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Chapter: 4 Chemical Bonding and StructureTitle: Lesson 1 Ionic Bonding
Learning Objectives:
• Reflect on prior knowledge of bonding• Refresh knowledge and understanding of ionic bonding
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Recapping ionic bonding An ionic bond is:
The electrostatic attraction between two oppositely charged ions
sodium fluoride lithium oxide
Ionic bonds typically form between a metal and a non-metal
Ionically bonded compounds are often referred to as salts
Li+O2-Li+Na+F-
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The names of ionic compounds
The cation gives the first part of the name Normally a metal except in the case of ammonium (NH4
+) In the case of transition metals, Roman numerals tell you the
charge on the metal ion
The anion gives the second part of the name Simple ions: ‘-ide’…e.g. chloride, fluoride, nitride etc Complex ions: just their name: sulphate, phosphate etc
Note: the ‘-ate’ ending usually refers to polyatomic ions containing oxygen, which provides the negativity…more on this in the redox unit
Examples: CaF2: calcium fluoride Fe3(PO4)2: iron (II) phosphate
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Your turn Deduce the formulae and names of the ionic
compounds formed between:1. Lithium and fluorine
2. Magnesium and iodine
3. Aluminium and oxygen
4. Iron (II) and sulphur
5. Calcium and nitrogen
6. Sodium and sulphate ions
7. Chloride and ammonium ions
8. Iron (III) and sulphate ions
9. Iron (II) and nitrate ions
10. Potassium and carbonate ions
11. Work through the simulation here: http://www.learner.org/interactives/periodic/groups_interactive.html
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Formation of simple ions Positive ions (cations) - Metals
Positive ions are formed when metals lose their outer shell electrons Group 1: Li Li+ + e-
Group 2: Ca Ca2+ + 2e-
Group 3: Al Al3+ + 3e-
Transition metals – form multiple different ions Fe Fe2+ + 2e-
Fe Fe3+ + 3e-
Negative ions (anions) – Non metals Negative ions are formed when non-metals gain enough
electrons to complete their outer shells Group 5: N + 3e- N3-
Group 6: O + 2e- O2-
Group 7: F + e- F-
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Polyatomic ions
Many ions are made of multiple atoms with an overall negative charge
The negative ones are mostly acids that have lost their hydrogens
You need to know about: Sulphate, SO4
2-
Phosphate, PO43-
Nitrate, NO3-
Carbonate, CO32-
Hydrogen carbonate, HCO3-
Ethanoate (acetate), CH3CO2-
Hydroxide, OH-
Ammonium, NH4+
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The formula of ionic compounds
Ionic compounds are always neutral, so the charges must balance
Example 1: calcium reacting with fluorine: Calcium forms Ca2+, fluorine forms F-
The formula is CaF2 so two F- charges cancel the one Ca2+
Example 2: iron (II) reacting with phosphate Iron (II) is the Fe2+ ion, phosphate is PO4
3-
The formula is Fe3(PO4)2
The 6+ charges from iron (2+ x 3) balance the 6- charges (3- x 2) from phosphate Look for the lowest common multiple
Ionic compounds do not form molecules so these are always empirical formulae
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Use this table for question 1!
3.1 Ionic bonding
Why do elements in the same group have similar patterns of bonding?
Because of the octet rule. Atoms try to gain noble gas configurations
Sodium has one outer electron. It gains stability by giving an electron to chlorine. Chlorine also become stable by gaining one electron.
Sodium has lost a negative charge and so become a positive ion.Chlorine gains a negative charge and becomes a negative ion
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SODIUM CHLORIDE
Cl
SODIUM ATOM2,8,1
Na
CHLORINE ATOM2,8,7
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SODIUM CHLORIDE
Cl
SODIUM ION2,8
Na
CHLORIDE ION2,8,8
both species now have ‘full’ outer shells; ie they have the electronic configuration of a noble gas
+
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SODIUM CHLORIDE
Cl
SODIUM ION2,8
Na
CHLORIDE ION2,8,8
Na Na+ + e¯2,8,1 2,8
ELECTRON TRANSFERRED
Cl + e¯ Cl¯2,8,7 2,8,8
+
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MAGNESIUM CHLORIDE
Cl
MAGNESIUM ATOM2,8,2
MgCHLORINE ATOMS
2,8,7
Cl
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MAGNESIUM CHLORIDE
Cl
MAGNESIUM ION2,8
MgCHLORIDE IONS
2,8,8
Cl
2+
Ionic bonding in MgCl2
In each case, the ions are held together by attractive electrostatic forces. They form giant structures
NaCl
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GIANT IONIC CRYSTAL LATTICE
Cl-Chloride ion
Na+
Sodium ion
Oppositely charged ions held in a regular3-dimensional lattice by electrostatic attraction
The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
The Na+ ion is small enough relative to a Cl¯ ion to fit in the spaces so that both ions occur in every plane.
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GIANT IONIC CRYSTAL LATTICE
Each Na+ is surrounded by 6 Cl¯ (co-ordination number = 6)and each Cl¯ is surrounded by 6 Na+ (co-ordination number = 6).
Oppositely charged ions held in a regular3-dimensional lattice by electrostatic attraction
The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
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GIANT IONIC CRYSTAL LATTICE
Na+ is surrounded by 6 Cl¯ (co-ordination number = 6)and each Cl¯ is surrounded by 6 Na+ (co-ordination number = 6).
Oppositely charged ions held in a regular3-dimensional lattice by electrostatic attraction
The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
•No such thing as “an ionic bond”!
•Every cation attracts every anion, and vice versa
•Unlike covalent bonding, ionic bonding is non-directional
NB : “NaCl” is an empirical formula
simplest ratio of ions not a molecule!
Properties of ionically bonded compounds
List the properties of ionic compounds
Solid at room temperatureGiant structureHigh melting pointsCrystallineBrittle - shatter easilyConductors in liquid or solvated statePolar, Hydrophilic
Why are they brittle?
Ions of the same charge are now adjacent
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Physical properties of ionic compounds
Melting pointvery high A large amount of energy must be put in to overcome the
strong electrostatic attractions within the lattice and separate the ions. Higher charges on the metal ion increases melting point.
StrengthVery brittle Any dislocation leads to the layers moving and similar
ions being adjacent. The repulsion splits the crystal.
Electrical Don’t conduct when solid - ions held strongly in the latticeconduct when molten or in aqueous solution - the ionsbecome mobile and conduction takes place.
Solubility Insoluble in non-polar solvents but soluble in waterWater is a polar solvent and stabilises the separated ions.
Much energy is needed to overcome the electrostatic attraction and separate the ions. Stability attained by being surrounded by polar water molecules compensates for this.
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IONIC COMPOUNDS - ELECTRICAL PROPERTIES
SOLID IONIC COMPOUNDS DO NOT CONDUCT ELECTRICITY
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
IONS ARE HELD STRONGLY TOGETHER
+ IONS CAN’T MOVE TO THE CATHODE
- IONS CAN’T MOVE TO THE ANODE
MOLTEN IONIC COMPOUNDS DO
CONDUCT ELECTRICITY
Na+ Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
IONS HAVE MORE FREEDOM IN A LIQUID SO CAN MOVE TO THE ELECTRODES
SOLUTIONS OF IONIC COMPOUNDS IN
WATER DO CONDUCT ELECTRICITY
DISSOLVING AN IONIC COMPOUND IN WATER BREAKS UP THE STRUCTURE SO IONS ARE FREE TO MOVE TO THE ELECTRODES
Solubility in detailWhen a molecule is polar, there is some separation of charges in their structure.
At the contact surface, the partial charges in the water molecules are attracted to ions of opposite charges.
Ions are separated from the lattice, they become surrounded by water molecules are hydrated.
Solubility Video Pearson
Task
Draw dot cross diagrams to show how CaCl2 is formed
The Octet Rule
http://liakatas.org/chemblog/?page_id=17#Videos
Ionic bonding and orbitals
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Key Points
Ionic bonds are the attraction between two oppositely charged ions
Ionic bonds form between metals and non metals Metals lose their outer shell Non-metals complete their outer shell
The number of each ion in the formula is determined by the lowest common multiple of their charges
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Homework
Research and make notes on metallic bonding. Including: Description of the nature of the metallic bond Factors affecting the strength of metallic bonds Explanation of the malleability of metals Explanation of the electrical conductivity of metals Factors affecting the conductivity of metals
