Group 7 The Halogens and group 2 The Alkaline metals

What is the electron configuration of the elements in group 2 of the periodic table

Each of these elements have 2 electrons in an outermost s orbtial which is increasing more distant from the Nuecleus

Be Mg Ca Sr Ba

[He] 2s² [Ne] 3s² [Ar]4s² [Ar]5s² [Xe]6s²

What is the atomic radius trend for group 2

There is an increase in atomic radius down group 2 as the outermost electrons are in a principal quantum shell that is increasingly more distant from the nucleus

What is the trend in ionic radius down the group

Same reason as atomic radius. The ions are much smaller than their respective atoms due to the outer electrons being in an energy level closer to the nucleus so less shielding and greater attraction from the nucleus to the outer e^-

What is the trend in ionisation energy as you go down group 2?

As you go down group 2 the 1st ionisation energy decreases. As outer electron is lost from an energy level further from nucleus. So greater shielding and weaker attraction from nucleus to outer e^-

Trend in melting point of group 2

The melting points decrease down the group. Discontinually at Ca due to change from hexagonal to face centred cubic packing. The reason why it decreases is because the size of the ions increase down the group and the ions become increasingly less able to attract the deloclaised electrons, there is also greater shielding.

What is the general structureof a metal

They consist of cations in fixed positions in a lattice with the outside electrons delocalised and free to move. The metallid bond is the force of attraction between the positively charged ions for the delocalised electrons.

Observation and equation of mg reacting with water

Observation: very slow fizzing, mg sparingly dissolves, very fast reaction and white solid produced.

Equation: Mg +2H₂O_(l) → Mg(OH)₂ + H₂ or Mg + H₂O_(g) → MgO + H₂

Observation and Equation for Calcium reacting with water

Observation : fast production of bubbles, fully dissolves. (If number in front of letter (little) if behind (big) )

Equation: Ca + 2H2O → Ca(OH)2 +H2

Observation and Equation of reacting strontium with water

Observation: Very fast production of bubbles, fully dissolves

Equation: Sr + 2H2O → Sr(OH)2 +H2

Observation and Eqaution for reacting barium with water

Observation: fastest production of bubbles fully dissolves.

Equation: Ba + 2H2O → Ba(OH)2 +H2

Trend of reactivity of group 2 metals and explanation of trend

Ba> Sr> Ca> Mg

Most Least (Opposite to trend in first ionisation energy)

Why? → A metal atom gets larger, outer electrons are held further from the nucleus, greater shielding, weaker attraction from nucleus to outer electron, outer electron is more easily lost.

Why is beryllium unique with the chemical reactivity regarding water

It does not react with cold water or steam

What is the trend for group 2 metals of their reactivity with water

It dcreases down the group

Magnesium reaction with cold water and steam (w EQUATION)

It reacts slowly with cold water but quickly with steam

Equations: Cold water: Mg +2H2O (l) → Mg (OH)2 +H2

Steam: Mg + H2O (g) → MgO + H2

Reaction of Calcium, strontium and barium down the group.

They react with cold water with increasing vigor as they go down the group

Trend in solubility in hydroxides

Increases as you go down the group

Ba(OH)2 > Sr(OH)2 > Ca(OH)2 > Mg(OH)2

Mg(OH)2 → Slightly soluble Ca(OH)2 → Slightly soluble

Ba(OH)2 → Soluble Sr(OH)2 → Soluble

Equation for precipitates formed by group 2 hydroxides

Mg²⁺ + 2OH^- → Mg(OH)2

Ca²⁺ + 2OH^- → Ca(OH)2

Why does Iodine sublime?

Because as a solid and liquid the van der waals forces between molecules are very similar in both states.

Solubility trend for group 2 sulphates

Decreases down the group

BaSO4 < SrSO4 < CaSO4 < MgSO4

MgSO4 → Soluble CaSO4 → Soluble

SrSO4 → Slightly Soluble BaSO4 → Insoluble

Ionic equation for formation of any precipitate.

