chemistry - definitions - IMFs

electronegativity

a measure of tendency of an atom to attract a bonding pair of electrons.

covalent bonding

the sharing of at least one pair of electrons between atoms.

Ionic bond

the transfer of electrons and subsequent electrostatic attraction.

mixture

a combination of two or more substances in which each substance retains its identity

solution

a homogenous mixture of two or more substances

intermolecular forces

a force of attraction between molecules or atoms of a noble gas

intramolecular forces

bond which occurs between atoms in a molecule

Polar/dipole molecules

A molecule in which the electrons are unevenly distributed resulting in a partial positive or partial negative end

Non-polar molecule

A molecule that has an even distribution of electrons and therefore no net charge on the overall molecule

What are the three types of Intermolecular forces?

1. London Dispersion
2. Dipole-Dipole
3. Hydrogen Bondin

how does dipole-dipole attraction work?

When one molecule comes into contact with another molecule, the positive pole of the one molecule will be attracted to the negative pole of the other.

Why is hydrogen bonding strong?

- Large EN difference
- The NOF atoms have high electron density therefore very strong dipoles form
- Small atomic radii (< bond length)

What type of molecules and atoms can experience london forces?

non-polar molecules, noble gases

How does London Forces work? (4)

- Electrons are in constant motion
- There will be times when there is an uneven distribution of electrons
- This causes a momentary Dipole to be formed
- These momentary Dipoles induce dipoles in neighbouring molecules/atoms
- . ' . Dipole- Induced dipole interactions take place

What are some factors that influence intermolecular forces?

- ↑Size of the molecule = ↑intermolecular force
- Shape of Molecule (↑straighter = ↑intermolecular force)
- ↑Polarity = ↑intermolecular force

Define boiling point

The temperature at which the vapour pressure of a substance equals the atmospheric pressure

Define Melting point

The temperature at which the solid and liquid phases of a substance are at equilibrium

Compare the boiling points of Water (H₂O) and methanol (CH₃OH)

- Water experiences Hydrogen Bond forces of attraction where methanol experiences both London and Hydrogen Bond forces.
- But Water molecules make 4 hydrogen bonds with another water molecule whereas the methanol only has 1 region where a hydrogen bond exists.
- The strength of the intermolecular forces for water are stronger than that for methanol molecules
- Therefore, more energy is required to overcome the forces between water molecules than methanol molecules

Why is methane a gas at room temperature where as methanol is a liquid?

- Methane experience London Forces whereas methanol experiences hydrogen bond forces
- Hydrogen bonding is stronger than London Forces
- Therefore, molecules of methanol are held more tightly to each other therefore existing as a liquid
- Molecules of methane are less tightly held and therefore spread apart in gas molecules

Explain the difference in boiling points of HCL and HI

- Both molecules are polar molecules and experience dipole-dipole forces of attraction
- But HI is a bigger molecule with greater number of electrons.
- Therefore, a stronger dipole is set up between molecules of HI compared to that of HCL and HI experiences stronger intermolecular forces
- Therefore, more energy is required to overcome the forces between HI molecules
- Therefore, HI has a higher boiling point

Explain why nitrogen gas is insoluble in water whereas ammonia is soluble?

- Nitrogen molecules are non-polar and therefore experience London forces.
- Ammonia is a polar molecule with hydrogen bond forces of attraction.
- Water as the solvent is a polar molecule with also hydrogen bond forces of attraction.
- Since ammonia and water are of similar strength of forces therefore ammonia will dissolve in water.
- The strength of forces between nitrogen molecules are too weak.