Ch 1 · Arrangement of Elements · IGCSE Chemistry 0620
Topic 1 of 5 in The Periodic Table — IGCSE Chemistry 0620 — 48 lessons.
Introduction
The Periodic Table is a map of the elements. Once you can read it, you can predict how an element behaves and what charge its ion carries, even for an element you have never met. This lesson covers the layout of the table and the reasoning that links position to electronic configuration and chemistry.
Key ideas — Periods, groups and proton number
The Periodic Table is an arrangement of the elements in order of increasing proton (atomic) number, laid out so that elements with similar properties fall in the same vertical column.
🧑🏫 Teacher's explanation
Think of the Periodic Table like a massive apartment complex. The 'Periods' are the floors of the building; if you are on floor 3, you have 3 levels of living space (shells) in your unit. The 'Groups' are the vertical columns of apartments. Everyone living in column 1 has exactly one balcony (outer electron), which dictates how they interact with their neighbors.
📖 Definitions
🔍 Worked example — Easy
An element has the electronic configuration 2, 8, 4. State its group number and period number.
🔍 Worked example — Standard
Magnesium has a proton number of 12. Determine its group and period.
🔍 Worked example — Exam-style
An unknown element X is in Group VII and Period 3. If it reacts with Sodium (Na) to form an ionic compound, what is the formula of the compound formed? (Assume Na is in Group I).
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the number of electrons in the outer shell of element Y. [1] (b) Predict the charge of the ion formed by element Y. [1] (c) Describe the trend in metallic character across Period 3 from left to right. [1] [3 marks]
Key ideas — Metallic to non-metallic character across a period
Moving from left to right across a period, the elements change from metals to non-metals. In Period 3, sodium, magnesium and aluminium are metals; silicon is a metalloid with some properties of each; phosphorus, sulfur, chlorine and argon are non-metals. A zigzag "staircase" line separates the metals on the left from the non-metals on the right.
🧑🏫 Teacher's explanation
Imagine a playground with a sliding board on one side and a climbing wall on the other. On the left side (the metals), the elements are like kids who find it very easy to let go of their toys (electrons) to move around freely. Because they lose these negative pieces, they become positive and can carry an electric charge easily.
📖 Definitions
🔍 Worked example — Easy
An element in Period 3 has the electronic configuration 2, 8, 1. Identify if it is a metal or a non-metal and state the charge of the ion it forms.
🔍 Worked example — Standard
Compare the oxide of Magnesium (MgO) and the oxide of Sulfur (SO_2) in terms of their pH in aqueous solution.
🔍 Worked example — Exam-style
Predict the properties of an unknown element in Period 3, Group 17 based on its position.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the type of element (metal or non-metal) that X is. [1] (b) Describe the change in the nature of oxides as you move from element X to an element in Group 17 in the same period. [2] [3 marks]
Key ideas — Group number, ionic charge and similar properties
The charge on the ion an element forms follows directly from its group number:
🧑🏫 Teacher's explanation
Think of the Periodic Table as a giant sorting machine. Instead of sorting by color or size, it sorts elements by their 'personality'—specifically, how many electrons they have in their outermost shell. Elements in the same vertical column (a group) are like siblings: they look a bit different, but they behave in very similar ways because they share the same number of outer electrons.
📖 Definitions
🔍 Worked example — Easy
An element X is in Group II of the periodic table. State the charge on the ion it forms when it reacts with a non-metal.
🔍 Worked example — Standard
Chlorine is in Group VII. Write the formula of the chloride ion formed by chlorine.
🔍 Worked example — Exam-style
Magnesium reacts with oxygen to form magnesium oxide. Write the balanced chemical equation for this reaction, including state symbols, given that Magnesium is in Group II and Oxygen is in Group VI.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the charge on the ion formed by element Y. (b) Predict the formula of the compound formed when element Z reacts with element Y. [3 marks]
Key ideas — Predicting properties from position
🧑🏫 Teacher's explanation
Think of the Periodic Table as a giant, organized filing cabinet. Instead of filing by name, chemists file elements by their 'personality'—specifically, how many electrons they have in their outermost shell. If you know which drawer (Group) an element is in, you already know its most important habits, like how many electrons it wants to lose or gain to become stable.
📖 Definitions
🔍 Worked example — Easy
An unknown element, X, is in Group II of the Periodic Table. Predict the formula of its chloride when it reacts with chlorine.
🔍 Worked example — Standard
Predict whether the oxide of an element located in the bottom-left of the Periodic Table is acidic, basic, or amphoteric.
🔍 Worked example — Exam-style
Element A is in Group I and Element B is in Group VII. If both are in the same period, which element will have a higher melting point, and which will be more reactive with water?
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Predict the formula of the compound formed when Y reacts with Z. [2] (b) State whether the oxide of element Y is acidic, basic, or amphoteric. [1] [3 marks]
Worked example
Question. Element E has proton number 20.
🔍 Worked example — Easy
An element has the electronic configuration 2, 8, 5. Identify its group and period.
🔍 Worked example — Standard
Magnesium has a proton number of 12. Write its electronic configuration and the charge of the ion it forms.
🔍 Worked example — Exam-style
Element X is in Group I and Period 3. Predict the formula of its oxide.
⚠️ Common errors
Common mistakes
Practice
Answers In order of increasing proton number [B1]; in periods (rows) and groups (columns) so that elements with similar properties are in the same group [B1]. 2,8,3 [B1]; Group III [B1]; mathrmAl^3+ [B1]. Changes from metallic to non-metallic [B1]; sodium, magnesium and aluminium are metals, silicon is a metalloid and phosphorus, sulfur and chlorine are non-metals [B1]. Both are in Group VII and have the same number of outer-shell electrons, seven [B1]; chemical properties depend on the outer electrons, so both gain one electron to form 1− ions [B1]. SrO [B1]; more reactive, because reactivity increases down a group of metals [B1].