C4: Predicting and identifying reactions and products
Chapter 4.1: Predicting chemical reactions
Group 1: alkali metals
Properties
● React with water to form alkaline solutions
● Metals
● Have some typical properties of metals:
○ Shiny when freshly cut
○ Good conductors of electricity
○ Solid at room temperature
● Atypical properties:
○ Soft enough to cut with a knife
○ Lithium is hardest and they get softer as you go down group
○ Density typically increases as you go down group (sodium is denser than expected)
○ Melting point decreases as you go down group
Reactions
● Lithium, sodium and potassium react rapidly with oxygen and water so stored in oil
● Reacts with water to produce metal hydroxide and hydrogen
● Reactivity of alkali metals with water increases as you go down group:
○ Lithium freezes steadily and slowly disappears
○ Sodium melts to form silvery ball, fizzes vigorously and quickly disappears
○ Potassium immediately ignites, burns with lilac flame and very quickly disappears
Explaining trend in reactivity
● Alkali metals have similar properties - all have 1 electron in outer shell
● The easier it is for alkali metal to lose outer electron, the more reactive it is
● Large atoms means it is easier to lose outer electron
Group 7: halogens
Properties
● Non-metals
● Typical properties of non-metals eg. brittle and poor conductors of electricity
● All elements exist as diatomic with weak intermolecular forces
● Fluorine: pale yellow gas
● Chlorine: green gas
● Bromine: orange-brown liquid that vaporises easily
● Iodine: shiny grey-black crystalline solid that sublimes to form purple vapour
● Density, melting and boiling points increase as you go down group
Reactions
● Reacts with metals to produce salts
● Reacts vigorously with group 1 elements, especially if metal is heated
● Reactivity of halogens decrease as you go down group
Explaining trend in reactivity
● Halogens have similar properties - all have 7 electrons in outer shell
● The easier it is for halogen to gain electron the more reactive it is
● Small atoms make it easier to attract electron to get full outer shell
Halogen displacement reactions
● Halogens can react with halides in solution
● Halides: compound of group 7 element and one other element, usually hydrogen or metal
● Example:
, ○ Cl2 (g) + 2NaBr (aq) → 2NaCl (aq) + Br2 (aq)
○ Reaction mixture turns orange-brown as bromine is produced
○ Chlorine displaces (push out) bromine from sodium bromide in displacement reaction
● Halogen will displace a less reactive halogen from its halide ions in solution - smaller atom so
can attract electron
● Safety:
○ Use aqueous solutions of chlorine, bromine and iodine than pure elements in school
○ Wear eye protection - can be irritating to eyes
○ Asthmatics should take extra care to not breathe in any chemical fumes
Group 0: noble gases
Properties
● Non-metals
● All gases at room temperature
● Very rarely react
● Monatomic - exist as single atoms
● Weak forces between atoms that can be easily overcome
● Attractive forces between atoms get stronger as you go down group
● Boiling point and density increases as you go down group
Lack of reactivity
● All have full outer shells
● No tendency to lose or gain electrons to form ions or share electrons to form molecules in
reactions
● As a result, noble gases are very unreactive
Transition metals
Properties
● Metals
● Typical metal properties:
○ Shiny when freshly cut
○ Good conductors of electricity
○ Strong
○ Malleable
● Compared to group 1:
○ Stronger and harder
○ Higher densities and higher melting points (except mercury)
● Means transition metals are good for making everyday objects
Chemical properties
● Less reactive than group and react slowly (if at all)
● Iron reacts slowly with water and oxygen to produce rust, hydrated iron (III) oxide
● Gold, platinum and iridium don’t react with water or oxygen at all
● Alkali metals produce white or colourless ionic compounds but transition metals produce
coloured ionic compounds:
○ Sodium: colourless
○ Iron (II): light green
○ Iron (III): yellow
○ Copper: blue
○ Nickel: dark green
○ Cobalt: red
● Alkalis can only form ions with single positive charge but many transition metals can form
multiple types of ions eg. iron (II) and iron (III)
● Transition metals often good catalysts
, ● Catalysts: substances that increase rate of chemical reactions without being used up
● Platinum, rhodium and palladium used in catalytic converters - converts harmful gases in
vehicle exhaust fumes into less harmful ones