Sr²⁺ + SO4^3- → Sr SO4

Ba²⁺ + SO4^2- → BaSO4

Observation and Equation for the reaction between barium chloride and sulphuric acid

Ba ²⁺ +SO4^2- → BaSO4

Observation white precipitate.

Observation and equation of Barium chloride and sodium hydroxide

No reaction

Observation and equation for magnesium chloride and sodium hydroxide

Mg²⁺ +2OH^- → Mg(OH)2

Observation: white precipitate

Observation of calcium chloride and equation

Ca²⁺ +2OH^- → Ca(OH)2

Small amount of white ppt

Observation and equation of reaction between calcium chlordie and sulphuric acid

No reaction

Observation and Equation of magnesium chloride and sulphuric acid

No reaction

Use of these compounds ( Mg(OH)2) Ca(OH)2 BaSO4)

Mg(OH)2, indigestion tablets/ antacid. Ca(OH)2 neutralising acidic soil. BaSO4, Barium meal as BaSO4 is insoluble

Group2 metal carbonates properties

Insoluble and react with acids

Equations for Group 2 metal carbonates and acids

MgCO3 + 2HNO3 → Mg(NO3)2 + H2O + CO2

CaCO3 + H2SO4 → CaSO4 +H2O +CO2

BaCO3 + 2HCl → BaCl2 +H2O +CO2

What do group 2 metal carbonates always produce with acid

all produce water and bubbles of CO2, to test for CO2 bubble through limewater and if it turns cloudy it is present.

How to extract titanium

Rutile titanium (IV) oxide (TiO2) is first converted to titanium (IV) chloride using carbon and chlorine

TiO2 +2Cl2 +2C → TiCl4 +2CO Cl2 = oxidising agent C= reducing agent

The TiCl4 is purified by fractional distillation before being reduced to Ti by Mg at 1000 degrees celsius in an argon atmosphere. TiCl4 +2Mg → MgCl2 + Ti

(Mg is reducing agent)

Removal of sulfur dioxide from flue gases

Burning fossil fuels produce SO2(g) due to sulphuric impurities. This is an ACIDIC GAS and is removed from flue gases with an ALKALI or BASE by WET SCRUBBING. A slurry is made by mixing calcium oxide (CaO) or calcium carbonate (CaCO3) with water and sparying on flue gas. A solid waste product calcium sulfate (IV) is formed

CaO + SO2 → CaSO3 (s)

or CaCO3 +SO2 → CaSO3(s) + CO2

How to complete a flame test

Dip nichrome wire in HCL ti clean it, then dip into known compound. Hold the loop in the clear blue port of the flame. Hold the loop in the clear blue port of the flame (Nichrome wire = High melting point)

Results of flame tests for positive ions

Sodium (Na+) = yellow

Calcium (Ca2+) = orange/red

Lithium (Li+) = Crimson

Potassium (K+) = lilac

Magnesium (Mg2+) = white

Barium (Ba2+) = green

Strontium (Sr2+) = red

Test for ammonium ions

Add dilute NaOH to unknown solution and warm gently

NH4⁺ + OH^- → NH3 + H2O

Test the ammonia with damp red litmus paper will turn blue (alkaline)

Test for sulphate ions

Add nitric acid to remove any carbonate ions which would give a white ppt. Then add barium chloride (BaCl2) or Barium nitrate (Ba(NO3)2) solution. A white ppt of barium sulfate is formed ( Ba2+ + SO42- → BaSO4)

Test for hydroxide ions

These are alkaline so use red litmus, a positive result will turn red litmus paper to blue

Test for Halide ions

1) add nitric acid (aq) to the solution being tested → removes any other ions that could give a precipitate with silver nitrate (aq) (CO32- +2H+ → CO3 + H2O)

2)add silver nitrate (aq) to the solution being tested → this produces a precipitate for Cl-, Br-, I-

3) Add ammonia (aq) (dilute and conc) to the precipitate (This is used to see if the precipitate re dissolves to help confirm their identity).

