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Periodicity Period 3 - elements AS Chemistry
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AS Chemistry. Periodicity Period 3 - elements. Starter activity. Can you write one fact about each of the following elements? Na Mg Al Si P S Cl Ar. Learning Objectives. Candidates should be able to: - PowerPoint PPT Presentation
Transcript of AS Chemistry
Periodicity
Period 3 - elements
AS Chemistry
Can you write one fact about each of the following elements?
Na Mg Al Si P S Cl Ar
Starter activity
Learning Objectives
Candidates should be able to:
•describe qualitatively (and indicate the periodicity in) the variations in atomic radius, ionic radius, melting point and electrical conductivity of the elements (see the Data Booklet)
•explain qualitatively the variation in atomic radius and ionic radius
•interpret the variation in melting point and in electrical conductivity in terms of the presence of simple molecular, giant molecular or metallic bonding in the elements
•explain the variation in first ionisation energy.
Na [Ne] 3s1
Mg [Ne] 3s2
Al [Ne] 3s2 3px1
Si [Ne] 3s2 3px1 3py
1
P [Ne] 3s2 3px1 3py
1 3pz1
S [Ne] 3s2 3px2 3py
1 3pz1
Cl [Ne] 3s2 3px2 3py
2 3pz1
Ar [Ne] 3s2 3px2 3py
2 3pz2
Electronic configurations
Atomic radius
0
0.05
0.1
0.15
0.2
0.25
Na Mg Al Si P S Cl Ar
Element
Ato
mic
rad
ius
(nm
)
www.chemguide.co.uk/atoms/properties/atradius.html
Atomic radius – what about argon?
What is atomic radius?
www.rjclarkson.demon.co.uk/found/period3_atomrad.gif
An atomic radius is a measure of the distance from the nucleus to the bonding pair of electrons.
From sodium to chlorine, the bonding electrons are all in the 3rd shell being screened by the electrons in the first and second levels, i.e. the screening remains fairly constant.
The increasing nuclear charge as you go across the period pulls the bonding electrons more tightly towards it.
Explaining the trend
You have to ignore the noble gas at the end of each period. Because neon and argon don't form bonds, you can only measure their van der Waals radius - a case where the atom is pretty well "unsquashed". All the other atoms are being measured where their atomic radius is being lessened by strong attractions. You aren't comparing like with like if you include the noble gases.
Leaving the noble gases out, atoms get smaller as you go across a period.
IONIC RADIUS
Ions aren't the same size as the atoms they come from. Compare the sizes of sodium and chloride ions with the sizes of sodium and chlorine atoms.
Positive ionsPositive ions are smaller than the atoms they come from. Sodium is 2,8,1; Na+ is 2,8. You've lost a whole layer of electrons, and the remaining 10 electrons are being pulled in by the full force of 11 protons.
Negative ionsNegative ions are bigger than the atoms they come from. Chlorine is 2,8,7; Cl- is 2,8,8. Although the electrons are still all in the 3-level, the extra repulsion produced by the incoming electron causes the atom to expand. There are still only 17 protons, but they are now having to hold 18 electrons.
0
0.5
1
1.5
2
2.5
3
3.5
Na Mg Al Si P S Cl Ar
Element
Paul
ing
elec
tron
egati
vity
val
ueElectronegativity
0
200
400
600
800
1000
1200
1400
1600
Na Mg Al Si P S Cl Ar
Element
Firs
t io
nisa
tion
ene
rgy
(kJ m
ol-1
)First ionisation energy
Electronegativity
Na Mg Al Si P S Cl ArStructure
Giant metallic
Giant metallic
Giant metallic
Giant covalent
Simple molecule
Simple molecule
Simple molecule
Monatomic
Type of element
Metal Metal Metal Non-metal
Non-metal
Non-metal
Non-metal
Non-metal
Bonding Metallic Metallic Metallic Covalent Covalent Covalent CovalentFormula P4 S8 Cl2 ArType of force broken on melting/boiling
Metallic bond
Metallic bond
Metallic bond
Covalent bond
vdW vdW vdW vdW
Does the element conduct electricity?
