Elements, Reactions & Earth
The Periodic Table
History, trends, and organisation
Mendeleev's Periodic Table
In 1869, Russian chemist Dmitri Mendeleev arranged all known elements in order of their properties. He noticed patterns and left gaps for elements that hadn't been discovered yet - many of which were found later!
Key Principles
- • Elements arranged by atomic mass
- • Similar properties in same columns
- • Left gaps for undiscovered elements
- • Predicted properties of missing elements
Modern Table
- • Arranged by atomic number (protons)
- • Groups = vertical columns (same electrons)
- • Periods = horizontal rows (same shells)
- • Metals on left, non-metals on right
Element Explorer - First 20 Elements
Click on an element to see its details. Notice the patterns across periods and groups!
Click an element to learn more
Periodic Table Trends
Across a period (left to right):
- • Atoms get smaller
- • Elements become less metallic
- • Reactivity decreases (metals)
Down a group:
- • Atoms get larger
- • Metals become more reactive
- • Non-metals become less reactive
Combustion
The chemistry of burning
The Fire Triangle
Three things are needed for combustion (burning) to occur:
Remove any one side of the triangle and the fire goes out!
Complete Combustion
Plenty of oxygen - clean burning:
Blue flame, less soot, more energy released
Incomplete Combustion
Not enough oxygen - dirty burning:
Yellow flame, soot, CO is toxic!
Air Pollution from Combustion
Carbon Monoxide (CO): From incomplete combustion. Poisonous - blocks oxygen transport in blood.
Sulfur Dioxide (SO₂): From burning coal/oil with sulfur impurities. Causes acid rain.
Carbon Dioxide (CO₂): Greenhouse gas contributing to climate change.
Particulates (soot): From incomplete combustion. Damages lungs, causes smog.
Oxidation Reactions
Gain of oxygen
What is Oxidation?
Oxidation = Gain of oxygen
When a substance reacts with oxygen, it is oxidised
Metals + Oxygen
Metals react with oxygen to form metal oxides:
The metal oxide is often a powder or coating on the metal surface.
Non-metals + Oxygen
Non-metals also react with oxygen:
Rusting - A Special Oxidation
Iron and steel rust when they react with oxygen AND water:
Prevention methods:
- • Painting (barrier)
- • Oiling/greasing (waterproof)
- • Galvanising (zinc coating)
Conditions needed:
- • Both oxygen AND water needed
- • Salt speeds up rusting
- • Without either, no rust forms
Reactions of Metals
How metals react with water and acids
Metals + Water
Some metals react with water to produce a metal hydroxide and hydrogen gas:
| Metal | Reaction with Water | Observation |
|---|---|---|
| Potassium (K) | Very vigorous | Explodes with lilac flame |
| Sodium (Na) | Vigorous | Fizzes rapidly, melts, orange flame |
| Calcium (Ca) | Moderate | Fizzes, white solid forms |
| Magnesium (Mg) | Very slow with cold water | Slight fizz with steam |
| Iron, Copper | No reaction | - |
metal + water → metal hydroxide + hydrogen
Metals + Acids
Many metals react with acids to produce a salt and hydrogen gas:
metal + acid → salt + hydrogen
Hydrochloric Acid + Metal
Produces a chloride salt:
Sulfuric Acid + Metal
Produces a sulfate salt:
Testing for Hydrogen
The hydrogen produced can be tested using the 'squeaky pop' test:
Lighted splint
Squeaky pop!
If the gas is hydrogen, it burns rapidly with a characteristic 'pop' sound.
Earth's Structure
Layers of our planet
The Four Layers
Crust (5-70 km)
Thinnest layer. Solid rock. We live on this! Two types: continental (thicker) and oceanic (thinner, denser).
Mantle (2900 km thick)
Largest layer. Mostly solid but flows very slowly over millions of years. Source of magma.
Outer Core (2200 km thick)
Liquid iron and nickel. Creates Earth's magnetic field as it flows.
Inner Core (1200 km radius)
Solid iron and nickel. Extremely hot (5000°C) but solid due to immense pressure.
Types of Rocks
The rock cycle
The Three Rock Types
Click a rock type to learn more
The Rock Cycle
Oxygen in Air
Composition of the atmosphere
Composition of Dry Air
Nitrogen (N₂)
Oxygen (O₂)
Other gases
Other gases include: Argon (0.93%), Carbon dioxide (0.04%), Water vapour (variable), Trace gases
Measuring Oxygen Percentage
A classic experiment uses the reaction of copper with oxygen:
Method: Pass air over heated copper. Copper reacts with oxygen to form copper oxide. Measure the decrease in volume - about 21% of the air is used up.
copper + oxygen → copper oxide
Practice Questions
Test your understanding
Periodic Table [3 marks]
Describe how elements are arranged in the modern Periodic Table. Explain why Mendeleev left gaps.
Answer:
Arrangement: Elements are arranged in order of increasing atomic number (number of protons). [1 mark] Elements with similar properties are in vertical columns called groups. Horizontal rows are called periods. [1 mark]
Gaps: Mendeleev left gaps for undiscovered elements that he predicted would have specific properties based on the patterns. When these elements were later discovered, they matched his predictions, confirming his table was correct. [1 mark]
Combustion [4 marks]
a) Name the three components of the fire triangle. [3 marks]
b) Explain how a carbon dioxide fire extinguisher puts out a fire. [1 mark]
Answer:
a) Fire triangle: Fuel (something to burn), [1 mark] Oxygen (from air), [1 mark] Heat (to reach ignition temperature). [1 mark]
b) CO₂ extinguisher: Carbon dioxide is heavier than air and blankets the fire, cutting off the oxygen supply. Without oxygen, the fire cannot continue burning. [1 mark]
Rusting [3 marks]
A student sets up three test tubes: A with iron nail in boiled water (no air), B with iron nail in tap water, C with iron nail in dry air. Which nail(s) will rust? Explain your answer.
Answer:
Only nail B will rust. [1 mark]
Explanation: Rusting requires BOTH oxygen AND water. [1 mark]
- Nail A has water but no oxygen (boiled water removes dissolved air)
- Nail B has both water and oxygen from air
- Nail C has oxygen but no water
Therefore only B has both conditions needed for rusting. [1 mark]
Metal Reactions [3 marks]
Write a word equation for the reaction between magnesium and hydrochloric acid. How would you test for the gas produced?
Answer:
Word equation: magnesium + hydrochloric acid → magnesium chloride + hydrogen [1 mark]
Gas test: The gas produced is hydrogen. [1 mark] Test by placing a lighted splint at the mouth of the test tube - if it's hydrogen, it will burn with a 'squeaky pop' sound. [1 mark]
Continue Learning
Explore Year 8 Physics or move on to Year 9 Chemistry.