Group 7 elements

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Lesson notes

What are the halogens?

Group 7 elements are called the **halogens**.
They are all **non-metals**.
They do **not** conduct electricity or heat well.
They have **low melting and boiling points**.

Trends in group 7

As you go **down** group 7, melting and boiling points **increase**.
This is because larger molecules have **larger intermolecular forces**.
As you go **down** group 7, **reactivity decreases**.
Halogens are **very reactive** and **toxic**.

Uses of halogens

Chlorine gas was used as a **weapon** in World War One.
In low concentrations, chlorine is used to limit **bacteria growth** in swimming pools.

Displacement reactions

A **displacement reaction** occurs when a more reactive element replaces a less reactive element in a compound.
Both metals and halogens can undergo displacement reactions.
If fluorine is in a compound, it ends with **'fluoride'**; chlorine → **'chloride'**; bromine → **'bromide'**; iodine → **'iodide'**; astatine → **'astatide'**.
These compounds are collectively called **halides**.
Example: sodium bromide + chlorine → sodium chloride + bromine (chlorine is more reactive than bromine).
No reaction occurs if the displacing element is less reactive: sodium bromide + iodine → no reaction.
Another example: potassium iodide + chlorine → potassium chloride + iodine (colour change from colourless to brown).

Bohr model of a chlorine atom, showing electron configuration 2,8,7 (7 valence electrons).

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Practice questions

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1.Which of the following is a halogen?
Easy
- AChlorine
- BSodium
- CCarbon
- DOxygen
2.Which halogen has the highest melting point?
Medium
- AFluorine
- BChlorine
- CBromine
- DIodine
3.Which property is true for all halogens?
Easy
- AThey are all gases at room temperature
- BThey are all reactive and toxic
- CThey are all good conductors of electricity
- DThey all have high melting points
4.What is a displacement reaction?
Medium
- AA reaction where a more reactive element replaces a less reactive element in a compound
- BA reaction where two elements swap places in a compound
- CA reaction where an element combines with oxygen
- DA reaction that releases heat
5.Why does a displacement reaction occur between potassium bromide and chlorine?
Medium
- AChlorine is more reactive than bromine
- BBromine is more reactive than chlorine
- CPotassium is more reactive than chlorine
- DThe reaction produces a gas
6.Balance the equation: ___ KBr + Cl2 → ___ KCl + Br2
Hard
- A2, 2
- B1, 2
- C2, 1
- D1, 1
7.Which of the following is a sign that a chemical reaction has taken place?
Easy
- AA change in colour
- BAn increase in temperature
- CFormation of a gas
- DAll of the above
8.Complete the word equation: potassium iodide + bromine → ?
Medium
- Apotassium bromide + iodine
- Bpotassium iodide + bromine (no reaction)
- Cpotassium bromine + iodine
- Dpotassium + iodine bromide

