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Revision System · 4 Steps

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01

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02
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04
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Step 1 · Notes

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IGCSE· Edexcel· Chemistry Chapter 1

Structure of the Atom

Learning Objectives

Describe the structure of an atom — nucleus and electron shells
State relative charges and masses of protons, neutrons, electrons
Define atomic number and mass number

Every atom contains a small, dense nucleus surrounded by electrons arranged in shells.

The Nucleus

The nucleus contains protons and neutrons; the surrounding electrons occupy fixed energy shells.

Misconception

Electrons are not inside the nucleus — they occupy shells around it.

Examiner Insight

Always link atomic number to the number of protons.

Key Fact

Mass number = protons + neutrons. In a neutral atom, protons = electrons.

Step 2 · Flashcards

Test recall. Strengthen memory.

Active recall through clean, focused revision cards.

Question

What determines the atomic number of an element?

Tap to reveal answer

Answer

The number of protons in the nucleus.

Atomic number = proton count

Card 3 of 12

Step 3 · MCQs

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Question 3 of 10 Not quite

Which set of elements is common to all four classes of biological macromolecules?

A Hydrogen, oxygen, sulfur
B Carbon, oxygen, phosphorus
C Carbon, hydrogen, nitrogen
D Carbon, hydrogen, oxygen

Not quite

Why D is correct

Carbon, hydrogen, and oxygen are found in all four major biological macromolecule classes.

Why A is incorrect

Sulfur is found only in proteins, not in all four macromolecule classes.

Step 4 · Summary

Review. Consolidate. Excel.

Concise chapter summaries for confident final revision.

Structure of the Atom — Key Points

4 points

Protons (+1, mass 1) and neutrons (0, mass 1) form the nucleus
Electrons (−1, mass ≈ 0) occupy shells outside the nucleus
Atomic number = proton count — defines the element
Isotopes share atomic number but differ in mass number

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