bonding

types of crystal structure

types of crystal structure

ionic, metallic, simple molecular, macromolecular

Ionic bonding

involves electrostatic attraction between oppositely charged ions

Sulfate formula

SO4 2-

hydroxide formula

OH-

nitrate formula

NO3-

carbonate formula

CO3 2-

ammonium formula

NH4+

covalent bond

the electrostatic force of attraction between two nuclei and the shared pair of electrons
occurs in non metals only

A co-ordinate (dative covalent) bond

contains a shared pair of electrons with both electrons supplied by one atom.

metallic bonding

involves attraction between delocalised electrons and positive ions arranged in a lattice

molecular ion

molecule with one electron knocked off

miscible

liquids that dissolve freely in one another in any proportion

properties of ionic compounds

Form crystal lattices, conduct electricity in solution, and have high melting and boiling points.

factors affecting the strength of ionic compounds

charge - higher the charge, higher the electrostatic forces of attraction, greater the strength
size - smaller ions that are compatible with each other are stronger

Properties of simple covalent molecules e.g. iodine

low melting/boiling point - weak intermolecular forces between the molecules which are easy to overcome

unable to conduct electricity - no free ions to carry charge

diamond structure and properties

diamond is giant covalent structure

each carbon atom bonds to four other carbon atoms

doesn’t conduct electricity

hard because it isn’t layered

high mp and bp due to strong covalent bonds that need to be overcome

graphite structure and properties

graphite is a giant covalent structure

each carbon atom bonds to three other carbon atoms leaving one electron from each carbon atom

this forms a sea of delocalised electrons

conducts electricity because electrons are free to move and can carry the charge

soft due to the layers that can slide over each other

high mp and bp due to strong covalent bonds that requires lots of energy to be overcome

lone pair of electrons

a pair of electrons that are not involved in the bonding with other atoms

linear molecule

refers to a molecule in which the atoms are arranged in a straight line (180°)

2 pairs of bonding electrons

trigonal planar

molecule in which angles between atoms are 120°

3 pairs of bonding electrons

tetrahedral

molecule in which angles between atoms are 109.5°

4 pairs of bonding electrons

trigonal pyramidal

molecule in which angles between atoms are 107°

4 pairs of electrons

3 pairs of bonding electrons 1 lone pair

bent/ angular molecule

molecule with angles of 104.5°

4 electron pairs

2 bonding pairs, 2 lone pairs

trigonal bypyramidal

molecule with angles of 120° and 90°

5 bonding pairs

seesaw

molecule with angles less than 90

4 bonding pairs, 1 lone pair

t-shape

molecule with angles

3 bonding pairs, 2 lone pairs

octahedral

molecule with angles of 90 and 180

6 bonding pairs

square pyramid

molecule with angles of 90

5 bonding pairs, 1 lone pair

square planar

molecule with angles of 90

4 bonding pairs, 2 lone pairs

electronegativity

the power of an atom to attract a pair of electrons in a covalent bond

most electronegative elements/atoms

F O N Cl

factors affecting electronegativity

nuclear charge

atomic radius

shielding

how does nuclear charge affect electronegativity

the more protons, the stronger the attraction between the electrons and the nucleus and so higher the electronegativity

how does atomic radius affect electronegativity

the closer to the nucleus, the stronger the attraction between the electrons and the nucleus and so the higher the electronegativity

how does shielding affect electronegativity

less shells of electrons, less shielding (less repulsion), stronger attraction between electrons and nucleus, the higher the electronegativity

polar molecule

a molecule that has a charge on one side that is not cancelled out

across a period electronegativity

increases

down a group electronegativity

decreases

why electronegativity increases across a period

atomic radius decreases

nuclear charge increases

stronger attraction between nucleus and electrons

why electronegativity decreases down a group

atomic radius increases

nuclear charge decreases

shielding increases

explain how van der waal forces arise

- uneven distribution of electrons in one molecule which generates an instantaneous dipole

- when two polar molecules come together it induces a dipole in neighbouring molecule

- δ+ attracts δ- in adjacent molecules

explain how permanent dipole-dipole forces arise

a more electronegative atom (e.g. Cl)will pull electrons towards itself giving it a negative charge and the other a positive charge e.g. (H)

when another of these molecules get close, their permanent dipoles lead to an attraction

hydrogen bonding

only involves F, O, N

between two molecules

difference in electronegativity between a slightly positive charged H and slightly negative element of F, O or N