Account for the following statements or observations in terms of atomic-, ionic- or molecular-level — Atomic Structure and Periodicity / Chemical Bonding Chemistry Question

The Mg²⁺ ion is smaller and has a higher charge than the Mg⁺ ion, so the lattice energy that arises when Mg²⁺ ions form compounds is much greater than what would be observed if Mg⁺ ions formed compounds. The increase in lattice energy more than offsets the larger ionization energy of the Mg²⁺ ion.

Ti (atomic number 24) has a valence electron configuration of 4s23d₂ and can form +2 ions by losing it’s two 4s electrons, +3 ions by losing the two 4s electrons and one 3d electron and +4 by losing all four of the valence electrons. The +2 and +3 ions are colored because of electronic transitions between d orbitals. The +4 ion does not exhibit color because it has no valence d-electrons to undergo electronic transitions.

Carbon dioxide (O=C=O) molecules are nonpolar and interact with each other only through weak dispersion forces. These weak forces are easily overcome so CO₂ is a gas at room temperature. SiO₂ doesn’t have the same molecular formula, because Si does not form double bonds as readily as carbon does. Si^-O form single bonds that lead to a network solid held together with strong, covalent bonds, so it is a solid that has a high melting point.

Nitrogen can form three bonds (NF₃) but not five (NF₅) because it lacks d orbitals that are energetically available for the formation of hybrid orbitals (or alternatively, because it is too small to accommodate five atoms.) Both NF₃ and PF₃ are trigonal pyramidal because the central atom has three bonding pairs and one lone pair of electrons (leading to sp₃ hybridization). PF₅ is trigonal bipyramidal because it has five bonding pairs (leading to dsp₃ hybridization.)