23 terms

Chemistry Chapter 4

2 Theories of Matter
Continuous: Aristotle
Discontinuous: Democritus; world was made up of empty space and tiny particles called atoms, which are indivisible
"Father of modern chemistry" responsible for the law of conservation of mass
Law of Definite Proportions: for a substance the elements are always in the same ratio by mass
Dalton's Atomic Theory (1803)
1. Matter is composed of atoms that cant be broken down
2. All atoms of the same element are alike
3. Atoms of different elements are different
4. Atom can combine in different ratios to form compounds

Atom was an empty circle
noted under comstant comditions volumes of gas reactants and products were in small whole # ratios
Avagrado's Hypothesis
Equal volumes of gases under the same temperature and pressure have equal number of molecules
William Crooke (1870's)
developed the Crooke's Tube or the Cathode Ray Tube
J.J. Thomson (1897)
discovered electrons; placed the cathode ray tube in an electric field which caused the rays to bend toward the positive plate, and away from the negative plate; concluded rays were negatively charged
J.J. Thomson (1987)
e/m charge to mass ratio of an electron
"oil drop experiment" determined the charge of electrons
1.60 x 10^-19 columb
mass of electron 9.11 x 10^-28 g
Electron Mass
Rutherford "Gold Foil Experiment" (1911)
Alpha particle- helium nucleus
Came up with idea of an atom with a positiveky charged nucleus
discovered protons
Chadwick (1932)
discovered Neutrons
Roentgen (1895)
discovered x-rays
a combination of rays and particles by spontaneous breakdown of atoms' nuclei
Becquerel (1896)
discovered radioactivity by using Uranium rocks. The rocks in a dark drawer caused image on film
Ways to detect radiation (3)
Gieger Counter
Rutherford (before 1909 experiment)- discovered 3 tupes pf radiation
Beta (high energy electrons)
Gamma Ray energy
Bohr (1913)
modified Rutherford's model
proposed electrons were located in energy levels with a positive nucleus
atoms of the same element, with same # of protons but different # of neutrons
Mass Number
total number of protons and neutrons
Atomic Number
# of protons (measured by Mosely)