Group Properties & Trends (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards

When sodium reacts with water, it fizzes more vigorously than lithium, moves rapidly on the surface, and produces hydrogen gas and a sodium hydroxide (alkaline) solution.

The halogens are the Group VII non-metals (fluorine, chlorine, bromine, iodine and astatine). They are diatomic, poisonous and form halide ions by gaining one electron.

At room temperature: chlorine is a pale yellow-green gas, bromine is a red-brown liquid and iodine is a grey-black solid.

Reactivity decreases going down Group VII. As the number of electron shells increases, the outer shell is further from the nucleus and there is more electron shielding, reducing the force of attraction for an incoming electron.

True.

All halogens exist as diatomic molecules, meaning each molecule contains two atoms. For example, chlorine is Cl₂ and bromine is Br₂.

Two trends in properties going down Group VII:

1. Density increases

2. Reactivity decreases

The melting and boiling points also increase down the group.

False.

Solid iodine is grey-black, aqueous iodine is brown and iodine vapour is purple. These are three distinct colours.

Going down Group VII, the colour of the halogens becomes darker and the density increases.

Astatine is at the bottom of Group VII. Following the trend of increasing density and darker colour, astatine is predicted to be a black solid at room temperature.

A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide salt. The more reactive halogen gains electrons (is reduced) while the halide ions lose electrons (are oxidised).

Chlorine is more reactive than bromine, so it can oxidise bromide ions to bromine. Bromine is less reactive than chlorine, so it cannot oxidise chloride ions. A halogen can only displace a less reactive halide.

When chlorine is added to potassium bromide solution, the solution turns orange as bromine is formed.

True.

Bromine is more reactive than iodine, so it can displace iodide ions from solution. The solution turns brown as iodine is formed.

The solution turns brown as iodine is displaced and formed in the solution. The bromine solution changes from orange to brown as the more reactive bromine displaces iodide ions.

In a halogen displacement reaction, the more reactive halogen displaces the less reactive halide from solution.

False.

Chlorine solution is very pale green and often appears colourless in dilute aqueous solution. It is bromine that appears orange in solution.

2Br^- (aq) + Cl₂ (aq) → 2Cl^- (aq) + Br₂ (aq)

Chlorine molecules gain electrons to form chloride ions, while bromide ions lose electrons to form bromine molecules.

Transition elements are metals found in the central block of the Periodic Table, between Group 2 and Group 3. They have typical metallic properties and show characteristic behaviour such as forming coloured compounds and acting as catalysts.

Transition elements are found between Group 2 and Group 3 in the Periodic Table.

Transition elements: form ions with different charges (e.g. Fe²⁺ and Fe³⁺), act as catalysts and form coloured compounds. They are also typically hard, strong and have high melting points and densities.

False.

Mercury is a transition element that is a liquid at room temperature because it has an unusually low melting point. All other transition elements are solid at room temperature.

Iron (Fe) is used as a catalyst in the Haber process for making ammonia. Vanadium(V) oxide (V₂O₅) is used as a catalyst in the Contact process for making sulfuric acid.

Iron forms two ions: Fe²⁺ and Fe³⁺. This ability to form ions with different charges is a characteristic of transition elements.

Transition elements have partially filled inner electron shells that allow electrons to absorb and emit specific wavelengths of visible light, producing colour. Group I metals do not have this electronic arrangement, so their compounds are generally colourless (white).

True.

Copper forms coloured compounds as a transition element. Copper(II) sulfate solution is characteristically blue due to the Cu²⁺ ion.

Monatomic means that an element exists as individual, single atoms rather than as molecules. All noble gases are monatomic.

Noble gases have full outer electron shells, giving them extremely stable electronic configurations. They have no tendency to gain, lose or share electrons, so they do not form bonds with other elements.

The noble gases are in Group VIII of the Periodic Table and have full outer electron shells.

True.

All noble gases are colourless and exist as gases at room temperature. They also have very low melting and boiling points.

Argon has the electronic configuration 2, 8, 8. Its outer shell is completely full with 8 electrons, so it has no tendency to gain, lose or share electrons and does not react.

Helium has the electronic configuration 2 and neon has the electronic configuration 2, 8. Both have full outer shells.

False.

Noble gases are monatomic — each atom exists on its own, not bonded to another atom. This is because their full outer shells mean they have no need to form bonds.

Noble gases have 8 electrons in their outer shell (except helium, which has 2 filling its only shell). The group number indicates the number of outer electrons, so Group VIII reflects the full outer shell configuration of the noble gases.