Learning physics and chemistry easily and freely - Science for elementary school, middle school and high school

Free online chemistry lesson for elementary school, middle school and high school.


Air and atmosphere

Atmosphere protects us

The Earth's atmosphere has played and still plays a vital role in protecting life on Earth.

- The Earth's atmosphere protects us from meteorites:
Meteorites are blocks of ice and rock that come from space where they move at high speeds.
On entering the atmosphere they undergo very important frictions that raise their temperature and eventually make them explode.
However some large meteorites can reach the ground and cause damage depending on their size of their speed.

- The ozone layer protects us from harmful radiation:
Located in the stratosphere this layer of only 3 mm thick stops most of ultraviolet  radiations (UV) that could be harmful for humans and all other living organisms.

- The Earth's atmosphere maintains an ideal temperature for life.
Without this atmosphere the temperatures would be extreme: from one hundred degrees Celsius above zero during the day, to one hundred degrees Celsius below zero at night. The atmosphere reduces the temperature fluctuations.
The atmosphere also allows us to benefit from higher temperatures through the greenhouse effect. Without it the temperatures on Earth would be too low: It can trap some of the heat received from the Sun. Instead of being returned and lost in space this heat is kept in the atmosphere.

Science class

Mechanics lessons

Water on Earth
Changes of state in the nature: the water cycle
Water in human body
Test for water
Properties of water in different states

States of matter

States of matter and its changes
Boiling water
Water: freezing and melting
Changes of state: mass and volume
Molecules in different states of matter

Mixtures and solutions

Heterogeneous mixtures
Homogeneous mixtures
Vaporization of water
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

Mass and volume

Volume and its units
Measuring volume with a graduated cylinder
Mass and its units
Measuring the mass of a liquid
Mass of a liter of water
Volumetric mass density

Air and atmosphere

Earth's atmosphere protect us
Threats to the Earth's atmosphere
Composition of air
Air and life

Atoms and molecules

Molecules in mixtures and pure substances
Molecules and states of matter
Composition of molecules
Constituents of the atoms
The electrical neutrality of the atom


Basics of combustion
The combustion of carbon
The combustion of butane

Atoms and chemical reactions

Chemical reactions
Chemical equations
Law of conservation of mass
Chemical synthesis


Most common metals
How to distinguish metals ?

Corrosion of metals
Electrical conductivity of solid materials
Electrons and free electrons
Electric current in metals


The conductivity of aqueous solutions
Aqueous solutions and ions
The direction of movement of ions
Formation of ions
Tests for ions

Acidic and basic solutions

pH of aqueous solutions
Ions in acidic and basic solutions
Dilution of acids and bases
Composition of hydrochloric acid
Chemical reaction between iron and hydrochloric acid

Electrochemical cells and chemical energy

Chemical reaction beteween a copper sulphate solution and zinc
Copper sulfate and zinc battery
Basics of electrochemical cell


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