EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记：1.7.2 Covalent Bonds: Dot & Cross Diagrams

• Covalent substances tend to have small molecular structures, such as Cl₂, H₂O or CO₂
• These small molecules are known as simple molecules
• Small covalent molecules can be represented by dot and cross diagrams
• You need to be able to describe and draw the structures of the following molecules using dot-and-cross diagrams: hydrogen (H₂), chlorine (Cl₂), oxygen (O₂), nitrogen (N₂), hydrogen chloride (HCl), water (H₂O), ammonia (NH₃) and methane (CH₄)
• The correct dot and cross diagrams for these molecules are shown below:

Diatomic Molecules

Dot & cross representation of a molecule of hydrogen

Dot & cross representation of a molecule of chlorine

Dot & cross representation of a molecule of oxygen

Dot & cross representation of a molecule of nitrogen

Dot & cross representation of a molecule of hydrogen chloride

Inorganic Molecules

Dot & cross representation of a molecule of water

Dot & cross representation of a molecule of ammonia

Dot & cross representation of a molecule of carbon dioxide

Organic Molecules

Dot & cross representation of a molecule of methane

Dot & cross representation of a molecule of ethane

Dot & cross representation of a molecule of ethene