C4.1 - Predicting Chemical reactions

Where are Group 1 metals found on the periodic table?

Far left, in the first column.

They are called the alkali metals: lithium, sodium, potassium, rubidium, caesium and francium

What are the physical properties of Group 1 metals?

Soft metals that can be cut with a knife.

Low density — Li, Na and K are less dense than water so they float.

Shiny when freshly cut but tarnish quickly in air

Low MP/BP

What is the trend in melting point down Group 1?

Melting point decreases as you go down the group — Group 1 metals have unusually low melting points for metals

What is the trend in reactivity down Group 1 and why?

Reactivity increases down the group.

The outer electron is further from the nucleus and more shielded, so it is lost more easily

— making the metal more reactive

What happens when lithium reacts with water?

Li + H₂O → LiOH + H₂.

Fizzes steadily across the surface.

Produces lithium hydroxide and hydrogen gas

What happens when sodium reacts with water?

Na + H₂O → NaOH + H₂.

Fizzes vigorously, melts into a ball and moves quickly across the surface.

Produces sodium hydroxide and hydrogen gas

What happens when potassium reacts with water?

K + H₂O → KOH + H₂.

Very vigorous — the hydrogen gas produced ignites producing a lilac/purple flame. More violent than sodium

What happens when rubidium and caesium react with water?

React even more vigorously than potassium —

the reaction can be explosive.

Far too dangerous to demonstrate safely

What are the products when any Group 1 metal reacts with water?

A metal hydroxide (which is alkaline)

and hydrogen gas

What are the products when Group 1 metals react with oxygen?

Metal oxides —

e.g. 4Li + O₂ → 2Li₂O, 4Na + O₂ → 2Na₂O, 4K + O₂ → 2K₂O

What are the products when Group 1 metals react with chlorine?

Metal chlorides (ionic salts) — e.g. 2Na + Cl₂ → 2NaCl.

Reactivity of the reaction increases down the group,

same as with water

What are the elements of Group 7 called and what do they all have in common?

The halogens.

They all have 7 electrons in their outer shell and form diatomic molecules (e.g. Cl₂, Br₂, I₂)

What are the colours and states of the halogens at room temperature?

Fluorine = yellow gas.

Chlorine = pale yellow-green gas.

Bromine = red-brown liquid.

Iodine = purple-black solid

What are the colours of the halogens when dissolved in water?

Chlorine = very pale green.

Bromine = orange.

Iodine = brown

What is the trend in melting and boiling points down Group 7 and why?

Increases down the group.

The molecules get larger so intermolecular forces are stronger — more energy is needed to overcome them

What is the trend in reactivity down Group 7 and why?

Reactivity decreases down the group.

It becomes harder to gain an electron as the outer shell is further from the nucleus and more shielded

What is a halogen displacement reaction?

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

The more reactive halogen takes the electron instead

Which displacement reactions occur between chlorine, bromine and iodine?

Cl₂ displaces both Br and I.

Br₂ displaces I only.

I₂ displaces neither.

Summary: Cl > Br > I in reactivity

What is the equation for chlorine displacing bromine?

Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq).

Yellow-orange colour appears as bromine forms

What is the equation for chlorine displacing iodide?

Cl₂(aq) + 2KI(aq) → 2KCl(aq) + I₂(aq).

Brown colour appears as iodine forms

What is the equation for bromine displacing iodide?

Br₂(aq) + 2KI(aq) → 2KBr(aq) + I₂(aq).

Brown iodine forms

[HIGHER] What are the half equations for halogen displacement?

Cl₂ + 2e⁻ → 2Cl⁻ (reduction/gain of electrons). 2Br⁻ → Br₂ + 2e⁻ (oxidation/loss of electrons).

The halogen is reduced; the halide is oxidised

What ionic compounds do halogens form with metals?

Metal halides — e.g. sodium chloride NaCl, calcium bromide CaBr₂.

The halogen gains 1 electron to form a 1− ion.

The formula depends on the charge of the metal ion

What are the non-metal halides formed by halogens?

Halogens react with hydrogen to form hydrogen halides (e.g. HCl, HBr, HI).

They can also react with non-metals including other halogens

What are the Group 0 elements called and why are they unreactive?

The noble gases: He, Ne, Ar, Kr, Xe, Rn.

They have full outer electron shells so have no tendency to gain, lose or share electrons

What are the physical properties of noble gases?

Colourless, monatomic gases at room temperature.

They have very low melting and boiling points which increase down the group.

Density also increases down the group

What is the trend in boiling point down Group 0 and why?

Boiling point increases because atoms get larger,

so intermolecular forces between them get stronger

and more energy is needed to separate them

What are the uses of noble gases?

He — balloons and airships (non-flammable, less dense than air).

Ne — lighting (glows red/orange).

Ar — filling light bulbs and welding (inert atmosphere).

All used where unreactivity is needed

Where are transition metals found on the periodic table?

In the central block between Groups 2 and 3 (periods 4 and 5).

Examples: Fe, Cu, Ni, Cr, Mn, Co, Zn

What are the physical properties of transition metals?

High melting points (except Hg),

high density,

hard and strong —

much denser and stronger than Group 1 metals

What is special about the ions transition metals form?

They can form ions with different charges (variable oxidation states) — e.g. Fe²⁺ and Fe³⁺, Cu⁺ and Cu²⁺.

This is unlike Group 1 metals which only form one type of ion

Why do transition metals form coloured compounds?

Their compounds are coloured because of the way electrons in d-orbitals absorb light.

E.g. Cu²⁺ = blue, Fe²⁺ = pale green, Fe³⁺ = orange/brown, Mn²⁺ = pink, Cr³⁺ = green

Why are transition metals used as catalysts?

Their ability to change oxidation state allows them to donate and accept electrons — making them effective at speeding up reactions.

Fe is used in the Haber Process; V₂O₅ in the Contact Process; Ni in hydrogenation

What is the reactivity series order (most to least reactive)?

Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Zinc, Iron, Hydrogen, Copper, Silver, Gold. Mnemonic:

Please Send Little Camels Maybe Also Zipping In Hot Conditions, Sometimes Gets Dirty

Which metals react with cold water and what do they produce?

K, Na, Li, Ca react with cold water → metal hydroxide + hydrogen gas.

Mg reacts very slowly with cold water but readily with steam

Which metals react with dilute acid?

All metals above hydrogen in the reactivity series react with dilute acid to produce a salt and hydrogen gas.

Metals below hydrogen (Cu, Ag, Au) do not react with acid

What is a displacement reaction in terms of the reactivity series?

A more reactive metal can displace a less reactive metal from a solution of its compound.

The more reactive metal takes the place of the less reactive one e.g. Zn + CuSO₄ → ZnSO₄ + Cu

How do you predict whether a displacement reaction will occur?

Compare positions in the reactivity series.

If the metal being added is higher (more reactive) than the metal in the compound, displacement occurs.

If not, no reaction takes place

How do the transition metals compare to Group 1 metals in terms of reactivity?

Transition metals are far less reactive — they do not react vigorously with water or air,

have much higher melting points and densities,

and are much harder and stronger