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Atomic TheoryAtomic Theory
– The thesis that all elements are composed of tiny, indestructible particles called atoms
– All atoms of the same element are alike and have the same mass
How Small? How Big?How Small? How Big?
If an atom occupied a football field, the nucleus would be like a marble in the center.
Democritus (460 – 370 B.C.)Democritus (460 – 370 B.C.)
All matter is made of small, indivisible particles called “atomos” also know as atoms.
His model was a tiny, hard, uncuttable sphere.
John John DaltonDalton (1766-1844) (1766-1844)
The ratios of the masses of elements in a compound can always be reduced to small whole numbers
Law of Multiple Proportions
DaltonDalton’’s Atomic Theorys Atomic Theory 1) all matter is composed of tiny particles
called atoms 2) the atoms of an element are always
identical while the atoms of different elements are different
3) compounds form when atoms combine; atoms combine in small whole number ratios
4) reactions involve reorganization of atoms; the atoms themselves do not change
DaltonDaltonProposed the “Billiard-ball
model” of the atomHis model was a solid,
indivisible sphere
J.J. J.J. Thomson 1897Thomson 1897Produced a “cathode ray” which was
deflected by a negative electric field
Thus the ray must be made of negative particles (electrons)
Thompson was awarded the 1906 Nobel Prize for his discovery
J.J. J.J. Thomson and CrookeThomson and CrookeSince atoms are neutral, they
must also have a positive areaPlum pudding model
Ernest Ernest RutherfordRutherford (1911) (1911)
Tests Thomson’s Plum Pudding Model by shooting alpha particles through a sheet of gold foil
Ernest Ernest RutherfordRutherford
Nuclear Model of the Atom
Protons were found to be 1836 X the mass of an electron
Charge of proton is +1
James James Chadwick 1932Chadwick 1932Discovered high energy
particles with no charge and the same mass as the proton –
the neutron
Niels Niels BohrBohr (1912) (1912)
Electrons “orbit” the nucleus somewhat like planets orbit the sun
Planetary Model
Arnold Arnold SommerfeldSommerfeld
Expanded the Bohr model
Electrons travel in orbitals, but
the orbitals are not the same shape
-- this leads to the electron cloud model of the atom
Electron Cloud ModelElectron Cloud Model
ERWIN SCHRODINGERERWIN SCHRODINGER
Was awarded the 1933 Nobel Prize for his Electron Cloud Model
His model was based on mathmatical probabilities, not a physical model.
Modern View of the AtomModern View of the AtomTiny nucleus surrounded by
electron “cloud”Nucleus accounts for all of the
massArrangement of electrons
causes different chemical properties
Electron Cloud ModelElectron Cloud Model
Note: Just as no map can equal a territory, no concept of an atom can possibly equal its nature. These models of the atom simply served as a way of thinking about them, though they contained limitations (all models do).
How do we know the identity of an How do we know the identity of an element?element?The number of protons (atomic #)
distinguishes one element from another
Mass NumberMass Number
The total number of protons and neutrons in the nucleus
(protons + neutrons=mass number of an element)
IsotopesIsotopes Isotopes are
atoms that have the same atomic number but a different mass number– Same element– Different numbers
of neutrons in the nucleus
Ordinary Hydrogen
Deuterium
Tritiumproton neutron
Atomic MassAtomic Mass
The average mass of an elementMost elements occur as two or more
isotopes in nature, and therefore have differing atomic masses—this is why the atomic mass is an average, each isotope is figured in to the average
What Can We See?What Can We See?
This is the surface of a platinum-nickel alloy as imaged by a Scanning Tunneling Microscope.
Light colors are closer, black deeper in the surface. The brighter blobs are the Ni atoms. The very large white blobs are surface impurities. Ni has 28 protons and 30 neutrons, which are not distinguishable.
Vienna University of Technology
An Alloy In The Process …An Alloy In The Process …
These are lead atoms working their way into copper to form an alloy.
MetalsMetals
HardShiny – have lusterDuctileMalleableGood conductors of heat and
electricity
NonmetalsNonmetals
DullBrittle solids or gases at room temp.Insulators
MetalloidsMetalloids
They have properties of both metals and nonmetals.
Found on each side of the zig zag line between metals and nonmetals
Alkali Metal GroupAlkali Metal Group
Group 1 or IA (except for H)Most active metal groupSoft, shiny, very reactive with H2O
Wants to lose 1 electron
Alkaline Earth Metal GroupAlkaline Earth Metal Group
Group 2 or IIAHarder than the alkali metalsWants to lose 2 electrons
Transition MetalsTransition Metals
Group 3-12 or IB-VIIIB
HalogensHalogens
Group 17 or VIIAMost active group of nonmetalsWants to gain 1 electron
Noble Gas FamilyNoble Gas Family
Group 18 or VIIIAInertSo stable they do not want to react
with other elements
Periodic LawPeriodic Law
The properties of the elements are periodic functions of their atomic numbers
Henry Moseley-arranged the periodic table by increasing atomic number (# of protons) instead of increasing atomic mass.
Period or seriesPeriod or series
Horizontal rows on the Periodic Table
Groups or FamiliesGroups or Families
Vertical columns on the Periodic Table