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Understand and Describe Group 7

Worksheet Overview

QUESTION 1 of 10

Chlorine is used to make water safe to drink, but was also the original chemical weapon during World War One. Chlorine is one of the halogen elements, in Group 7 of the periodic table. What are they like, and why?

The main Group 7 elements are fluorine, chlorine, bromine and iodine. Together, this group of elements is called the halogens. They are all in the same column of the periodic table, one column in from the right hand side. This means that they are non-metals, and they all form small covalent molecules with two atoms. Fluorine is F2, chlorine is Cl2, bromine is Br2, iodine is I2.

All the halogens are very reactive. This is why they are good for killing microbes. Chlorine is used to purify water, and iodine is used to clean wounds, stopping them becoming infected. Fluorine is the most reactive halogen, then the reactivity decreases as you go down Group 7.

Elements go in the same Group of the periodic table because they have the same number of electrons in their outermost electron shell. For halogens, there are seven electrons in the outermost shell, so all halogens need one more electron to have a stable outermost shell. Chlorine (atomic number 17) is 2.8.7, so it looks like this;

Fluorine is 2.7; bromine is 2.8.18.7. All the halogens have seven electrons in their outermost shells, and one empty site. The single empty site explains why the halogens are so reactive; they are very close to having a stable outer shell, so will react strongly with other elements to capture another electron.

Halogen reactions

All the halogen elements react with other elements in similar ways. There are two reactions you need to know;

alkali metal + halogen → alkali halide

For example, sodium + chlorine → sodium chloride (chlorine becomes chloride)

In symbols, 2 Na (s) + Cl2 (g) → 2 NaCl (s)

We can replace sodium with any other alkali metal, and chlorine with any other halogen, and this reaction pattern works in the same way, so

2 Cs (s) + Br2 (l) → 2 CsBr (bromine is liquid at room temperature, which is why the state symbol is different.)

hydrogen + halogen → hydrogen halide

For example, hydrogen + chlorine → hydrogen chloride

In symbols, H2 (g) + Cl2 (g) → 2 HCl

Group 7 trends

As you go down Group 7 (from fluorine to astatine);

the elements become less reactive;

the melting point and boiling point increase (so they are less likely to be a gas at room temperature);

the colour becomes darker.

Testing reactivity with displacement reactions

We can show which halogens are more reactive by looking for displacement reactions between them. The rule is the same one as for metal displacement reactions;

The more reactive element can displace the less reactive element from a compound.

The experiment works like this;

  1. Start with an alkali halide compound dissolved in water- for example potassium bromide.
  2. Add another halogen, either dissolved in water, or as bubbles of gas.
  3. Check for any colour changes, which would tell us a reaction had happened.

So if we add chlorine to potassium bromide, we get this reaction, because chlorine is more reactive than bromine;

potassium bromide + chlorine → potassium chloride + bromine, and we see the mixture turn orange (becuase of the bromine)

If we add iodine to potassium bromide, nothing happens, because iodine is less reactive than bromine.

There's a lot you need to know about halogens. It might seem a bit daunting at first, but start with the electron structure. That explains why they form covalent molecules, and why they are all so reactive. Try the questions now, to secure your understanding of what's going on.

 

 

Which of these elements are halogens?

aluminium

bromine

carbon

chlorine

fluorine

selenium

Look at these outlines of the periodic table. Which one has the halogens highlighted?

A
B
C

 

A

B

C

Which of these electron structures are for halogens?

2.5

2.7

2.8.7

2.8.8

2.8.18.6

2.8.18.7

What is the chemical formula for a molecule of fluorine?

F

F2

Fl

Fl2

Use these part equations to construct the equation for the reaction between potassium and iodine.

F

F2

Fl

Fl2

Use these part equations to construct the equation for the reaction between sodium and fluorine.

F

F2

Fl

Fl2

Match these elements with their boiling points.

Column A

Column B

chlorine
59 °C
bromine
184 °C
iodine
-34 °C

Match these elements with their colours.

