Bonding and structure Flashcards
Definition of ionic bonding
A strong electrostatic attraction between oppositely charged ions.
Physical properties of ionic bonding
- Mpt/Bpt: Very high because a lot of energy is required to overcome the strong electrostatic force of attraction between opoositely charged ion.
- Electrical conductivity: Does not conduct electricity when solid because ions aren’t free to move- in a fixed position within the lattice. Do conduct electricity when molten or in solution because the ions are free to move, so can carry a charge, as the lattice has broken down.
Definition of covalent bonding
An electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms.
Definition of dative covalent bonding
Covalent bonds which are formed when both electrons are donated by only one of the atoms in the bond.
Valence shell electron pair repulsion theory
- The number and the type of electron pairs around the central atom.
- Electron pairs will repel each other, as far away as possible.
- Lone pairs of electrons repel more than bonded pairs (if applicable).
Linear shape
2 bonded pairs
0 lone pairs
Bond angle is 180
Examples: BeCl2 / BeF2 / CO2
Trigonal planar shape
3 bonded pairs
0 lone pairs
Bond angle is 120
Examples: AlCl3 / BF3 / BCl3 / AlBr3
Tetrahedral shape
4 bonded pairs
0 lone pairs
Bond angle is 109.5
Examples: CH4 / NH4^+ / CCl4 / SiCl4 (Tends to be group 4 molecules).
Pyramidal shape
3 bonded pairs
1 lone pair
Bond angle is 107
Examples: NH4 / PF3 / NCl3 / PCl3 (Tends to be group 5 molecules).
Non-linear shape
2 bonded pairs
2 lone pairs
Bond angle is 104.5
Examples: H2O / OF2
Octet shape
6 bonding pairs
0 lone pairs
Bond angle is 90
Example: Sulphur hexafluoride
Definition of electronegativity
The ability of an atom to attract electrons towards itself in a covalent bond.
(Electronegativity increases across a period and up a group, so the most electronegative element is fluorine).
Definition of non-polar
The electrons are shared equally between the 2 atomsbecause the atoms have the same (or very similar) electronegativity.
Definition of polar
The electrons are unequally shared because one atom has a greater electronegativity than the other.
(The greater the difference in electronegativity between the two atoms, the more polar the molecules will be).
Symmetrical = non-polar
non-symmetrical = polar
Induced dipole-dipole interactions (London forces)
The weakest intermolecular force of attraction between non-polar molecules.
Examples: Cl2 / CH4
Permanant dipole-dipole interactions
Slightly stronger than London forces. Intermolecular forces of attraction between polar molecules.
Examples: HCl / CH3Cl / H2S
Hydrogen bonding
These are the strongest intermolecular forces of attraction occurring between hydrogen bonded to F, O, N and a lone pair of electrons.
When asked to compare London forces, always state…
… as the number of electrons increases, the induced dipole-dipole force of attraction will increase.
Anamolous properties of water
- High mpt/bpt: energy is used to break the hydrogen bonds, which are relatively strong, so a lot of energy is required.
- A simple molecular lattice is formed when water turns to ice. Water as a solid is less dense than liquid because the hydrgen bonds hold the water molecules further apart in an open lattice structure in ice.
Defintion of a simple molecular lattice
A simple structure with covalent bonds between atoms where molecules are held together by intermolecular forces.
Examples: Neon, Nitrogen and Iodine.
Physical properties of simple moelcular lattices
- Low mpt/bpt: little energy is needed to break the weak intermolecular forces.
- Electrical conductivity: non-conductorsbecause the electrons are localised in bonds and can’t move.
- Solubility: soluble in non-polar solvents as induced dipole-dipole forces will form between the structure and the solvent. insoluble in polar water.
Definition of a giant covalent lattice
A three-dimensional structure of atoms, all bonded together by stron covalent bonds.
Examples: diamond, graphite and graphene (single layer of graphite), Si and SiO2.
Properties of giant covelent lattices
- High melting points because all the atoms are held together by strong covalent bonds which require a lot of energy to break.
- Non-conductors of electricity because all electrons are localised in bonds. An exception for conduction is graphite as it conducts electricity because each carbon has 1 delocalised electron that can move to carry a charge.
- insoluble in all solvents because each carbon atom is bonded to every other carbon atom by strong covalent bonds. Atoms cannot interact with solvent molecules.
Definition of metallic bonding
A strong electrostatic attraction between the delocalised sea of electrons and the positive ions.
Properties of metallic bonding
- Conductivity: metals conduct electricity because the delocalised electrons can move.
- Mpt/Bpt: metals have a high melting point and boiling point because a lot of energy is needed to overcome the strong electrostatic forces of attraction between the sea of delocalised electrons and the positive ions.
Explain why induced dipole-dipole forces are weak
At any moment in time, the electrons in an tom/molecule are unevenly distributed randomly. Thid creates a temporary dipole which induces an induced dipole in the neighbouring molecule/atom. The two dipoles attract each other. This is the weakest force of attraction.
