Unit 2 – Atoms, Elements, & Compounds This unit will cover portions of chapters 14, 15, & 16
Atomic Time Line The next series of slides gives you a brief history of we have come to understand the structure of the atom. Like the lab yesterday, we cannot see what is inside.
Leucippus & Democritus – 400 BC First definition of the atom. The smallest part of a thing, that still is that thing. Examples.
John Dalton – Early 1800s Famous for his atomic theory. 1. Each element is made of atoms. 2. All atoms of an element are identical. 3. Atoms of different elements have different properties such as mass and density. 4. Atoms cannot change during a reaction. 5. Compounds are formed from two or more atoms. 6. Compounds are defined by proportions.
John Dalton – Early 1800s Dalton’s picture of the atom? Very small spheres that were solid.
J.J. Thomason Discovered the electron by accident.accident We can conduct this experiment today. We have to review a bit of atomic interactions. + and + - and – + and –
J.J. Thomason Thomason’s picture of the atom? Plum pudding model or today?
Hantaro Nagaoka Figured out that electrons are moving around the center of the atom, like planets do around the sun.
Hantaro Nagaoka Planetary model
Ernst Rutherford Gold Foil ExperimentExperiment
Ernst Rutherford Gold Foil Experiment Results
Ernst Rutherford Conclusion Atom is mostly empty space. What is at the middle, must be positive. Discovered the proton and named the nucleus.
Neils Bohr Electrons move in energy levels. When an electron moves between energy levels, it gives off some energy, a.k.a., light. Each element has a unique display of colors.
Neils Bohr
James Chadwick Saw that atoms were twice as heavy as they should be. p’se’sn’s charge mass
James Chadwick Atomic Models – always 3D
Modern Picture of the Atom The atomic cloud