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