Metallic bonding
The attraction between delocalised outer shell electrons and positive metal ions in a lattice
Giant
Endlessly reprating
Delocalised
Not associated with a particular atom
What does the number of delocalised electrons depend on?
How many electrons are lost from each metal ion
Metallic bonding of sodium
Metallic bonding of magnesium
Ionic bonding
The electrostatic attraction between oppositely charged ions in a lattice
Diagram of a giant ionic lattice
Boron bonding
Don't for ions (but will form covalent compounds)
Carbon and silicon bonding
Don't form ions
Tin bonding
Sn4+ is most stable but can form Sn2+
Lead bonding
Pb2+ is most stable but can form Pb4+
Transition metal bonding
Form more than one stable ion
Ammonium
NH4 +
Hydroxide
OH -
Nitrate (III)
NO2 -
Nitrate (V)
NO3 -
Cyanide
CN -
Hydrogen carbonate
HCO3 -
Hydrogen sulfate
HSO4 -
Do hydrogen phosphate
H2PO4 -
Carbonate
CO3 2-
Sulfate (IV)
SO3 2-
Sulfate (VI)
SO4 2-
Hydrogen phosphate
HPO4 2-
Phosphate (V)
PO4 3-
Covalent bond
A shared pair of electrons
Lone pair
A pair of electrons which is not bonded
Non-octet molecules
Molecules where the central atom doesn't have a noble gas electron arrangement eg BF3, SF6
Coordinate bond
A covalent bond in which both electrons of the shared pair come from the same atom
How do coordinate bonds form?
The atom that donates electrons has a lone pair. The atom that accepts the electron pair doesn't have a full outer shell (it is electron deficient) and can fit a lone pair
How are coordinate bonds shown?
Using an arrow pointing from the the atom donating the electron
What is a molecules shape based on?
The total number of electron pairs around the central atom The number of bonding pairs of electrons The number of lone pairs of electrons
Electron Pair Repulsion Theory
Pairs of electrons repel each other so that they as far apart as possible Lone pairs are more compact so repel more The molecule takes up a shape which minimises repulsion Lone pairs reduce bond angles by 2.5° each
Bond on the plane of the paper
Straight line
Bond coming out of the paper
A wedge
Bond going into the paper
Dotted line
2 bond pairs 0 lone pairs
Linear - 180°
3 bond pairs 0 lone pairs
Trigonal planar - 120°
4 bond pairs 0 lone pairs
Tetrahedral - 109.5°
5 bond pairs 0 lone pairs
Trigonal Bipyrimidal - 90° and 120°
6 bond pairs 0 lone pairs
Octahedral - 90° (and 180°)
2 double bonds 0 lone pairs
Linear - 180°
3 double bonds 0 lone pairs
Trigonal planar - 120°
2 bond pairs 1 lone pair
V-shaped/bent - 117.5°
3 bond pairs 1 lone pair
Trigonal pyramidal - 107°
2 bond pairs 2 lone pairs
V-shaped/bent - 104.5°
3 bond pairs 2 lone pairs
Trigonal planar - 120°
4 bond pairs 2 lone pairs
Square planar - 90°
How to explain molecule shape
Number of lone pairs and bond pairs and where. Electron pairs repel. Lone pairs repel more. State the bond angle and why
Define electronegativity
The power of an atom to attract the pair of electrons in a covalent bond
Trend of electronegativity across a period
Increases as nuclear charge (proton number) increases
Trend of electronegativity down a group
Decreases as the number of shells increases so atomic radius and shielding increases
What is the most electronegative element?
Fluorine
What makes a bond polar?
When there is an uneven distribution of electrons
What makes a non-polar covalent bond?
No or very small difference in electronegativity. The electron pair is shared equally with no dipole in the bond
Non polar covalent bond examples
H2, Cl2, O2, NaCl, CH
What makes a polar covalent bond?
A difference in electronegativity. The electron pair is closer to the more electronegative atom, making it slightly negative
Polar covalent bond examples
HCl CCl BeCl
What makes an ionic bond?
A large difference in electronegativity. Electrons are pulled so far towards the electronegative atom that the less electronegative atom loses the electron
Permanent dipole
A small charge difference across a bond resulting from a difference in electronegativities of the bonded atoms
What can happen if there are multiple dipoles in a molecule?
