how to distinguish whether molecule is a giant ionic or covalent bond or just a simple molecular structure?

Question

There is a question about the bonding btw 1.(fluorine and magnesium) 2.(fluorine and bromine). I don't know how to distinguish the three bonding.

Answer 1

These can generally be distinguished by melting and boiling points, strength and conductivity. A giant ionic compound is one where there is a metal and non metal and the metal donates the electron(s) and non metal accepts the electron(s) leaving a cation and anion. These are attracted to form a large lattice structure. Melting and boiling points are high and they conduct a current. Examples: sodium chloride (NaCl), magnesium chloride (MgCl₂), etc.

A giant covalent compound is one in which a lot of non metal atoms are joined to other adjacent atoms by covalent bonds (sharing electrons) and arranged to form a giant lattice structure. These have very high melting and boiling points (higher than giant ionic) and they generally do not conduct a current (graphite being an exception). Example: graphite, diamond.

A simple molecular structure is just a covalent molecule where atoms are joined by covalent bonds (sharing electrons) but do not form a large lattice structure. The have lower melting and boiling points and generally do not conduct a current. Examples: methane, ethane, glucose, etc.