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Chapter 2

CH-1010 Chapter Notes - Chapter 2: J. J. Thomson, Cathode Ray Tube, Ernest Rutherford

Course Code
Laura Lanni

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Chapter 2
Important people to know for test
John Dalton
J.J. Thomson
R.A. Millikan
E. Rutherford
2.1 The Rutherford Model of atomic structure
Subatomic Particles: neutrons, protons, and electrons in an atom
oDiscovered by Joseph John Thomson
Joseph John Thomson: Cathode ray tube
Cathode ray: streams of electrons emitted by the cathode in a partially
evacuated tube
oElectrons: a subatomic particle
Discovered by Thomson
Robert Millikan: oil drop experiment
omolecule/ion: loses electrons and loses negative charge
one less electron on the molecule makes it more positive
oMolecular ion: an atom or molecule that has a positive or negative
The nitrogen ion becomes positive.
Note: charges here on the right add up to zero (+1
charge + -1 charge= 0)
An atom may lose more than one electron
oCations: atoms that lose 2,3 or 4 electrons
Positively charged ions
“Cats Tear”
Charges= 2+, 3+, 4+
oAnions: atoms or molecules that gain electrons
“Ants build”
negative charged ions
gain 1 electron= 1- gain 2 electrons= 2-
osame charge: repel
odiff charge: attract
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Radioactivity: spontaneous emission of high energy radiation and particles
by radioactive materials
Ernest Rutherford: Gold foil experiment
oBeta () particles: a radioactive emission that is a high energy
Negatively charged
oAlpha() particle: radioactive emission with a charge of 2+ and a
mass equivalent to that of a helium nucleus
Positively charged
oProton: positively charged subatomic particle
Alpha particle= 4 protons
Assumption made by Ernest Rutherford
oNeutrons: electrically neutral subatomic particles
Atomic mass unit (amu): unit used to express the relative masses of atoms
and subatomic particles
o1 amu= 1/12 mass of a carbon atom
John Dalton: Atomic theory
o4-part atomic theory
Elements are composed of tiny particles called atoms
All atoms of one element are identical; atoms of different
elements are distinguishable
Compounds are made of more than one element. Ratio of
atoms of 2 elements in a compound is always an integer or
simple fraction.
Mass is conserved in a chemical reaction. (atoms are not
created or destroyed, just rearranged)
oDaltons: a unit of mass is equal to 1 atomic mass unit
1 amu= Kg
2.2 Nuclides and their symbols
isotopes: atoms of an element containing the same number of protons
but DIFFERENT number of neutrons
oneutrons change here
nuclide: any atom of any element that has a particular number of
neutrons in its nucleus
Element: matter composed of atoms all having the same number of
protons in their nuclei
Atomic number (Z): number of protons
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Nucleons: neutrons and protons
Mass number(A): number of nucleons (neutrons + Protons) in an atom
Generic symbol for nuclide:
oA: mass number. Atomic number. X: element symbol (i.e. He)
oI.e. mass number: 16. Protons/atomic number: 8
2.3 Navigating the periodic table
Periodic table of elements: chart of elements in order of atomic number
Periods: 7 horizontal rows on periodic table
Groups: 18 columns
oSometimes called families
Lanthanides: elements in row with atomic numbers from 58-71
Actinides: elements with atomic numbers b/w 90 and 103
Group 1: Alkali Metals
Elements of Group 1: From Lithium to Francium
oExclude hydrogen
Group 2: Alkaline Earth Metals
From Beryllium to Radium
Form ionic compound with halogens
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