Module 3: Periodic table and energy OCR A ALEVEL CHEMISTRY

Where are the halogens?

Group 7

Where are the alkali earth metals?

Group 2

What is the period table arranged by?

Arrangement of elements by increasing Atomic number

What are groups in the periodic table?

Elements arranged in vertical columns called groups, they have the same number of outer shell electrons. So have similar chemical properties

What are periods in the periodic table

Elements arranged in horizontal rows called periods. Elements in the same period have the same number of shells

How is the periodic table arranged in terms of periodicity

Across each period, there is a repeating trend in properties of the elements.

What is the periodic trend on electron configuration

Period 2:
2s sub-shell fill with 2 electrons
Followed by 2p sub-shell with 6 electrons

Period 3:
Same pattern of filling repeated for 3s & 3p

Period 4: goes 4s, 3d to 4p

How do you classify elements into blocks

The blocks are s, p and d blocks
The elements in the periodic table can be divided into blocks corresponding to their highest energy sub-shell

What is the first ionisation energy?

The energy required to remove an electron from 1 mole of gaseous atoms of an element to form 1 mole of gaseous 1+ ions.

Equation for ionisation energy

X(n-1) [g] —> X(n+) [g] + e-

What is the equation for the first ionisation energy of sodium?

Na(g) --> Na+(g) + e-

What 3 factors affect ionisation energy?

Atomic radius,
Nuclear charge,
Electron shielding.

How does atomic radius affect ionisation energy?

The greater the distance between the nucleus and the electrons, the less the nuclear attraction to the electron

How does nuclear charge affect ionisation energy?

The more protons in the nucleus the greater the attraction to the electrons.

How does electron shielding affect ionisation energy?

Electrons are negatively charged.

So inner shell electrons repel outer shell electrons.

This reduces the attraction between the nucleus and outer electrons.

What is the equation for the 2nd ionisation of iron?

Fe+(g) --> Fe2+(g) + e-

Why is second ionisation energy always more that the first?

Once 1 electrons goes, the remaining electrons are pulled closer to the nucleus. This reduces ionic radius and increases nuclear attraction to the remaining electrons.

What does a large increase in ionisation energy mean?

The electron removed where the big jump was, is from a different shell. A shell that is closer to the nucleus with less shielding

What predictions can be made from successive ionisation energies?

Number of electrons in outer shell.
Group of the element.
Identity of the element.

What happens to 1st ionisation energy down a group?

Decreases

What happens to 1st ionisation energy across a period?

Increases

Why does 1st ionisation decrease down a group?

Atomic radius increases.
More shells = more shielding effect
This outweighs increase in atomic charge.
Nuclear attraction decreases, so its easier to lose an electron from outer shell

Why does 1st ionisation energy increase across a period?

Nuclear charge (proton number) increase.
Same shell = similar shielding.
Decrease in atomic radius.
Nuclear attraction increases, so its harder to lose an electron from the outer shell

Why is there a drop in first ionisation energy between group 2 and 3?

The P sub shell is a higher energy level than an S sub shell. So it is easier to remove one of the P electrons that one of the S electrons.

Why is there a drop in ionisation energy between group 5 and 6?

Group 5 highest energy electron is in a P sub shell.
In group 6 the paired electrons in one of the P orbitals repel each other making it easier to remove an electron.

What is metalling bonding?

A strong electrostatic attraction between cations and delocalised electrons

What is a giant metallic lattice structure

In a metal structure, billions of metal ions are held together by metallic bonding to make a giant metallic lattice

How are electrons delocalised in metallic bonding?

Each atom had donated its electrons to a sea of shared electrons. Which is spread across the whole structure.

What maintains the structure of a metal?

The cations which are fixed in position

What are properties of metals

Strong metallic bonds - electrostatic attraction between positive ions and delocalised electrons

High electrical conductivity

High melting and boiling point

Insoluable

Why can metals conduct electricity?

The delocalised electrons can move and carry charge. This happens in all states

Why do metals typically have high boiling points?

Needs a lot of energy to overcome the strong electrostatic attraction between cations and delocalised electrons.

What does the melting point of a metal depend on?

Strength of metallic bonding

Why don't metals dissolve?

Any interaction between lattice and solution would lead to a reaction.

What are the 3 solid giant covalent lattice structures of carbon?

Diamond, graphite and graphene

What is a giant covalent lattice?

A 3D structure of billions of atoms held together by strong covalent bonds.

What two elements have the most common covalent lattice structures?

Carbon and silicon

What is the bond angle in diamond?

