Unit 1-Topic 1 (A&B&C)

Chemistry
AS-level
SIR.MUHAMMAD ABDUL MAGEID

Unit 1: STRUCTURE, BONDING AND
INTRODUCTION TO ORGANIC CHEMISTRY
01. FORMULAE, EQUATIONS AND AMOUNT OF SUBSTANCE
02. ATOMIC STRUCTURE AND THE PERIODIC TABLE
03. BONDING AND STRUCTURE
04. INTRODUCTORY ORGANIC CHEMISTRY AND ALKANES
05. ALKENES

1A. ATOMS, ELEMENTS AND MOLECULES
01. FORMULAE, EQUATIONS
AND AMOUNT OF SUBSTANCE
1B. EQUATIONS AND REACTION TYPES
1C. ENERGY
1D. EMPIRICAL AND MOLECULAR FORMULAE
1E. CALCULATIONS WITH SOLUTIONS AND GASES

ATOMS, ELEMENTS
AND MOLECULES
1A.
CHEMISTRY AS-LEVEL

 An element is a substance that contains atoms of only one type.
 Elements are chemically the simplest substances so they cannot
be broken down using chemical reactions.
WHAT IS AN ELEMENT?
WHAT IS AN ATOM?
 An atom can be described as the smallest part of an element that has
the properties of that element
 Atoms contain even smaller particles (protons, neutrons and electrons).
WHAT IS A MOLECULE?
 A molecule as a particle made of two or more atoms bonded together.
 If a molecule contains atoms of the same element, then the result is
a molecule of an element . If a molecule contains atoms of two or more
different elements, then the result is a molecule of a compound

TYPES OF MOLECULES
A molecule of an element A molecule of a compound
a molecule contains atoms of the
same element
a molecule contains atoms of two or
more different elements
For example, a molecule that
contains two atoms of hydrogen
joined together can be represented
by the formula 𝐻2
For example, a molecule that
contains two atoms of hydrogen and
one atom of oxygen joined together
can be represented by the
formula 𝐻2 𝑂

 is a substance containing atoms of different elements combined
together. Note that some compounds contain large numbers of
atoms bonded together, but other compounds contain molecules
with only two atoms. Some compounds contain oppositely
charged ions
WHAT IS A COMPOUND?
WHAT IS AN ION?
 One way to describe an ion is as a species consisting of one or more
atoms joined together and having a positive or negative charge

TYPES OF IONS
CATION ANION
An ion with a positive charge An ion with a negative charge
Number of positive protons is greater
than that of negative electrons
Number of positive protons is less than
that of negative electrons
For example,
SODIUM CATION 𝑁𝑎+
For example,
CHLORIDE ANION 𝐶𝑙−

Table A shows diagrams to illustrate the terms referred to.
Each atom is shown as a circle containing the symbol of an element. The lines
show bonds between atoms

 Elements that are made up of single atoms are described as monatomic.
One example is helium, the gas used in weather balloons. The symbol for
helium is 𝐻𝑒.
 Elements and compounds made up of two atoms joined together are
described as diatomic. The two main diatomic gases in the atmosphere
are nitrogen (𝑁2) and oxygen (𝑂2).
 Elements and compounds with molecules made up of several atoms
joined together are described as polyatomic. Examples of polyatomic
molecules are phosphorus (𝑃4) and methane (C𝐻4).
 The same terms can be used for ions. Chloride ( 𝐶𝑙−) is an example of
a monatomic ion. Hydroxide (𝑂𝐻−
) is a diatomic ion. A sulfate ion (𝑆𝑂4
2−
)
is polyatomic as it contains five atoms.
OTHER TERMS

WRITING CHEMICAL
EQUATIONS
1B.1
CHEMISTRY AS-LEVEL

 WRITING FORMULAE FOR NAMES
WRITING EQUATIONS: WHAT TO REMEMBER

 WRITING AN EQUATION FROM A DESCRIPTION
 You will need to convert words into formulae and decide which ones are reactants
and which ones are products.
 Consider this description: when carbon dioxide reacts with calcium hydroxide, calcium
carbonate and water are formed.
 The wording of the description makes it clear that carbon dioxide and calcium
hydroxide are the reactants, and that calcium carbonate and water are the products.
 Now you have to write the formulae in the correct places:
𝐶𝑂2 + 𝐶𝑎(𝑂𝐻)2 → 𝐶𝑎𝐶𝑂3 + 𝐻2 𝑂
 The next step is balancing the equation. You need to add up the numbers of all the
atoms to make sure that, for each element, the totals are the same on both the left
and the right side of the equation.
 The equation is already balanced.

