Unit 1a: Chemistry, The Atom and Atomic Theory

Chemistry

The study of matter, its nature, and the changes it can undergo

Matter

Anything that has mass and takes up space

Mass

the amount of matter in an object

Weight

A measure of the force of gravity on an object

Democritus

Greek philosopher that said all matter is made of tiny particles called "atomos" or atoms

Dalton

Created the first practical model of the atom.

Dalton's Atomic Theory

1) all matter is composed of tiny particles called atoms.

2) all atoms of an element are identical

3) atoms of different elements are different from all others

4) atoms of different elements combine in simple ratios to form compounds

5) during a chemical reaction, atoms are neither created nor destroyed but they join together, or they separate from one another, or they are rearranged.

Crooke

DId experiments involving cathode ray tubes. found some properties of electrons

Crooke's Experiments and Conclusions 1-2

1) in a CRT a glow was created regardless of the element used for the cathode

2) a thin cross was inserted in a CRT , a sharp clear and focused shadow was produced. Cathode rays travel in a straight line and cannot penetrate metal

Crooke's Experiments and Conclusions 3-4

3) a paddle wheel was inserted into the CRT. the paddle was free to move on the track. the wheel moved away from the cathode. Cathode rays exert a force therefore they have mass

4) a magnet was brought near a CRT. Cathode Rays were deflected by the magnet. Cathode Rays have a negative charge.

Thomson's Model of the Atom

Showed that the electron had a much lower mass than the lightest atom. He pictured the atom as a sphere with a positive charge spread uniformly through the atom with electrons embedded in them. The "Raisin Bun" model

Rutherford's Discovery

Gold foil experiment, discovered nucleus

Bohr's Model

planetary model of the atom

Isotopes

Atoms of the same element that have different numbers of neutrons

average atomic mass formula

(mass)(%)+(mass)(%)/100