GCSE Atomic Structure & Periodic Table 2 — Questions and Answers
Question 1: An element has 17 protons and 18 neutrons. What is its mass number?
- 17
- 18
- 35 (Correct answer)
- 36
Correct answer: 35
Mass number = protons + neutrons = 17 + 18 = 35.
Question 2: Which of the following best describes isotopes of the same element?
- Same mass number, different atomic number
- Same atomic number, different number of neutrons (Correct answer)
- Same number of neutrons, different number of protons
- Same number of electrons, different number of electrons
Correct answer: Same atomic number, different number of neutrons
Isotopes have the same atomic number (protons) but differ in neutron count, giving different mass numbers.
Question 3: In the modern periodic table, elements are arranged in order of increasing:
- Atomic mass
- Number of neutrons
- Atomic number (Correct answer)
- Electronegativity
Correct answer: Atomic number
Mendeleev used atomic mass, but the modern periodic table orders elements by atomic number (number of protons).
Question 4: Which subatomic particle determines the chemical properties of an element?
- Neutrons
- Protons
- Electrons (Correct answer)
- Nucleons
Correct answer: Electrons
Electrons, especially the outermost shell electrons, determine how an element reacts chemically.
Question 5: Sodium has atomic number 11. How many electron shells does a sodium atom have?
- 1
- 2
- 3 (Correct answer)
- 4
Correct answer: 3
Sodium's electron configuration is 2,8,1 — filling three shells.
Question 6: What happens to the atomic radius as you move across a period from left to right?
- It increases
- It decreases (Correct answer)
- It stays the same
- It first increases then decreases
Correct answer: It decreases
Atomic radius decreases across a period because increasing nuclear charge pulls electrons closer without adding a new shell.
Question 7: Which group in the periodic table contains the alkali metals?
- Group 0
- Group 1 (Correct answer)
- Group 2
- Group 7
Correct answer: Group 1
Alkali metals (Li, Na, K, etc.) are in Group 1 and have one electron in their outermost shell.
GCSE Atomic Structure & Periodic Table 2
An element has 17 protons and 18 neutrons.
What is its mass number?