If they make the molecule electronically symmetrical eg CO2, the dipoles cancel out
Define intermolecular forces
The forces of attraction between molecules
What are van der Waals' forces?
These are the weakest intermolecular forces which occur between all substances between molecules of atoms
Instantaneous dipole
A constantly forming a disappearing dipole caused by the movement of electrons which unbalanced the charge distribution within the molecule
Why do non polar substances have low boiling points?
They only have van der Waals forces between molecules which are very weak
What determines the strength of van der Waals forces?
Bigger molecules have more electrons so the induced dipoles are large resulting in stronger forces
What causes van der Waals forces?
The random movement of electrons causes an instantaneous dipole across the molecule which indices a dipole in neighbouring molecules resulting in weak forces of attraction
Which substances only have van der Waals forces?
Simple molecules and simple atomic substances
What are permanent dipole-dipole forces?
These occur between molecules which have a permanent dipole in addition to van der Waals forces. The negative pole of one molecule attracts another's positive pole. These are generally stronger than van der Waals forces
What are hydrogen bonds?
These are the strongest intermolecular forces which occur between molecules which contain a hydrogen atom bonded to either F, O or N. The bond forms between the slightly positive H atom in one molecule and a lone pair in the other
Properties of hydrogen bonds
Higher boiling point than expected due to the strength of the hydrogen bonds Substances which can hydrogen bond tend to dissolve in water because they form hydrogen bond with water
What must be broken to melt or boil an ionic, metallic or macromolecular structure?
The bonds
What must be broken to melt or boil a simple molecular or atomic substance?
The intermolecular forces
What is needed to conduct electricity?
Charged particles which are free to move such as delocalised electrons or ions
What is the solubility rule?
Substances can dissolve if dilute and solvent molecules attract one another - like dissolves like. Ionic and polar substances dissolve in polar solvent sand non polar substances dissolve in non polar solvents
Structure of ionic compounds
A giant ionic lattice structure where negative and positive ions alternate so each ion is surrounded completely by oppositely charged ion held together by ionic bonds
Why do ionic compounds have high melting points?
The ions are held together by many strong ionic bonds that need a lot of energy to break
Why are ionic compounds brittle?
If enough force is applied, the layers can slide over each other. Like charges will move next to each other, causing repulsion which breaks down the lattice structure
Why do ionic compounds only conduct electricity when molten or aqueous?
The ions are only free to move in theses states so can carry current
Why do metals have high melting and boiling points?
Metallic bonds are generally strong so large amounts of energy is needed to break them
Why can metals conduct electricity?
The delocalised electrons can move through the structure and carry the current
Why are metals strong?
Metallic bonds are strong and extend through the giant metallic lattice structure
What does metallic bond strength depend on?
The size and charge of the metal ion (it's charge density). Smaller and more highly charged ions form stronger bonds
Malleable
Can be hammered or pressed into shape without breaking or cracking
Ductile
Can be drawn into thin wires
Why are metals ductile and malleable?
The layers of ions in the giant metallic lattice can slide over each other into new positions without disrupting the metallic bond
Types of covalent substances
Simple molecular and macromolecular
Why do simple covalent molecules have low melting points?
The forces of attraction between molecules are weak. Not much energy is needed to break the intermolecular forces
Why can't simple covalent molecules conduct electricity?
They don't contain ions or delocalised electrons so can't carry a charge
Solubility rule of simple covalent molecules
Generally insoluble in water unless they can form hydrogen bonds with water or react with it
Structure of diamond
A giant arrangement of carbon atoms bonded to four other carbon atoms
Structure of graphite
A giant arrangement of carbon atoms bonded to three other carbon atoms in layers
Structure of diamond
A giant arrangement of carbon atoms bonded to four other carbon atoms
Why do diamond, graphite and graphene have high melting points?
Many covalent bonds between all the atoms which take lots of energy to break
Structure of graphene
A single sheet of graphite
Why do graphite and graphene conduct electricity?
One electron per carbon isn't involved in bonding and is delocalised along the layer allowing it to carry a current
Why are diamond, graphite and graphene insoluble in water?
The covalent bonds are very strong and the lattice does not break up when any solvent is added