Worksheet on atomic structure and bonding - Chemistry - Free Printable

Let’s go through each question step by step.

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1. What name is given to the following in the periodic table:

(a) vertical columns → These are called groups.
(b) horizontal rows → These are called periods.

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2. How many valence electrons do the following have?

Valence electrons = electrons in the outermost shell.

(a) alkali metals (Group 1) → 1
(b) halogens (Group 17) → 7
(c) alkaline earth metals (Group 2) → 2
(d) noble gases (Group 18) → 8 (except helium, which has 2 — but usually we say 8 for this level)
(e) carbon (Group 14) → 4
(f) aluminium (Group 13) → 3

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3. Complete the following table

| Name of particle | Where found in atom | Relative mass | Charge |
|------------------|----------------------------|---------------|------------|
| proton | nucleus | 1 | +1 |
| neutron | nucleus | 1 | 0 |
| electron | outside nucleus (shells) | ~0 (or 1/1840)| -1 |

*(Note: For school level, relative mass of electron is often written as “negligible” or “~0”, and charge as -1.)*

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4. For each electronic configuration, state: symbol, group number, valence electrons

We add up the numbers to get total electrons = atomic number → find element → group = last number (for main groups), valence electrons = last number.

(a) 2,8,4 → total = 14 → Silicon (Si) → Group 14 → Valence = 4
(b) 2,8,8,1 → total = 19 → Potassium (K) → Group 1 → Valence = 1
(c) 2,7 → total = 9 → Fluorine (F) → Group 17 → Valence = 7
(d) 2,8,2 → total = 12 → Magnesium (Mg) → Group 2 → Valence = 2
(e) 2,8,6 → total = 16 → Sulfur (S) → Group 16 → Valence = 6
(f) 2,4 → total = 6 → Carbon (C) → Group 14 → Valence = 4
(g) 2,2 → total = 4 → Beryllium (Be) → Group 2 → Valence = 2
(h) 2,8,3 → total = 13 → Aluminium (Al) → Group 13 → Valence = 3
(i) 2,8,5 → total = 15 → Phosphorus (P) → Group 15 → Valence = 5

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5. (a) Explain the difference between mass number and atomic number.

- Atomic number = number of protons in the nucleus. It tells you what element it is.
- Mass number = number of protons + neutrons in the nucleus. It tells you the total weight of the atom (approximately).

Example: Carbon always has atomic number 6 (6 protons). But it can have different mass numbers like 12 or 14 depending on how many neutrons it has.

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(b) Explain what isotopes are.

Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons. So they have the same atomic number but different mass numbers.

Example: Carbon-12 and Carbon-14 are isotopes. Both have 6 protons, but C-12 has 6 neutrons and C-14 has 8 neutrons.

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(c) Copper consists of two isotopes, Cu-63 and Cu-65. The relative atomic mass of copper is 63.5. Explain which isotope is present in greater amount.

The average (relative atomic mass) is 63.5, which is closer to 63 than to 65. That means there must be more Cu-63 atoms pulling the average down toward 63.

So: Cu-63 is present in greater amount because the average mass (63.5) is closer to 63 than to 65.

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Final Answer:

1. (a) groups
(b) periods

2. (a) 1
(b) 7
(c) 2
(d) 8
(e) 4
(f) 3

3.
proton: nucleus, 1, +1
neutron: nucleus, 1, 0
electron: outside nucleus, ~0, -1

4.
(a) Si, 14, 4
(b) K, 1, 1
(c) F, 17, 7
(d) Mg, 2, 2
(e) S, 16, 6
(f) C, 14, 4
(g) Be, 2, 2
(h) Al, 13, 3
(i) P, 15, 5

5. (a) Atomic number = protons; mass number = protons + neutrons
(b) Isotopes = same element, different neutrons
(c) Cu-63, because 63.5 is closer to 63 than 65