Chemical bonding

Question 1

noble gases

Answer 1

they are inert as they are stable due the their full outer shell

Question 2

The octet rule

Answer 2

except noble gases , atoms of other elements generally combine with eachother to achieve a full outer shell

either by transferring eletrons- ionic
or sharing electrons- covalent

results in atom having same electron configuration as nearest noble gas- octet rule

Question 3

ionic bonding

Answer 3

The electrostatic attraction between opp charged ions

consists of opp charge ions usually positive metal ion and negative non metal ion

electrons transfer from metal to non metal

use dot and cross models to show this remember to surround with brackets

Question 4

covalent bonding

Answer 4

the sharing of a pair of electrons, the strong electrostatic attraction between shared pair of electrons and nuclei of bonded atoms

consists of atoms bonded together occurs between non metals

pair of electrons are shared between bonding atoms

shown as a dot and cross

Question 5

metallic bonding

Answer 5

the strong electrostatic attraction of a lattice of positive metal ions to a sea of delocalised electrons

which are shared by all the bonded metal atoms

occurs in metals

electrons are delocalised

drawn as solid packed lattice

Question 6

ionic bonding dot and cross diagrams

Answer 6

uses dots to show one elements electrons and crosses for the other

when electrons are transferred you uses a dot or cross, the opposite of the one previously used on the element to show that an electron for the other element is transferred

if there is more than 1 of an element u can just draw one diagram and put a big 2 in front or whatever numer infront

them put brackets around and lable the charge of the ion- should be neutral overall but they should both have charges alone

Question 7

different structure types

Answer 7

where particals have a regular arrangement and are held together by the forces of attraction

these can be intermolecular bonds, London forces ect

strength of forces impacts physical properties

4 diff structures
giant ionic lattice- high melting and boiling point due to strong electrostatic forces of attraction so lots of energy need to break bonds
conducts when molten/ aqueous as ions mobile and can carry charge.Otherwise don’t conduct
soluble In water due to opp charges attracting H+ and OH- ions
example- sodium chloride

giant metallic- high Mp and BP due to strong forces of attraction between atoms and electrons
Good conductors and delocalised electrons carry charge
not soluble
example- Magnesium

simple covalent-low MP and BP as only weak intermolecular forces not much energy need to overcome
don’t conduct as nothing free to carry charge
soluble in non polar solvents as they can form induced dipole dipoles with non polar molecules
example- iodine,

giant covalent- High MPs and BP many strong bonds need lots of energy to break
doesn’t conduct as no mobile ions or electrons
insoluble in diamond and graphite as C-C bonds are strong and non polar
e.g diamond and graphite

Question 8

allotropes of carbon

Answer 8

diamond- 4 covalent bonds, tetrahedral arrangement makes it extremely hard and very high melting point, doesn’t conduct electricity

graphite- layers of carbon atoms each forming 3 covlent bonds and has van der walls between layers, fairly soft and layers slide over eachother, still has high Mp and BP
Buckminsterfulleren- carbon 60, spherical cage
also get carbon nanotubes strong light and conduct

Question 9

Covalent bonding dot and cross diagrams

Answer 9

they share electrons

electrons not involved but still in outer shell are called lone pairs

ones involved are called bonded electrons

single covalent bond only share one pair of electrons

you can also have double or triple covalent bonds where more than one pair are shared

dative covalent bonds are shown by an arrow, these are the strond electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms where only of the atoms supplies both the shared electrons

sometimes there are covalent bond within ionic bonds here just do them as usual and place in bracket with charge use a 3rd symbol to show transferred electrons

Question 10

Average bond enthalpy

Answer 10

Average bond enthalpy can be used as a measure of covalent bond strength

large the value the greater the bond strength

it is the average enthalpy change when 1 mole of gaseous bonds is broken by homolytic fission, comparable to the energy nessecary to break bonds

Question 11

electron- pair repulsion theory

Answer 11

electron pairs repel eachother to get as far away as possible

lone pairs repel more strongly than bonded pairs

shape is determined by the no and type if electron pairs around CENTRAL atom

Question 12

Shapes of molecules

Answer 12

linear-
2bps and 0 lps,
has a bond angle of 180 degrees
e.g Cl——Be——Cl beryllium chloride

