ALLCBTs

Chemistry Questions for Secondary School.

Published on Jul 21, 2025 • Education

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Good day everyone!
Today, we shall be exploring some of the top secondary school chemistry questions, focusing on one of the most essential topics in early chemistry: atomic structure and the periodic table.

Let’s dive right in with insightful explanations to help you prepare for your school exams or national assessments.

You can watch the full class in the video below:

Question 1: Which Element Has the Smallest Atomic Radius?

Options:

• A. Sodium
• B. Magnesium
• C. Aluminium
• D. Chlorine

Explanation:
Atomic radius refers to the size of an atom, which is influenced by its atomic number. As you move across a period from left to right, atomic radius decreases due to increased nuclear charge pulling electrons closer.

Among the given options, chlorine has the smallest atomic radius.

Correct Answer: D. Chlorine

Question 2: What Does the Principal Quantum Number Determine?

Options:

• A. The size of the orbital
• B. The shape of the orbital
• C. The orientation of the orbital
• D. The spin of the electron

Explanation:
The principal quantum number (denoted as n) represents the energy level or size of the orbital. A higher value of n means a larger and more energetic orbital.

Correct Answer: A. The size of the orbital

Question 3: Isotopes of an Element Have the Same...

Options:

• A. Number of neutrons
• B. Atomic mass
• C. Number of protons
• D. Mass number

Explanation:
Isotopes are atoms of the same element with the same number of protons (i.e., the same atomic number), but different numbers of neutrons.

Correct Answer: C. Number of protons

Question 4: What is the Electron Configuration of Copper(II) Ion (Cu²⁺)?

Note: The correct interpretation of the question is for copper two plus (Cu²⁺).

• Copper (Cu) has atomic number 29.
• Ground state electron configuration for neutral Cu: 1s2 2s2 2p6 3s2 3p6 3d10 4s1\text{1s}^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 3d^{10}\, 4s^11s22s22p63s23p63d104s1
• For Cu²⁺, remove two electrons, first from the 4s orbital, then from 3d: Cu2+=3d9\text{Cu}^{2+} = 3d^9Cu2+=3d9

Correct Answer:
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹

Question 5: Which Property Decreases Across a Period?

Options:

• A. Ionization energy
• B. Atomic radius
• C. Electronegativity
• D. Electron affinity

Explanation:
Across a period (left to right in the periodic table):

• Atomic radius decreases (due to increased nuclear charge).
• Ionization energy, electronegativity, and electron affinity generally increase.

Correct Answer: B. Atomic radius

Watch more educational videos and past questions: https://youtube.com/@allcbts

Key Takeaways:

• Understanding atomic structure builds the foundation for learning chemical bonding, reactivity, and periodic trends.
• Remember the trends: atomic radius decreases across a period and increases down a group.
• Electron configurations are critical for predicting ion formation.

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• atomic structure questions and answers
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• electron configuration of copper ion
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