Topic 2: Bonding and Structure

ionic bonding is the strong, net electrostatic attraction between oppositely charged ions

Giant, regular ionic structure, with a cubic shape and giant repeat pattern

Most dissolve in water as water is polar. The slightly + H is attracted to anions and the slightly - O attracts cations, breaking the structure. The water molecules surround the ions in a process called hydration.

Ionic radii increases down the group because of more electron shells. This means there is more electron shielding.

For isoelectric ions, as atomic number increases, ionic radius decreases. This is bc the attractive force from the nucleus increases due to more protons, so it pulls the other shell more in.

The physical properties of ionic compounds provide evidence for ions. Eg molten ionic compounds conduct electricity and undergo electrolysis such as sodium chloride. + Na ions are reduced at the cathode - Cl ions are oxidised at the anode

Metal ions are smaller than metal atoms due to the loss of the outer electron shell and increased proton:electron ratio. Therefore there is a stronger attraction between the nucleus and each electron and ionic radius decreases. The opposite is true for non metals

cv bonds are formed by the overlap of 2 atomic orbitals that each contain a single electron. It’s a strong electrostatic attraction. Shared pair of e-

single= 1 shared e pair double=2 shared e pairs triple=3 shared e pairs

1 atom donates 2 of its electrons to an atom or ion to form a bond. Eg H+ ion bonds w/ NH3 to form NH4. NH3 gives 2 e to share w/ H+. An arrow represents the dative/coordinate bond

It has a double covalent bond AND a dative covalent bond. so in the overlap of the dot cross diagram draw 2 pairs AND 2 dots. These 2 dots came from the oxygen.

Bond strength is the amount of energy required to break one mole of bond in the gaseous state. For similar bonds, shorter bond = greater strength. This is bc closer bonds mean more electrostatic attraction between the two nuclei and the electrons in overlapping orbitals. Lone pairs make bonding weaker as they repel each other

Bond length: distance entre nuclei of 2 atoms covalently bonded. In covalent molecules there are attractive forces between nuclei and the shared e. Also, there are repulsive forces between the 2 nuclei and between e. Theres a balance between these forces, resulting in bond length

A higher e density increases the attractive force between atoms. Therefore atoms are pulled in further towards each other. This leads to shorter bond length, increasing bond strength and therefore increasing bond enthalpy

Draw the dot cross diagram to find the no of lone pairs and bond pairs. For cations, remove e from the central atom eg: in NH4+ N would have 4 e instead of 5 as it is a + ion For anions, add e to the central atom. If the dot cross has a lone pair, subtract 2.5 from the bond angle. If hay 2 lone pairs, subtract 2 x 2.5= 5 ALWAYS draw in 3D! (dashed lines etc)

Bonds have electrons so they want to be as far apart as possible. Bond pairs repel each other equally. If a molecule has lone pairs, these repel more than bond pairs. Molecules have a certain shape/bond angle to achieve minimum repulsion between pairs of electrons.

CH4 is tetrahedral, with a bond angle of 109.5. Hay 4 bonding pairs and zero lone pairs.

2 bond pairs, no lone pairs. Bond angle is 180°

NH4 is trigonal pyramidal, Bond angle 107. 3 bond pairs and 1 lone pair.

SO3 is a trigonal planar. Three bonding pairs, no lone pairs. The bond angle is 120°

PCl5 Is the trigonal bipyramidal. Five bonding pairs, no lone pairs. The bond angles are 90° and 120°

Two bond pairs and two lone pairs. Example of this is water. Bond angle is 104.5°

The solvent and substance bonds must break. New bonds are formed between the solvent and the substance. The new bonds formed must be the same strength or greater than those broken, otherwise the substance won’t dissolve. Eg Al2O3 has ionic bonding too strong to be broken so its insoluble despite being ionic.

They have polarity. Some have H bonds like water, called an aqueous solvent. Some have dipole dipole and London forces, called nonaqueous solvents