More questions

9.Complete the word equation: sodium chloride + fluorine → ?
Hard
- Asodium fluoride + chlorine
- Bsodium chloride + fluorine (no reaction)
- Csodium fluorine + chloride
- Dsodium + chlorine fluoride
10.What colour change occurs when chlorine displaces iodine from potassium iodide?
Medium
- AColourless to brown
- BBrown to colourless
- CColourless to green
- DGreen to brown
11.Which of the following is NOT a halogen?
Easy
- AChlorine
- BBromine
- CSodium
- DIodine
12.As you go down Group 7, the melting and boiling points of the halogens increase. What is the reason for this trend?
Medium
- AThe atoms become smaller
- BThe inter-molecular forces become larger
- CThe elements become more reactive
- DThe atoms gain more electrons in their outer shell
13.A student reacts chlorine solution with potassium iodide solution. Which colour change would indicate a reaction?
Medium
- AColourless to brown
- BBrown to colourless
- CColourless to green
- DGreen to colourless
14.Which displacement reaction will occur?
Hard
- ASodium bromide + iodine → sodium iodide + bromine
- BSodium iodide + bromine → sodium bromide + iodine
- CPotassium chloride + fluorine → no reaction
- DPotassium iodide + chlorine → no reaction
15.Which of the following correctly lists the halogens in order of decreasing reactivity?
Medium
- AFluorine > chlorine > bromine > iodine
- BIodine > bromine > chlorine > fluorine
- CFluorine > bromine > chlorine > iodine
- DChlorine > fluorine > bromine > iodine
16.Which of the following halogens has the highest melting point?
Medium
- AFluorine
- BChlorine
- CBromine
- DIodine
17.Which of the following is a property of all halogens?
Easy
- AThey are good conductors of electricity
- BThey are non-metals
- CThey have high melting points
- DThey are all gases at room temperature
18.Chlorine gas is toxic. Which of the following is a reason why chlorine is used in swimming pools?
Hard
- AIt kills bacteria in low concentrations
- BIt makes the water clear
- CIt reacts with dirt to remove it
- DIt neutralises acid in the water
19.A student adds chlorine water to a solution of potassium bromide. After the reaction, which substances are present?
Hard
- APotassium chloride and bromine
- BPotassium bromide and chlorine
- CPotassium chloride and chlorine
- DPotassium bromide and bromine
20.What is the name given to compounds of halogens with metals?
Medium
- AHalogens
- BHalides
- CHalates
- DHalites
21.Which of the following statements about Group 7 elements is correct?
Medium
- AReactivity increases down the group
- BMelting points decrease down the group
- CThey are all gases at room temperature
- DThey are all non-metals
22.A student tests the electrical conductivity of four substances: fluorine, chlorine, bromine, and iodine. Which result would be expected?
Hard
- AAll four conduct electricity
- BNone of them conduct electricity
- COnly fluorine and chlorine conduct
- DOnly iodine conducts
23.A student adds chlorine water to a solution of potassium bromide. Which observation confirms that a displacement reaction has occurred?
Medium
- AThe solution turns from colourless to brown.
- BThe solution turns from brown to colourless.
- CA white precipitate forms.
- DBubbles of gas are released.
24.A student tests the electrical conductivity of four halogen elements. Which result is expected?
Medium
- AAll halogens conduct electricity because they are metals.
- BNone of the halogens conduct electricity because they are non-metals.
- COnly fluorine conducts electricity because it is the most reactive.
- DOnly iodine conducts electricity because it is a solid.
25.Which statement about the toxicity of halogens is correct?
Easy
- AHalogens are non-toxic because they are used in swimming pools.
- BHalogens are toxic and can be used as chemical weapons.
- COnly chlorine is toxic; other halogens are safe.
- DHalogens become less toxic as you go down the group.
26.A student reacts fluorine gas with sodium chloride solution. Which products would be formed?
Hard
- ASodium fluoride and chlorine
- BSodium chloride and fluorine (no reaction)
- CSodium and chlorine fluoride
- DSodium fluoride and hydrogen
27.The melting points of halogens increase down the group. What is the reason for this trend?
Medium
- AAtoms become smaller and attract more strongly.
- BMolecules become larger and have larger intermolecular forces.
- CReactivity decreases, so melting points increase.
- DElectronegativity increases, strengthening bonds.
28.A student places a piece of filter paper soaked in potassium iodide solution into a gas jar of chlorine. What colour change would be observed on the filter paper?
Hard
- AWhite to brown
- BColourless to green
- CBrown to colourless
- DColourless to purple
29.Which of the following word equations represents a reaction that will occur?
Medium
- Apotassium bromide + iodine → potassium iodide + bromine
- Bsodium chloride + bromine → sodium bromide + chlorine
- Cpotassium iodide + chlorine → potassium chloride + iodine
- Dsodium fluoride + chlorine → sodium chloride + fluorine
30.A student carries out an experiment to compare the reactivity of chlorine, bromine, and iodine. They add chlorine water to sodium bromide solution and observe a brown colour. Then they add bromine water to sodium iodide solution and observe a brown colour. Which conclusion is correct?
Hard
- AChlorine is more reactive than bromine, and bromine is more reactive than iodine.
- BChlorine is more reactive than bromine, but bromine is less reactive than iodine.
- CChlorine is less reactive than bromine, and bromine is more reactive than iodine.
- DChlorine is less reactive than bromine, and bromine is less reactive than iodine.
31.Which of the following is a correct statement about the physical properties of halogens?
Medium
- AThey are all gases at room temperature.
- BThey have low melting and boiling points.
- CThey are good conductors of electricity.
- DThey are all coloured.
32.Which halogen is used in low concentrations to limit bacteria growth in swimming pools?
Easy
- AFluorine
- BChlorine
- CBromine
- DIodine
33.In an experiment, a student adds bromine water to a solution of potassium chloride. What will be observed?
Hard
- AThe solution turns brown as chlorine is displaced.
- BNo reaction occurs and the solution remains colourless.
- CA white precipitate of potassium bromide forms.
- DThe solution turns green as bromine is displaced.
34.What is the name given to Group 7 elements?
Easy
- AHalogens
- BNoble gases
- CAlkali metals
- DTransition metals
35.As you go down Group 7, the melting and boiling points of the halogens:
Easy
- Aincrease
- Bdecrease
- Cstay the same
- Dfirst increase then decrease
36.Which of the following statements about the reactivity of halogens is correct?
Medium
- AReactivity decreases as you go down the group
- BReactivity increases as you go down the group
- CAll halogens have the same reactivity
- DFluorine is the least reactive halogen
37.Halogens are toxic. Which of the following uses a halogen in low concentration to limit bacterial growth?
Easy
- AChlorine in swimming pools
- BIodine in table salt
- CFluorine in toothpaste
- DBromine in fireworks
38.In a displacement reaction between potassium iodide and chlorine, which colour change is observed?
Medium
- AColourless to brown
- BBrown to colourless
- CGreen to yellow
- DNo colour change
39.Which of the following statements about the displacement reaction between potassium bromide and chlorine is correct?
Hard
- AChlorine is more reactive than bromine, so it displaces bromine
- BBromine is more reactive than chlorine, so it displaces chlorine
- CNo reaction occurs because both are halogens
- DPotassium bromide and chlorine do not react
40.A student reacts chlorine water with a solution of sodium bromide and observes a colour change. The student then reacts bromine water with a solution of sodium chloride and observes no colour change. What is the order of reactivity of chlorine, bromine, and sodium?
Hard
- AChlorine > bromine > sodium
- BSodium > chlorine > bromine
- CBromine > chlorine > sodium
- DChlorine > sodium > bromine

