Topic 1: Particles - Subtopic 2: Atomic Structure
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What were the three key ideas in which John Dalton based his atomic theory on in 1803?
• Matter is made of atoms which are tiny particles that cannot be created, destroyed, or divided • Atoms of the same element are identical, and atoms of different elements are different • Different atoms combine together to form new substances
Describe Thomson’s Plum Pudding Model
• Discovered electron in 1897 • Used cathode-ray tube • Identified electron as negatively charged subatomic particle, hence proving atoms are divisible • Proposed model, depicted electrons spread throughout positively charged material
Describe Rutherford, Geiger and Marsden’s Model
• Fired positively charged alpha particles at thin sheet of gold foil • Expected particles to pass through due to plum pudding model • Some particles scattered at large angles or bounced back • Rutherford proposed atoms have dense, positively charged nucleus containing most of atom’s mass and a lot of empty space with electrons orbiting
Describe The Bohr Model
• Proposed electrons orbit in fixed shells • Each shell had different energy with higher energy further away from nucleus • Solved why atom does not collapse inwards due to attraction between positive nucleus and negative electrons • Led to discovery of proton
What is the size of an atom?
Radius of 1 x 10⁻¹⁰ metres
What is the difference between radius of atom and nucleus?
• Radius of the nucleus about 10 000 times smaller than that of the atom • Extremely small region of space
What is the relative charge and mass of a proton?
Charge: +1 Mass: 1
What is the relative charge and mass of a neutron?
Charge: 0 Mass: 1
What is the relative charge and mass of an electron?
Charge: -1 Mass: 1/1836
What is the atomic number?
• Number of protons/electrons • Symbol is Z • Unique to element • Does not change in chemical reaction
What is the mass number?
• Total number of protons and neutrons • Symbol is A • Collectively called nucleons
What are isotopes?
• Atoms of same element that contain same number of protons but different number of neutrons • Same chemical characteristics as no. of electrons in shells don’t change • Add mass only
What are ions?
• Atom that has a positive or negative electrical charge • Happens when atom gain or lose electrons to become stable changing overall charge Loses electron: Cation Gains electron: Anion