Group 7: the Halogens

Lab Brief #6

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

Color changes mean atoms are rearranging — even if you can't see them.

What you'll learn

Halogens have seven outer electrons and gain one to form −1 ions. Down the group they get darker and less reactive, because the incoming electron is added further from the nucleus. A more reactive halogen displaces a less reactive one from its salt.

Key words

halogen
A Group 7 element with seven outer electrons, forming a −1 ion.
displacement reaction
A reaction in which a more reactive element takes the place of a less reactive one.

Make a hypothesis first

Before you mix: what color do you think it'll turn?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

spotting tile
chlorine water
bromine water
iodine solution
potassium bromide solution
potassium iodide solution
dropping pipettes

Get ready

⚠️ Safety first

Halogen solutions are toxic and irritant — work in a fume cupboard with goggles and gloves.
Bromine water burns skin; rinse any splash immediately and tell an adult.

Step 1 of 4 · Read

Think about what you just learned: say what "halogen" and "displacement reaction" mean in your own words before you start.

Step 2 of 4 · Do

Carry out halogen displacement in a spotting tile: add chlorine, bromine and iodine water to potassium bromide and potassium iodide solutions. Record every colour change in a grid and deduce the reactivity order.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

Chlorine displaces bromine from potassium bromide because chlorine is:

How sure are you?😐 maybe

Question 2 of 2

Halogens form ions with a charge of:

How sure are you?😐 maybe

Mind = blown

🌈 Every color you see is your brain inventing a translation of light frequencies.

Nice work!

You got 0 of 2 right.

Next: The Noble Gases All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: This is happening in your kitchen right now — every time food cooks.

🏆 Stretch challenge (try it this week): Find one ingredient in a snack and look up what it does.

👨‍👩‍👧 For the dinner table: “What's something we cook that mixes things together this way?”

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Group 7: the Halogens

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