Topic 17 - Groups in the Periodic Table Flashcards
6.1 - Explain why elements are classified as alkali metals
The periodic table arranges elements so that in the same vertical column there are elements with similar physical and chemical properties.
Alkali metals are in group 1 and they have similar properties, they are malleable and conduct electricity.
6.2 - What are the main properties of alkali metals?
Alkali metals have low melting points and are soft, so easily cut.
They are also very reactive and readily form compounds with non-metals.
6.3 - How do different alkali metals react with water?
All alkali metals are easily oxidised and burn brightly in air.
When alkali metals react with water, a metal hydroxide and hydrogen gas are the products.
Lithium bubbles fiercely on the surface of water.
Sodium melts into a ball and fizzes on the surface of the water.
Potassium bursts into flames and flies on the surface of the water.
6.4/6.5 - What is the pattern in the reactivity of alkali metals?
Reactivity of alkali metals increase as you go down the group.
Alkali metals have one electron in their outer shells, when they react with non-metals their outer electron is transferred to the non-metal.
As you go down group 1, the atoms get larger as an extra electron shell is added in each period.
Therefore the attraction between the positive nucleus and the negative outer electron decreases as electron shells are added.
This explains the trend in reactivity of alkali metals, for example sodium is more reactive than lithium because it is easier to transfer the outer electron from sodium.
6.6 - What are the colours and physical states of halogens at room temperature?
Chlorine is a green gas at rtp.
Bromine is a brown liquid at rtp.
Iodine is a purple/black solid at rtp.
6.7 - Describe the trend in the physical properties of halogens
Elements in group 7 are halogens, they show similar properties and a trend.
All halogens exist as diatomic molecules ( two atoms held by a covalent bond ).
All halogens are non-metals, which are poor conductors of heat/electricity.
All halogens are toxic and corrosive, so must be handled with care.
As you go down group 7, the melting/boiling point and density increases.
6.8 - Describe the chemical test for chlorine
When damp litmus paper is placed in chlorine gas, it turns red then bleaches white.
If the paper turns red then bleaches in the unknown gas, then chlorine is present.
6.9 - How do halogens react with metals?
Halogen + Metal –> Metal Halide
Halogens react with metals to form ionic compounds called salts, containing halide ions.
For example : Cl2(g) + Mg(s) –> MgCl2(s)
6.10 - How do halogens react with hydrogen and water?
Halogens react with hydrogen to form hydrogen halides.
These hydrogen halides react with water to form acidic solutions due to the break up of the hydrogen halides into ions, forming H+ ions which are acidic.
For example hydrogen reacts with chlorine and explodes to form hydrogen chloride, which dissolves with water to form hydrochloric acid.
6.10 - What are the uses of halogens?
Halogens made into halide salts like sodium chloride which is table salt and sodium bromide which is a disinfectant in swimming pools.
All halogens can be used as disinfectants and bleaches as they kill microorganisms and remove colour from materials.
6.11 - How can displacement reactions be used to find the reactivity of halogens?
Halogens become less reactive as you go down the group.
In displacement reactions, the more reactive element takes place of the less reactive element ( displaces it ).
The more reactive halogen would displace the less reactive halogen from the halide compound its in.
For example : Chlorine displaces bromine from NaBr but bromine can’t displace chlorine from NaCl as it is less reactive.
Cl2(aq) + NaBr(aq) –> NaCl(aq) + Br(aq)
6.12 - What happens to halogen atoms and halide ions during displacement?
When an element loses electrons during ionic/covalent bonding it is called oxidation.
When an element gains electrons during ionic/covalent bonding it is called reduction.
Both processes occur during a displacement reaction hence the name redox reactions.
For example in a displacement reaction : F2(g) + 2Cl-(aq) –> 2F-(aq) + Cl2(g)
The fluorine atoms are more reactive and gain electrons, so are reduced.
The chlorine atoms are less reactive and lose electrons, so are oxidised.
6.13 - Explain the reactivity of halogens
Group 7 elements gain one electron when they react.
As you go down the group, the distance between the nucleus of the halogen and the outermost electrons increases.
This means the force of attraction between the positive nucleus and the negative electron needed to complete the outer shell decreases.
Therefore ions don’t form compounds so easily as reactivity decreases.
6.14 - Explain why noble gases are chemically inert
Noble gases are inert/unreactive meaning they don’t react with anything easily.
They exists as atoms as they don’t form bonds with other elements easily.
This is because all elements in Group 0 have a complete outer shell of electrons.
When atoms form bonds, it is done o become more stable, this is done by the transfer or sharing of electrons.
Noble gases are unreactive due to their atoms having a stable electronic configuration of an outer shell.
6.15 - How can noble gases be used?
Krypton is used in photography lighting as it produces a white light when electricity passes through it.
Argon is denser than air, so is added on to the space above wine in a wine barrel to stop oxygen reacting with the wine.
Helium has a low density and is non-flammable, so is used in weather balloons.
Neon produces a red-orange light when electricity is passed through it, so is used in long-lasting illuminated signs.