109.5

Physical properties of giant covalent lattices

High melting/boiling point
Insolubility
No electrical conductivity (graphite and graphene are exceptions)

Why do giant covalent lattices have such high melting/boiling points

Covalent bonds are strong and they need high temperatures to overcome them and break those strong covalent bonds

Why are giant covalent lattices insoluble?

Covalent bonds holding the covalent lattice together are too strong to be broken by interactions with solvents

Can giant covalent lattices conduct electricity

They are non conductors of electricity (like diamond and silicon)

Exceptions to this are graphite and graphene

What are the two giant covalent lattices which conduct electricity?

Graphite and graphene

Why don't diamond or silicon conducts electricity?

All 4 outer electrons are used in covalent bonding

What is the structure graphite?

A hexagonal carbon structure where 1 electron is donated to pool of delocalised electrons.
Layers of hexagonal carbon arrangements are weakly bonded by London forces.

What is graphene?

A single layer of graphite

Why is there such variation in melting points in periods 2 and 3?

Li, Be, Na, Mg, Al all form giant metallic structures.
B, C, Si all form giant covalent structures.
The rest form simple molecular.

What are the strengths of of the bonding in periods 2 and 3?

Covalent is strongest.
Then metallic.
Then simple molecular.

What electrons do group 2 metals loose?

The two outer shell 2s electrons, are lost in redox reactions forming 2+ ions.

Why is a group 2 metal always a reducing agent?

It is always oxidised and reduces another species

What is the trend in reactivity of group 2 elements

Reactivity Increases down the group

Group 2 elements follow the same pattern for redox reactions with OXYGEN, what is the general formula

2X(s) + O2(g) —> 2XO(s)

Group 2 elements follow the same pattern for redox reactions with WATER, what is the general formula

X(s) + 2H2O(l) —> X(OH)2[aq] + H2(g)

Group 2 elements follow the same pattern for redox reactions with DILUTE ACIDS, what is the general formula

X(s) + 2HCl(aq) —> XCl2(aq) + H2(g)

What is the most reactive group 2 metal?

Radium

What happens to 1st and 2nd ionisation energy as you go down the group 2?

Decreased ionisation energy.
Because decreased nuclear attraction due to shielding and atomic radius

What happens to the reaction of group two metals with water as you go down the group?

Becomes more vigorous due to an increase in reactivity

What does reacting water with a group 2 oxide do?

•reacting water with group 2 oxide releases hydroxide and group 2 ions
XO(s) + H2O(l) —> X 2+(aq) + 2OH-(aq)
•you can see the resulting product is alkaline solutions of the metal and hydroxide.

When the solution becomes saturated, the metal and hydroxide ions will form a solid alkaline precipitate
X 2+(aq) + 2OH-(aq) —> X(OH)2 (s)

What happens to solubility of group 2 hydroxides as you go down the group?

Solubility increases, causing pH to increase

What are the pH's of the group 2 hydroxides?

Mg: 10
Ca: 11
Sr: 12
Ba: 13
Ra: 14

How would you measure ph of a group 2 oxide solution?

1)Add a spatula of group 2 oxide to water.
2) shake
3)measure the pH

Why is the test tube pH test for a group 2 oxide inaccurate?

Not enough water to dissolve metal hydroxide, so some white solid will form at the bottom

What can you use calcium hydroxide for?

Used by farmers who add it to fields as lime to increase the pH of the acidic soils.
Calcium hydroxide neutralises it forming neutral water

Formula for Calcium hydroxide in acidic soils

Ca(OH)2[s] + 2H+[aq] —> Ca 2+[aq] + 2H2O(l)

What are the uses of group 2 compounds in medicine

Used as antacids for acid indigestion
Most common group 2 compounds for this are Magnesium carbonate and calcium carbonate.

Acid in stomach is mainly HCl and the metal carbonates are used to neutralise it.

Equation for magnesium hydroxide neutralising HCl

Mg(OH)2 [s] + 2HCl [aq] —> MgCl2 [aq] + 2H2O [l]

Equation for calcium carbonate neutralising HCl

CaCO3 [s] + 2HCl [aq] —> CaCl2 [aq] + H2O [l] + CO2 [g]

What type of molecules are the halogens?

Diatomic.
Cl2, Br2, I2

What type of intermolecular force is between halogen molecules?

London forces,
So they're simple molecular lattices

Why does boiling pint increase down the halogens?

More electrons.
Stronger London forces.
More energy needed to break London forces.
Boiling point increases

What is the electron configuration of halogens

Halogens have an electron config of -s2p5 (7 electrons)
They need one more electron to have the electron config of a noble gas.

