WJEC Chemistry for AS: Study and Rev Guide

Knowledge and Understanding U1 The Language of Chemistry, Structure of Matter and Simple Reactions This unit begins with an introduction to chemical language followed by some important fundamental ideas about atoms and the use of the mole concept in calculations. The usefulness of materials depends on their properties that in turn depend on their internal structure and bonding. By understanding the relationship between these, chemists can design new useful materials. The types of forces between particles are studied along with several types of solid structures to show how these influence properties. The building blocks of materials are the elements and the relationship of their properties to their position in the Periodic Table is illustrated by a study of the elements of the s-block and Group 7. The key principles governing the position of equilibrium between reactants and products are considered and applied to the important field of acid-base reactions. Re v i s ed i t ! 1.1 Formulae and equations The ability to represent reactions using balanced chemical (and ionic) equations is essential in chemistry. Using chemical formulae enables equations to be written. Oxidation number can be used to express the combining power of elements to form compounds. p8–10 1.2 Basic ideas about atoms Atoms have an internal structure comprising protons, neutrons and electrons. Some atoms are unstable and the nucleus splits up to form smaller particles – this is called radioactive decay. Radioactive emission can have adverse consequences or can be used beneficially. Evidence for the arrangement of electrons in an atom is given by ionisation energies, and emission and absorption spectra. p11–20 1.3 Chemical calculations Masses of atoms are expressed relative to the carbon-12 isotope. Relative atomic masses are determined by mass spectrometry. The mole can be used to calculate the masses of solids, concentration of solutions or volumes of gases reacting or being formed. The concentration of an unknown solution can be found using an acid-base titration and percentage error in measurements can be calculated. p21–33 Basic notes Good grasp Fully revised AS Chemistry: Study and Revision Guide 6