What is produced when Silber nitrate/ dilute NH3/ Concentrated NH3 is added to Fluoride ion

AgNO3= No reaction, Dilute NH3 = ———— Cocentrated NH3 = —————

What is produced when Silber nitrate/ dilute NH3/ Concentrated NH3 is added to chloride ion

AgNO3 = white precipitate of AgCl (Ag+ + Cl- → AgCl) Dilute NH3 = dissolves Concentrated NH3 = dissolves

What is produced when Silber nitrate/ dilute NH3/ Concentrated NH3 is added to bromide ion

AgNO3 = Crean ppt of AgBr (Ag+ + Br- → AgBr) Dilute NH3 = insoluble Concentrated NH3 = dissolves

What is produced when Silber nitrate/ dilute NH3/ Concentrated NH3 is added to iodide ion

AgNO3 = Yellow ppt (Ag+ + I- → AgI) Dilute NH3 = insoluble Concentrated NH3 = insoluble

Test for carbonates

Add nitric acid and a fizz of CO2 gas is produced (CO32- + 2H+ → CO2 + H2O)

Bubble gas through limewater and it will turn cloudy/milky (Ca(OH)2 + CO2 → CaCO3(s) +H2O)

What are 2 unique things about group 7 the halogens

They are non metals and exist as discrete diatomic molecules F2, Cl2, Br2, I2,

They only need 1 electron to achieve their full outer shell.

Trend in properties of group 7 (image) (states in flashcard)

Fluorine (gas)

Chlorine (gas)

Bromine (liquid)

Iodine (Solid)

What is the trend in atomic radii down grouo 7 and the reason

The atomic radii increase down the group as the outermost electrons are in a principal quantum shell increasingly more distant from the nucleus. Increasing atomic radius as outer shell electrons in an energy level further from the nucelus so weaker shielding and weaker attraction from the nucleus to outer shell electrons

What is the trend of ionic radius in group 7 halogens down the group and the reason

There is an increase in ionic size down the group. The ionic radius though is slightly larger than the corresponding atomic radius, the ion is slightly larger than its corresponding atom because there are more electrons in the same outer energy level; so they are held further from the nucleus.

Trend in melting and boiling points for group 7 halogens and the reason

All halogens are simple covalent, n on polar molecules. As the molecules get larger (Mr increases) the van der waals forces between the molecules get stronger. More energy required to break.

What is the trend in electronegativity down group 7 and why

As you go down group 7 the electronegativity decreases, this is because as the atomic radius increases down the group there is greater shielding and weaker attraction from the nucleus to bonding electrons.

What is the trend in the oxidising properties of the halogens and why?

As you go down the group the oxidising power of the halogens decreases. This is because when a halogen acts as an oxidising agent, it is itself reduced and gains an electron. As the size of the halogen atoms increases down the group , the incoming electron is held at a greater distance from the nucleus which, therefore has less of a hold over the incoming electron (F2 most powerful oxidising agent, I2 least powerful oxidising agent)

Process of the reduction of halogens (halogen acts an oxidsing agent)

X= halogen ½ X2 (g) + e- → X- (g)

Why specifically is fluorine such a strong oxidising agent

The weakness of the F-F bond means that fluorine is a particularly strong oxidising agent

Displacement reactions amongst halides and halogens

What is the reducing power of halide ions down the group

The reducing power increases, as fluorine is the most powerful oxidising agent of the group 7 elemetns, it follows that the fluoride ion is the last powerful of the halides as a reducing agent; as iodine is the least powerful oxidising agent, it also follows that the iodide ion is the most powerful halide reducing agent. This is because larger ions means greater shielding and more likely to lose an electron

process of oxidation of halide (halide is reducing agent)

X-(g) → ½ X2 (g) + e-

How do you differentiate between the different halide ions

Reactions with concentrated sulphuric acid can be used to distinguish between the halide ions. In the first instance, the hydrogen halides are displaced from their salts by the less volatile sulphuric acid. HF and HCL do not react further as they are not sufficiently powerful reducing agents to reduce the concentrated sulphuric acid.

