A non-metal element which lies in the third row of the Periodic Table forms a gaseous compound H2Y with hydrogen and the compound

Li2Y with lithium, which has a solid crystalline structure and a high melting point (greater than 900 °C).

A non-metal element which lies in the fourth row of the Periodic Table forms a gaseous compound HZ with hydrogen and the compound KZ with potassium, which has a solid crystalline structure and a high melting point (greater than 700 °C).
(i)
Identify to which Group of the Periodic Table the elements Y and Z belong and hence write down the name and chemical symbol of Y and
Z. Give brief reasoning on how you arrived at your answers, including the likely valency of Y and Z in the compounds given.
(ii)
What type of bonding is involved in compounds Li2Y and KZ? Give your reasoning.
(iii) State two different conditions under which you would expect
compounds Li2Y and KZ to conduct electricity. Explain your answer in terms of the type of bonding found in the compounds

(i) To identify the Group to which elements Y and Z belong, we can use the information provided.

For Y: Since it forms a gaseous compound H2Y with hydrogen and a solid crystalline compound Li2Y with lithium, we can infer that Y is a non-metal element. Additionally, it is mentioned that Y lies in the third row of the Periodic Table. Therefore, by referring to the Periodic Table, we can see that Y belongs to Group 16 (also known as Group VIA) since the elements in this group are non-metals and situated in the third row.

The chemical symbol for the element belonging to Group 16 is oxygen, so Y is Oxygen (O).

Regarding the valency of Y, it is likely to have a valency of 2- since it forms the compound H2Y with hydrogen.

For Z: As mentioned, Z forms a gaseous compound HZ with hydrogen and a solid crystalline compound KZ with potassium. We are informed that Z lies in the fourth row of the Periodic Table. By referring to the Periodic Table, we can see that Z belongs to Group 14 (also known as Group IVA) since the elements in this group are non-metals situated in the fourth row.

The chemical symbol for the element belonging to Group 14 is carbon, so Z is Carbon (C).

The valency of Z in the compounds given can be deduced based on the number of hydrogen or potassium atoms it combines with. Considering Z forms the compounds HZ with hydrogen and KZ with potassium, it is likely that Z has a valency of 4+.

(ii) In compounds Li2Y (Li2O) and KZ (KC), the type of bonding involved can be identified by examining the nature of the compounds and the elements involved.

Li2Y: Since Y (oxygen) is a non-metal and lithium is a metal, the bonding between them in Li2Y is likely to be ionic bonding. This is because metals generally form positive ions (cations), and non-metals form negative ions (anions). In this case, lithium (Li) loses two electrons to form a 2+ cation, while oxygen (O) gains two electrons to form a 2- anion. The electrostatic attraction between the oppositely charged ions results in the ionic bonding in Li2Y.

KZ: In the case of KZ, both elements involved (potassium and carbon) are metals. Therefore, the bonding in KZ is likely to be metallic bonding. Metallic bonding occurs between metal atoms when the valence electrons delocalize and form a "sea" of electrons. This delocalized electron sea allows for the high electrical and thermal conductivity typically observed in metals.

(iii) Compounds Li2Y and KZ can conduct electricity under specific conditions based on the type of bonding found in the compounds.

Li2Y (Li2O): Ionic compounds like Li2Y conduct electricity when they are in a molten state or dissolved in water. This is because in these states, the ionic compound dissociates into its constituent ions, which are then free to move and carry electric charge. In the solid state, ionic compounds are generally non-conductive since the ions are held in a fixed arrangement.

KZ (KC): Metallic compounds like KZ conduct electricity in both the solid and molten states. This is due to the presence of delocalized electrons in the metallic bonding structure. These delocalized electrons are free to move throughout the metal, allowing for the conduction of electric current.

I'll give you a couple of hints but leave you with the remainder to go through.

Y probably is the element S and Z probably is the element Br.
Good luck.

The chemical name of element Y