Atomic Structure Notes

History of the Atom 1808 John Dalton 1897 Joseph Thomson Matter made of tiny particles called atoms 1897 Joseph Thomson Discovery of electrons using cathode rays 1909 Robert Millikan Discovery of negative charge on electrons 1911 Ernest Rutherford Discovery of nucleus, lots of open space in an atom 1914 Neils Bohr Electrons orbit the nucleus in different shells Modern Atomic Theory

Atom – The smallest particle of an element that retains the chemical properties of that element. Nucleus – Positively charged center of the atom that consisting of protons and neutrons that contain nearly all the atoms mass with a very low volume.

Proton – Subatomic particle of the nucleus that has a positive charge. Neutron – Subatomic particle of the nucleus that has a neutral charge. Electron – Subatomic particle outside the nucleus that has a negative charge.

Proton Neutron Nucleus + N N + Electron - Electron Region

Subatomic Particles Name Charge Weight Proton + 1 amu Neutron N Electron - .0005 amu

Atomic Mass Unit – 1 amu, exactly 1/12 the mass of a carbon-12 atom. Average Atomic Mass – The weighted average of the atomic masses of the naturally occurring isotopes of an element. Isotopes – Atoms of the same element that have different masses.

Atomic Number – The number of protons in the nucleus of each atom of that element. Used to identify elements. Mass Number – The total number of protons and neutrons in the nucleus of an atom. Mass # = Protons + Neutrons Neutrons = Mass # - Protons

Mass Number, Protons, Neutrons and Electrons Element Protons Neutrons Electrons Mass # Hydrogen 1 Carbon-12 6 12 Carbon-14 8 14 Oxygen-16 16 Oxygen-17 9 17

Hyphenated Notation Carbon – 14 Element Mass #

Atomic Number and Mass Notation 14 6 Mass # Atomic # Symbol C

Relation of atomic mass and molar mass Carbon-12 Atomic mass = 12.011 amu Molar mass = 12.011 g/mol The only difference is the units 