Column A

Column B

astatine
pale green
bromine
black
chlorine
brown

Potassium iodide solution is colourless, as is chlorine water (water with chlorine dissolved in it).

If we react them together, the solution turns brown. What can we conclude from this? Tick all the correct answers.

Iodine is produced

Potassium is produced

Potassium chloride is produced

Iodine chloride is produced

Chlorine is more reactive than iodine

Astatine is a very rare chemical element (its name is based on the greek word for "unstable"), so it is almost impossible to study its chemical reactions directly.

What would you expect to be produced if you reacted astatine (dissolved in water) with sodium bromide?

astatine

bromine

iodine

sodium astatide

sodium bromide

  • Question 1

Which of these elements are halogens?

CORRECT ANSWER
bromine
chlorine
fluorine
EDDIE SAYS
The halogens are the elements in Group 7 of the periodic table; fluorine, chlorine, bromine, iodine and astatine.
  • Question 2

Look at these outlines of the periodic table. Which one has the halogens highlighted?

A
B
C

 

CORRECT ANSWER
B
EDDIE SAYS
The halogens are in Group 7. That's one column in from the right of the Periodic Table.
  • Question 3

Which of these electron structures are for halogens?

CORRECT ANSWER
2.7
2.8.7
2.8.18.7
EDDIE SAYS
The thing that makes halogens similar is that they all have seven electrons in their outermost shell, so they all need one more electron to have a complete shell.
  • Question 4

What is the chemical formula for a molecule of fluorine?

CORRECT ANSWER
F2
EDDIE SAYS
All the halogens form molecules with two atoms- these are also called diatomic.
  • Question 5

Use these part equations to construct the equation for the reaction between potassium and iodine.

CORRECT ANSWER
EDDIE SAYS
You can do these by memorising the pattern, and just changing the elements. To work it out properly, remember that elemental halogens are always in molecules with 2 atoms; you need 2 atoms of the alkali metal to react with these, and they make two units of the compound.
  • Question 6

Use these part equations to construct the equation for the reaction between sodium and fluorine.

CORRECT ANSWER
EDDIE SAYS
This is the same idea as the last question, and uses the same pattern. The extra thing to be careful about here is the state symbols. At room temperature, fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
  • Question 7

Match these elements with their boiling points.

CORRECT ANSWER

Column A

Column B

chlorine
-34 °C
bromine
59 °C
iodine
184 °C
EDDIE SAYS
This question is about trends in Group 7. As you go down the group, the boiling temperature increases, which tells us that the intermolecular bonds are becoming stronger.
  • Question 8

Match these elements with their colours.

CORRECT ANSWER

Column A

Column B

astatine
black
bromine
brown
chlorine
pale green
EDDIE SAYS
The trend here is that halogens get darker as you go down Group 7. (Iodine is a very dark purple-black). The question is a bit sneaky, because the elements are listed in alphabetical order, so you need to sort them into periodic table order first.
  • Question 9

Potassium iodide solution is colourless, as is chlorine water (water with chlorine dissolved in it).

If we react them together, the solution turns brown. What can we conclude from this? Tick all the correct answers.

CORRECT ANSWER
Iodine is produced
Potassium chloride is produced
Chlorine is more reactive than iodine
EDDIE SAYS
The colour change tells us that a chemical reaction has happened. The chlorine displaces the iodine from the compound, so we produce potassium chloride + iodine; the iodine turns the water brown. Since chlorine ends up in the compound, it is the more reactive halogen.
  • Question 10

Astatine is a very rare chemical element (its name is based on the greek word for "unstable"), so it is almost impossible to study its chemical reactions directly.

What would you expect to be produced if you reacted astatine (dissolved in water) with sodium bromide?

CORRECT ANSWER
astatine
sodium bromide
EDDIE SAYS
Astatine is the least reactive of the halogens, so it wouldn\'t be able to displace bromine from sodium bromide. No reaction would take place. Because astatine is radioactive, it decays to other elements. As a result, there is probably about 1 g of astatine in the Earth\'s crust.
---- OR ----

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