c) State the chemical family to which element Y belongs.

9. c) State the chemical family to which element Y belongs.
Element Y (Potassium) is in Group 1 of the periodic table.

• Chemical family: Alkali metals

9. d) Predict the type of ion formed by element Y and explain why.
Element Y has 1 valence electron. It will lose this electron to achieve a stable electron configuration.

• Type of ion: Cation (specifically, K⁺)
• Explanation: Element Y loses its single valence electron to attain a stable octet electron configuration, similar to a noble gas. Losing an electron results in a positive charge.

9. d) State two reasons why noble gases are chemically stable.

*i) Noble gases have a full outermost electron shell (a stable octet, or duplet for helium).

*ii) This stable electron configuration means they do not readily gain, lose, or share electrons, making them unreactive.

9. e) Give an example of an element under the following category.

*i) Alkaline earth metal: Magnesium (Mg)

*ii) Halogen: Chlorine (Cl)

*iii) Noble gas: Neon (Ne)

10. a) Write the electron arrangement (s and p notation) for the following ions:

i) Na⁺
Neutral sodium (Na) has an atomic number of 11, so its electron configuration is $1s^2 2s^2 2p^6 3s^1$. When it forms Na⁺, it loses one electron from the $3s$ orbital.

• Electron arrangement: $\boxed{1s^2 2s^2 2p^6}$

ii) O²⁻
Neutral oxygen (O) has an atomic number of 8, so its electron configuration is $1s^2 2s^2 2p^4$. When it forms O²⁻, it gains two electrons to fill the $2p$ orbital.

• Electron arrangement: $\boxed{1s^2 2s^2 2p^6}$

10. b) Using valency or oxidation numbers, write the chemical formula of:

i) Magnesium chloride
Magnesium (Mg) has a valency of 2 (forms Mg²⁺). Chlorine (Cl) has a valency of 1 (forms Cl⁻). To balance the charges, one Mg²⁺ ion combines with two Cl⁻ ions.

• Chemical formula: $\boxed{MgCl_2}$

ii) Aluminium oxide
Aluminium (Al) has a valency of 3 (forms Al³⁺). Oxygen (O) has a valency of 2 (forms O²⁻). To balance the charges, two Al³⁺ ions combine with three O²⁻ ions.

• Chemical formula: $\boxed{Al_2O_3}$

10. c) Balance the following chemical equation:

$$Fe + O_2 \rightarrow Fe_2O_3$$