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🧪 The Periodic Table

Spec 5.1.2.1 📗 Foundation
📖 In-Depth Theory

Structure of the Periodic Table

The PERIODIC TABLE arranges all known elements in order of increasing ATOMIC NUMBER.
Key features:
ROWS are called PERIODS — each period represents a new electron shell being filled.
COLUMNS are called GROUPS — elements in the same group have the same number of OUTER ELECTRONS and similar chemical properties.
Period numbers tell you how many electron shells the element has:
Period 1: 1 shell (H and He)
Period 2: 2 shells (Li to Ne)
Period 3: 3 shells (Na to Ar)
Group numbers (1–7 and 0) tell you how many OUTER electrons:
Group 1: 1 outer electron
Group 7: 7 outer electrons
Group 0: full outer shell (8 electrons, or 2 for helium)
The periodic table is divided into:
METALS — left and centre (most elements are metals).
NON-METALS — top right.
METALLOIDS/SEMI-METALS — along the dividing line (e.g. silicon, germanium).

Trends Across Periods and Down Groups

ACROSS A PERIOD (left to right):
Atomic number increases.
Number of electrons in outer shell increases (1 to 8).
Metallic properties decrease — non-metallic properties increase.
From metal (Group 1) to non-metal (Group 7) to noble gas (Group 0).
DOWN A GROUP:
Another electron shell is added.
Atoms get LARGER (more shells = bigger atom).
OUTER ELECTRONS are further from the nucleus — less strongly attracted.
METALS become MORE REACTIVE going down (easier to lose outer electron).
NON-METALS become LESS REACTIVE going down (harder to gain another electron — outer electrons are further away).
These trends allow chemists to PREDICT the properties of elements from their position in the periodic table.

Transition Metals

Between Groups 2 and 3 lies the TRANSITION METALS block (the long middle section).
Transition metals are harder and have higher melting points than Group 1 metals.
They are typically dense, strong, shiny metals.
Examples: iron (Fe), copper (Cu), zinc (Zn), titanium (Ti), nickel (Ni), gold (Au), silver (Ag).
Key properties of transition metals:
Form COLOURED COMPOUNDS — e.g. copper sulfate is blue; iron(II) compounds are pale green; iron(III) compounds are orange.
Can act as CATALYSTS — e.g. iron catalyst in the Haber process; nickel in hydrogenation.
Can have MULTIPLE OXIDATION STATES — e.g. iron can be Fe²⁺ or Fe³⁺.
Compare with Group 1 metals: transition metals are less reactive, harder, have higher melting points and form coloured compounds. Group 1 metals are soft, very reactive and their compounds are usually white.
⚠️ Common Mistake

The GROUP NUMBER tells you the number of OUTER ELECTRONS — not the total electrons or the period. The PERIOD NUMBER tells you how many shells. So an element in Period 3, Group 2 has 3 shells and 2 outer electrons — electronic configuration 2.8.2 (magnesium). Don't confuse groups and periods.

📌 Key Note

Periodic table arranged by atomic number. Period = row = number of shells. Group = column = number of outer electrons. Same group = same outer electrons = similar properties. Metals: left and centre. Non-metals: top right. Noble gases: Group 0 (right edge).

🎯 Matching Activity — Match the Periodic Table Feature

Match each feature to its correct description. — drag the symbols on the right to match the component names on the left.

Period
Drop here
Group
Drop here
Group 0
Drop here
Transition metals
Drop here
Group 1
Drop here
Noble gases — full outer shells, very unreactive
A horizontal row — each new period means another electron shell
A vertical column — elements share the same number of outer electrons
Alkali metals — 1 outer electron, very reactive, soft, low density
Hard, dense metals with high melting points — form coloured compounds, act as catalysts
🎯 Test Yourself
Question 1 of 2
1. An element is in Period 3 and Group 2. What is its electronic configuration?
2. Why do all Group 7 elements have similar chemical properties?
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