 WRITING AN EQUATION FROM A DESCRIPTION
 Most equations are balanced using whole-number coefficients, but using fractions or
decimals is usually acceptable. This is especially the case in organic chemistry.
 Consider this unbalanced equation for the complete combustion of butane:
𝐶4 𝐻10 + 𝑂2 → 𝐶𝑂2 + 𝐻2 𝑂
 The balanced equation can be either:
2𝐶4 𝐻10 + 13𝑂2 → 8𝐶𝑂2 + 10𝐻2 𝑂 OR: 𝐶4 𝐻10 + 6 1
2 𝑂2 → 4𝐶𝑂2 + 5 𝐻2 𝑂
 Using 6.5 instead of 6 1
2 is also acceptable.

 USING STATE SYMBOLS
Many chemical equations include state symbols. The symbols are:
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous (dissolved in water).
It is important to distinguish between (l) and (aq). A common error is to write
𝐻2 𝑂(𝑎𝑞) instead of 𝐻2 𝑂(𝑙).

USING STATE SYMBOLS
 Here is another description:
 when aqueous solutions of silver nitrate and calcium chloride are mixed, a white
precipitate of silver chloride forms. As this precipitate settles, a solution of calcium
nitrate becomes visible.
 After writing the correct formulae, balancing the equation and including state symbols,
the equation is:
2𝐴𝑔𝑁𝑂3 (𝑎𝑞) + 𝐶𝑎𝐶𝑙2(𝑎𝑞) → 2𝐴𝑔𝐶𝑙(𝑠) + 𝐶𝑎(𝑁𝑂3)2 (𝑎𝑞)

ARROWS IN EQUATIONS
 Most equations are shown with a conventional (left to right) arrow →.
 Some important reactions are reversible. This means that the reaction can go both in
the forward and backward (reverse) directions. The symbol ⇋ is used in equations
for these reactions

IONIC EQUATIONS ---- SIMPLIFYING FULL EQUATIONS
 Ionic equations show any atoms and molecules involved, but only the ions that react
together, and not the spectator ions.
 This is the easiest method to follow for simplifying equations:
1- Start with the full equation for the reaction.
2- Replace the formulae of ionic compounds by their separate ions.
3- Delete any ions that appear identically on both sides.
 Spectator Ion : an ion that is there both before and after the reaction but is not
involved in the reaction

Problem Vs Solution
● The full equation is:
𝑁𝑎𝑂𝐻 𝑎𝑞 + 𝐻𝑁𝑂3 𝑎𝑞 → 𝑁𝑎𝑁𝑂3 𝑎𝑞 + 𝐻2 𝑂 𝑙
● You should now consider which of these species are ionic and replace
them with ions.
𝑵𝒂(𝒂𝒒)
+
+ 𝑶𝑯(𝒂𝒒)
−
+ 𝑯(𝒂𝒒)
+
+ 𝑵𝑶 𝟑 (𝒂𝒒)
−
→ 𝑵𝒂(𝒂𝒒)
+
+ 𝑵𝑶 𝟑 (𝒂𝒒)
−
+ 𝑯 𝟐 𝑶(𝒍)
After deleting the identical ions (spectator ions), the equation becomes
𝑶𝑯(𝒂𝒒)
−
+ 𝑯(𝒂𝒒)
+
→ 𝑯 𝟐 𝑶(𝒍)
WORKED EXAMPLE 1
Solution
● What is the simplest ionic
equation for the
Neutralisation of sodium
hydroxide solution by
dilute nitric acid?

Problem Vs Solution
WORKED EXAMPLE 2
Solution
What is the simplest ionic equation for the
reaction that occurs when solutions of
lead(II) nitrate and sodium sulfate react
together to form a precipitate of lead(II)
sulfate and a solution of
sodium nitrate?

Problem Vs Solution
WORKED EXAMPLE 3
Solution
Carbon dioxide reacts with calcium
hydroxide solution to form water and a
precipitate of calcium carbonate.

