting point due to the amount of energy needed to break apart the charged ions.

How can the properties of a metal be modified by alloying the metal with some other substance?
Answer:  The presence of a second metal’s atom in a metal’s lattice changes the properties. Steels with relatively high carbon content are exceptionally strong. Steels produced by alloying iron with nickel, chromium, and cobalt are more resistant to corrosion than iron itself.