Reactivity of elements
Metals reacting with water and dilute acids
● Metals form positive ions in reactions
● More easily this happens, the more reactive the metal
● Metal can react with water or dilute acids if more reactive than hydrogen
● Metal + water = metal hydroxide + oxygen
● Metal + acid = salt + hydrogen
Rate of reaction
● Metal reaction with water or dilute hydrochloric acid can be used to put metals in order of
reactivity
● More reactive the metal, the greater the rate of hydrogen production - more vigorous bubbling
(use eye protection)
● If there is no bubbling, heat water up - don’t heat acid (dangerous to boil it)
Metal displacement reactions
● More reactive metal can displace less reactive metal from solutions of its compounds
● Displacement reactions are examples of redox reactions - more reactive metal is oxidised,
less reactive metal is reduced
Predicting reactions using periodic table
● Elements in group 0 don’t react
● Reactive non-metals may form covalent bonds with each other
● Metals may form ionic compounds with reactive non-metals
● Metals in group 1 & 2 are more reactive than transition & other metals and more reactive
down the group
● Non-metals in group 7 become less reactive down group
Chapter 4.2: Identifying products of chemical reactions
Detecting gases
Detecting carbon dioxide
● Use limewater - calcium hydroxide solution
● Turns cloudy white when carbon dioxide bubbled through it
● Change caused by calcium hydroxide reacting with carbon dioxide to form water and white
precipitate of calcium carbonate
Detecting chlorine
● Chlorine dissolves in water to form acidic solution
● Bleaches dyes - changes them from coloured to colourless
● Perform simple laboratory test for chlorine based on these properties:
○ Hold a drop of tap water to dampen a piece of blue litmus paper
○ Hold paper near to a container that holds substance
○ If chlorine is present, the paper turns red then white
Smelling substances
● Can use sense of smell to detect substances eg. chlorine
● Must not breathe in a lungful of anything
● Follow these steps:
○ With container well away from nose, breathe in enough air to almost fill lungs
○ Hold container few cm away from nose and waft any smell towards you - take a
cautious sniff
Chapter 4.1: Predicting chemical reactions
Group 1: alkali metals
Properties
● React with water to form alkaline solutions
● Metals
● Have some typical properties of metals:
○ Shiny when freshly cut
○ Good conductors of electricity
○ Solid at room temperature
● Atypical properties:
○ Soft enough to cut with a knife
○ Lithium is hardest and they get softer as you go down group
○ Density typically increases as you go down group (sodium is denser than expected)
○ Melting point decreases as you go down group
Reactions
● Lithium, sodium and potassium react rapidly with oxygen and water so stored in oil
● Reacts with water to produce metal hydroxide and hydrogen
● Reactivity of alkali metals with water increases as you go down group:
○ Lithium freezes steadily and slowly disappears
○ Sodium melts to form silvery ball, fizzes vigorously and quickly disappears
○ Potassium immediately ignites, burns with lilac flame and very quickly disappears
Explaining trend in reactivity
● Alkali metals have similar properties - all have 1 electron in outer shell
● The easier it is for alkali metal to lose outer electron, the more reactive it is
● Large atoms means it is easier to lose outer electron
Group 7: halogens
Properties
● Non-metals
● Typical properties of non-metals eg. brittle and poor conductors of electricity
● All elements exist as diatomic with weak intermolecular forces
● Fluorine: pale yellow gas
● Chlorine: green gas
● Bromine: orange-brown liquid that vaporises easily
● Iodine: shiny grey-black crystalline solid that sublimes to form purple vapour
● Density, melting and boiling points increase as you go down group
Reactions
● Reacts with metals to produce salts
● Reacts vigorously with group 1 elements, especially if metal is heated
● Reactivity of halogens decrease as you go down group
Explaining trend in reactivity
● Halogens have similar properties - all have 7 electrons in outer shell
● The easier it is for halogen to gain electron the more reactive it is
● Small atoms make it easier to attract electron to get full outer shell
Halogen displacement reactions
● Halogens can react with halides in solution
● Halides: compound of group 7 element and one other element, usually hydrogen or metal
