��̳

Atomic structure - (CCEA)Compounds

Scientists’ ideas about atoms have changed over time. Today, they agree that atoms have a positively-charged nucleus made of protons and neutrons, and negatively-charged electrons that orbit the nucleus in shells.

Part of Chemistry (Single Science)Structures, trends, chemical reactions, quantitative chemistry and analysis

Compounds

A is two or more elements chemically combined.

The table below shows some common compounds. It’s useful to know that mono means one, and di means two.

carbon monoxide has one atom of oxygen
carbon dioxide has two atoms of oxygen

Compound	Formula	Elements present
water	H₂O	hydrogen, oxygen
carbon monoxide	CO	carbon, oxygen
carbon dioxide	CO₂	carbon, oxygen
sulfur dioxide	SO₂	sulfur, oxygen
sulfur trioxide	SO₃	sulfur, oxygen
nitrogen monoxide	NO	nitrogen, oxygen
nitrogen dioxide	NO₂	nitrogen, oxygen
ammonia	NH₃	nitrogen, hydrogen
hydrochloric acid	HCl	hydrogen, chlorine
nitric acid	HNO₃	hydrogen, nitrogen, oxygen
sulfuric acid	H₂SO₄	hydrogen, sulfur, oxygen

Compound	water
Formula	H₂O
Elements present	hydrogen, oxygen

Compound	carbon monoxide
Formula	CO
Elements present	carbon, oxygen

Compound	carbon dioxide
Formula	CO₂
Elements present	carbon, oxygen

Compound	sulfur dioxide
Formula	SO₂
Elements present	sulfur, oxygen

Compound	sulfur trioxide
Formula	SO₃
Elements present	sulfur, oxygen

Compound	nitrogen monoxide
Formula	NO
Elements present	nitrogen, oxygen

Compound	nitrogen dioxide
Formula	NO₂
Elements present	nitrogen, oxygen

Compound	ammonia
Formula	NH₃
Elements present	nitrogen, hydrogen

Compound	hydrochloric acid
Formula	HCl
Elements present	hydrogen, chlorine

Compound	nitric acid
Formula	HNO₃
Elements present	hydrogen, nitrogen, oxygen

Compound	sulfuric acid
Formula	H₂SO₄
Elements present	hydrogen, sulfur, oxygen

Test your understanding

Calculating relative atomic mass for elements

More guides on this topic

Related links