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IONIC COMPOUNDS
Sodium, an alkali metal, has a very low electronegativity and low ionisation energy, meaning that little energy is needed to remove the single valence electron of a sodium atom
IONIC BONDINGSodium 1s22s22p63s1
Chlorine, a non-metal halogen, has a very high electronegativity and as such can attract electrons towards its nucleus relatively easily
IONIC BONDINGChlorine 1s22s22p63s23p5
IONIC BONDINGChlorine 1s22s22p63s23p5Sodium 1s22s22p63s1
The combination of these factors means that when sodium reacts with chlorine, the sodium atom readily transfers an electron to the chlorine atom, which it readily accepts
IONIC BONDINGChlorine anion 1s22s22p63s23p6Sodium cation 1s22s22p6
After the electron transfer, both atoms now have a completely filled outermost shell, giving them the same electron configuration of as stable noble gases
1+1-
IONIC BONDINGChlorine anion 1s22s22p63s23p6Sodium cation 1s22s22p6
The sodium atom becomes a positively charged cation
The chlorine atom becomes a negatively charged anion
Na+ Cl-
1+1-
IONIC BONDINGChlorine anion 1s22s22p63s23p6Sodium cation 1s22s22p6
This results in a strong electrostatic attraction forming between the positive cations and negative anions, which leads to the formation of an ionic bond
Na+ Cl-
[Na]+[Cl]-NaCl
IONIC BONDING MODEL
Strong ionic bonds form between other nearby ions, leading the formation of an ionic network lattice
IONIC BONDING MODEL
Within the lattice, each cation is surrounded by six anions, and each anion is surrounded by six cations, strengthening the forces of attraction, which holds each ion firmly in place
IONIC BONDING MODEL
Within the lattice, each cation is surrounded by six anions, and each anion is surrounded by six cations, strengthening the forces of attraction, which holds each ion firmly in place
IONIC BONDING MODEL
Within the lattice, each cation is surrounded by six anions, and each anion is surrounded by six cations, strengthening the forces of attraction, which holds each ion firmly in place
IONIC BONDING MODEL
For every positive cation there is one negative anion, ensuring that the overall charge of the ionic lattice is neutral
PROPERTIES OF IONIC COMPOUNDSMEDIUM - HIGH MELTING / BOILING POINTS
A lot of energy is required to overcome the strong electrostatic attraction between ions in a ionic lattice
PROPERTIES OF IONIC COMPOUNDSCRYSTALLINE STRUCTURE
Each type of ionic compound has a symmetrical lattice structure
Sodium chloride, for instance, has a cubic lattice symmetry
PROPERTIES OF IONIC COMPOUNDSCRYSTALLINE STRUCTURE
Each type of ionic compound has a symmetrical lattice structure
Sodium chloride, for instance, has a cubic lattice symmetry
PROPERTIES OF IONIC COMPOUNDSHARD / BRITTLE
The strong electrostatic force within ionic compounds makes them very hard to break, but with sufficient force, ions of like charge move towards each other, causing the lattice to shatter
PROPERTIES OF IONIC COMPOUNDSHARD / BRITTLE
The strong electrostatic force within ionic compounds makes them very hard to break, but with sufficient force, ions of like charge move towards each other, causing the lattice to shatter
There are charged particles in ionic compounds (positive cations, negative anions) but these are not able to move freely
PROPERTIES OF IONIC COMPOUNDSNOT ELECTRICAL CONDUCTIVE AS SOLID
However, when in molten form, or dissolved in water, the charged particles are able to move
PROPERTIES OF IONIC COMPOUNDSELECTRICAL CONDUCTIVE AS MELT OR AQUEOUS SOLUTION
Water molecules are able to move in between the ions and free them by disrupting the rigid crystal structure
Water is a polar
moleculeδ+ δ+
δ-
Water is a polar
moleculeδ+ δ+
δ-
Water molecules are able to move in between the ions and free them by disrupting the rigid crystal structure
Eventually, all ions are able to move freely, making the solution electrically conductive
If the water of the ionic solution were evaporated, the strong electrostatic attraction between the ions would lead to the recrystallisation of the ionic network lattice
