Chemistry of Selected Elements: Properties and Reactions

This document provides detailed notes on the chemistry of selected elements, focusing on their properties and characteristic reactions. These notes are intended for Cambridge A-Level Chemistry (9701) students.

Group 1: Alkali Metals

Properties

Alkali metals (Li, Na, K, Rb, Cs) are highly reactive metals. Key properties include:

• Low melting and boiling points (increasing down the group)
• Soft, silvery-white metals
• Low density (increasing down the group)
• Highly reactive with water and air
• React vigorously with halogens
• Electronegativity decreases down the group

Reactions

Reaction with Water

The reactivity of alkali metals with water increases down the group. The reaction produces hydrogen gas and a metal hydroxide.

For example, the reaction of sodium with water is:

$$2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)$$

Reaction with Halogens

Alkali metals react directly with halogens (fluorine, chlorine, bromine, iodine) to form ionic halides.

For example, the reaction of potassium with chlorine is:

$$2K(s) + Cl_2(g) \rightarrow 2KCl(s)$$

Trends

Property	Trend down Group
Melting Point	Increases
Boiling Point	Increases
Reactivity with Water	Increases
Density	Increases

Group 2: Alkaline Earth Metals

Properties

Alkaline earth metals (Be, Mg, Ca, Sr, Ba) are reactive metals, though generally less reactive than alkali metals. Key properties include:

• Higher melting and boiling points than alkali metals
• Harder and denser than alkali metals
• Less reactive than alkali metals
• React with water (though less vigorously than alkali metals)
• React with halogens

Reactions

Reaction with Water

Alkaline earth metals react with water to produce hydrogen gas and a metal hydroxide, but the reaction is slower than that of alkali metals.

For example, the reaction of calcium with water is:

$$Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g)$$

Reaction with Halogens

Alkaline earth metals react with halogens to form ionic halides.

For example, the reaction of magnesium with chlorine is:

$$2Mg(s) + Cl_2(g) \rightarrow 2MgCl_2(s)$$

Group 17: Halogens

Properties

Halogens (F, Cl, Br, I) are highly reactive non-metals. Key properties include:

• Exist as diatomic molecules (F₂, Cl₂, Br₂, I₂)
• Colorless or pale-colored
• Liquid at room temperature (Br₂)
• Electronegativity decreases down the group
• Reactivity decreases down the group
• Strong oxidizing agents

Reactions

Reaction with Metals

Halogens react with metals to form ionic halides.

For example, the reaction of sodium with chlorine is:

$$2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)$$

Reaction with Hydrogen

Halogens react with hydrogen to form hydrogen halides.

For example, the reaction of chlorine with hydrogen is:

$$H_2(g) + Cl_2(g) \rightarrow 2HCl(g)$$

Reactivity Trends

Reactivity decreases down the group: F > Cl > Br > I

Group 18: Noble Gases

Properties

Noble gases (He, Ne, Ar, Kr, Xe, Rn) are very unreactive. Key properties include:

• Exist as monatomic gases
• Inert (do not readily form chemical compounds)
• Low boiling points
• Low reactivity

Reactions

Noble gases are generally unreactive, but some heavier noble gases (like Xenon and Krypton) can form compounds under specific conditions.

For example, Xenon can form compounds with fluorine.

Other Important Elements

Carbon

Carbon exists in various allotropes, including diamond and graphite. It is a non-metal and a key element in organic chemistry.

Nitrogen

Nitrogen is a diatomic gas (N₂) and is relatively unreactive. It is a major component of the atmosphere.

Oxygen

Oxygen is a diatomic gas (O₂) and is essential for respiration and combustion. It is a strong oxidizing agent.

Sulfur

Sulfur exists in various allotropes and is a non-metal. It is involved in many chemical reactions and is a component of some minerals.