Molecular substance

Key concepts for explanation:

• Draw Lewis diagram of the molecule

• Identify the centre atom and regions of electronegativities (electrons clusters) around the centre atom

• Commenting on the shape of separation (Tetrahedral for 4 regions, Trigonal planar for 3 regions, linear for 2 regions)

• Commenting on how many bonding regions and how many non-bonding regions around the centre atom.

• Determine the final shape of the molecule 

Key concepts for explanation:

• Commenting on the polarity of bond by linking the electronegativity of the atoms that form the bond (non-polar if the atoms are the same; polar if the atoms are different).

• Commenting on the symmetry of the molecule (symmetrical: tetrahedral, linear, trigonal planar; asymmetrical: bent, trigonal pyramidal)

• Determine the polarity of molecule based on the type of bond and shape of molecule

Types of Solid (molecular, Metallic, Ionic, Giant 3D Net Work)

Key concepts for explanation:

• Commenting on the structure of the solids

• Commenting on the type of bonds that hold the particles within the solid ( Intermolecular forces, Covalent bond, Ionic bond, Metallic bond)

• Elaborating the physical properties and how they are linked with the structure and the specific type of bonding within the solid.

• Key physical properties: Boiling and Melting points, Malleability, Ductility, Electricity conductivity, Hardness, Solubility

Thermal Chemistry 

Exothermic reaction: 

An exothermic reaction is a chemical reaction that releases energy, usually in the form of heat, making the surroundings warmer.

Key information that you should include for an exothermic diagram:

-Energy Level of Reactants: The diagram starts with a higher energy level for the reactants on the left side.

-Energy Drop: As the reaction progresses, there’s a downward slope showing a drop in energy, indicating energy release.

-Energy Level of Products: The products appear at a lower energy level than the reactants, meaning the reaction has released energy.

-Activation Energy: There’s often a small “hump” between reactants and products, representing the activation energy (the initial energy needed to start the reaction).

-Overall Energy Release: The difference in height between the reactants and products shows the total energy released by the reaction.

Endothermic reaction:

An Endothermic reaction is a chemical reaction that absorbs energy, usually in the form of heat, making the surroundings cooler.

Key information that you should include for an endothermic diagram:

-Energy Level of Reactants: The diagram starts with the reactants at a lower energy level on the left side.

-Energy Increase: As the reaction progresses, there’s an upward slope, indicating that energy is absorbed during the reaction.

-Energy Level of Products: The products are at a higher energy level than the reactants, meaning the reaction has taken in energy.

-Activation Energy: There’s typically a “hump” between the reactants and products, representing the activation energy (the minimum energy needed to start the reaction).

-Overall Energy Absorption: The difference in height between the reactants and products shows the total energy absorbed by the reaction.

Calculations in Thermal Chemistry

Type 1: Calculation by using bond enthalpy

Type 2: Calculation by using stoichiometry

More Thermal Chemistry Calculation Practice