higher chemistry - structure and bonding

metallic bond

strong electrostatic forces that exist between the positive nuclei and the delocalised outer shell electrons.

when the number of electrons of an atom increases, what happens to the metallic bond?

the greater the number of electrons in the outer shell, the stronger the metallic bond.

metal boiling point trends down a group:

atomic size increases, so outer shell is further away from the attraction of the positive nuclei. therefore, there is a weaker metallic bond, so there is a lower boiling point

metal boiling point trend across a period (left to right)

number of electrons in outer shell increases and the charge on the metal ion increases, so there is a greater attraction between the metal ion and the positive nuclei. therefore the strength of the metallic bond increases

why are metals malleable?

because the metal atoms can “slip” past each other as the metallic bond is not fixed and acts in all directions.

explain how metals can conduct electricity/thermal energy

electrons can move freely throughout the lattice

why does aluminium conduct better than sodium?

aluminium is in group 3, so has 3 delocalised electrons. Sodium is in group 1, so only has 1 delocalised electron. As aluminium has more delocalised electrons, it has a higher conductivity.

example of a monatomic element

noble gases

what are monatomic elements

elements that are normally found as single atoms

definition of intermolecular forces

attractive forces between neighbouring atoms/molecules

are intermolecular forces stronger or weaker than intramolcular forces

weaker

what is the other name for intermolecular forces

van der waals forces

what are the 3 types of van der waal forces

london dispersion forces, hydrogen bonding, permanent dipole to permanent dipole interactions

dipole

a permanent separation of charge in a polar covalent bond that happens because bonded atoms have different electronegativities

london dispersion forces

an electrostatic attraction between temporary dipoles & induced dipoles in neighbouring atoms/molecules caused by the movement of electrons in atoms and molecules.

london dispersion forces are weaker than other bonding types

true

what happens to the london dispersion forces as the size of atom/molecule increases

the number of electrons increases, so the strength of the london dispersion forces increases

the greater the intermolecular attractive forces between the molecules the…

greater the boiling point

trend of boiling point down the group of noble gases

boiling points increase down the group as the number of electrons increases, causing an increased size of temporary and induced dipoles. this causes the london dispersion forces to increase in strength, so increasing the energy needed to seperate the molecules and cause boiling.

what happens to the covalent bonds during boiling for simple covalent molecules

the covalent bonds are not broken

examples of simple covalent molecular structures

H2, N2, O2, Cl2, I2, Br2 and P4, S8, C60

examples of covalent network structures

diamond, graphite, silicon

do giant covalent network structures have intermolecular forces

no

state and explain the trend in boiling point of the halogens

bp increases down the group as the size of elements increases down the group, leading to an increase of the number of electrons, increases the temporary and induced dipoles. leading to an increase in the strength of the london dispersion forces. therefore, more energy is needed to overcome the forces.

fullerenes

molecules of carbon shaped like hollow balls or closed tubes - the carbon atoms are arranged in hexagonal/pentagonal rings

why are fullerenes solids at room temp?

fullerenes are large molecules, so therefore have stronger london dispersion forces. therefore, more energy is needed to seperate the molecules, so melting point increases.

is the mp/bp of covalent networks high or low

very high. so tend to be solids at room temp due to large number of covalent bonds that all need to be broken for the atom to undergo a state change.

are covalent networks soluble or insoluble?

insoluble in both polar and non polar solvents as the covalent bonds are too strong to be broken.

can covalent networks conduct electricity

dont conduct electricity as there is no mobile ions or electrons. but graphite can conduct electricty

strength of covalent networks

hard - rigid 3D structure with strong covalent bonds (diamond and silica) but graphite is soft.

what are polar solvents

substances that have permanent dipoles.

in the first 20 elements of the periodic table, what elements are covalent network elements?

boron, carbon, silicon

structure and properties of graphite:

every carbon atom is covalently bonded to 3 other carbon atoms forming hexagonal layers in a giant network lattice. But it is very soft because there are weak london dispersion forces between the layers. Graphite is an electrical conductor as the 4th electron of each atom is free to move about

out of the first 20 elements of the periodic table, which elements are metallic?

Li, Be, Na, Mg, Al, K, Ca

out of the first 20 elements of the periodic table, which elements are covalent molecular?

H2, N2, O2, F2, Cl2, P4, S8, C(fullerenes)

out of the first 20 elements of the periodic table, which elements are covalent network?

B, C (diamond, graphite), Si

out of the first 20 elements of the periodic table, which elements are monatomic?

noble gases

trend in boiling and melting point down group 1

bp and mp increase due to increased london dispersion forces

covalent bond

electrostatic forces of attraction between positive charged nuclei and negative charged shared electrons in atoms

name for the type of molecule of CH4, SiH4, GeH4

tetrahedral

name for type of molecule of NH3, PH3, AsH3

pyramidal

name for type of molecule of H2O, H2S, H2Se

bent / v-shaped

name for type of molecule of F2, Cl2, HF, HCl

linear

electronegativity

a measure of an atoms attraction for the shared pair of electrons in a bond

a greater attraction to bonding electrons means an atom has a ___ electronegativity

higher

where can you find a non polar bond

in any diatomic element (no change in electronegativity)

what is created due to different electronegativities

polar bond and a permanent dipole

the 4 most electronegative elements in increasing order

Cl, N, O, F

pauling scale

scale for measuring electronegativity

do values increase or decrease of electronegativity across periods from left to right

increase

do values increase or decrease of electronegativity up groups

increase

explain the trend in electronegativity across a period from left to right

electronegativity increases across a period from left to right as the number of protons increases, so therefore electrons on the shells are more attracted to the protons and are pulled closer to the nucleus. therefore the atom size decreases and this results in greater attraction from the nucleus for the bonding pair of electrons.

explain the trend in electronegativity down a group

electronegativity decreases as you move down a group as the number of shells increases, increasing shielding and therefore the atom size increases. this results in less attraction from the nucleus for the bonding pair of electrons.

when the distribution of electrons is unequal, what is formed?

a polar covalent bond

dipole

the uneven distribution of electrons

if the difference in electronegativity is 0, what bond is present

non polar

if the difference in electronegativity is small, what bond is present

polar covalent

if the difference in electronegativity is very large, what bond is present

ionic