Explanation:
SiO2 has a giant covalent structure where each Si atom is singly bonded to four oxygen atoms (while maintaining a Si

ratio of 1:2).
As there are four electron domains around each silicon atom, the structure has a tetrahedral arrangement. SiO2 is held together by strong covalent bonds requiring a large amount of energy to overcome, resulting in a high melting point.
The strong bonds, together with the fact that there are no charged particles present, lead to insolubility in polar solvents such as water.

Explanation:
Triple bonds are stronger than double bonds which are in turn stronger than single bonds. The greater the number of shared pairs of electrons, the stronger the bond and the greater the bond enthalpy.

Explanation:
Choice A refers to ionic bonding;
Choice B could refer to ionic bonding or specifically coordinate (dative) bonding;
Choice C refers to hydrogen bonding.

Explanation:
There is no polyatomic ion with the formula of CO42−COX42−. The correct formula for the carbonate ion is CO32−COX32−. The formulas and charges of the other ions are correct.

Explanation:
To answer this question, the student must apply the data to the van Arkel-Ketelaar triangle to determine the type of bonding present in the molecule.

The bonding triangle analysis shows that the material is an ionic compound. Therefore, characteristic properties include that it is a crystalline lattice with a high melting point.

This question is categorized as easy since the student only needs to apply the data to Section 17 of the data booklet and then recall the basic properties of matter.

Explanation:
Alloys are homogeneous mixtures of metals with other metals or nonmetals.

Explanation:

Lithium is in group 1 and so forms Li+ ions. The formula of the nitride ion is N3−as nitrogen is in group 15. For the positive and negative charges to cancel out, three Li+ ions are needed for each N3− ion.

Explanation:
Electrostatic forces of attraction between the positive ions and delocalized electrons (metallic bonds) must be broken for metal to melt. The stronger the metallic bond, the higher the melting point.

Explanation:
There are three bonding pairs and no lone pairs around the central B atom giving it a trigonal planar shape. As this is symmetrical, there is no net dipole even though the individual bonds are polar. There are only six electrons around the central B atom making it electron deficient (it has not achieved its octet).

Explanation:
The higher the charge of the ions, the stronger the electrostatic forces of attraction and, therefore, the greater the lattice enthalpy.
The smaller the ion, the greater the charge density and the stronger the electrostatic attraction between oppositely charged ions.
Statement I is incorrect since the smaller the lattice enthalpy, the weaker the electrostatic attraction and the lower the melting point is.

Explanation:
NH3 has all of the bonds/forces named above, but its high boiling point is due to the presence of hydrogen bonds which are the strongest intermolecular forces. Hydrogen bonding is possible due to the presence of N−H bonds.

Explanation:
N2 has a triple bond, O2 has a double bond, and H2only has a single bond.
The greater the number of shared pairs of electrons, the stronger the bond.

Explanation:
Graphite is made up of individual graphene layers. Both have carbon atoms with three electron domains and trigonal planar shapes. Each carbon atom in diamond has four electron domains resulting in tetrahedral arrangements.

Explanation:
There is no polyatomic ion with the formula of CO4 ^2−. The correct formula for the carbonate ion is CO3^2−. The formulas and charges of the other ions are correct.

Explanation:
Simple molecular covalent structures cannot conduct electricity due to an absence of charged particles. $\mathrm{NaCl}$ is an ionic compound that has ions that are free to move when in a molten state.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2 is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:
The strength of metallic bonding and therefore melting point, decreases down a group due to increasing atomic radius (more energy levels) and greater separation of the nuclei. Cs is in period 6, while all other 3 elements are in period 5. Hence, Cs has the lowest melting point. Since atomic radius decreases across a period due to increased effective nuclear charge, the strength of metallic bonding, and therefore melting point, increases from Rb to Zr.

Explanation:
2-methylpentane is branched and therefore has a lower surface area. The lower the surface area, the weaker the London (dispersion) forces and the lower the boiling point.

Explanation:
Neither material is electrically conductive. Diamond has no delocalized electrons, while the delocalized electrons in buckminsterfullerene are confined within the molecule. There is no extended lattice of bonds through which the electrons can move in response to an applied potential difference. Diamond is a hard material; a large force is required to break the strong covalent bonds between atoms.

Buckminsterfullerene, however, is soft, as only a small force is needed to overcome the weak intermolecular (London / dispersion) forces between molecules.

This question is moderately difficult, as the student must recall multiple features of the two carbon allotropes or deduce their physical properties from the diagrams given.

Explanation:
The other three in theory, can form hydrogen bonds due to O−H and F−H bonds present.

Explanation:
Strontium is in group 2 and so forms Sr2+ ions. The formula of the sulfide ion is S2− as sulfur is in group 16. For the positive and negative charges to cancel out, one of each ion is required.

Explanation:
All three central atoms (N, C, and O) have four electron domains. An increasing number of lone pairs reduces the angle between the bonding pairs.
In CH4 there are no lone pairs and it has a tetrahedral shape with bond angles of 109.5$°$.
In NH3 there is one lone pair and it has a trigonal pyramidal shape with bond angles of 107°.
In H2O, there are two lone pairs, and it has a bent shape with bond angles of 104.5$°$.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2 is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2 is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.