Chapter 9: Periodicity

Question 1

Why are noble gases highly inert? (unreactive)

Answer 1

This is due to a complete octet of electronic on their valence shells, providing high stability and hence reluctance to bond or react with other chemicals.

Question 2

State some uses of noble gases with reference to them being highly insert

Answer 2

1. Argon and new are used in lightbulbs
2. Helium is used in weather balloons
3. Argon is used to manufacture steel

Question 3

State the characteristics of Group 1 Metals (Alkali Metals)

Answer 3

Alkali Metals are a collection of relatively soft, low density metals with a high reactivity in water.

Question 4

Describe and explain the trend in melting points for Alkali metals

Answer 4

As alkali metals have only one delocalised electron per atom, electrostatic forces between the positive ions and the delocalised electrons are relatively weak, requiring less energy to overcome, leading to low melting points
Down the group, the increasing size of the positive ion results in electrostatic attractions becoming weaker, requiring less energy to overcome, and hence the melting point decreases

Question 5

Describe and explain the trend in reactivity of Alkali metals

Answer 5

As alkali metals have only one valence electron, less energy os needed to remove that electron to form a positive ion with a noble gas configuration. Hence alkali metals have a high tendency to form positive ions, resulting in high reactivity.
Down the group, the valence electron gets further from the nucleus, and is less attracted to the nucleus. Hence there is a greater tendency to lose electrons and the reactivity increases.

Question 6

How do the respective alkali metals react with cold water?
Li 
Na
K
Rb
Cs

Answer 6

Li
- Effervescence of a colourless, odourless gas
- Metal floats on water
Na
- Vigorous effervescence of a colourless, odourless gas
- Metal melts into a ball, darts about the surface of the water
- Orange sparks observed
K
- Vigorous effervescence of a colourless, odourless gas
- Metal melts into a ball, darts about the surface of the water
- Lilac flam observed

Rb and Cs
-Explosive reaction

Question 7

What are transition metals

Answer 7

Transition Metals are a collection of metals with high melting point, high density and the ability to form ions with variable charges and compounds with a coloured appearance.

Question 8

What are the colours and state of F, Cl, Br, I, At respectively

Answer 8

F - pale yellow gas
Cl -Greenish-yellow gas
Br - Reddish-brown liquid
I - Black solid
At - Black solid

Question 9

Explain the trend in melting points of Halogens

Answer 9

Halogens are diatomic, simple molecular structures with weal intermolecular traction requiring less energy to overcome and hence have low melting points.
Down the group, the increase in molecular size results in stronger intermolecular attractions, requiring more energy to overcome, and the melting point increases.

Question 10

Explain the trends in reactivity in Halogens

Answer 10

Halogens have seven valence electrons, and only need to take in one more electron to form a negative ion with noble gas configuration. Hence halogens have a high tendency to form negative ions, resulting in high reactivity.
Down the group, the valence shell gets further away from the nucleus, and it becomes more difficult to attract the additional electron and hence the reactivity decreases.