SC3 - Atomic Structure ✓

● Used a cathode-ray tube to conduct an experiment ● This discovery identified an error in Dalton’s atomic theory. Atoms can be divided into smaller parts. ● Because the beam moved away from the negatively charged plate and toward the positively charged plate, Thomson knew that the particles must have a negative charge. ● Thomson proposed a model of an atom called the “plum-pudding” model, in which negative electrons are scattered throughout soft blobs of positively charged mat

• Protons and neutrons centred in a nucleus. • Electrons orbiting outside in electron shells.

• All matter is made up of atoms • Atoms are small, hard, spheres cannot be broken down into smaller parts • Atoms cannot be created or destroyed • The atoms in an element are all identical

• Protons: • M: 1 • C +1 • Neutron: • M: 1 • C Neutral (0) • Electron: • M: 1/1835 (negligible) • C -1

James Chadwick

• Most of the alpha particles passed straight through the gold foil.

• Ernest Rutherford shot alpha particles at a sheet of gold foil and predicted that the particles would go through the sheet, but some of them refracted off.

• The number of protons + neutrons in an atom (the mass). • The top number on the symbol for an element.

The number of protons in an atom. the bottom number on the symbol for an element

• Some of the alpha particles were being deflected and very few were bouncing right back. These proved the existence of a small, positively charged, central nucleus.

(M1 x A1) + (M2 x A2) (etc.) ÷ 100 (M=Mass A=Abundance)

• Relative Atomic Mass. • The average mass of the naturally occurring form(s) of an element in relation to a Carbon-12 atom

Two atoms (of the same element) with the same atomic number but different mass numbers (amounts of neutrons)

• It is its relative mass. • There are two isotopes of chlorine, 35 and 37. • Chlorine - 35 is more abundant than 37.

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