● Example:
, ○ Cl2 (g) + 2NaBr (aq) → 2NaCl (aq) + Br2 (aq)
○ Reaction mixture turns orange-brown as bromine is produced
○ Chlorine displaces (push out) bromine from sodium bromide in displacement reaction
● Halogen will displace a less reactive halogen from its halide ions in solution - smaller atom so
can attract electron
● Safety:
○ Use aqueous solutions of chlorine, bromine and iodine than pure elements in school
○ Wear eye protection - can be irritating to eyes
○ Asthmatics should take extra care to not breathe in any chemical fumes
Group 0: noble gases
Properties
● Non-metals
● All gases at room temperature
● Very rarely react
● Monatomic - exist as single atoms
● Weak forces between atoms that can be easily overcome
● Attractive forces between atoms get stronger as you go down group
● Boiling point and density increases as you go down group
Lack of reactivity
● All have full outer shells
● No tendency to lose or gain electrons to form ions or share electrons to form molecules in
reactions
● As a result, noble gases are very unreactive
Transition metals
Properties
● Metals
● Typical metal properties:
○ Shiny when freshly cut
○ Good conductors of electricity
○ Strong
○ Malleable
● Compared to group 1:
○ Stronger and harder
○ Higher densities and higher melting points (except mercury)
● Means transition metals are good for making everyday objects
Chemical properties
● Less reactive than group and react slowly (if at all)
● Iron reacts slowly with water and oxygen to produce rust, hydrated iron (III) oxide
● Gold, platinum and iridium don’t react with water or oxygen at all
● Alkali metals produce white or colourless ionic compounds but transition metals produce
coloured ionic compounds:
○ Sodium: colourless
○ Iron (II): light green
○ Iron (III): yellow
○ Copper: blue
○ Nickel: dark green
○ Cobalt: red
● Alkalis can only form ions with single positive charge but many transition metals can form
multiple types of ions eg. iron (II) and iron (III)
● Transition metals often good catalysts
, ● Catalysts: substances that increase rate of chemical reactions without being used up
● Platinum, rhodium and palladium used in catalytic converters - converts harmful gases in
vehicle exhaust fumes into less harmful ones
Reactivity of elements
Metals reacting with water and dilute acids
● Metals form positive ions in reactions
● More easily this happens, the more reactive the metal
● Metal can react with water or dilute acids if more reactive than hydrogen
● Metal + water = metal hydroxide + oxygen
● Metal + acid = salt + hydrogen
Rate of reaction
● Metal reaction with water or dilute hydrochloric acid can be used to put metals in order of
reactivity
● More reactive the metal, the greater the rate of hydrogen production - more vigorous bubbling
(use eye protection)
● If there is no bubbling, heat water up - don’t heat acid (dangerous to boil it)
Metal displacement reactions
● More reactive metal can displace less reactive metal from solutions of its compounds
● Displacement reactions are examples of redox reactions - more reactive metal is oxidised,
less reactive metal is reduced
Predicting reactions using periodic table
● Elements in group 0 don’t react
● Reactive non-metals may form covalent bonds with each other
● Metals may form ionic compounds with reactive non-metals
● Metals in group 1 & 2 are more reactive than transition & other metals and more reactive
down the group
● Non-metals in group 7 become less reactive down group
Chapter 4.2: Identifying products of chemical reactions
Detecting gases
Detecting carbon dioxide
● Use limewater - calcium hydroxide solution
● Turns cloudy white when carbon dioxide bubbled through it
● Change caused by calcium hydroxide reacting with carbon dioxide to form water and white
precipitate of calcium carbonate
Detecting chlorine
● Chlorine dissolves in water to form acidic solution
● Bleaches dyes - changes them from coloured to colourless
● Perform simple laboratory test for chlorine based on these properties:
○ Hold a drop of tap water to dampen a piece of blue litmus paper
○ Hold paper near to a container that holds substance
○ If chlorine is present, the paper turns red then white
Smelling substances
● Can use sense of smell to detect substances eg. chlorine
● Must not breathe in a lungful of anything
● Follow these steps:
○ With container well away from nose, breathe in enough air to almost fill lungs
○ Hold container few cm away from nose and waft any smell towards you - take a
cautious sniff