Acid base reactions of sodium fluoride and concentrated sulphuric acid and sodium chloride and concentrated sulphuric acid

NaF + H2SO4 → NaHSO4 +HF

NaCl + H2SO4 → NaSO4 + HCL

HF and HCL are shown as steamy white fumes

Both reactions stop here, there is no redox as F- and Cl- are not strong enough reducing agents

Acid base and redox reaction of Potassium bromide and sulphuric acid

KBr + H2SO4 → KHSO4 + HBr (HBr white fumes)

Followed by redox as Br- is a strong enough reducing agent to reduce the concentrated sulphuric acid

Redox: 2Br- → Br2 + 2e- (Oxidation)

H2SO4 + 2e- + 2H+ → SO2+ 2H2O (reduction)

Overall: H2SO4 +2HBr → SO2 +Br2 + 2H2O

SO2 = Colorless pungent gas, Br2 = orange/brown fumes

Acid base and redox reaction a) between Potassium iodide and concentrated sulphuric acid

Initially acid base reaction KI + H2SO4 → KHSO4 + HI

HI = steamy white fumes

Then one or more of the following redox reactions occur:

a) 2I- → I2 + 2e- (oxidation)

(S = +6 → +4) H2SO4 + 2e- +2H+ → SO2 +2H2O reduction

overall H2SO4 + 2H+ + 2I- → SO2 + I2 + 2H2O

SO2 = colourless pungent gas I2 = purple vapour

redox reaction b) between Potassium iodide and concentrated sulphuric acid

2I- → I2 + 2e- (oxidation)

(S = + 6 → O) H2SO4 +6e- + 6H+ → S + 4H2O (reduction)

Overall: H2SO4 + 6HI → S + 3I2 + 4H2O

redox reaction c) between Potassium iodide and concentrated sulphuric acid

2I- → I2 +2e- (oxidation)

( S = + 6 → 2) H2SO4 +8e- + 8H+ → H2S +4H2O (reduction)

Overall: H2SO4 + 8HI → H2S + 4I2 + 4H2O

H2S = (Smell of rotten eggs) I2 = (purple vapour)

Oxidising and reducing agents and products for Acid base and redox reactions of halide ions

HBr/ HI = reducing agents

H2SO4 = oxidising agent

Br2/I2 = oxidation products

SO2/ S / H2S = reduction products

Why is the reasction between NaOH anc Cl2 a very important industrial process

It is responsible for the production of domestic bleach

Reaction with cold water wtih chlorine

= (reversible reaction symbol)

→ add NaOH - reacts with HCL/H+ Cold water: Cl2 (green) + H2O = HCl + HClO

Ox state: o 1 -2

add HCL ←

Reaction of hot water/ sunlight with chlorine

Cl2 + H2O → 2HCl + ½ O2 (oxidation of water)

What is the element that has been disproportionated in this reaction? (Oxidation and reduction occurs to one element)

Cl2

Chlorine reaction with sodium hydroxide

Cl2 + 2NaOH = NaCl + NaClO + H2O

NaCl = Sodium chloride, ox state of Cl = -1

NaClO = Sodium chlorate (I) ox state of Cl = +1

These are both disproportionation reactions

Water treatment explained

Add Cl2 to make water safer to drink/swim in since ClO- ions/ chlorate kills bacteria. Chlorine kills disease causing microrganisms and prevents the growth of algae and reinfection further down the supply.

Why is a low concentration of chlorine used in water treament

Chlorine is toxic, chlorine irritates the respiratory system and can cause chemical burns.