Yes Yes Yes No No No No No
Bonding, Structure and Properties
Structure and Properties
Electrical conductivity
0
500
1000
1500
2000
2500
3000
Melting and boiling points
Periodicity
Period 3 - oxides
AS Chemistry
Starter activity
Complete these sketches to show how these properties change as you go along Period 3 from Na to Ar.
Starter activity
Starter activity
Learning ObjectivesCandidates should be able to:
describe the reactions, if any, of the elements with oxygen to give Na2O, MgO, Al2O3, P4O10, SO2 and SO3.
state and explain the variation in oxidation number of the oxides.
describe the reactions of the oxides with water.
describe and explain the acid/base behaviour of oxides and hydroxides, including, where relevant, amphoteric behaviour in reaction with NaOH and acids.
Group number 1 2 3 4 5 6Element in Period 3
Na Mg Al Si P S
Nuclear charge
11+ 12+ 13+ 14+ 15+ 16+
[Ne] electronic configuration
3s1 3s2 3s2 3p1 3s2 3p2 3s2 3p3 3s2 3p4
Trend in Atomic radius decreasesTrend in 1st ionisation energy
increases
Trend in electronegativity
increases
Formula of oxide/s
Na2O MgO Al2O3 SiO2 P4O10 SO2/SO3
Oxidation state
+1 +2 +3 +4 +5 +4/+6
Reactions with oxygen
SodiumSodium burns in oxygen with an orange flame to produce the white solid sodium oxide.
MagnesiumMagnesium burns in oxygen with an intense white flame to give white solid magnesium oxide.
Reactions with oxygen
AluminiumAluminium will burn in oxygen if it is powdered, otherwise the strong oxide layer on the aluminium tends to inhibit the reaction. If you sprinkle aluminium powder into a Bunsen flame, you get white sparkles. White aluminium oxide is formed.
SiliconSilicon will burn in oxygen if heated strongly enough. Silicon dioxide is produced.
Reactions with oxygen
PhosphorusWhite phosphorus catches fire spontaneously in air, burning with a white flame and producing clouds of white smoke - a mixture of phosphorus(III) oxide and phosphorus(V) oxide. The proportions of these depend on the amount of oxygen available. In an excess of oxygen, the product will be almost entirely phosphorus(V) oxide:
Reactions with oxygen
Reactions with oxygen
SulphurSulphur burns in air or oxygen on gentle heating with a pale blue flame. It produces colourless sulphur dioxide gas.
In an excess of pure oxygen, some SO3 is also formed. This utilises the highest oxidation state of sulphur.
Reactions with oxygen
Which is which?
Melting points of oxides
Na2O MgO Al2O3 SiO2 P4O10 SO2
Tm/K 1548 3125 2345 1883 573 200
Bonding Ionic Ionic Ionic Covalent
Covalent
Covalent
Structure
Giant lattice
Giant lattice
Giant lattice
Giant lattice
Simple molecul
ar
Simple molecul
ar
Giant ionic and covalent solids contain only strong bonds and have high melting points. Simple molecules have weak vdW forces between molecules and have low melting points.
Reaction with water pH
Na2O + H2O 2Na+ + 2OH- 14
MgO + H2O Mg2+ + 2OH- 9
Al2O3 insoluble – no reaction 7
SiO2 insoluble – no reaction 7
P4O10 + 6H2O 4H3PO4 0
SO2 + H2O H2SO3 3
SO3 + H2O H2SO4 0
Acid/base properties of the oxides
Acid/base behaviour of aluminium oxide
BASE:
Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O
ACID:
Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4
Periodicity
Period 3 - chlorides
AS Chemistry
Learning Objectives
Candidates should be able to:
• describe the reactions, if any, of the elements with chlorine to give NaCl, MgCl2, Al2Cl6, SiCl4, and PCl5.
• describe and explain the reactions of the chlorides with water.
Element Na Mg Al Si PDescription of reaction with chlorine
Very vigorous Vigorous Vigorous Slow Slow
Formula of chloride/s NaCl MgCl2 Al2Cl6 SiCl4 PCl3 / PCl5
Oxidation state of period 3 element
+1 +2 +3 +4 +3 / +5
State of chloride at r.t.p.
