Group Properties And Trends

Group I – The Alkali Metals

• Group I metals are called alkali metals because they form alkaline solutions when they react with water.
• They include lithium (Li), sodium (Na) and potassium (K).
• All have one electron in their outer shell.

Physical Properties of Group I

• They are soft and easy to cut; they get softer down the group.
• They have shiny silvery surfaces when freshly cut.
• They have low melting points (decrease down the group) and low densities.

Which statement about Group I metals is correct?

• They become harder as you go down the group.
• Their melting points increase down the group.
• They are stored under oil to prevent reaction with air.
• They have high densities compared to other metals.

Reactions with Water

• Group I metals react with water to form an alkaline metal hydroxide and hydrogen gas.
• General equation: 2M + 2H₂O → 2MOH + H₂.
• Reactivity increases down the group: lithium fizzes slowly, sodium moves rapidly, potassium burns with a lilac flame.

When sodium reacts with water, the products are sodium ____ and ____ gas.

Trends in Group I

• Down the group: melting point decreases, density increases, reactivity increases.
• Francium at the bottom is the most reactive; lithium at the top is the least reactive.
• Predictions can be made for rubidium, caesium and francium based on trends.

Which of these are true about Group I metals?

• Lithium is more reactive than potassium.
• Density increases down the group.
• They all have one electron in their outer shell.
• Melting point increases down the group.

Group VII – The Halogens

• Group VII elements are non-metals called halogens: fluorine, chlorine, bromine, iodine, astatine.
• They are diatomic (molecules of two atoms: F₂, Cl₂, Br₂, I₂).
• All have seven electrons in their outer shell and gain one electron to form halide ions.

Physical States and Colours

• At room temperature: chlorine is a pale yellow-green gas, bromine is a red-brown liquid, iodine is a grey-black solid.
• Density increases down the group.
• Colour becomes darker down the group.

What is the colour of bromine at room temperature?

• Pale yellow-green
• Red-brown
• Grey-black
• Purple

Reactivity Trend in Group VII

• Reactivity decreases down the group (opposite to Group I).
• As you go down, atomic radius increases and electron shielding increases, making it harder to attract an electron.
• Fluorine is the most reactive; astatine is the least reactive.

The reactivity of halogens ____ down the group because the attraction for an incoming electron ____.

Displacement Reactions

• A more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
• Example: chlorine displaces bromine from potassium bromide: 2KBr + Cl₂ → 2KCl + Br₂.
• The solution turns orange when bromine is formed, brown when iodine is formed.

What is observed when chlorine water is added to potassium iodide solution?

• No reaction
• A yellow-orange colour
• A brown colour
• A purple vapour

Transition Elements

• Transition elements are in the centre of the Periodic Table between Group 2 and Group 3.
• They are typical metals: lustrous, hard, strong, conduct heat and electricity, high melting points (except mercury).
• Unique properties: form ions with different charges (e.g. Fe²⁺ and Fe³⁺), act as catalysts, form coloured compounds.

Which of these are properties of transition elements?

• They form colourless compounds.
• They can act as catalysts.
• They have variable oxidation states.
• All have low melting points.

Noble Gases

• Group VIII (Group 0) elements are noble gases: helium, neon, argon, krypton, xenon.
• They are monatomic, colourless gases with very low melting and boiling points.
• They are unreactive (inert) because they have full outer electron shells.

Why are noble gases unreactive?

• They have low melting points.
• They are monatomic.
• They have full outer electron shells.
• They are colourless.