Honors Chemistry Chapter Honors Chemistry Chapter 44
The Structure of the The Structure of the AtomAtom
Early Theories of MatterEarly Theories of Matter
•Atomic TheoryAtomic Theory–DemocritusDemocritus–DaltonDalton
Dalton’s Atomic TheoryDalton’s Atomic Theory
• Based on experimental resultsBased on experimental results
• Matter consists of atomsMatter consists of atoms
• All the atoms of an element are alikeAll the atoms of an element are alike
• Atoms of one element differ from Atoms of one element differ from atoms of other elementsatoms of other elements
• Atoms are indestructible and only Atoms are indestructible and only rearranged during chemical reactions rearranged during chemical reactions
• Atoms can combine in simple, whole-Atoms can combine in simple, whole-number ratios to form compoundsnumber ratios to form compounds
• Pg. 102Pg. 102
Discovery of the electronDiscovery of the electron
•Cathode ray tube (Crooke’s tube)
•Pg. 105 picture•Cathode rays
–Particles with negative charge
JJ Thompson Used cathode ray tube to
determine charge/mass ratio of particles
Identified the particles as electrons
Robert Millikan
Calculated the charge and mass of an electron
“Oil drop” experiment Electron carries exactly one unit of
negative charge Mass is 1/1840 the mass of a
hydrogen atom
• Each electron carries one unit of negative charge
• Proposed “plum pudding” model of the atom
• “chocolate chip cookie” model• Electrons stuck in positive
“dough”
Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment
pg. 107pg. 107
IMPORTANT RESULTS!!!!
New atomic model
•Atom mostly empty space
•Tiny, dense central core – nucleus
Rutherford's gold foil experiment
Contains all the atoms positive charge
Volume of space in which the electrons move huge compared to volume of the nucleus
Book analogy:If an atom had a diameter of
2 football fields, the nucleus would be the size of a nickel!
Don’t you wish you were here right now?
WELL YOU’RE NOT – SO PAY ATTENTION!!!!!!!!!!!!!!!!!!!!!
Atomic Theory song!!!
NUCLEONS – particles located within the nucleus
Protons and neutronsProtons
Positive chargeMass of 1 amu (atomic
mass unit)
NeutronsNeutrons–No charge (neutral)No charge (neutral)–Mass = 1 amuMass = 1 amu
ElectronsElectrons
Located outside the nucleus in Located outside the nucleus in “shells”“shells”
Each carries one unit of negative Each carries one unit of negative chargecharge
Mass 1/1840 amuMass 1/1840 amu
Pg. 106 chart for subatomic Pg. 106 chart for subatomic particlesparticles
Atomic numberAtomic number
Number of protons in the nucleusNumber of protons in the nucleus
Identifies the atom as an atom of a Identifies the atom as an atom of a particular elementparticular element
Determines its position on the Determines its position on the Periodic TablePeriodic Table
Atomic # = #protons = #electronsAtomic # = #protons = #electrons
MASS NUMBER
Number of protons + number of neutrons
Number of neutrons =
mass number – atomic number
Isotopes
Isotope Notation
Pg. 112 Sample and practice
Average atomic mass
Weighted average of the naturally occurring isotopes of that element
Is a decimal because of the existence of isotopes
Pg. 114 Table 4.3 Pg. 116-117 #21-24 Video: How to Calculate an Average Atom
ic Weight.
Periodic Table
Arrangement of elements where the elements are separated into groups bases on a set of repeating properties
Can compare properties of elements based on their position on the table
Arranged according to increasing atomic number
Horizontal rows – periods Vertical columns – groups (families)
• Elements within a group have similar chemical and physical properties
