OCR Chemistry A-Level - Modules for Revision Questions and Answers

What is water of crystallisation? water molecules that make up part of the crystal structure of a solid Define relative isotopic mass the ass of an atom of an isotope of an element relative to one twelfth the mass of an atom of C-12 Why is relative atomic mass written as a decimal? it is a weighted average mass Define molecular formula the actual number of atoms of each element in a compound Define what an orbital is a region within an atom that can hold up to two electrons of opposite spins What shape are S orbitals? spherical What shape are orbitals? figure of 8 How can you make out the electron structure of an element using the periodic table? period = energy level Columns = electrons Group = subshell Show the oxidation of sodium and the reduction of chlorine Na - Na+ + e- Cl + e- - Cl- Ions always go on the RHS whether oxidation or reduction Define ionic bond the electrostatic force of attraction between positive and negative ions Ionic bonding occurs between metals and non-metals but which ion is the exception? NH4+ Define covalent bond the strong electrostatic force of attraction between the shared pair of electrons and the nuclei of the bonded atoms When non-metals covalently bond, what is their aim? the octet rule: