Presentation on theme: "Chapter: 4 Chemical Bonding and Structure Title: Lesson 1 Ionic Bonding Learning Objectives: Reflect on prior knowledge of bonding Refresh knowledge and."— Presentation transcript:
Chapter: 4 Chemical Bonding and Structure Title: Lesson 1 Ionic Bonding Learning Objectives: Reflect on prior knowledge of bonding Refresh knowledge and understanding of ionic bonding
Main Menu 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 + O 2- Li + Na + F-F-
Main Menu The names of ionic compounds The cation gives the first part of the name Normally a metal except in the case of ammonium (NH 4 + ) 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: CaF 2 : calcium fluoride Fe 3 (PO 4 ) 2 : iron (II) phosphate
Main Menu 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 http://www.learner.org/interactives/periodic/groups_interactive.html
Main Menu 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 Ca 2+ + 2e - Group 3: Al Al 3+ + 3e - Transition metals – form multiple different ions Fe Fe 2+ + 2e - Fe Fe 3+ + 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 - N 3- Group 6: O + 2e - O 2- Group 7: F + e- F -
Main Menu 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, SO 4 2- Phosphate, PO 4 3- Nitrate, NO 3 - Carbonate, CO 3 2- Hydrogen carbonate, HCO 3 - Ethanoate (acetate), CH 3 CO 2 - Hydroxide, OH - Ammonium, NH 4 +
Main Menu The formula of ionic compounds Ionic compounds are always neutral, so the charges must balance Example 1: calcium reacting with fluorine: Calcium forms Ca 2+, fluorine forms F - The formula is CaF 2 so two F - charges cancel the one Ca 2+ Example 2: iron (II) reacting with phosphate Iron (II) is the Fe 2+ ion, phosphate is PO 4 3- The formula is Fe 3 (PO 4 ) 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
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 Sodium has lost a negative charge and so become a positive ion. Chlorine gains a negative charge and becomes a negative ion
StopwatchStopwatch Graph HomeGraphHome SODIUM CHLORIDE Cl SODIUM ATOM 2,8,1 Na CHLORINE ATOM 2,8,7
StopwatchStopwatch Graph HomeGraphHome SODIUM CHLORIDE Cl SODIUM ION 2,8 Na CHLORIDE ION 2,8,8 both species now have ‘full’ outer shells; ie they have the electronic configuration of a noble gas +
StopwatchStopwatch Graph HomeGraphHome SODIUM CHLORIDE Cl SODIUM ION 2,8 Na CHLORIDE ION 2,8,8 NaNa + + e¯ 2,8,1 2,8 ELECTRON TRANSFERRED Cl + e¯ Cl¯ 2,8,7 2,8,8 +
Ionic bonding in MgCl 2 In each case, the ions are held together by attractive electrostatic forces. They form giant structures In each case, the ions are held together by attractive electrostatic forces. They form giant structures NaCl
StopwatchStopwatch Graph HomeGraphHome GIANT IONIC CRYSTAL LATTICE Cl - Chloride ion Na + Sodium ion 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 The Na + ion is small enough relative to a Cl¯ ion to fit in the spaces so that both ions occur in every plane.
StopwatchStopwatch Graph HomeGraphHome 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 regular 3-dimensional lattice by electrostatic attraction The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
StopwatchStopwatch Graph HomeGraphHome 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 regular 3-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 temperature Giant structure High melting points Crystalline Brittle - shatter easily Conductors in liquid or solvated state Polar, Hydrophilic Solid at room temperature Giant structure High melting points Crystalline Brittle - shatter easily Conductors in liquid or solvated state Polar, Hydrophilic Why are they brittle? Ions of the same charge are now adjacent
StopwatchStopwatch Graph HomeGraphHome Physical properties of ionic compounds Melting point very highA 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. Strength Very brittleAny dislocation leads to the layers moving and similar ions being adjacent. The repulsion splits the crystal. ElectricalDon’t conduct when solid - ions held strongly in the lattice conduct when molten or in aqueous solution - the ions become mobile and conduction takes place. SolubilityInsoluble in non-polar solvents but soluble in water Water 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.
StopwatchStopwatch Graph HomeGraphHome 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 detail When 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 CaCl 2 is formed
The Octet Rule http://liakatas.org/chemblog/?page_id=17# Videos
Main Menu 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
Main Menu 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