CHEMLEC: Atomic Symbol, Atomic Mass and Isotopes

Atomic Mass

(sometimes called atomic weight) is the mass of the atom in atomic mass units or amu. depends on the number of electrons, protons, and neutrons it contains

Isotopes

are atoms of the same element (same atomic number) but different number of neutrons or different mass number.

Natural abundance or percent abundance

proportion of atoms of each isotope in a natural sample of an element or the percentage of atoms of a particular isotope

Atomic number (Z)

the number of protons in the nucleus of each atom of an element All atoms of a particular element have the same number of protons in their nucleus. In a neutral atom, the number of protons is equal to the number of electrons, so the atomic number also indicates the number of electrons present in the atom Atomic no. = no. of protons = no. of electrons Example: Copper atom has 29 protons in its nucleus atomic number of copper = 29 number of electrons of copper = 29

Average atomic mass

the weighted average of the atomic masses of the naturally occurring isotopes of an element an element is the weighted average of all the element's isotopes based on their natural abundance or percent abundance.

Mass number (A)

total number of neutrons and protons present in the nucleus of an atom of an element an estimate of the mass of an atom the mass of the electrons is not considered because it is so small that they never affect the atomic mass mass number = number of protons + number of neutrons number of neutrons = mass number - number of protons Example: a copper atom that has 29 protons and 34 neutrons - mass number of copper = 29 protons + 34 neutrons - mass number of copper = 63