atom An atom is the simplest particle of an element that can exist on its own in a stable environment. have very little massThe amount of matter an object contains. Mass is measured in grams (g)., so theyâre difficult to measure accurately. Instead, chemists use a scale. On this scale the mass of a 12C atom is exactly 12.
For example:
24Mg has a relative mass of 24 â it is twice as heavy as a 12C atom.
1H has a relative mass of 1 â it is 12 times lighter than a 12C atom.
These masses are called relative atomic massIs the mass of the atom compared with that of the carbon-12 isotope, which has a mass of exactly 12, and it is the weighted mean of the mass numbers.. They use the symbol Ar.
The term weighted mean mass is used to take into account the contribution made by each isotope Atoms which have the same number of protons (so they are atoms of the same element) but they have a different number of neutrons (so they have a different mass number). to the overall mass of an element An element is a substance that consists of only one type of atom and it cannot be broken down into anything simpler by chemical means..
For example:
25% of chlorine atoms are 37Cl and 75% are 35Cl. The weighted mean mass of chlorine is 35.5.
The relative atomic mass of an element is a weighted mean mass of the isotopes of an element compared with that of the 12C isotope, which has a mass of exactly 12.