Consider the electron configuration of the following elements: Q = 1s2 2s2 2p1, R = 1s2 2s2 2p6 3s2, S = 1s2 2s2 2p6 3s2 3p1, T = 1s2 2s2 2p6, U = 1s2 2s2 2p6 3s2 3p5. Which element(s) (i) belong(s) to the same group? (ii) belong(s) to the same period?

Here are the answers to the questions:

a)

(i) Differentiate between a fine chemical and a heavy chemical.

• Fine chemicals are produced in small quantities, have high purity, and are used for specific, high-value applications (e.g., pharmaceuticals, specialized reagents).
• Heavy chemicals are produced in large quantities, have lower purity, and serve as basic raw materials for various industries (e.g., sulfuric acid, ammonia).

(ii)
I. Name two chemicals used in the treatment of water for town supply.

1. Chlorine
2. Alum (Aluminum sulfate)

II. State the function of each of the chemicals named in (a)(ii)I.

1. Chlorine: Used as a disinfectant to kill bacteria and other microorganisms in the water.
2. Alum: Used as a coagulant to cause small suspended particles to clump together, making them easier to remove by sedimentation and filtration.

(iii) Mention one source of air pollution.
Vehicle exhaust (from burning fossil fuels in cars, trucks, etc.)

(iv) Suggest one way of reducing air pollution in our cities.
Promoting the use of public transportation or renewable energy sources.

c) Consider the electron configuration of the following elements:
Q = $1s^2 2s^2 2p^1$
R = $1s^2 2s^2 2p^6 3s^2$
S = $1s^2 2s^2 2p^6 3s^2 3p^1$
T = $1s^2 2s^2 2p^6$
U = $1s^2 2s^2 2p^6 3s^2 3p^5$

To determine group and period:

• Period is the highest principal quantum number (n).
• Group is determined by the number of valence electrons (electrons in the outermost shell).

Let's analyze each element:

• Q: Highest n = 2 (Period 2). Valence electrons = $2s^2 2p^1 = 3$. (Group 13)
• R: Highest n = 3 (Period 3). Valence electrons = $3s^2 = 2$. (Group 2)
• S: Highest n = 3 (Period 3). Valence electrons = $3s^2 3p^1 = 3$. (Group 13)
• T: Highest n = 2 (Period 2). Valence electrons = $2s^2 2p^6 = 8$. (Group 18)
• U: Highest n = 3 (Period 3). Valence electrons = $3s^2 3p^5 = 7$. (Group 17)

Which element(s)

(i) belong(s) to the same group?
Elements with the same number of valence electrons belong to the same group.
Q and S (both have 3 valence electrons).

(ii) belong(s) to the same period?
Elements with the same highest principal quantum number (n) belong to the same period.
Q and T (both are in Period 2).
R, S, and U (all are in Period 3).