OCR Chemistry A-Level - Modules 1-4 with complete solution
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Module
OCR Chemistry A-Level
Institution
OCR Chemistry A-Level
OCR Chemistry A-Level - Modules 1-4 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
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OCR Chemistry A-Level - Modules 1-4 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+ + 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:
- 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
what creates a polar bond?
- lone pairs offset symmetry by 102.5 degrees each
- asymmetrical molecule
- dipoles do not cancel out
- bonded atoms with different electronegativities
what are London forces?
- uneven distribution of electrons causes a temporary dipole on one molecule
- this induces an opposite dipole on the next molecule
which type of molecules are London forces common to?
- all molecules
- however London forces are most obvious in nonpolar molecules
what are permanent dipole-dipole forces?
- the permanent dipole on one molecule will attract the opposite permanent dipole in a
neighbouring molecule
- this includes polar molecules
what is hydrogen bonding?
the attraction between the positive dipole on an H atom and the lone pair of electrons on
an O, F or N on a different molecule
between which type of molecules do intermolecular forces occur?
simple covalent molecules
give the properties of giant ionic compounds
- high melting and boiling points as the lattice of strong ionic bonds requires a lot of
energy to overcome
- soluble in polar solvents as the ions interact with the dipole on water molecules
- do not conduct when solid as the ions are fixed in place in the lattice
- conduct when molten/aqueous solution as the ions are mobile
why does boiling point increase down group 17?
- the number of electrons in the molecules increase
- larger dipoles are induced which means stronger London forces
- more energy is required to overcome the intermolecular forces
give the properties of simple covalent molecules
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