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