Core relationships

Topic 1: Stoichiometric relationships

& Different types of bonding affect the properties of substances including changes of state (1.1).

Topic 2: Atomic structure

Ionic compounds are formed as the result of electron transfer. The electrons that are transferred result in the ions formed having the same electron arrangement as a noble gas (2.2).

Topic 3: Periodicity

In order to predict whether a compound formed between two elements will be covalent or ionic their position in the periodic table and their electronegativities need to be taken into account (3.1 and 3.2).

Topic 5: Energetics/thermochemistry

To be able to explain the relationship between the number of bonds and bond strength it is necessary to be able to calculate the enthalpy changes associated with breaking and making bonds (5.3).

Topic 6: Chemical kinetics

The rate of a reaction increases as the temperature is increased because the extra energy increases the likelihood of the shared pair of electrons in a covalent bond having the necessary activation energy to split apart when molecules collide (6.1).

Topic 7: Equilibrium

Resonance structures such as those shown in benzene and the carbonate anion are not in dynamic equilibrium (7.1) with each other. Resonance structures are extreme forms and the true structure lies between the resonance structures.

Topic 8: Acids & bases

When weak acids dissociate in aqueous solution (8.4) a covalent bond needs to be broken to form a hydronium ion, H₃O⁺ and the acid radical.

Topic 9 Redox processes.

The formation of ionic compounds (such as NaCl or MgO) from their elements involves the transfer of electrons so that it can always be classified as a redox reaction. The species that has lost electrons is oxidized and the species that has gained electrons is reduced (9.1).

Topic 10: Organic chemistry

Nucleophiles are electron-rich species that contain a non-bonding pair of electrons that they donate to an electron-deficient carbon (10.2). The donated pair of electrons form a coordinate bond.

Topic 11: Measurement & data processing

The relative polarity of bonds can be predicted from electronegativity values. These values are not exact and there are different scales of measurement. Pauling’s scale gives the values to one decimal place whereas some other other values used in periodicity (e.g. atomic mass) are given to two decimal places. (11.1).