Element: fundamental
substance into which material can be separated by chemical means,
with characteristic atomic properties and behavior (examples:
He, H, Fe, O, Si)
Atom: smallest particle that retains all properties of a given element
Atom = protons + neutrons + electrons
Number of protons defines an element: the atomic number
Number of protons + neutrons defines the mass:
the mass or isotopic number
One element can have several isotopes (# neutrons)
Different isotopes (=masses) measured in a mass spectrometer
Some isotopes fall apart spontaneously (unstable
isotopes): RADIATION
Parent | Daughter | + product |
14/6 C | 14/7 N | |
40/19 K | 40/18 Ar | |
235/92 U | 207/82 Pb | |
238/92 U | 206/82 Pb | |
87/37 Rb | 87/38 Sr |
The time during which half of the parent isotopes
decay to daughter isotopes is constant for each unstable isotope:
the half life
Examples:
Parent | Daughter | Half life |
14 C | 14 N | 5,730 year |
40 K | 40 Ar | 1,300,000,000 (1.3 x 109 y) |
235 U | 207 Pb | 700,000,000 year (.7 x 109 y) |
238 U | 206 Pb | 4,500,000,000 year (4.5 x 109 y) |
87 Rb | 87 Sr | 48,800,000,000 year (48.8 x 109 y) |
Basic radiometric age calculation:
1 measure parent now (P)
2 measure daughter (D)
3 P + D = original amount of P (Po)
4 D/Po ratio gives age. The larger the ratio, the older the sample.