Trends and Properties in the Periodic Table

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Trends and Properties in the Periodic Table

What do you already know about the groups of the periodic table?

Learning Objective

At the end of the lesson you will be able to describe and predict the trends and properties of elements in Groups I, VII and the transition elements, and explain the behaviour of noble gases.

The Periodic Table: A Summary

The periodic table organises elements into groups and periods, showing patterns in their properties.

Group I: Alkali Metals

Group I elements include lithium, sodium and potassium. These metals show clear trends in their physical and chemical properties.

Physical Properties of Alkali Metals

Alkali metals are relatively soft. They can be cut with a knife and have a shiny surface when freshly cut.

Trends in Alkali Metals

Density & Reactivity

Melting points decrease as you go down the group, from lithium to potassium.

Melting Point

Density and reactivity both increase as you move down the group.

Chemical Reactivity Trends

Lithium reacts slowly with water, sodium reacts faster, and potassium reacts very vigorously. This shows increasing reactivity down the group.

Predicting Other Group I Properties

Given the trends, rubidium and caesium (below potassium) would likely be even denser, have lower melting points, and be more reactive.

Group VII: The Halogens

The halogens are diatomic non-metals, meaning they exist as pairs of atoms (e.g., Cl₂, Br₂, I₂).

Physical States of Halogens

Chlorine is a pale yellow-green gas, bromine is a red-brown liquid, and iodine is a grey-black solid at room temperature and pressure.

Trends in Group VII

Density increases as you go down the group: chlorine < bromine < iodine.

Density

Reactivity decreases down the group: chlorine is most reactive; iodine is least.

Reactivity

Displacement Reactions of Halogens

A more reactive halogen can displace a less reactive halogen from its salt. Example: chlorine displaces bromine from potassium bromide.

Predicting Properties of Other Halogens

Astatine, below iodine, is expected to be a solid, denser, and the least reactive halogen.

Transition Elements: An Introduction

The transition elements are found in the centre of the periodic table, between Groups II and III.

Transition Elements—Typical Properties

They have high densities and high melting points, form coloured compounds, and often act as catalysts.

Variable Oxidation Numbers

Transition elements can form ions with different charges. Iron, for example, forms Fe²⁺ and Fe³⁺ ions.

Quick Facts: Alkali vs Transition Metals

Alkali Metals

Transition Elements

High density, hard, less reactive, high melting point.

Low density, soft, very reactive, low melting point.

Group VIII: Noble Gases

Noble gases are unreactive, monatomic gases. Examples: helium, neon, argon.

Why Are Noble Gases Unreactive?

Their outer electron shells are full, making them stable and unlikely to react.

Summary: Trends Across the Table

Group I: melting point ↓, density & reactivity ↑ Group VII: density ↑, reactivity ↓ Transition elements: coloured ions, variable oxidation numbers Noble gases: unreactive, monatomic

Check Your Understanding!

Can you now explain the main trends for Group I, Group VII, transition elements, and noble gases?

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