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Dalton
Five Key Points:
1. Atoms are building blocks of matter.
2. Atoms are indivisible.
3. Atoms of the same element are identical.
4. Atoms of different elements are different,
5. Atoms unite in small, whole # ratios to form compounds.
He also discovered the partial pressure of gases. -
J.J. Thomson
Discovered electron. Atoms of electricity are surrounded by a soup of positive charge to balance electrons negative charge. "plum pudding model"-negatively charged electrons embedded in a ball of positive charge.
Cathode Ray Experiement
-led to discovery of electrons -
Rutherford
Found nucleus. Declared J.J. Thomson's "plum pudding model" incorrect. An atom os made up of subatomic particles. Much of an atoms charge is concentrated in a tiny volume at the center of the atom; nucleus has nucleons. Positive charge-proton. Negative charge-neutron.
Gold Foil Experiement
-aimed alpha particles at gold foil, most particles passed through, a few were deflected, some bounced back
=most of atom is empty space (most went through) and nucleus is positive (bounced back) -
Bohr
Small, positively charged nucles surrounded by electrons that travel in circular orbits around the nucleus. -
Chadwick
Discovered neutron. Neutrons play key role in nuclear fission (the splitting of atoms). Divided nucleus into protons and neutrons. -
Modern Model
Atom has electrons in waves or clouds that surround the nucleus. Electron cloud model.
