OCR Chemistry A-Level - Modules 1-4 | Questions and Answers with complete solution

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+ + eCl + e- -> Clions always go on the RHS whether oxidation or reductiondefine 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: - to reach a noble gas configuration (8 electrons in the outer shell) what are there exceptions to the octet rule? - - NO (odd number of electrons) - BF3 (boron has less than 8 outershell electrons) - SF6 (sulfur has more than 8 outershell electrons) why can sulfur have more than 8 electrons in its outershell? - it has an empty 3d subshell define a dative covalent bond - a shared pair of electrons which has been provided by only one of the bonding atoms give some common examples of ions with a dative bond - NH4+ H3O+ what is a base? - proton (H+) acceptors what is the shape of an atom determined by? - - the number of electron pairs - electron pairs repel to become as far apart as possible - lone pairs of electrons repel more strongly than bonding pairs define electronegativity - the ability of an atom to attract the bonding electrons in a covalent bond