IGCSE Atomic Structure and Periodic Table: Complete Guide | Tutopiya
IGCSE Atomic Structure and the Periodic Table: Complete Guide for Cambridge IGCSE Chemistry
IGCSE atomic structure and the periodic table are fundamental topics in Cambridge IGCSE Chemistry that form the foundation for understanding all chemical behavior. Mastering atomic models, electron configuration, and periodic trends is essential for achieving top grades in IGCSE Chemistry exams.
This comprehensive IGCSE atomic structure and periodic table guide covers everything you need to know, including the structure of atoms, subatomic particles, electron shells, the periodic table organization, periodic trends, step-by-step worked examples, common exam questions, and expert tips from Tutopiya’s IGCSE chemistry tutors. We’ll also show you how to avoid the most common mistakes that cost students valuable marks.
🎯 What you’ll learn: By the end of this guide, you’ll know how to describe atomic structure, explain electron configuration, understand periodic trends, predict element properties, and apply these concepts to solve problems in IGCSE Chemistry exams.
Already studying with Tutopiya? Practice these skills with our dedicated IGCSE Chemistry practice deck featuring exam-style questions and instant feedback.
Why IGCSE Atomic Structure and the Periodic Table Matter
IGCSE atomic structure and the periodic table are essential foundation topics in IGCSE Chemistry. Here’s why they’re so important:
- Foundation topic: Required for understanding bonding, reactions, and all chemistry concepts
- High frequency: Questions about atomic structure and periodic trends appear in almost every IGCSE chemistry paper
- Exam weight: Typically worth 10-15 marks per paper
- Real-world applications: Essential for understanding element properties and chemical behavior
- Link to all topics: Connects to bonding, reactions, and material properties
Key insight from examiners: Students often struggle with electron configuration or confuse atomic number with mass number. This guide will help you master these concepts systematically.
Structure of an Atom
An atom consists of a nucleus (containing protons and neutrons) surrounded by electrons in shells.
Subatomic Particles
| Particle | Location | Charge | Relative Mass | Symbol |
|---|---|---|---|---|
| Proton | Nucleus | +1 | 1 | p⁺ |
| Neutron | Nucleus | 0 | 1 | n⁰ |
| Electron | Shells | -1 | 1/1840 (negligible) | e⁻ |
Key Facts
- Nucleus: Contains protons and neutrons, very small but dense, positively charged
- Electrons: Orbit nucleus in shells, very light, negatively charged
- Atom is neutral: Number of protons = Number of electrons
Atomic Number and Mass Number
Atomic Number (Z)
Atomic number = Number of protons in the nucleus
- Unique for each element: No two elements have the same atomic number
- Defines the element: Determines which element it is
- In neutral atom: Also equals number of electrons
Example: Carbon has atomic number 6, so it has 6 protons (and 6 electrons if neutral).
Mass Number (A)
Mass number = Number of protons + Number of neutrons
- Not unique: Different atoms of same element can have different mass numbers (isotopes)
- Whole number: Always a whole number
- Relative mass: Indicates relative mass of atom
Example: Carbon-12 has mass number 12: 6 protons + 6 neutrons = 12
Notation
Elements are written as: ᴬX or X-A
Where:
- A = Mass number
- Z = Atomic number (often shown as subscript)
- X = Element symbol
Example: ¹²₆C or C-12 means carbon with mass number 12 and atomic number 6.
Electron Shells (Energy Levels)
Electrons are arranged in shells (also called energy levels) around the nucleus.
Shell Capacity
- Shell 1 (K): Maximum 2 electrons
- Shell 2 (L): Maximum 8 electrons
- Shell 3 (M): Maximum 8 electrons (for IGCSE)
- Shell 4 (N): Maximum 8 electrons (for IGCSE)
Electron Configuration Rules
- Electrons fill lowest energy shells first (closest to nucleus)
- Shells must be filled in order (1, then 2, then 3, etc.)