TYPICAL
REACTIONS
OF ACIDs
1B.2
CHEMISTRY AS-LEVELSIR.MUHAMMAD ABDUL MAGEID

1-ACIDS WITH METALS

2-ACIDS WITH METAL OXIDES AND INSOLUBLE METAL HYDROXIDES

3- ACIDS WITH ALKALIS (NEUTRALISATION REACTIONS)

4- ACIDS WITH CARBONATES

5- ACIDS WITH HYDROGENCARBONATES

DISPLACEMENT
REACTIONS
1B.3
CHEMISTRY AS-LEVELSIR.MUHAMMAD ABDUL MAGEID

WHAT IS A DISPLACEMENT REACTION?
 Displacement reaction : a reaction in which one element replaces another, less
reactive, element in a compound
DISPLACEMENT REACTIONS INVOLVING METALS

DISPLACEMENT REACTIONS INVOLVING METALS

METAL DISPLACEMENT REACTIONS IN AQUEOUS SOLUTION
 When magnesium metal is added to copper(II) sulfate solution, the blue colour of the
solution becomes paler. If an excess of magnesium is added, the solution becomes
colourless, as magnesium sulfate forms. The magnesium changes in appearance from
silvery to brown as copper forms on it.
Mg(s) + CuSO4(aq) → Cu(s) + MgSO4(aq)
 The equation can be rewritten as an ionic equation:
𝑀𝑔(𝑠) + 𝐶𝑢(𝑎𝑞)
2+
+𝑆𝑂4 (𝑎𝑞)
2−
→ 𝐶𝑢(𝑠) + 𝑀𝑔(𝑎𝑞)
2+
+𝑆𝑂4 (𝑎𝑞)
2−
Cancelling the ions that appear identically on both sides (Spectator ions) gives:
𝑀𝑔(𝑠) + 𝐶𝑢(𝑎𝑞)
2+
→ 𝐶𝑢(𝑠) + 𝑀𝑔(𝑎𝑞)
2+
 Now you can see that this is a redox reaction. Electrons are transferred from
magnesium atoms to copper(II) ions, so magnesium atoms are oxidised (loss of
electrons) and copper (II) ions are reduced (gain of electrons).

METAL DISPLACEMENT REACTIONS IN THE SOLID STATE
2𝐴𝑙(𝑠) + 𝐹𝑒2 𝑂3(𝑠) → 2𝐹𝑒(𝑠) + 𝐴𝑙2 𝑂3(𝑠)

DISPLACEMENT REACTIONS INVOLVING HALOGENS
 More reactive halogens can displace less reactive halogens from their
compounds. For example, chlorine will displace bromine from a
potassium bromide solution. The full, ionic and simplified ionic
equations for this reaction are:

PRECIPITATION
REACTIONS
1B.4

CARBON DIOXIDE
CHEMICAL TESTS
 This may be your earliest memory of a precipitation reaction. When carbon dioxide
gas is bubbled through calcium hydroxide solution (often called limewater), a white
precipitate of calcium carbonate forms. The relevant equation is:
𝐶𝑂2 (𝑔) + 𝐶𝑎(𝑂𝐻)2 𝑎𝑞 → 𝐶𝑎𝐶𝑂3 𝑠 + 𝐻2 𝑂 𝑙
 The formation of the white precipitate was probably described as the limewater going
milky or cloudy

TESTING CARBON DIOXIDE
𝐶𝑂2 (𝑔) + 𝐶𝑎(𝑂𝐻)2 𝑎𝑞 → 𝐶𝑎𝐶𝑂3 𝑠 + 𝐻2 𝑂 𝑙

SULFATES
CHEMICAL TESTS
 The presence of sulfate ions in solution can be shown by the addition of barium ions
(usually from solutions of barium chloride or barium nitrate). The white precipitate that
forms is barium sulfate.
 For example, when barium chloride solution is added to sodium sulfate solution, the
relevant equations are:
𝑁𝑎2 𝑆𝑂4 (𝑎𝑞) + 𝐵𝑎𝐶𝑙2 (𝑎𝑞) → 𝐵𝑎𝑆𝑂4 𝑠 + 2𝑁𝑎𝐶𝑙 𝑎𝑞
𝑆𝑂4 (𝑎𝑞)
2−
+ 𝐵𝑎(𝑎𝑞)
2+
→ 𝐵𝑎𝑆𝑂4 𝑠

HALIDES
CHEMICAL TESTS
 The presence of halide ions in solution can be shown by the addition of silver ions
(from silver nitrate solution). The precipitates that form are silver halides.
 For example, when silver nitrate solution is added to sodium chloride solution, the
relevant equations are:
𝑁𝑎𝐶𝑙(𝑎𝑞) + 𝐴𝑔𝑁𝑂3(𝑎𝑞) → 𝑁𝑎𝑁𝑂3 (𝑎𝑞) + 𝐴𝑔𝐶𝑙 𝑠
𝐶𝑙 (𝑎𝑞)
−
+ 𝐴𝑔(𝑎𝑞)
+
→ 𝐴𝑔𝐶𝑙 𝑠

PRECIPITATION REACTION
reaction in which an insoluble solid is formed when
two solutions are mixed

