Chemistry (Quick Refresher)
Dalton’s Atomic Theory
1. All matter is made up of tiny particles called atoms.
2. Atoms of the same element are chemically alike.
3. Atoms cannot be created, destroyed or subdivided.
4. Atoms combine in small whole number ratios.
5. In chemical reactions, atoms are separated, rearranged, and/or combined.
Atom smallest piece of matter that can still be identified as that matter
What’s in it?
1890s J.J. Thomson
Notified a stream of negatively charged particles emitted from an anode
Realized all had same mass and charge
1909 – Rovert. Millikan
mass of electron is 1/2000 mass of H atom
confirmed negative charge 9.109 x 10 kg (mass of electron)
1. Where does mass of the atom come from
Must be more massive particles in the atom
2. Electrons are negatively charged, but the whole atom is neutral
Must be positive particles somewhere in atom
Particle Symbol Charge Location
Electrons e- -1 Around and outside