What happens in redox reactions with halogens

In redox reactions, each halogen is reduced, gaining one electron to form a 1- halide ion with the electron config of the nearest noble gas

X2 + 2e- —> 2X- (halogen is reduced; gained an electron)

Why are halogens called oxidising agents

Because it has oxidised another species in a redox reaction. The other species lost electrons to the halogen.

What is the type of reaction that shows reactivity of halogens using reactions with other halide ions

Halogen-halide displacement reactions

What happens in a halogen displacement reaction

The displacement reaction can be carried out on a test-tube scale.

Solution of each halogen is added to aqueous solutions of the other halides

If the halogen added is more reactive than then aqueous halide than:
•reaction takes place, halogen displaces halide from solution
•solution changes colour.

The results of the displacement reaction shows that the reactivity of the halogens decreases down the group.

What is the colour of halogen solutions in water

Cl2 - pale green
Br2 - orange
I2 - brown

When you are trying to tell if the halogen displaced the halide what is a problem (regarding colour of halogen) that can occur

Solutions of iodine (brown) can appear similar to solutions of bromine (orange) you may assume that the colour of them haven't changed but they have.

To solve this: cyclohexane can be added, the colours of bromine and iodine are easier to tell apart

What are the colours of halogen in cyclohexane

Cl2 - pale green
Br2 - orange
I2 - violet

What are the results of the halogen-halide displacement reactions

(Most reactive)

•Chlorine halogen reacts with both Br- and I- halides
•Bromine halogen reacts with I- halide only
•Iodine halogen hasn't reacted at all

(least reactive)

Why does reactivity decrease down the halogens?

Atomic radius increases.
More shells so More shielding.
Less nuclear attraction to gain an electron.
Reactivity decreases.

What is disproportionation?

Redox reaction where the same element is both oxidised and reduced

What is the equation that illustrates disproportionation using the reaction of chlorine with water

Cl2(aq) + H2O(l) —> HClO(aq) + HCl(aq)

Cl2 oxidation no: 0
Cl in HClO oxidation no: +1 [oxidation]
Cl in HCl oxidation no: -1 [reduction]

What is the equation that illustrates disproportionation using the reaction of chlorine with cold, dilute aqueous sodium hydroxide

Cl2(aq) + 2NaOH(aq) —> NaClO(aq) + NaCl(aq) + H2O(l)

Cl2 oxidation no: 0
Cl in NaClO oxidation no: +1 [oxidation]
Cl in NaCl oxidation no: -1 [reduction]

Why is chlorine used in water treatment?

Both products are acids. Bacteria killed by HCl and ClO- ions.

What are the risks of treating water with chlorine?

Respiratory irritant.
React with hydrocarbons to form chlorinated hydrocarbons, these cause cancer.

What are the benefits of water chlorination?

Kills bacteria,
Prevents cholera

What is equation for halide ions with aqueous silver ions

Aqueous halide ions react with aqueous silver ions.

Ag+(aq) + X-(aq) —> AgX(s)

How do you test for sulphates?

Add Ba2+ (barium nitrate) ions to from a white precipitate

What would be a problem with testing for sulfate with barium chloride?

Cannot test for halides after as you are adding chloride ions to solution

What colour precipitate does silver chloride produce?

White

What colour precipitate does silver iodide produce?

Yellow

What colour precipitate does silver bromide produce?

Cream

How can you use ammonia to tell between the silver halides?

AgCl dissolves in dilute ammonia.

AgBr dissolves in concentrated ammonia.

AgI is insoluble in concentrated ammonia.

What order should you carry out the test tube tests?

Carbonated,
Sulfates,
Halides.

Why is the must the halide test be carried out last?

Because AgCO3 and AgSO4 both from precipitates.

Carbonates and sulfates must be ruled out before first.

Why must the Carbonate test be done first?

Neither sulfate and halide ions produce bubbles with weak acids.
So there won't be an incorrect conclusion.

Why must the sulfate test be done before the Carbonate test?

BaCO3 also produces a white precipitate. You must rule out the Carbonate first. Then move into sulfate when you it is clear there is no Carbonate.

How to you test for multiple ions?

1. Carbonates - add Nitric acid until the bubbling stops. This removes all Carbonate ions.

2. Sulfate - add excess barium nitrate, all sulfate ions will precipitate out. The filter the solution to remove barium sulfate.

3. Halide - normal test.

Why must a solution be warmed to release NH3 gas?

It is very soluble so will just dissolve at room temperature.

Why must you use nitric acid to test for carbonates?

Hydrochloric contains Cl- ions.
Sulfuric contains SO4 2- ions.