5.2 Ionic bonding Flashcards
define an
Ionic Bond
electrostatic attraction between positive and negative ions.
How are ionic bonds formed?
By atoms losing or gaining electrons
More electronegative non-metal atoms GAIN electronsFROM metal atoms
Ions are isoelectronic with nearest noble gas
two atoms,ions or molecules that have the same electronic structure and same number of valence electrons.
ANIONS
(-) are formed
when atoms (USUALLY
NON-METALS) gain
electrons from metal
CATIONS
(+) are formed
when atoms (USUALLY
METALS) lose electrons
to non-metal
Group 4 :
Group 4 :
🡺No 4+ ions : too much energy to remove 4 e-
🡺 No 4- ions: too much repulsion between 4 added e-
🡺 some 2+ ions: lower in group eg Sn2+ and Pb2+
define
ion
An ion is just a charged particle. Whereby atoms have either lost or gained electrons.
Dot and cross diagrams
Drawing full diagrams from the first shell to their current valence shell (valence refers to the
outer shell, or shell/electrons used in bonding), takes a lot of time and effort.
At A-level, only outer shells are needed.
describe the structure of
ionic compounds
On a small scale we have looked at the lowest common ratio of ions needed to form a
particular ionic compound.
However, salts form bonds in all directions. This results in the formation of a giant ionic
lattice – containing millions upon billions of ions in a repeating pattern.
GIANT IONIC LATTICE
Oppositely charged ions held in a regular
3-dimensional lattice by electrostatic attraction
The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
list the three
Properties of ionic compounds
- High Melting and boiling points that increase as with greater ionic charge beaceue stronger attraction between ions
- Solubility- only once ionic lattice is broken and water molucules suround ions
- Electrical Conductivity
explain
Melting and boiling points in ionic compounds
- The bonds between ions are very strong, and at low temperatures there is insufficient energy
to overcome these electrostatic forces of attraction. - Higher temperatures provide greater amounts of energy to overcome these electrostatic
forces of attraction. - Ionic lattices with greater ionic charges have higher melting points due to a stronger
attraction between ions.
e.g. melting points
- NaF: 993oC, where as CaF2: 1423oC
-Na2O: 1275oC where as CaO: 2614oC
explain
Electrical conductivity of ionic compounds in dif states
Electrical conductivity – SOLID:
In a solid state, ionic compounds do NOT conduct electricity.
The ions are held too strongly in the fixed position of the giant ionic lattice, and therefore
can not move and carry the charge.
Electrical conductivity – AQUEOUS or MOLTEN
When the ionic compound is dissolved in water, or melted, it DOES conduct electricity.
The solid ionic lattice breaks down, allowing the ions to move freely. They are now mobile
and can carry the charge.
explain s
solubility of ionic compounds
- Many ionic compounds require a polar solvent to dissolve. E.g. water
- Polar water molecules have the ability to break down the ionic lattice and then surround
each ion in each solution. - If the forces of attraction are too strong, the ability of the ionic lattice to be broken down
is reduced rendering the compound sparingly soluble. - For ionic compounds, the solubility decreases as the ionic charge increases
(or the electrostatic forces of attraction get stronger)
solubility requires two main
processes:
- The ionic lattice must be broken down
- Water molecules must attract and surrounded the ions
Physical properties of ionic compounds
Strength
Very brittle. Any dislocation leads to the layers moving and similar ions being adjacent.
The repulsion splits the crystal.
