Compounds, Molecules & Mixtures

• True or false? Something counts as a 'molecule' when it's made from 2 or more atoms, and those atoms are held together by chemical bonds.

  True
• O2 consists of 2 oxygen atoms, covalently bonded together. Does oxygen count as a molecule?


  Yes
• What is a compound?


  A compound is a substance made from two or more different elements that are chemically bonded together.
• Oxygen molecules (O2) consist of two oxygen atoms. Is an oxygen molecule a compound?


  No oxygen only contains 1 element (oxygen), so doesn't count as a compound.
• Is carbon dioxide (CO2) a molecule, a compound, or both?

  Both

  CO2 is a molecule because it contains 3 atoms chemically bonded together. It is also a compound as it contains atoms of 2 elements (carbon and oxygen).
• How many oxygen atoms are there in 1 molecule of H2SO4?

  4
• What is the definition of a mixture?

  A mixture contains two or more substances that are not chemically combined.
• Is the air all around us a compound or a mixture?

  Mixture

  Air contains many different substances, such as N2, O2, and CO2. Importantly, these substances are not chemically bonded to each other, so air is a mixture. 
• Is seawater a compound or a mixture?

  Seawater contains many different substances, mainly H2O and salts like NaCl, but also lots of other substances. Importantly though, these substances are not chemically bonded to each other, so seawater is a mixture
• What is a molecule?


  A molecule is a substance that contains two or more atoms held together by chemical bonds.
• What is a compound?

  A compound is a substance formed from two or more elements, where the atoms of each are in fixed proportions, and are held together by chemical bonds.
• Do compounds have the same properties as the atoms they’re made from?

  No
• What is a mixture?


  A mixture is a group of different elements or compounds which are not chemically bonded together.