Trigonal planar-
3 bps and 0 lps
bond angle 120 degrees
e.g. BrF3

Tetrahedrol-
4bps and 0 lps
109.5 degrees
e.g. Ammonium ion,NH4 +

octahedral-
6bps and 0lps
90 degree
e.g.Sulfur hexaflouride, SF6

pyramidal-
3 bps and 1lps
107 degrees
e.g Ammonia, NH3

Non linear-
2bps 2lps
104.5 degrees
e.g. H20

lone pairs lone pair repels the most then Lps to Bps and the bps to bps repels least

show lone pairs as dots, bonds as lines, bold wedges for bond coming towards u and dotted line for bond pointing away from u

as double bonds count as 2 bonded pairs but only 1 bonded region so CO2 is still linear not tetrahedral

Question 13

Electronegativity

Answer 13

if bonding atoms are the same then bonding electrons are equally shared
if not one atom is likely to attract the bonding electrons more strongly.

the bonding atom with a greater nuclear attraction is more electronegative than the other atom

Electonegativity is the ability of an atom to attract the bonding electron towards itself in a covalent bond

Question 14

non polar bonds

Answer 14

these are when both atoms have the same electronegativity

bonding electrons are evenly distributed between bonded atoms

e.g. C-H F-F Br-Br usually the same element

Question 15

polar covalent bonds

Answer 15

when one atom is more electronegative so the distribution of electrons is uneven

the more electronegative element attracts electrons closer

as the electron cloud around that atom is denser there is a permanent dipole across the bond

Question 16

how polar are atoms of each element?

Answer 16

Fluorine is most electronegative along with things like O and N as well as the other halogens being high up there

increase diagonally (up and right) on the periodic table not including most noble gases

greater the difference greater the perment dipole and more polar the bond

Question 17

how to tell if a molecule is polar

Answer 17

symmetrical molecules are non polar as dipoles cancel out

each bond may be polar but because the molecule is symmetrical the dipoles cancel so there is no net dipole and so non polar

e.g CCl4

unsymmetrical molecules that contain polar bonds are polar as dipoles don’t cancel out
e.g. NH3

Jam donut- should have a certain charge at the center surrounded by the opposite charge if non polar as well

only polar molecules can contain H bonds or/and permanent dipoles

Question 18

induced dipole dipole

Answer 18

induced dipole dipole interactions (london)-
weakest intermolecular forces between molecules- takes least energy to break bonds- lowest Mp and bps

exist between all molecules polar or not

at any moment there may be a uneven distribution of electrons in a molecule causing a temporary dipole, induced dipole in 1 molecule causes one in neighbouring molecule + of dipole in one molecule attracts - of dipole in neighbouring molecule to produce London force

Question 19

permanent dipole dipole

Answer 19

permanent dipole dipole interactions

second weakest intermolecular forces and are the weak attractive forces between polar molecule- takes medium amount of energy to break bonds- medium Mp and BPs

only in polar molecules

slightly positive dipole of 1 atom attracts slightly negative dipole of neighbouring atom to produce a permanent dipole dipole force of attraction between the molecules e.g. H–Cl*H–Cl
** show permanent dipole dipole

stronger than induced weaker than H bonds

Question 20

hydrogen bonds

Answer 20

the strongest of the intermolecular forces- requires most energy to break- highest mp and BP

they are strong dipole dipole interactions between covalent molecules contains O-H, N-H or F-H bonds (Polar- only occur in polar molecules)

H bonds exist between a slightly positive H atom in one molecule and a lone pair on a highly electeonegative atom on another molecule

H bonds should be shown as a labeled dotted straight line starting a lone pair and ending at the H atom

ones containg F-H are most electronegative so have highest bps and mps, then O-H as it had two lone pairs so is more electronegative than N-H which only has 1 so has lowest Bps and Mps

Question 21

how to decide which intermolecular bonds are present

Answer 21

is the molecule polar?
No- London forces
yes- Are there any N-H O-H F-H bonds present?
No- permanent dipole dipole
yes- Hydrogen

Question 22

anomalous properties of Water

Answer 22

these are due to the hydrogen bonds between water molecules

Ice is less dense than water-
as in a solid h20 molecules are held further apart by H bonds creating an open lattice structure making it less dense

Water has a relatively high melting and boiling points-
higher than expected as H bonds are relatively strong and therefore stronger than other intermolecular forces so more energy is needed to break the H bonds