2.2 - electron structure

where are electrons found?

shells orbiting the nucleus

what is an orbital?

a region in space where an electron is likely to be found

how many electrons can orbitals hold?

up to 2 - have opposite spin

what are the 4 orbitals?

s, p, d, f

what shape is the s orbital

spherical

what shape is the p orbital

dumbbell

how many s orbitals are there?

one (2 electrons)

how many p orbitals are there?

three (6 electrons)

how many d orbitals are there?

five (10 electrons )

How many f orbitals are there?

7 (14 electrons)

what does isoelectronic mean?

ions with the same electronic structure

what are bonding pairs?

pairs of electrons used in bonding

what are lone pairs?

pair of electrons in the outer shell NOT used in bonding

what is the octet rule?

tendency of atoms to bond in order to acquire electron configuration of a noble gas

what are exceptions of the octet rule?

• not enough electrons

• common in group 1, 2, 3

• some have incomplete octets

what is expanding the octet?

group 5-7 can pair up with many electrons

how can group 5 expand its octet?

for 3/5 covalent bonds

how can group 6 expand its octet?

for 2/4/6 covalent bonds

how can group 7 expand its octet?

for 1/3/5/7 covalent bonds

what is a coordinate/dative bond?

• a covalent bond formed when both shared electrons are provided by only one atom

• electron pair comes from a lone pair on the donor atom

• atom accepting and sharing the lone pair must have an incomplete outer energy level

what is different between covalent bonds and coordinate bonds?

physically and chemically identical except method or formation

how is the shape of molecules predicted and explained?

VSEPR theory

valence shell electron pair repulsion

how does the VESPR theory work?

• electron pairs repel eachother and get as far aboard as possible to minimise repulsions

• only happens if bonding pairs ONLY (symmetrical shape)

what are symmetrical molecules?

have at least 3 plains of symmetry at 90 degrees

what is the shape and bond angles in a molecule with 2 bond pairs?

• linear

• bond angle 180

what is the shape and bond angles in a molecule with 3 bond pairs?

• trigonal planar

• bond angle 120

what is the shape and bond angles in a molecule with 4 bond pairs?

• tetrahedral

• bond angle 109.5

what is the shape and bond angles in a molecule with 5 bond pairs?

• trigonal bipyramid

• band angles 90 and 120

what is the shape and bond angles in a molecule with 6 bond pairs?

• octahedral

• bond angle 90

how close are love pairs to the nucleus compared to bond pairs?

lone pairs are closer to the nucleus

list the strength of repulsions in increasing order of bond pairs and lone pairs

3. BP by BP

2. LP by BP

1. LP by LP

what is the change in the bond angle of non symmetrical shapes?

bond angles reduce by 2.5 per lone pair

what is electronegativity?

the ability of an atom to attract the shared pair of electrons in a covalent bonf

what is the most electronegative element?

fluorine

what factors affect electronegativity?

• higher nuclear charge - more protons in nucleus attract shared electrons more strongly

• smaller size of atom - less shells so electrons closer to nucleus giving greater attracttion

how does electronegativity change from left to right of the periodic table?

increases from left to right

how does electronegativity change going down a group of elements?

decreases down a group

what makes a bond non-polar?

atoms have same electronegativity so electrons shared equally

what makes a bond polar?

atoms have difference in electronegativity. more electronegative atom attracts shared electrons more strongly so electron pair lies closer to this atom causing a small separation in charge

what is a permanent dipole?

small charge difference across a bond that results from a difference in the electronegativity of the bonded atoms

how can electronegativity be used to predict the bond type?

pure covalent - electronegativity difference: 0

polar covalent - electronegativity difference- between 0 and 1.8

ionic - electronegativity difference: >1.8

what is a polar molecule?

has an overall dipole taking into account any dipoles across bonds

what must a molecule have to be a permanent dipole?

• difference in electronegativity

• not symmetrical - bond dipoles reinforce eachother

what are intermolecular forces?

attractions between different molecules

what are the strength of intermolecular forces compared to bonds

weaker than bonds

what are the three types of intermolecular forces?

• induces dipole-dipole

• permenant dipole

• hydrogen bonding

what is an induced dipole-dipole intermolecular force?

• weak attractions

• exist between all molecules

• one end becomes temporarily charged due to chance and introduces charge to nearby molecule

what changes strength of induced dipole-dipole forces?

size of atom/molecule - larger have more electrons so stronger - higher BP and MP

surface area - straight is stronger than branched - less surface area of branched reduces contact between molecules lessening forces

what is an induced dipole-dipole intermolecular force?

• stronger than induced dipole-dipole

• exist where there is a polar covalent bond

• attractions between partially positive and partially negative ends