periodic table I and II

Question 1

melting points from phosphorus to chlorine

Answer 1

low melting and boiling points
they have simple molecular structures. The presence of weak id-id interactions between the molecules require little energy to overcome.
However, cl2 < p4 < s8, because greater the size of the electron cloud, the greater the number of electrons and the greater the strength of id-id interactions.

Question 2

electrical conductivity from Na to Al

Answer 2

increases, due to increasing number of delocalised valence electrons

Question 3

is Na a good conductor of electricity?

Answer 3

Yes, it has a giant metallic structure where electrostatic forces of attraction exist between the metallic cations and sea of delocalised electrons. Presence of sea of delocalised valence electrons can act as mobile charge carriers.

Question 4

explain deviation from expected trend or melting points of ionic oxides [melting point did not increase from Na2O to Al2O3]

Answer 4

this is because there is difference in their packing in the solid state and the slight covalent character of Al2O3 due to the high charge density and thus high poliarising power of Al3+.

Question 5

explain why SiCl4 can hydrolyse in water but CCl4 cannot.

Answer 5

This is because Si has a larger valence orbital than C and thus this results in less steric hindrance for the water nucleophile to attack, allowing for nucleophilic attack to occur more readily. Furthermore, Si is in period 3 and thus has a low-lying vacant 3d orbital which allows it to expand its octtet and accept the lone pair of electrons from the water nucleophile.

Question 6

explain why MgCl2 is a solid with a high melting point while SiCl4 is a volatile liquid

Answer 6

MgCl2 has a giant ionic structure and thus a large amount of energy is required to overcome the strong ionic bonds between the oppositely charged Mg2+ and Cl- ions
on the other hand, SiCl4 has a simple covalent structure and thus little energy is required to overcome the weak intermolecular id-id interactions between the SiCl4 molecules.

Question 7

MgO is insoluble in water whereas BaO dissolves to give an alkaline solution. An aqueous solution of SO3 is acidic.

Answer 7

Ba2+ and Mg2+ have the same charge but the ionic radius of Ba2+ is larger so this results in the lattice energy of BaO being less negative than that of MgO.
A larger amount of energy needed to break the ionic bonds within MgO and hence MgO is insoluble in water [energy released from the formation of ion-dipole interactions is insufficient to compensate for the energy required to overcome the strong ionic bonds]

BaO dissolves in water to form Ba2+ and O2-. The strongly basic O2- ions cause the solution to be alkaline.

SO3 is soluble in water because it reacts with water to form H2SO4 which is a strong acid.

Question 8

expalin why oxides of sodium and silicon have these formulae.
[Na2O ,SiO2

Answer 8

Na has 1 valence electron while oxygen has 6 valence electron. Na loses 1 electron to become Na+ while O2 gains 2 electrons to become O2-. To maintain electrical neutrality, the formula of sodium oxide is Na2O.

Si has 4 valence electrons. 1 Si atom shares one valence electron

Question 8

expalin why oxides of sodium and silicon have these formulae.
[Na2O , SiO2]

Answer 8

Na has 1 valence electron while oxygen has 6 valence electron. Na loses 1 electron to become Na+ while O2 gains 2 electrons to become O2-. To maintain electrical neutrality, the formula of sodium oxide is Na2O.

Si has 4 valence electrons. 1 Si atom shares one valence electron with 4 O atoms while 1 O atom shares 1 electron each with 2 Si atom. Hence, formula is SiO2