Periodic Trends, Hydrides, Oxides & Halides

What is the general periodic trend down a group for main group elements?

Metallic character increases; elements become better conductors with delocalized bonding.

What is the general periodic trend across a period for main group elements?

Non-metallic character increases; elements become insulators with localized bonding.

What are metalloids and where are they found in the periodic table?

Elements like boron and silicon at the metal-nonmetal boundary; low conductivity that increases with temperature.

How are hydrides usually formed?

By reaction of a metal with hydrogen, e.g., Na(s) + H₂(g) → NaH(s).

What determines the type of hydride formed?

Difference in electronegativity between the element and hydrogen.

What type of hydrides do highly electropositive metals form?

Ionic hydrides (M⁺H⁻).

What type of hydrides do elements in the center and right of the periodic table form?

Covalent hydrides.

What is the structure of BH₃?

Hydrogen-bridged oligomer (B₂H₆).

What is the structure of CH₄?

Molecular covalent.

What is the structure of HCl?

Molecular covalent.

How do ionic hydrides react with water?

Form hydroxide and release hydrogen gas, e.g., NaH + H₂O → NaOH + H₂.

How are oxides formed?

By reaction of a metal with oxygen.

What are the three types of oxides?

Normal oxide, peroxide, superoxide.

What determines oxide bonding type?

Difference in electronegativity between element and oxygen.

What type of oxides do highly electropositive metals form?

Ionic oxides.

What type of oxides do less electropositive elements form?

Covalent oxides (often polar).

What happens to oxide bonding across a period?

Changes from ionic → amphoteric → polymeric covalent → molecular covalent.

What is an amphoteric oxide?

An oxide that can act as both an acid and a base.

Give examples of amphoteric oxides.

Al₂O₃, SiO₂.

What type of solutions do ionic oxides form in water?

Basic solutions.

What type of solutions do oxides of Groups 15, 16, 17 form?

Acidic solutions.

How does Na₂O react with water?

Forms a strong base: Na₂O + H₂O → NaOH.

How does Al₂O₃ react with water?

Dissolves in both acidic and basic solutions.

How does SiO₂ react with water?

Dissolves in both acidic and basic solutions.

How does CO₂ react with water?

Forms a weak acid (H₂CO₃).

How does SO₃ react with water?

Forms a strong acid (H₂SO₄).

How are halides formed?

By combination of a metal and halogen, e.g., Na(s) + Cl₂ → NaCl(s).

What is the periodic trend for halide bonding?

Left side (Groups 1 & 2) form ionic, water-soluble, conducting halides; right side (Groups 13-15) form covalent halides.

What happens when covalent halides of Groups 13-15 react with water?

They often produce acidic solutions, e.g., HCl formation.