Groups of the periodic table

Question 1

Classification of Alkali Metals, Halogens, and Noble Gases

Answer 1

Alkali Metals (Group 1):
Located in Group 1 of the periodic table.
Highly reactive metals.
Have one electron in their outer shell.
Examples: Lithium (Li), Sodium (Na), Potassium (K).

Halogens (Group 7):
Located in Group 7 of the periodic table.
Non-metals that exist as diatomic molecules (e.g., Cl₂, Br₂, I₂).
Have seven electrons in their outer shell.
Examples: Chlorine (Cl), Bromine (Br), Iodine (I).

Noble Gases (Group 0):
Located in Group 0 (or Group 18).
Colourless, odourless, and inert gases.
Have a full outer electron shell (stable configuration).
Examples: Helium (He), Neon (Ne), Argon (Ar).

Question 2

Main Physical Properties of Alkali Metals

Answer 2

Low Density: They are light metals; lithium, sodium, and potassium can float on water.
Soft: Can be cut with a knife.
Shiny: Have a metallic luster when freshly cut.
Low Melting and Boiling Points: These decrease down the group.

Question 3

Reactions of Lithium, Sodium, and Potassium with Water

Answer 3

Lithium: Fizzes gently, forms lithium hydroxide and hydrogen gas.
Sodium: Reacts more vigorously, forms sodium hydroxide and hydrogen gas, may melt into a ball.
Potassium: Reacts very vigorously, forms potassium hydroxide and hydrogen gas, may ignite with a lilac flame.

Word Equation (for all):
Metal + Water → Metal Hydroxide + Hydrogen
(e.g., Lithium + Water → Lithium Hydroxide + Hydrogen)

Balanced Equations:

Lithium: 2Li (s) + 2H₂O (l) → 2LiOH (aq) + H₂ (g)
Sodium: 2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)
Potassium: 2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)

Question 4

Pattern of Reactivity of Alkali Metals

Answer 4

Reactivity Increases Down the Group: Lithium reacts less vigorously, potassium reacts explosively.

Question 5

Explanation of Alkali Metals’ Reactivity (Electronic Configuration)

Answer 5

Alkali metals have 1 electron in their outer shell.

As you go down the group, the outer electron is further from the nucleus.

The attraction between the outer electron and the nucleus decreases.

This makes it easier to lose the outer electron, increasing reactivity down the group.

Question 6

Appearance of Chlorine, Bromine, and Iodine at Room Temperature

Answer 6

Chlorine (Cl₂): Greenish-yellow gas.
Bromine (Br₂): Reddish-brown liquid.
Iodine (I₂): Purple-black solid.

Question 7

Trends in Colour, Melting Point, and Boiling Point of Halogens

Answer 7

Colour: Becomes darker down the group (Chlorine → Green, Bromine → Red-brown, Iodine → Purple-black).

Melting/Boiling Point: Increases down the group (Chlorine has the lowest, iodine has the highest).

Prediction: A halogen below iodine would likely be a solid with an even higher melting/boiling point and darker colour.

Question 8

Chemical Test for Chlorine Gas

Answer 8

Chlorine turns damp blue litmus paper red, then bleaches it white.

Question 9

Trends in Reactions of Halogens with Metals

Answer 9

Reactivity Decreases Down the Group.

More reactive halogens will displace less reactive halogens from solutions of their salts (e.g., chlorine displaces bromine from sodium bromide).

Question 10

Word and Balanced Chemical Equations for Halogens with Metals

Answer 10

Sodium + Chlorine → Sodium Chloride
Na (s) + ½Cl₂ (g) → NaCl (s)

Magnesium + Bromine → Magnesium Bromide
Mg (s) + Br₂ (g) → MgBr₂ (s)

Question 11

Hydrogen Halides and Their Properties

Answer 11

Hydrogen Halides: Compounds formed between hydrogen and halogens (e.g., HCl, HBr, HI).
Properties:

Form acidic solutions in water (e.g., HCl forms hydrochloric acid).
HCl is a gas at room temperature but dissolves in water to form hydrochloric acid.

Question 12

Relative Reactivity of Halogens

Answer 12

Reactivity Decreases Down the Group: Chlorine is more reactive than bromine, which is more reactive than iodine.

Question 13

Displacement Reactions of Halogens

Answer 13

More reactive halogens displace less reactive halogens from their compounds in solution.

Example:
Chlorine + Potassium Bromide → Potassium Chloride + Bromine
Cl₂ (g) + 2KBr (aq) → 2KCl (aq) + Br₂ (l)

Question 14

Displacement Reactions as Redox Reactions

Answer 14

Oxidation: The less reactive halogen (e.g., bromine) loses electrons.

Reduction: The more reactive halogen (e.g., chlorine) gains electrons.

Example:
Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

Question 15

Ionic Equations for Displacement Reactions of Halogens

Answer 15

Chlorine displacing bromine:
Cl₂ (g) + 2Br⁻ (aq) → 2Cl⁻ (aq) + Br₂ (l)

Question 16

Explanation of Halogens’ Reactivity (Electronic Configuration)

Answer 16

Reactivity decreases down the group because it becomes harder to gain an electron.

As you go down the group, the outer electron shell is farther from the nucleus, so the attraction between the nucleus and the incoming electron weakens.

Question 17

Noble Gases’ Inertness (Electronic Configuration)

Answer 17

Full Outer Shell of Electrons (stable configuration).

This means they don’t need to gain, lose, or share electrons, making them chemically inert.

Question 18

Uses of Noble Gases Linked to Their Properties

Answer 18

Helium: Used in balloons because it is
lighter than air and non-flammable.

Neon: Used in neon signs because it glows when electricity passes through it.

Argon: Used in lightbulbs as an inert atmosphere to prevent filament oxidation.

Question 19

Trends in Physical Properties of Noble Gases

Answer 19

Boiling Points Increase Down the Group.

Density Increases Down the Group.

Question 20

Boiling Points Increase Down the Group.
Density Increases Down the Group.

Answer 20

A noble gas below xenon (like radon) would have a higher boiling point and be denser.