Subatomic Particles

Atom

The smallest particle of an element that retains the properties of that element; is electrically neutral, spherical in shape, and composed of protons, neutrons, and electrons

Atomic mass (average atomic mass)

The weighted average mass of the isotopes of that element

Atomic Mass Unit (amu)

One twelfth the mass of a carbon-12 atom

Atomic Number

The number of protons in the nucleus of an atom

Electron

A negatively charged, fast-moving particle with an extremely small mass that is found in all forms of matter and moves through the empty space surrounding an atom's nucleus (has charge of -1)

Isotope

Atoms of the same element with the same number of protons but DIFFERENT numbers of neutrons

Mass number

The number after an element's name, representing the sum of its protons and neutrons

Neutron

A neutral, subatomic particle in an atom's nucleus that has a mass nearly equal to that of a proton

Nucleus

The extremely small, positively charged, dense center of an atom that contains positively charged protons and neutral neutrons

Proton

A subatomic particle in an atom's nucleus that has a positive charge of 1+

Ion

An atom or group of atoms that has a positive or negative charge.

Anion

Negatively charged ion (gained electrons)

Cation

Positively charged ion (lost electrons)

Nuclide symbol

Symbol for a nuclide in which the mass number is written as a superscript and the atomic number as a subscript on the left of the symbol for the element

Democratis

First to discover/ think of the atom, said that all matter consists of very small, indivisible particles called atoms

John Dalton's Atomic Theory

1. elements are made from tiny particles called atoms. 2. all atoms of a given element are identical 3.atoms cannot be subdivided, created or destroyed. 4. atoms combine in simple whole number ratios to form compounds 5. in chemical reactions, atoms are rearranged

JJ Thomson

Used the cathode ray tube to discover electrons

James Chadwick

Discovered the neutron

Ernest Rutherford

Gold foil experiment, discovered nucleus

Robert Millikan

1909 oil drop experiment, calculated the charge of the electron, calculate the mass of electrons

Henry Moseley

Found that all atoms of a given element contained the same number of protons in the nucleus

Cathode Ray Experiment

An experiment that showed that electrons had mass and a charge

Gold Foil Experiment

Conducted by Ernest Rutherford in which alpha particles that were shot at gold foil were deflected when they hit the positive center of gold atoms. The nucleus was discovered as a result of this experiment.

Oil Drop Experiment

A drop of oil was placed in a cylinder with negative and positive plates, the drops were charged using an x-ray. Different waves of xrays let the drops fall at different rates. Determined that the mass of the electron is 9.10 x 10^-28 by Robert Milikan