Edexcel IGCSE Chemistry 复习笔记 1.7.2 Covalent Bonds: Dot & Cross Diagrams
Edexcel IGCSE Chemistry 复习笔记 1.7.2 Covalent Bonds: Dot & Cross Diagrams
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
Exam Tip
Simple covalent molecules are small and can be separated into individual molecular units without breaking any chemical bonds (although there will still be strong covalent bonds holding the atoms in each individual molecule together) Giant ionic and covalent structures form huge continuous networks of atoms that are bonded together and cannot be separated into individual units without breaking bonds.
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