COMPARING MASSES
OF SUBSTANCES
1C.1

RELATIVE ATOMIC MASS (Ar)
 After the discovery of isotopes, the
12
𝐶 isotope of carbon was used in the definition of
relative atomic mass.
 A suitable definition of relative atomic mass is : the weighted mean (average) mass of
an atom compared to
1
12
of the mass of an atom of 12 𝐶 It is often useful to remember
this expression:
𝐴 𝑟 =
mean mass of an atom of an element
1
12
of the mass of an atom of 12 𝐶

RELATIVE MOLECULAR MASS (Mr)
 Relative atomic masses are used for atoms of elements.
 Relative molecular masses are used for molecules of both elements and Compounds.
 They are easily calculated by adding relative atomic masses.
Table A shows values for some common elements taken from the Data Booklet.

Problem Vs Solution
WORKED EXAMPLE 1
Solution
● What is the relative
molecular mass of
carbon dioxide, 𝐶𝑂2?
𝑀𝑟 = 12.0 + (2 × 16.0) = 44.0
WORKED EXAMPLE 2
Solution
● What is the relative
molecular mass of
sulfuric acid, 𝐻2 𝑆𝑂4?
𝑀𝑟 = (2 × 1.0) + 32.1 + (4 × 16.0) = 98.1

RELATIVE FORMULA MASS (Mr)
 This term has the same symbol as relative molecular mass, but the ‘formula’ part
means that it includes both molecules and ions.
WORKED EXAMPLE 3
Solution
What is the relative
formula mass of hydrated
copper(II) sulfate,
𝐶𝑢𝑆𝑂4. 5𝐻2 𝑂?
𝑀𝑟= 63.5 + 32.1 + (4 × 16.0) + 5{(2 × 1.0) + 16.0}
= 249.6

MOLAR MASS (M)
 which is the mass per mole of any substance (molecular or ionic).
 Its symbol is M (not Mr) and it has
 the units 𝑔. 𝑚𝑜𝑙−1 (grams per mole)
𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑚𝑜𝑙 =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 (𝑔)
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 (𝑔.𝑚𝑜𝑙−1)
𝑜𝑟 𝑛 =
𝑚
𝑀

MOLAR MASS (M)
 Table B shows examples of working out the amounts in moles of some
substances using this expression
𝑛 =
𝑚
𝑀

THE AVOGADRO CONSTANT
 Avogadro constant (L) 6.02 × 1023 𝑚𝑜𝑙−1, the number of particles in one
mole of a substance
 For example , there are :
6.02 × 1023
helium atoms in 4.0 g of He
6.02 × 1023 carbon dioxide molecules in 44.0 g of CO2
6.02 × 1023 nitrate ions in 62.0 g of 𝑁𝑂3
−
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 = 𝑛 × L & 𝑛 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠
L

CALCULATIONS USING THE AVOGADRO CONSTANT
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 = 𝑛 × L & 𝑛 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠
L

CALCULATIONS
INVOLVING MOLES
1C.2

WHAT IS A MOLE?
 A mole is the amount of substance that contains the same number of
particles as the number of carbon atoms in exactly 12 g of the
12
𝐶 isotope.
Fig.A From left to right: tin (Sn), magnesium (Mg), iodine (I) and copper (Cu).
Each sample contains 6.02 × 1023
atoms.

CALCULATIONS USING MOLES
THE EQUATION FOR CALCULATING MOLES
𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 𝑖𝑛 𝑚𝑜𝑙 =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 (𝑔)
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 (𝑔.𝑚𝑜𝑙−1)
𝑜𝑟 𝑛 =
𝑚
𝑀

CALCULATIONS USING MOLES

CHECKPOINT

CALCULATIONS USING
REACTING MASSES
1C.3

CALCULATING REACTING
MASSES FROM EQUATIONS

CALCULATING REACTING MASSES FROM EQUATIONS

WORKING OUT FORMULAE AND EQUATIONS FROM REACTING MASSES

THE YIELD OF
A REACTION
1C.4

TERMINOLOGY RELATING TO ‘YIELD’
Theoretical yield : the maximum possible mass of a product in a reaction,
assuming complete reaction and no losses
Actual yield : the actual mass obtained in a reaction
Percentage yield : the actual mass obtained in a reaction

‘Percentage YIELD’
𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑦𝑖𝑒𝑙𝑑 =
𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
× 100
The actual yield is always less than the
theoretical yield
Percentage yield : the actual yield divided by the
theoretical yield, expressed as a percentage

Unit 1-Topic 1 (A&B&C)

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