definitions Flashcards
ionisation energy
the energy required to remove an electron from a gaseous atom or ion
factors affecting ionisation energy
charge on the nucleus (the more protons preset within the nucleus the more positive it becomes and hence the electrons that are attracted to it)
the distance between the nucleus and the electron (the closer the electron is to the nucleus the stronger the attractive force between them is and therefore the harder it will be to remove it)
shielding or screening
effective nuclear charge
Z (number of protons) - sigma (screening constant)
screening constant
write out electron configuration
group the electron groups (1s, 2s, 2p, 3s, 3p…)
ignore the outermost electron due to screening
outermost is 0.35 per electron
2s groups = 0.85 each
1s groups = 1.00 each
calculate overall nuclear charge (number of protons)
use formula
Zeff = Z - sigma
ionisation energy
increases across a period (no increase in screening)
decreases down a group (electrons in the outermost shell get further from the nucleus going down a group)
electron affinity
the amount of energy absorbed or released when an electron is added to a neutral atom in the gas phase
positively charged electron affinity = energy released when the electron is added to the atom
negatively charged electron affinity = energy is required t add the electron to the atom
atomic radius
half the distance between two nuclei in a molecule of two identical atoms
decreases going across a period (increasing nuclear rage decrease in screening)
increases going down a group (increasing number of shells)
ionic bond
one or more electrons are donated from one atom to another
covalent bond
valence electrons are shared
electronegativity
a measure of how well an atom is able to pull electrons towards the nucleus
difference >2 = ionic
difference <0.4 = covalent
0.4 <difference <0.2 = polar covalent
increases going across a period
decreases going down a group (due to increasing atomic radius, increasing the distance from the valence electrons to the nucleus)
polar covalent
electrons are shared (covalent) but shared unequally (polar)
intra vs inter
inter = between (weaker)
intra = within (stronger)
dipole
a partial charge on an atom
ion-dipole bonds are much stronger than dipole-dipole bonds as the charge of an ion is much stringer than any dipole
dipole-dipole forces
when two dipolar molecules interact with each other and the partially positive side of one dipolar molecule bonds with the partially negative side of the other dipolar molecule
London dispersion forces
the weakest intermolecular force
temporary electron arrangement that triggers a temporary dipole causes temporary dipoles in neighbouring molecules
factors that affect London dispersion forces (shape of molecule, number of electrons (more electrons lead to grater dispersion forces)
hydrogen bonding
Hydrogen covalently bonds to a highly electronegative atom (N O F)
strongest dipole-dipole force
bond pair and lone pair
a pair of electrons that is share between the two atoms (bond pair)
electrons not involved in bonding (Lone pair)
valency
the ability of an atom or a group of chemically bonded atoms to form chemical bonds with other atoms or groups of atoms
valency according to groups
group 1 = +1
group 2 = +2
group 3 = +3
group 4 = +/- 4
group 5 = -3
group 6 = -2
group 7 = -1
group 8 = 0
the preferred geometry of a molecule
is one that maximises the separation of electron pairs and that bonding and lone pairs will be as far apart as possible
shapes (no lone pairs)
linear = 180 (2 groups)
trigonal planer = 120 (3 groups)
Tetrahedral = 109.5 (4 groups)
trigonal bipyramidal = (3x groups = 120, 2x groups = 90)
octahedral = 90 (6 groups)
shapes (lone pairs present)
trigonal pyramidal = 107 (3 bond pairs, 1 lone pair)
bent = 104.5 = 2 bond pairs, 2 lone pairs (water)
naming inorganic compounds
binary ionic compounds (consist of only two elements, contain a cation + and an anion -)
the cation goes first and then the anion goes last
list of cations and anions
Cations (Hydrogen H+, Lithium Li+, Sodium Na+, Potassium K+, Caesium Cs+, Beryllium Be2+, Magnesium Mg2+, Calcium Ca2+, Barium Ba2+, Aluminium Al3+)
Anions (Hydride H-, Fluoride F-, Chloride Cl-, Bromide Br-, Iodide I-, Oxide O2-, Sulphide 2-, Nitride 3-, Phosphide 3-)
more than two ions in the series
more than two ions = ate gets prefix per
less than two ions = ite gets prefix hypo
broad structure of solids
crystalline (solids whose atoms/ions/molecules are ordered in well-defined arrangements, flat surfaces, highly regular shape and high defined melting point)(made up of repeating units called unit cells which form a lattice point, a lattice point is a point in space occupied by an atom ion or molecule).
amorphous (a large degree of disorder in their structure, broad melting point)
cubic unit cells
unit cells that have equal edge lengths and 90 degree angles at their corners
simple cubic (edge length is twice the radius of the atom)
body centred cubic
face centred cubic
lattice constant
to find the volume of the cube = (lattice constant)^3
simple cubic - lattice constant = 2r
face centred - 4r/square root of 2
body centred cubic: 4r/square root of 3
avogadros number
6.022x10^-23
moles =
mass / molecular weight
moles to molecules or atoms
multiply moles by avogadros number
sigma bond
head on overlap of orbitals
single bond has 1 sigma bond
double bond has 1 sigma bond and 1 pi bond
triple bond has 1 sigma bond and 2 pi bonds
pi bond
side on overlap of orbitals
bond strengths
the greater the orbital overlap, the stronger the bond and the shorter the bond will be
VB theory
describes how atoms form covalent bonds in molecules
hybridisation
the mixing of atomic orbitals on an atom to form new hybrid orbitals
percentage yield
actual yield/theoretical yield x 100