If the water of the ionic solution were evaporated, the strong electrostatic attraction between the ions would lead to the recrystallisation of the ionic network lattice
If the water of the ionic solution were evaporated, the strong electrostatic attraction between the ions would lead to the recrystallisation of the ionic network lattice
IONIC BONDING MODEL
There are a number of limitations of the ionic bonding model, of which many are similar to the limitations of the metallic bonding model
•Sodium metal does not simply react with chlorine gas, for instance energy is required to first split the chlorine molecule (Cl2) into atoms
•It also can not account for the range of melting points for different ionic compounds
•As with the metallic bonding model, drawing atoms as balls is a very simplistic way of dealing with atoms
ELECTROVALENCIES
Mg2+ Cl-
Ionic compounds are not always formed from metals and non-metals in equal molar amounts
For instance, magnesium transfers two electrons to two different chlorine atoms to become a stable ion
Cl-
ELECTROVALENCIES
MgCl2
To form a neutral ionic compound, each magnesium (Mg2+) ion must therefore react with two chlorine (Cl-) ions
The resultant charge of each ion is known as its electrovalency
Cl- Mg2+ Cl-
ELECTROVALENCIESThe electrovalencies of elements can be predicted (to some extent) from their group in the periodic table, as it shows how many electrons each element has in its outermost electron shell
H
Li
Na
K
Rb
Cs
Fr
Be
Mg
Ca
Sr
Ba
Ra
Sc
Y
Lu
Lr
Ti
Zr
Hf
Rf
V
Nb
Ta
Db
Cr
Mo
W
Sg
Mn
Tc
Re
Bh
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
Ni
Pd
Pt
Ds
Cu
Ag
Au
Rg
Zn
Cd
Hg
Cn
Ga
In
Tl
Uut
Ge
Sn
Pb
Uuq
As
Sb
Bi
Uup
Se
Te
Po
Uuh
Br
I
At
Uus
Kr
Xe
Rn
Uuo
B
Al
C
Si
N
P
O
S
F
Cl
He
Ne
Ar
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
ELECTROVALENCIESMetals lose electrons to form stable electron configurations, and so have positive electrovalencies
Non-metals gain electrons to form stable electron configurations, and so have negative electrovalencies
H
Li
Na
K
Rb
Cs
Fr
Be
Mg
Ca
Sr
Ba
Ra
Sc
Y
Lu
Lr
Ti
Zr
Hf
Rf
V
Nb
Ta
Db
Cr
Mo
W
Sg
Mn
Tc
Re
Bh
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
Ni
Pd
Pt
Ds
Cu
Ag
Au
Rg
Zn
Cd
Hg
Cn
Ga
In
Tl
Uut
B
Al
Ge
Sn
Pb
Uuq
C
Si
As
Sb
Bi
Uup
N
P
Se
Te
Po
Uuh
O
S
Br
I
At
Uus
F
Cl
Kr
Xe
Rn
Uuo
He
Ne
Ar
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1+
2+ 3+ 3- 2- 1-
2+
or
4+
No ions form
ed
ELECTROVALENCIESHowever for most elements, particularly transition metals, predicting the electrovalency is more complex
It is easier therefore to learn the electrovalency of individual atoms
H
Li
Na
K
Rb
Cs
Fr
Be
Mg
Ca
Sr
Ba
Ra
Sc
Y
Lu
Lr
Ti
Zr
Hf
Rf
V
Nb
Ta
Db
Cr
Mo
W
Sg
Mn
Tc
Re
Bh
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
Ni
Pd
Pt
Ds
Cu
Ag
Au
Rg
Zn
Cd
Hg
Cn
Ga
In
Tl
Uut
B
Al
Ge
Sn
Pb
Uuq
C
Si
As
Sb
Bi
Uup
N
P
Se
Te
Po
Uuh
O
S
Br
I
At
Uus
F
Cl
Kr
Xe
Rn
Uuo
He
Ne
Ar
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1+
2+
Most form 2+ ions, but can vary
3+ 3- 2- 1-
No ions form
ed
No ions
2+
or
4+
Some ionic compounds are formed from ions that contain more than one atom
These are known as polyatomic ions
These ions are a group of tightly bound atoms which act as a single entity
Each polyatomic ion has a fixed electrovalency
ELECTROVALENCIES
Ammonium ion NH4+
Carbonate ion CO32-
Sulfate ion SO42-
Phosphate ion PO43-
The electrovalency of common ions are listed in the electrovalency table
Using the table, along with a few naming rules, the name and empirical formula (whole number ratios) of ionic compounds can be deduced
NAMING IONIC COMPOUNDS
The number of cations and anions in the empirical formula should be such that the overall charge is neutral
Eg. Ag2O, MgO, Al2O3
The positive ion is always written first
The suffix of elemental anions is changed to -ide
Eg. Sodium chloride
NAMING IONIC COMPOUNDS
For atoms with more than one type of ion, the electrovalency of the cation is included in the formula, as roman numerals
Eg. FeIIO, Fe2IIIO3
For polyatomic ions, brackets are used, if necessary
Eg. Mg(NO3)2, NaNO3
NH4OH, (NH4)2SO4
NAMING IONIC COMPOUNDS
