what is the difference between: (a)molecules and elements (b)molecular mass and formula unit mass

Asked by devansh malhotra | 18th Jan, 2012, 08:31: PM

Expert Answer:

Molecule: A group of 2 or more atoms held together by chemical bonds. A molecule is formed when atoms of the same or different elements combine. A molecule is the smallest particle of a substance that can normally exist independently. When molecules are bonded together, they still have the same properties of that substance. For example- oxygen O2 molecule contains two oxygen atoms; water H2O molecule contains hydrogen and oxygen atoms.

Element: A substance that cannot be broken down to simpler substances, i.e. it contains atoms all of one type only. For example- hydrogen, oxygen, sodium is elements. Water is made up of the elements hydrogen and oxygen. 

The difference between Molecular Mass and Formula Unit Mass is that "Molecular Mass" term is used for covalent compounds and "Formula Unit Mass" term is used for ionic compounds. Formula unit mass is the mass of only one unit of the ionic compound, whereas the molar mass is the mass of one mole of the covalent compound not just one unit.

For example: CO2 (carbon dioxide) is formed by covalent bonds and is a molecule. Since it is a molecule, we will find its Molecular Mass.

On the other hand, Na2CO3 (Sodium Carbonate) has an ionic bond and is an ionic compound. So, we will  find it's Formula Mass.

Answered by  | 19th Jan, 2012, 09:50: AM

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