Atoms and orbitals

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Nuvola apps edu science.svg Subject classification: this is a chemistry resource.

We'll start with some definitions:

a particle that is indivisible during chemical reactions
atoms of the same atomic number

An atom = nucleus (positive charge) + electrons (negative charge)

Atomic number = number of protons in the nucleus = number of electrons (atoms are neutral - they have no overall charge)

have an electric charge of -1.6022 x 10-19 Coulomb and a mass of 9.11 x 10-31 kg
nuclear particle with a positive charge equal to that of an electron (+1.6022 x 10-19 Coulomb) and a mass of 1.6726 x 10-27 kg
particle in the nucleus, has about the same mass as a proton but no charge
mass number 
total number of protons and neutrons in the nucleus
particular nucleus characterized by atomic number (subscript) and mass number (superscript), e.g. 12C6 is an isotope of carbon with 6 protons and 6 neutrons in the nucleus
atoms with the same atomic number but different mass numbers (same number of protons, same number of electrons but different number of neutrons)