Abundance in the universe: group 17
These data are estimates of the average composition of the universe. Units are parts per billion by atoms. Values in any one location may well vary widely from the values given here.
ppb by atoms
Data given in different sources vary somewhat, reflecting the difficulty in assessing these numbers. Values given here are estimates derived by a consensus and averaging process for data abstracted from references 1-2.
The units used in WebElements for all abundance data are ppb by weight which means parts per billion by weight, that is mg tonne-3 or mg per 1000 kg. All abundance data are also presented as ppb by atoms, which means atoms of the element per billion atoms.
The reason for rescaling all data is as follows. It is common to see, say, solar abundances expressed as the number of atoms of the element relative to a scale upon which the abundance of hydrogen is defined as 1012. This makes comparison with, say, crustal abundances difficult, since crustal abundances are often expressed in terms of parts per million by weight. Hence a common scale is used throughout and I chose ppb as this gives manageable numbers for most elements.
For access to other abundance data as ppb by weight, select from:
For access to other abundance data as ppb by atoms, select from:
- W.W. Porterfield in Inorganic chemistry, a unified approach, Addison Wesley Publishing Co., Reading Massachusetts, USA, 1984.
- J. Selbin, J. Chem. Ed. 1973, 50, 306.