- Outer shell is called the valence shell
- Valence electrons are in the outermost shell
Writing Electron Configuration
Method: Write shell number, then number of electrons
Examples:
- Hydrogen (H): 1 electron → 1 (shell 1 has 1 electron)
- Helium (He): 2 electrons → 2 (shell 1 has 2 electrons)
- Lithium (Li): 3 electrons → 2,1 (shell 1 has 2, shell 2 has 1)
- Carbon (C): 6 electrons → 2,4 (shell 1 has 2, shell 2 has 4)
- Neon (Ne): 10 electrons → 2,8 (shell 1 has 2, shell 2 has 8)
The Periodic Table
The Periodic Table organizes elements by atomic number and groups elements with similar properties.
Organization
- Periods (Rows): Horizontal rows, numbered 1-7
- Elements in same period have same number of electron shells
- Groups (Columns): Vertical columns, numbered 1-18 (or 1-8 for older systems)
- Elements in same group have same number of valence electrons
- Similar chemical properties
Main Groups (IGCSE Focus)
Group 1 (Alkali Metals):
- 1 valence electron
- Very reactive
- Examples: Li, Na, K
Group 7 (Halogens):
- 7 valence electrons
- Very reactive non-metals
- Examples: F, Cl, Br, I
Group 0/8 (Noble Gases):
- Full outer shell (8 electrons, except He has 2)
- Unreactive
- Examples: He, Ne, Ar
Periodic Trends
Atomic Radius
Trend: Decreases across a period, increases down a group
- Across period: More protons pull electrons closer
- Down group: More shells, so atoms are larger
Ionization Energy
Trend: Increases across a period, decreases down a group
- First ionization energy: Energy to remove first electron
- Across period: Harder to remove (smaller radius, more protons)
- Down group: Easier to remove (larger radius, outer electrons farther)
Reactivity
Metals: Increases down Group 1, decreases across periods
Non-metals: Decreases down Group 7, increases across periods
Worked Examples
Example 1: Atomic Structure
An atom has 11 protons and 12 neutrons. Identify the element and write its notation.
Solution:
- Atomic number = 11 (number of protons) → Sodium (Na)
- Mass number = 11 + 12 = 23
- Notation:
²³₁₁NaorNa-23
Example 2: Electron Configuration
Write the electron configuration for phosphorus (atomic number 15).
Solution:
- 15 electrons total
- Shell 1: 2 electrons (maximum)
- Shell 2: 8 electrons (maximum)
- Shell 3: 5 electrons (remaining: 15 - 2 - 8 = 5)
- Configuration: 2,8,5
Common Examiner Traps
- Confusing atomic number and mass number - Atomic number = protons; Mass number = protons + neutrons
- Electron configuration errors - Fill shells in order, check maximum capacities
- Periodic trend direction - Remember trends across periods vs down groups
- Notation mistakes - Mass number top left, atomic number bottom left
IGCSE Atomic Structure and Periodic Table Practice Questions
Question 1: Atomic Structure
An element has atomic number 8 and mass number 16. How many protons, neutrons, and electrons does it have?
Solution:
- Protons = Atomic number = 8
- Neutrons = Mass number - Atomic number = 16 - 8 = 8
- Electrons = Protons (neutral atom) = 8
Answer: 8 protons, 8 neutrons, 8 electrons
Question 2: Electron Configuration
Write the electron configuration for magnesium (atomic number 12).
Solution:
- 12 electrons: 2,8,2
- Shell 1: 2, Shell 2: 8, Shell 3: 2
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Frequently Asked Questions
What is atomic number?
Atomic number is the number of protons in the nucleus. It defines which element it is and is unique for each element.
What is mass number?
Mass number is the total number of protons and neutrons in the nucleus. Different isotopes of the same element have different mass numbers.
How do I write electron configuration?
Write the number of electrons in each shell in order, separated by commas (e.g., 2,8,1 for sodium).
What are periodic trends?
Periodic trends are patterns in properties across periods and down groups, such as atomic radius, ionization energy, and reactivity.
Related IGCSE Chemistry Resources
- IGCSE Isotopes: Complete Guide - Master isotopes and atomic structure
- IGCSE Ions and Ionic Bonds: Complete Guide - Master ionic bonding
- IGCSE Chemistry Revision Notes - Complete syllabus overview
- IGCSE Past Papers Guide - Access free IGCSE past papers
Next Steps: Master IGCSE Atomic Structure and Periodic Table with Tutopiya
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Written by
Tutopiya Chemistry Faculty
IGCSE Specialist Tutors
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