2.2 Electrons, bonding and structure Flashcards
atomic orbitals definition
region around nucleus that can hold up to two electrons, with opposite spins
shape of s orbital
sphere
shape of p orbital
dumbbell / 8
number of orbitals in each subshell
s=1
p=3
d=5
f=7
order of orbitals
1s2s2p3s3p4s3d4p5s4d5p
ionic bonding definition
electrostatic attraction between positive and negative ions
how ionic lattices are formed in ionic compounds
oppositely charged ions strongly attracted in all directions
why ionic substances have high MP/BP
electrostatic forces of attraction are very strong, requiring lots of heat energy to overcome
solubility of ionic compounds
the greater the difference in charges in the ions in the compound, the less soluble they are as the polarity of water molecules isn’t enough to overcome such a strong electrostatic force of attraction
electrical conductivity in ionic substances
solid : not conductive (no free-flowing charge carriers)
melted / dissolved : conductive (free-flowing charge carriers present)
covalent bond definition
strong electrostatic attraction between shared pair of electrons and nuclei of bonded atoms
dative covalent (coordinate) bonding
covalent bonding when both electrons come from the same species
electron-pair repulsion theory
electron pairs surrounding central atom determines shape of molecule / ion
electron pairs as far apart as possible
arrangement of electron pairs minimises repulsion (holds bonded atoms in definite shape)
different numbers of electron pairs = different shapes
wedges in drawing 3D molecules on paper
solid line = bond in plane of paper
solid wedge = comes out of plane of paper
dotted wedge = goes into plane of paper
lone pair repulsion
slightly closer to central atom than bonded pair
occupies more space than bonded pair
repels more strongly than bonded pairs
bond angle between bonded pairs in tetrahedral shape (no lone pairs)
109.5°
bond angle between bonded pairs in tetrahedral shape (1 lone pair)
107° (decreases by 2.5° per lone pair in molecule / ion)
bond angle between bonded pairs in tetrahedral shape (2 lone pair)
104.5°
linear molecular shape
2 electron pair/ regions on same plane
180° bond angle
trigonal planar molecular shape
3 electron pairs/regions
120° bond angle
tetrahedral molecular shape
4 electron pairs / regions
109.5° bond angle
octahedral molecular shape
6 bonded pairs / regions
90° bond angle
octahedral because atoms are positioned at corners of octahedral
electronegativity definition
ability of atom to attract bonding electrons in a covalent bond
increases towards fluorine (F) in periodic table
why water is polar but carbon is not
two O-H have permanent dipole
two dipoles act in different but not exactly opposing directions
two C=O have permanent dipole
bonds act in directly opposing directions so cancel each other out
dipole definition
separation of opposite charges
polar bond definition
partial charges present in the bond
intermolecular forces definition
weak interactions between dipoles of different molecules
London forces
weak intermolecular forces between all molecules (polar or non-polar)
act between induced dipoles in different molecules
how instantaneous dipoles work
movement of electrons produce changing dipole in molecule (uneven distribution of electrons)
instantaneous dipole will exist but position constantly shifting
how induced dipole-dipole interactions work
instantaneous induces a dipole on neighbouring molecule
induced dipole induced further dipoles on further neighbouring molecules
only temporary
how number of electrons affect strength of induced dipole-dipole interactions
more electrons = larger instantaneous and induced dipoles = greater induced dipole-dipole interactions = stronger attractive forces between molecules
how permanent dipole-dipole interactions work
opposite polarity between different molecules causes attraction
extra energy required to break bond as well as London forces
simple molecular definition
made up of small units containing definite number of atoms with definite molecular formula
weak intermolecular forces between molecules
strong covalent bonds within molecules
MP/BP of simple molecular substances
low (weak intermolecular forces easily broken)
covalent bonds NOT broken
why non-polar simple molecular substances are soluble in non-polar solvents
intermolecular forces form between molecules and solvent
weakens and breaks intermolecular forces in simple molecular lattice
substance dissolves
why non-polar simple molecular substances are insoluble in polar solvents
little interaction between molecules in lattice and solvent molecules
intermolecular bonding within polar solvent too strong to be broken
solubility of polar simple molecular substances
may dissolve in polar solvents as polar molecules in solvent and solute attract each other (extends to liquids and gases)
depends on strength of dipole
hydrophilic parts will be polar and can interact with water
hydrophobic parts will be non-polar
electrical conductivity of simple molecular substances
no mobile-charged particles that can move to complete an electrical circuit
hydrogen bond
type of permanent dipole-dipole interaction
found between molecules containing electronegative atom with lone pair of electrons (e.g. O, N, F) and hydrogen atom attached to electronegative atom e.g. (H-O, H-N, H-F)
strongest intermolecular interaction
anomalous properties of water
solid (ice) is less dense than liquid (water)
has relatively high MP/BP
relatively high surface tension and viscosity
why ice is less dense than water
hydrogen bonds hold water molecules apart in open lattice structure
water molecules further apart in ice than water
holes in open lattice decreases density in ice
ice lattice collapses when melts and molecules move closer together
why water has relatively high MP/BP
water has London forces and hydrogen bonds
more energy required to break both London forces and hydrogen bonds
giant covalent compound properties
large lattices
high MP/BP (strong covalent bonds needed to be broken)
don’t conduct electricity except graphite/graphemes (no delocalised electrons)
trigonal bipyramidal shape
90° and 120° bond angle
5 bonding pairs
square planar shape
90°
4 bonding pairs, 2 lone pairs