Recap – Formula and bonding

Types of bonding: ionic, covalent, metallic

Types of formula: empirical, molecular, structural

Type of covalent materials: molecular, network

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H N

H

H

H2O2HO H O O H

2

Polarity of Water• The O-H bonds in water are polar.• The angular shape of the molecule

mean water is a ‘polar molecule’.

Fig.

4.2

Silb

erbe

rg

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Chemical ReactionsChemical reactions occur because:

• Products contain less energy than reactants and systems go to lowest energy state, eg burning gas.

• Energy supplied to force reactants to products which have higher energy, eg blast furnace.

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Chemical Equations• Word Equation

hydrogen plus oxygen forms water

• Symbolic Equations – use correct formula

H2 + O2 H2O

• Need to balance equations. Indicate states

2H2(g) + O2(g) 2H2O(l)

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Chemical Equations• Molecular Equation

eg H2(g) + I2(g) 2HI(g)C6H12O6(s) C6H12O6(aq)

• Ionic Equations eg NaCl (s) Na+(aq) + Cl-(aq)

Pb2+(aq) + 2I-(aq) PbI2(s)

Precipitate

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Reactions with Acid, H+

- e-

H+Hydrogenatom

Hydrogenion

• H+ cation is just a ‘bare proton’, no e-.

• In aqueous solution, H+ associates with H2O to give H3O+(aq), also called H+(aq).

+OH H

H

• Substances that provide H+ ions in water are called ACIDS.

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Metal + Acid Salt + Hydrogen

Formula EquationZn + 2HCl ZnCl2 + H2

Complete ionic equation  Zn(s) + 2H+(aq) + 2Cl-(aq) Zn2+(aq) + H2(g) +

2Cl-(aq)

Net ionic equationZn(s) + 2H+(aq) Zn2+(aq) + H2(g)

We can isolate the salt by evaporation of the solvent

Zn2+(aq) + 2Cl-(aq) ZnCl2(s)

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Carbonate + Acid Salt + H2O + CO2

Formula EquationCaCO3 + 2HCl CaCl2 + H2O

+ CO2

Complete ionic equation  CaCO3(s) +2H+(aq) + 2Cl-(aq) Ca2+(aq) + H2O(l) +

CO2(g) + 2Cl-(aq)

Net ionic equationCaCO3(s) + 2H+(aq) Ca2+(aq) + H2O(l)

+ CO2(g)

We can isolate the salt by evaporation of the solvent

Ca2+(aq) + 2Cl-(aq) CaCl2(s)

• By the end of this lecture, you should:− understand the reason that water dissolves some

ionic materials− know the component parts of a chemical equation− be able to balance a chemical equation− recognise a molecular equation, formula equation

and an ionic equation− be able to describe a chemical reaction in terms of

a chemical equation− understand an acid supplies H+ ions and exists in

water− recognise reactions involving dissolution,

precipitation and acids

− be able to complete the worksheet (if you haven’t already done so…)

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Learning Outcomes:

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Questions to complete for next lecture:

1. Balance the following chemical equations:a) CH4(g) + O2(g) CO2(g) + H2O(l)b) CaCl2 + AgNO3 Ca(NO3)2 + AgClc) Ag+(aq) + CrO4

2-(aq) Ag2CrO4(s)d) Ca(s) + H+(aq) Ca2+(aq) + H2(g)e) Mg(OH)2(s) + H+(aq) Mg2+(aq) + H2O(l)

2. Classify the above equations as ‘molecular’, ‘formula’, or ‘net ionic’.

3. Which of the equations in question 1 represent a precipitation reaction?

4. Which of the equations in question 1 represent a reaction with acid?

5. Would it matter if you used hydrochloric acid or sulfuric acid to perform the reaction represented by equation 1d?