OCR Chemistry A-Level - Modules 1-4
UPDATED Exam Questions and
CORRECT Answers
what is water of crystallisation? - CORRECT ANSWER- water molecules that make up part
of the crystal structure of a solid
define relative isotopic mass - CORRECT ANSWER- the ass of an atom of an isotope of an
el...
what is water of crystallisation? - CORRECT ANSWER- water molecules that make up part
of the crystal structure of a solid
define relative isotopic mass - CORRECT ANSWER- 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? - CORRECT ANSWER- it is a weighted
average mass
define molecular formula - CORRECT ANSWER- the actual number of atoms of each
element in a compound
define what an orbital is - CORRECT ANSWER- a region within an atom that can hold up to
two electrons of opposite spins
what shape are S orbitals? - CORRECT ANSWER- spherical
what shape are orbitals? - CORRECT ANSWER- figure of 8
how can you make out the electron structure of an element using the periodic table? -
CORRECT ANSWER- period = energy level
columns = electrons
group = subshell
show the oxidation of sodium and the reduction of chlorine - CORRECT ANSWER- Na ->
Na+ + e-
Cl + e- -> Cl-
, ions always go on the RHS whether oxidation or reduction
define ionic bond - CORRECT ANSWER- the electrostatic force of attraction between
positive and negative ions
ionic bonding occurs between metals and non-metals but which ion is the exception? -
CORRECT ANSWER- NH4+
define covalent bond - CORRECT ANSWER- 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? - CORRECT ANSWER- the octet rule:
- to reach a noble gas configuration (8 electrons in the outer shell)
what are there exceptions to the octet rule? - CORRECT ANSWER- - 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? - CORRECT ANSWER- it has an
empty 3d subshell
define a dative covalent bond - CORRECT ANSWER- 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 - CORRECT ANSWER- NH4+
H3O+
what is a base? - CORRECT ANSWER- proton (H+) acceptors
what is the shape of an atom determined by? - CORRECT ANSWER- - the number of
electron pairs
- electron pairs repel to become as far apart as possible
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