Revision notes

## Group 7 Elements (Halogens) - **Group 7 elements** are called **halogens**. They are all non-metals, so they do not conduct electricity or heat well and have low melting and boiling points. - **Trends down the group:** - Melting and boiling points **increase** (larger molecules have larger intermolecular forces). - Reactivity **decreases**. - Halogens are **very reactive** and **toxic** (e.g., chlorine used as a weapon in WWI; low concentrations used in swimming pools to limit bacteria). ### Displacement Reactions - A **displacement reaction** occurs when a more reactive element replaces a less reactive element in a compound. - Halogen compounds are called **halides** (e.g., fluoride, chloride, bromide, iodide, astatide). - **Example (reaction occurs):** sodium bromide + chlorine → sodium chloride + bromine (chlorine is more reactive than bromine). - **Example (no reaction):** sodium bromide + iodine → no reaction (iodine is less reactive than bromine). - **Another example:** potassium iodide + chlorine → potassium chloride + iodine (colour change from colourless to brown indicates a reaction). ### Key Facts (True/False from source) - Chlorine is a halogen. (True) - Bromine is less reactive than iodine. (False; bromine is more reactive) - Fluorine has a higher melting point than astatine. (False; astatine has higher melting point) - Group 7 elements are good electrical conductors. (False) - Group 7 elements are toxic and highly reactive. (True) - Group 7 elements have high melting and boiling points. (False; they have low melting and boiling points) ### Balancing Equations - Example: 2 KBr + Cl₂ → 2 KCl + Br₂ ### Word Equations (from source) - potassium iodide + bromine → potassium bromide + iodine - sodium chloride + fluorine → sodium fluoride + chlorine

Halogens: Elements in group 7 of the periodic table; non-metals that are reactive and toxic.
Displacement reaction: A reaction where a more reactive element replaces a less reactive element in a compound.
Halides: Compounds formed when a halogen combines with another element (e.g., fluoride, chloride, bromide, iodide, astatide).

Flashcards

What are the elements in group 7 of the periodic table called?

They are called the halogens.

Are halogens metals or non-metals?

Halogens are non-metals.

Do halogens conduct electricity or heat well?

No, they do not conduct electricity or heat well.

What happens to the melting and boiling points of halogens as you go down group 7?

They increase.

Why do melting and boiling points increase down group 7?

Because larger molecules have larger inter-molecular forces.

How does the reactivity of halogens change as you go down group 7?

Reactivity decreases.

Why are halogens toxic?

Because they are very reactive.

Name a historical use of chlorine gas.

It was used as a weapon in World War One.

What is a displacement reaction?

A reaction where a more reactive element replaces a less reactive element in a compound.

What is the name for compounds containing halogen atoms?

Halides.

What is the ending for a compound containing fluorine?

Fluoride.

What is the ending for a compound containing chlorine?

Chloride.

What is the ending for a compound containing bromine?

Bromide.

What is the ending for a compound containing iodine?

Iodide.

What is the ending for a compound containing astatine?

Astatide.

Complete the word equation: sodium bromide + chlorine → ?

sodium chloride + bromine

Does a reaction occur when sodium bromide reacts with iodine? Why?

No, because iodine is less reactive than bromine.

Complete the word equation: potassium iodide + chlorine → ?

potassium chloride + iodine

What colour change occurs when chlorine displaces iodine from potassium iodide?

Colourless to brown.

Balance: … KBr + Cl2 → … KCl + Br2

2 KBr + Cl2 → 2 KCl + Br2

Complete the word equation: potassium iodide + bromine → ?

potassium bromide + iodine

Complete the word equation: sodium chloride + fluorine → ?

sodium fluoride + chlorine

Which halogen is the most reactive?

Fluorine (at the top of group 7).

Which halogen has the highest melting point?

Astatine (at the bottom of group 7).

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