Bonding and structure

What is ionic bonding

The strong electrostatic attraction between oppositely charged ions

What are metal ions

Positive (cations)

What are non metal ions

Negative (anions)

What is an ionic lattice

Repeating pattern of oppositely charged ions

What are the properties in ionic compounds

• high melting and boiling point due to it having strong covalent bonds and being a giant structure

• Can’t conduct as solids as ions are fixed in place

• Can conduct when molten or aqueous as ions are free to move

What is covalent bonding

The strong electrostatic attraction between shared pair of electrons and the nuclei of the bonded atoms

• single, double or triple

What are the exceptions to the traditional covalent bonds

• sulfur hexaflouride as it has 12 electrons around sulfur

• Boron triflouride as it has 6 electrons around boron

What are dative covalent bonds

A shared pair of electrons where both electrons come from one atom

• occurs when the atoms have lone pairs

What to do with covalent bonds of ions

• represent the extra electrons with another shape

What is a bonded pair

The electron pair involved in a covalent bond

What is a lone pair

An electron pair which is not involved in covalent bonds

How many BP and LP does a linear shape have and what bond angle

• 2 BP

• 0 LP

• 180

How many BP and LP does a triagonal planar shape have and what bond angle

• 3 BP

• 0 LP

• 120

How many BP and LP does a tetrahedral shape have and what bond angle

• 4 BP

• 0 LP

• 109.5

How many BP and LP does a octahedral shape have and what bond angle

• 6 BP

• 0 LP

• 90

How many BP and LP does a pyramidal shape have and what bond angle

• 3 BP

• 1 LP

• 107

How many BP and LP does a non-linear shape have and what bond angle

• 2 BP

• 2 LP

• 104.5

Why do different molecules have different shapes

electron pairs repel and bonded pairs repel each other equally so the electrons are as far apart as possible

What are the pairs in order of repulsion

LP-LP > LP-BP > BP-BP

What does each pair reduce the bond angle by

2.5

What is metallic bonding

The strong electrostatic attraction between the positive metal ions and the delocalised electrons in a giant metal lattice

Why do metallic bonds get stronger as you move across a period

• there are more delocalised electrons per ion which also have a greater charge per ion

• They also get smaller

Why do metallic bonds get weaker as you move down a group

• each ion donates the same number of electrons

• The ions get bigger

• Therefore, the electrons are spread more thinly

Why are metals conductive

• the delocalised electrons are free to move through the whole structure and carry the charge

Why are metals malleable and ductile

• the electron sea continues to envelope the ions holding the lattice together despite the impact force

What is electronegativity

The ability of an atom to attract the bonding pair in the covalent bond

What is the pure covalent bonds

• the electron density is shared symmetrically and fully covalent

What are polar covalent bonds

the electron density is asymmetrical so one atom is more electronegative and attracts the bonding pair more strongly

Where are the most electronegative atoms on the periodic table

The top right barring noble gases

What determines if a molecule is non polar

• if it’s symmetrical as the dipoles will cancel out

  • E.g. linear, trigonal planar, tetrahedral, octahedral

What determines if a molecule is polar

• if it’s asymmetrical as dipoles don’t cancel out

  • E.g. pyramidal, non linear

What are intermolecular forces

Weak interactions between dipoles of different molecules

What are the three types of intermolecular forces

1. London forces = in all simple covalent molecules and group 0

2. Permanent dipole-dipole interactions = in covalent bond with a significant electronegative difference e.g. pyramidal

3. Hydrogen bonds

How are London forces formed

• there is a uneven distribution of electrons

• This creates a temporary dipole

• This causes an induced dipole in neighboring molecules

• Opposite dipoles attract each other

What do the strength of London forces depend on

• the size of molecules as if affects the number of electrons

• The surface area of molecules

What is a permanent dipole-dipole interactions

Electrostatic attraction between the opposite partial charges of adjacent molecules

What is hydrogen bonding

The lone pair in fluorine, oxygen and nitrogen attract the hydrogen in another molecule

Why does water have a higher than expected BP

It has relatively strong hydrogen bonds between molecules which require more energy to overcome

Why is ice less dense than ice

The hydrogen bonds are longer than the covalent bonds so water molecules are held apart in an open lattice structure

What are the giant covalent structures

• diamond / silicon

• Graphite / graphene

What shape is diamond

tetrahedral as each carbo is covalently bonded to 4 others

What are the properties of diamond

• High MP due to strong covalent bonds.

• Doesn’t conduct due to no mobile electrons

• Very hard

• Good thermal conductivity

What shape is graphite

• Trigonal planar as each carbon covalently bonded to 3 other carbons arranged in a hexagon

• There are weak London forces between layers

What are the properties of graphite

• High MP due to strong covalent bonds

• Slippery as the layers can slide over each other

• Can conduct as 4th electron is delocalised and mobile

• Low density