Solid Solid Solid Liquid liquid / solid
b.pt. of chloride (oC) 1465 1418 423 57 74 / 164
Structure of chloride Giant lattice Simple molecular
Bonding in chloride Ionic Covalent
Reaction with chlorine
Structure of Al2Cl6
Reaction with water pH
NaCl(s) Na+(aq) + Cl-(aq) 7
MgCl2(s) Mg2+(aq) + 2Cl-(aq) 6/7
Al2Cl6(s) + 12H2O(l) 2[Al(H2O)6]3+ 6Cl-(aq) 3
SiCl4(l) + 2H2O(l) SiO2(s) + 4HCl(g) 0
PCl5(l) + 4H2O(l) H3PO4(aq) + 5HCl(g) 0
Acid/base properties of the chlorides
Periodicity
Group 7 - Halogens
AS Chemistry
Starter activity
Can you complete task 1 – IGCSE revision on the halogens
Learning Objectives
Candidates should be able to:
• describe the trends in volatility and colour of chlorine, bromine and iodine.
• interpret the volatility of the elements in terms of van der Waals’ forces.
• describe the relative reactivity of the elements as oxidising agents.
• describe and explain the reactions of the elements with hydrogen.
• describe and explain the relative thermal stabilities of the hydrides.
• interpret these relative stabilities in terms of bond energies.
The Halogens
Ionic
Covalent
The Halogens
Trend in colour and physical state
Like dissolves like!
Periodicity
Group 7 – the halides
AS Chemistry
Starter activity
Can you complete the table ‘Reducing power of the halides’?
Trend in reducing ability
NaX Observations Products
Type of reaction
NaF steamy fumes HF acid-base (F- acting as a base)NaCl steamy fumes HCl acid-base (Cl- acting as a base)NaBr steamy fumes HBr acid-base (Br- acting as a base)
colourless gas SO2 redox (reduction product of H2SO4)
brown fumes Br2 redox (oxidation product of Br-)
NaI steamy fumes HI acid-base (I- acting as a base)colourless gas SO2 redox (reduction product of
H2SO4)
yellow solid S redox (reduction product of H2SO4)
smell of bad eggs
H2S redox (reduction product of H2SO4)
Grey solid, purple fumes
I2 redox (oxidation product of I-)
Learning ObjectivesCandidates should be able to:
• describe and explain the reactions of halide ions with aqueous silver ions followed by aqueous ammoniaconcentrated sulphuric acid.
• describe and interpret in terms of changes of oxidation number the reaction of chlorine with cold, and with hot, aqueous sodium hydroxide.
• explain the use of chlorine in water purification.
• recognise the industrial importance and environmental significance of the halogens and their compounds, (e.g. for bleaches; PVC; halogenated hydrocarbons as solvents, refrigerants and in aerosols).
Fluoride
Chloride
Bromide
Iodide
Relative reducing power
Summary of reducing power
Testing for halide ionsion present
observation
F- No precipitate
Cl- White precipitate
Br- Cream precipitate
I- Yellow precipitate
Silver fluoride is soluble, and so you don't get a precipitate.
Confirmatory tests
original precipitate
observation
AgCl Soluble in dilute NH3(aq)
AgBr Soluble in concentrated NH3(aq)
AgIInsoluble in concentrated NH3(aq)
E.g. AgCl(s) + 2NH3(aq) → [Ag(NH3)2]+
(aq) + Cl-(aq)
Cl2(g) + 2NaOH(aq) → NaClO(aq) + NaCl(aq) + H2O(l)
0 +1 -1
3Cl2(g) + 6NaOH(aq) → NaClO3(aq) + 5NaCl(aq) + 3H2O(l)
Reactions of chlorine with NaOH
Uses of halogens and their compounds
bleachrefrigerants
solvents
Aerosol propellants
PVC
Periodicity
Nitrogen and Sulphur
AS Chemistry
Starter activity
Can you use information in your textbooks to complete task 9?
