Chemical Changes & Structure

This section covers the fundamentals of reaction rates and factors that influence them in National 5 Chemistry.

Definition: The rate of reaction is calculated using the formula: rate = Δ quantity / Δ time

Factors that increase reaction rates include:

1. Increasing particle size (for solids)
2. Increasing concentration
3. Increasing temperature
4. Using catalysts

Vocabulary: Catalysts are substances that speed up chemical reactions without being consumed. They can be heterogeneous (different state from reactants) or homogeneous (same state as reactants).

Example: Enzymes are biological catalysts that speed up reactions in living cells.

The section also covers methods for following reactions by measuring changes in concentration, mass, or volume of reactants and products.

Highlight: The rate of reaction at a given stage is calculated using the formula: rate = 1 / t

An example graph is provided to illustrate how to calculate the rate of reaction during the first 120 seconds of a gas-producing reaction.

Periodic Table & Atoms (Part 2)

This section delves deeper into atomic structure and covalent bonding for National 5 Chemistry Unit 1.

Definition: An atom consists of a nucleus containing protons and neutrons, with electrons orbiting in energy levels.

The section explains the charges of subatomic particles and introduces the concept of atomic number and mass number.

Vocabulary: Isotopes are atoms with the same atomic number but different mass numbers.

The relative atomic mass is introduced as the average mass of all isotopes of an element, with a formula provided for its calculation.

The section then transitions to covalent bonding:

Definition: A covalent bond forms when two positive nuclei are held together by their common attraction for a shared pair of electrons.

Key points about covalent bonding include:

• It typically forms between non-metal atoms
• Atoms achieve stable electron arrangements similar to noble gases
• Some elements exist as diatomic molecules (e.g., H₂, Cl₂, N₂)
• Multiple bonds can form between atoms

The section concludes by mentioning that the shape of simple covalent molecules depends on various factors, setting the stage for further discussion in subsequent units.