what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
linear, 180 degrees, 2 electron pairs/regions, N/A bonded pairs, 0 lone pairs
what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
trigonal planar, 120 degrees, 3 electron pairs/regions, 3 bonded pairs, 0 lone pairs
what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
tetrahedral, 109.5 degrees, 4 electron pairs/regions, 4 bonded pairs, 0 lone pairs
what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
pyramidal, 107 degrees, 4 electron pairs/regions, 3 bonded pairs, 1 lone pair
what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
non-linear, 104.5 degrees, 4 electron pairs/regions, 2 bonded pairs, 2 lone pairs
what shape, angle, no. of electron pairs/regions, no. of bonded pairs and no. of lone pairs?
octahedral, 90 degrees, 6 electron pairs/regions, 6 bonded pairs, 0 lone pairs
order the electron pair types from greatest repulsion to smallest repulsion
lone pair-lone pair, lone pair-bonded pair, bonded pair-bonded pair
what is the electron pair repulsion theory?
a model that predicts the shapes of molecules and polyatomic ions and is dependent upon the arrangement of electron pairs around a central atom
what leads to the definite shape? (E.R.T)
the repulsion between pairs of electrons as electrons are negative
how do the electrons arrange themselves around the central atom? (E.R.T)
they arrange themselves in a way so that the repulsion between them is at a minimum
different numbers of electrons leads to… (E.R.T)
different shapes
what is electronegativity?
the measure of attraction of bonded atom for the pair of electrons in a covalent bond or the ability of an atom in a covalent bond to attract electrons towards it
what scale is used to compare the electronegativities of different atoms?
the pauling scale
the … the Pauling electronegativity, the …
the higher the Pauling electronegativity the greater the electronegativity
as the radius of an atom … the … the electronegativity and why?
as the radius of an atom increases the lower electronegativity because the bonding pair of electrons become further from the nucleus and so are less attracted to its positive charge
what is polarisation?
distortion of electron cloud
the … the electronegativity difference between atoms the … the polarisation of the bond
the greater the electronegativity difference between atoms the greater the polarisation of the bond
how does the polarisation change from covalent to ionic bonds?
the polarisation increases
what is a non-polar bond?
the bonded pair of electrons is shared equally and there is a symmetrical electron cloud
when does a non-polar bond occur?
when the 2 atoms in the covalent bond are identical and when the 2 atoms have the same electronegativity
what is a polar bond?
the bonded pair of electrons is not shared equally and there is a distortion in the electron cloud (polarisation)
when does a polar bond occur?
when the two atoms in the covalent bond have different electronegativities
in a polar covalent bond, what does the most electronegative atom do?
it pulls the electrons towards itself
when the most electronegative atom pulls the electrons towards itself, what does this result in?
it leads to a partial negative charge on the most electronegative atom and a partial positive charge on the least electronegative atom
why might molecules with more than 2 atoms have polar bonds but not be polar?
the dipoles may cancel out
what are the 3 types of intermolecular forces?
induced dipole-dipole interactions (London Forces), permanent dipole-dipole interactions and hydrogen bonding
what are induced dipole-dipole interactions?
when there is an electrostatic force of attraction between the negative charge on one atom and the positive charge on the other atom
what causes induced dipole-dipole interactions?
an uneven distribution of an electron cloud causing partial charges to develop on the atoms
where are induced dipole-dipole interactions present?
between all atoms and molecules but are weak
how long do induced dipole-dipole interactions last?
only for an instant before they disappear and the whole process happens again with other atoms/molecules
for induced dipole-dipole interactions, the greater number of electrons involved the …
the larger the instantaneous and induced dipoles and so the greater the interactions leading to stronger attractive forces between atoms
the stronger the forces the higher the higher the amount of energy required to seperate them therefore the higher the melting/boiling point
as the relative molecular mass increases, what happens to the boiling point and why?
it increases because the size of the molecule increases, more electrons are involved which creates more instantaneous dipoles increasing the attractive forces and therefore more energy is needed to seperate them
what is a permanent dipole-dipole interaction?
an intermolecular force between the dipoles of neighbouring molecules that is permanent
are permanent dipoles stronger or weaker than induced dipoles?
stronger
as permanent dipoles are stronger, what does this mean for molecules with polar bonds?
they have higher boiling points than non-polar molecules as they have the strength of both the permanent dipoles and the London Forces (which are weaker)
what are the boiling/melting points of simple molecular substances and why?
low because only low energies are needed to the break the intermolecular forces
what is the solubility of simple molecular substances?
non-polar molecules are soluble in non-polar solvents and polar molecules are soluble in polar solvents
what is the conductivity of simple molecular substances and why?
they are not conductive because there are no free electrons to carry the charge
what is hydrogen bonding?
a special type of permanent dipole-dipole interactions that only occurs between hydrogen and electronegative atoms (nitrogen, oxygen or fluorine)
what is the interaction between in hydrogen bonding?
between a lone pair of electrons on an electronegative atom with hydrogen
what is the strength of hydrogen bonds like in comparison to other intermolecular forces?
it is the strongest intermolecular force