Group 7 Flashcards

All 18 cards in this deck

What name is given to group 7 of the periodic table?

The halogens. (Not 'halides': halides are the compounds or ions they form.)

What are the colour and physical state of chlorine at room temperature?

Yellow-green (green) gas.

What are the colour and physical state of bromine at room temperature?

Red-brown liquid — the only halogen that is a liquid at room temperature.

What are the colour and physical state of iodine at room temperature?

Dark grey solid.

What is the chemical test for chlorine gas, and the result?

Damp blue litmus paper first turns red, then is bleached white (goes colourless).

What is the balanced symbol equation for the reaction of sodium with chlorine?

$2Na + Cl_2 \rightarrow 2NaCl$ (sodium chloride).

Name a halogen that reacts with hot iron more vigorously than bromine does.

Fluorine (or chlorine) — both are above bromine in group 7, so they are more reactive.

What is formed when a hydrogen halide dissolves in water?

e.g. hydrogen chloride

An acidic solution — hydrogen chloride dissolves to form hydrochloric acid.

What is a halogen displacement reaction?

A more reactive halogen takes the place of a less reactive halogen in a solution of its halide, e.g. chlorine + sodium bromide → sodium chloride + bromine.

What are the steps to predict the outcome of adding a halogen to a halide solution?

e.g. chlorine water added to potassium iodide solution

1. Compare positions in group 7: chlorine is above iodine, so more reactive.
2. More reactive halogen displaces the less reactive one: chlorine displaces iodine.
3. Products: potassium chloride + iodine — the solution turns brown.

True or false? Bromine displaces chlorine from sodium chloride solution.

False. Bromine is less reactive than chlorine, so no reaction occurs.

Will astatine displace iodine from potassium iodide solution?

No — astatine is below iodine in group 7, so it is less reactive and no reaction occurs.

What happens to the melting points and boiling points of the halogens going down group 7?

e.g. chlorine → bromine → iodine

They increase — chlorine is a gas, bromine a liquid and iodine a solid at room temperature.

Which two group 7 elements are solids at room temperature?

Iodine and astatine.

True or false? The halogens become more reactive going down group 7.

False. Reactivity decreases down group 7 — atoms have more electron shells, so an electron is gained less easily.

How many electrons does a halogen atom have in its outer shell, and what ion does it form?

Seven. It gains one electron to complete its outer shell, forming a 1− ion called a halide ion, e.g. $\mathrm{Cl^-}$.

What type of molecules do the halogen elements form?

Diatomic molecules — each molecule is two atoms joined together, e.g. $\mathrm{Cl_2}$, $\mathrm{Br_2}$ and $\mathrm{I_2}$.

What is seen when chlorine water is added to colourless potassium bromide solution, and why?

The solution turns orange. Chlorine is more reactive than bromine, so it displaces bromine from the bromide, and the bromine colours the solution.