2.1.1Physical Chemistry
Classification of an Element — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 52 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Structure of the Periodic Table
Elements are arranged by increasing atomic number so that similar outer-shell configurations line up in columns.
Periods
- Periods Each horizontal row is a period, and the period number equals the number of the outer occupied electron shell.
Groups
- Groups Each vertical column is a group, and elements in a group share the same number of outer-shell electrons.
Atomic number
- Atomic number Elements are placed in order of proton number, which is why the table is periodic in its chemical properties.
Periodicity
- Periodicity Repeating patterns in properties such as melting point and ionisation energy occur across each period.
Part 2 of 4Blocks of the Table
Blocks of the Table
s-block
- s-block Elements whose highest-energy electron occupies an s sub-shell, such as sodium with configuration 1s² 2s² 2p⁶ 3s¹.
p-block
- p-block Elements whose highest-energy electron occupies a p sub-shell, such as chlorine with outer configuration 3s² 3p⁵.
d-block
- d-block Elements whose highest-energy electron occupies a d sub-shell, which includes iron and the other transition metals.
| Block | Last electron enters | Examples |
|---|---|---|
| s-block | An s sub-shell | Groups 1 and 2, e.g. Na, Mg |
| p-block | A p sub-shell | Groups 13 to 18, e.g. Al, Cl |
| d-block | A d sub-shell | Transition metals, e.g. Fe, Cu |
Part 3 of 4Period 3 as a Case Study
Period 3 runs from sodium to argon and each element adds one more electron to the third shell.
1
Sodium and magnesium are metals with outer configurations 3s¹ and 3s², and they lose electrons to form Na⁺ and Mg²⁺.
2
Aluminium has outer configuration 3s² 3p¹ and loses three electrons to form Al³⁺, so it is a metal in the p-block.
3
Silicon (3s² 3p²) is a metalloid with a giant covalent structure, intermediate between metals and non-metals.
4
Phosphorus, sulfur and chlorine are non-metals that gain or share electrons, with outer configurations 3s² 3p³, 3p⁴ and 3p⁵.
5
Argon has the full outer configuration 3s² 3p⁶, so it is an unreactive noble gas and exists as single atoms.
Part 4 of 4Exam Checklist & Tips
2.1.1 – Key Points for the Exam
- Period A horizontal row of the periodic table, in which elements have the same number of shells.
- Group A vertical column of elements with the same number of outer-shell electrons and similar properties.
- Periodicity The repeating pattern of physical and chemical properties across successive periods.
- Block A region of the table defined by the sub-shell holding the highest-energy electron.
Common Mistakes
- Confusing periods (rows) with groups (columns) when describing trends.
- Placing helium in the s-block groups by configuration without realising it is a noble gas in Group 18.
- Saying atomic number is the number of outer electrons, when it is the number of protons.
- Assuming all p-block elements are non-metals, when aluminium is a metal.
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