Elements:
Hydrogen (H): This is the lightest element. It has an atomic number of 1. Hydrogen makes up about 75% of all the elemental mass in the universe.
Oxygen (O): With an atomic number of 8, oxygen is very important for breathing. It makes up about 21% of the air we breathe on Earth.
Compounds:
Water (H₂O): Water is made of 2 hydrogen atoms and 1 oxygen atom. It covers about 71% of the Earth's surface.
Carbon Dioxide (CO₂): This gas is made of 1 carbon atom and 2 oxygen atoms. The amount of carbon dioxide in the atmosphere has grown from around 280 parts per million (ppm) before the Industrial Revolution to more than 400 ppm today.
Mixtures:
Air: Air is a mix of gases. It contains about 78% nitrogen, 21% oxygen, and tiny amounts of other gases.
Saltwater: Saltwater is a solution of salt (sodium chloride) mixed in water. Ocean water has about 3.5% salt on average.
Elements:
Hydrogen (H): This is the lightest element. It has an atomic number of 1. Hydrogen makes up about 75% of all the elemental mass in the universe.
Oxygen (O): With an atomic number of 8, oxygen is very important for breathing. It makes up about 21% of the air we breathe on Earth.
Compounds:
Water (H₂O): Water is made of 2 hydrogen atoms and 1 oxygen atom. It covers about 71% of the Earth's surface.
Carbon Dioxide (CO₂): This gas is made of 1 carbon atom and 2 oxygen atoms. The amount of carbon dioxide in the atmosphere has grown from around 280 parts per million (ppm) before the Industrial Revolution to more than 400 ppm today.
Mixtures:
Air: Air is a mix of gases. It contains about 78% nitrogen, 21% oxygen, and tiny amounts of other gases.
Saltwater: Saltwater is a solution of salt (sodium chloride) mixed in water. Ocean water has about 3.5% salt on average.