Learning Objectives
Candidates should be able to:• explain the lack of reactivity of nitrogen.• describe the
o formation, and structure of, the ammonium iono the displacement of ammonia from its salts.
• understand the environmental consequences of the uncontrolled use of nitrate fertilisers.
• understand and explain the occurrence, and catalytic removal, of oxides of nitrogen.
• explain why atmospheric oxides of nitrogen are pollutants, including their catalytic role in the oxidation of atmospheric sulphur dioxide.
• describe the formation of atmospheric sulphur dioxide from the combustion of sulphur contaminated carbonaceous fuels.
• state the role of sulphur dioxide in the formation of acid-rain and describe the main environmental consequences of acid-rain.
• understand the industrial importance of sulphuric acid.• describe the use of sulphur dioxide in food preservation.
Gases in the air
Structure of nitrogen
Bond dissociation enthalpy = +946 kJ/mol
High energy
Enzymes
Nitrogen
The Haber Process
The ammonium ion
Ammonium
NH4+
Add sodium hydroxide solution to a solution of the substance and gently heat.
Ammonia gas is given off.
n. Any of a large number of natural and synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its capacity to support plant growth.
Fertiliser
Fertilisers
Ammonium nitrate
Potassium chloride
Ammonium phosphate
Nitric acid
NH3(g) + 2O2(g) HNO3(l) + H2O(l)
Pt/Rh catalyst 900oC
The environment and fertilisersfertilisers applied to farm land
too much used, at the wrong time of year, during wet weather,
if
Excessive growth of aquatic plants. The bacteria which live on dead plants
thrive and use up the oxygen in the water. The lack of oxygen causes death of fish.
This is called eutrophication.
Harm to infants - called‘blue baby’ syndrome
washed intorivers and lakes
causes
excess excess
contaminatesunderground
drinking water supplies
causes
Sulphur dioxide - SO2
Used as a food preservative:
Inhibits growth of moulds, yeasts and aerobic bacteria.
Acts as a reducing agent and retards the oxidation of foodstuffs.
Acid rain
SO2(g) + NO2(g) SO3(g) + NO(g)
SO3(g) + H2O(l) H2SO4(l)
Uses of sulphuric acid
Paints , pigments and dyestuffs
Detergents
Fertilisers
Periodicity
Group 2
AS Chemistry
Learning Objectives
Candidates should be able to interpret, and make predictions from, the trends in physical and chemical properties of the elements and their compounds.
Trends in Atomic Radius
The radius of an atom is governed by:
the distance of the outer electrons from the nucleus
the nuclear charge, and
the amount of shielding
Trends in First Ionisation Energy
Ionisation energy is also governed by:
the charge on the nucleus,
the amount of shielding by the inner electrons,
the distance between the outer electrons and the nucleus.
Trends in First Ionisation Energy
Increased nuclear charge ‘off-set’ by increased shielding. Outermost electron increasingly distant from pull of nucleus, less energy needed to remove it.
Trends in Electronegativity
Trends in Electronegativity
Trends in Electronegativity
As the metal atoms get bigger, any bonding pair gets further and further away from the metal nucleus, and so is less strongly attracted towards it.
Increasing nuclear charge ‘off-set’ by more shielding.
In other words, as you go down the Group, the elements become less electronegative.
Trend in Electronegativity
Trend in Melting Point
Going down Group 2:
• the number of delocalised electrons remains the same ...
• the charge on each metal cation stays the same at 2+, but ...
• the ionic radius increases ...
• so the attraction between the delocalised electrons and the metal cations decreases.
Trend in Melting point
Periodicity
Group 2 – chemical properties
AS Chemistry
Learning Objectives
Candidates should be able to:
• describe the reactions of the elements with oxygen and water.
• describe the behaviour of the oxides with water.• describe the thermal decomposition of the nitrates
and carbonates.• interpret, and make predictions from, the trends in
chemical properties of the elements and their compounds.
• explain the use of magnesium oxide as a refractory lining material and calcium carbonate as a building material.
• describe the use of lime in agriculture.
