1.3 - compounds and bonding Flashcards
when do non-polar (pure covalent bonds) form?
if the difference in electronegativity is less than 0.4
when does polar bonding occur?
if the difference in electronegativity is between 0.5 and 1.9
how do you actually determine if something is polar?
if a line can be drawn through the molecule to separate the positive end from the negative end
which end of a molecule is positive?
the end with the lowest electronegativity
which end of a molecule is negative?
the end with the greatest electronegativity
is carbon dioxide polar or non-polar?
- non-polar
- O=C=O
how can polar liquids be identified?
polar substances are deflected by a charged rod
intermolecular
found between molecules
intramolecular
covalent bonding within a molecule (never breaks)
what are the three types of intermolecular attractions (van der waal’s forces)?
- london dispersion forces
- permanant dipole - permanent dipole interactions
- hydrogen bonding
what are the features of london dispersion forces?
- present between all molecular/ monatomic
- only controls non-polar/monatomic substances properties
what is the weakest type of van der waal force?
london dispersion forces
the more electrons there are in an atom or molecule…?
the stronger the london dispersion forces
what are london dispersion forces?
an attraction which arises between a temporary dipole and a temporarily induced dipole caused by an unequal distrubution of electrons
what do permanent dipole - permanent dipole interactions occur between?
polar molecules/substances
what is a permanent dipole - permanent dipole interaction?
the attraction between a permanent dipole in one molecule and a permament dipole in a neighbouring molecule
what is hydrogen bonding?
a special type of permanent dipole - permanent dipole interaction involving molecules where hydrogen is directly bonded to nitrogen, oxygen or fluorine within a molecule
carbon to hydrogen bonds are always what?
non-polar
what happens as the size of non-polar molecules increase?
as the size of the molecules increase, the number of electrons increases, the greater the strength of the london dispersion forces
what do ionic substances dissolve in and why?
- polar solvents
- the strength of ionic bonding is compatible with the hydrogen bonding between water molecules
what is the phrase to remember regarding solubility?
like dissolves like
why do non-polar substances not dissolve in water?
as L.D.Fs are not compatible with the hydrogen bonding found in water
what do non-polar substances dissolve in?
non-polar solvents which have L.D.Fs present
what are polar substances which do not have hydrogen bonding present less likely to be soluble in and why?
- water
- as their permanent dipole attractions are not compatible with hydrogen bonding found in water
what polar substances will dissolve in water?
only polar substances which can form hydrogen bonds with water molecules will dissolve in water
what are the only compounds that will dissolve in water?
only ionic compounds and polar covalent compounds (which can hydrogen bond with water molecules) will dissolve in water
what is viscosity?
the viscosity of a liquid is a measure of how thick the liquid is
the more hydroxyl (OH) groups present in the molecule…?
the stronger the hydrogen bonding will be between the molecules, the more visocus the liquid will be
what are the five features of ionic compounds?
- giant lattice structure of ions
- electrostatic forces of attraction between ions
- high melting point and boiling point
- conducts electricity when in solution or molten
- often soluble in water (polar solvent) and insoluble in non-polar, covalent
what are the five features of covalent molecular substances?
- discrete molecules
- very weak L.D.Fs or weak hydrogen bonds between molecules
- low melting and boiling point
- non conducting
- often soluble in non-polar organic solvents
what are the four features of covalent network substances?
- (usually) 3D giant network with covalent bonds between atoms
- high melting and boiling points
- non conducting
- tend to not be soluble
