bonding + shapes of molecules Flashcards
orbital
region around nucleus that can hold up to 2 electrons of opposite spins
order of decreasing size, orbitals, sub shells, electrons, shells
shells > sub shells > orbitals > electrons
how does metallic bonding work
valence electrons in metal atom delocalise + form sea of free electrons - attraction between metal cations and delocalised electrons
why don’t metals dissolve easily
strong electrostatic attraction between cations and electrons
why is diamond a good thermal conductor
rigid structure means that vibrations easily can carry heat through the structure
why does graphite conduct electricity
one electron from each atom is delocalised, so it can move through the lattice and conduct energy
does silicon conduct electricity
yes - it is a semi conductor - conducts better when hotter as electrons have more energy
dative covalent bond
where both electrons from the shared pair are supplied by one atom only
average bond enthalpy
measure of the strength of a bond - larger value = stronger bond
London (dispersion forces) permanent?
no
London (dispersion forces) strength
weakest - depends on number of electrons in the molecule
London (dispersion/ Van Der Waal’s) forces
electrons are on one side of the molecule - instantaneous dipole - induces dipole in neighbouring molecules
permanent dipole-dipole strength (what molecules)
stronger then London forces - depends on number of electrons in the molecule
permanent dipole-dipole
dipole-dipole permanent interaction in POLAR molecules
hydrogen bonding
not a bond - an intermolecular force
hydrogen bonding requirements
must have H bonded to either F, O or N (v. electronegative)
must have lone pair of electrons
London (dispersion/ Van Der Waal’s) forces caused by
electron movement, giving an uneven electron distribution, inducing temporary dipole-dipole interaction in neighbouring molecules
hydrogen bonding strength
strongest
electronegativity trend down a group
decrease - shielding increase, atomic radius increase, less attraction
electronegativity
the power of an atom to attract the two electrons in a covalent bond
electronegativity across a period
increase - shorter atomic radius, same shielding, greater nuclear charge, stronger force of attraction between bonding pair and nucleus
why do ionic compounds dissolve in water
ions for polar bonds with water molecules
principle quantum number
shell number or energy level (n)
solubility of ionic substances
generally soluble in polar solvents
2 processes which must occur for an ionic substance to be soluble
- lattice must be broken down
- solvent molecules must attract and surround ions
trend in ionic solubility as ionic charge increases
decrease
solubility depends on…
relative strengths of attractions within giant ionic lattice and attractions between ions and solvent molecules
electrical conductivity of ionic substances
solid = unconductive
liquid/in solution = conductive
covalent bonding
strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms
covalent molecule
smallest part of a covalent compound that can exist whilst retaining the chemical properties of the compound
why do more bonds often = more stable
as energy released when bonds made, so becomes more stable
factors affecting electronegativity
- nuclear charge
- atomic radius
- shielding
element with highest electronegativity
fluorine
intermolecular forces in molecule with no polar bonds
van der Waals
intermolecular forces in molecule containing some polar bonds but all dipole moments cancel out (ie. linear)
van der Waals
intermolecular forces in molecule containing polar bonds and all dipole moments DO NOT cancel out
van der Waals AND dipole-dipole or H-bonding depending on molecule
non-polar covalent bond
2 atoms in a covalent have same electronegativity (eg. Cl-Cl) - 2 electrons shared equally
polar covalent bond
2 atoms in covalent bond have different electronegativities - 2 electrons not shared equally (eg. H-Cl)
solubility of non polar substances in polar solvents
insoluble/slightly soluble
solubility of non polar substances in non-polar solvents
usually soluble - intermolecular forces form between solvent and solute molecules
