Atomic Theory

ATOMIC THEORY DEVELOPMENT OF ATOMIC THEORY

VARIOUS ATOMS AND COMPOUNDS AS DEPICTED IN JOHN DALTON’S A NEW SYSTEM OF CHEMICAL PHILOSOPHY

THOMSON’S CROOKE’S TUBE IN WHICH HE OBSERVED THE DEFLECTION OF CATHODE RAYS BY AN ELECTRIC FIELD

PLUM PUDDING’S ATOMIC MODEL

THE RUTHERFORD’S GOLD FOIL EXPERIMENT

NEIL BOHR’S ATOMIC MODEL

Electron cloud Model or Quantum Mechanical Model

Scientist &  approximate  Date

Name of  Model, Sketch and main idea  of theory

Atom the indivisible particle Democritus    c.300 BC

Atomos (in ancient Greek) means "that which cannot be further broken down into smaller pieces".

Importance  and Improvement  on previous  model Atom as the smallest particle of matter. •Explains

certain natural occurrences such as the existence of elements `

Shortcomings  - Problems or why was it  changed

•Does

not give a scientific view of the atom only a conceptual definition •Does

not talk about subatomic particles (Electrons, Protons, Neutrons)

Explains how atoms combine to form molecules •

The solid  sphere model

Dalton   c.1800

•Explains

chemical Atoms are seen change better than the as solid, Particle Theory indestructible spheres (like •Confirms the billiard balls) basic Laws of Chemistry: Conservation of Mass & definite Proportions

• Does

not include the existence of the nucleus •Does

not explain the existence of ions or isotopes • •Does

not talk about subatomic particles (Electrons, Protons, Neutrons)

The raisin  bun Model or • Infers on the the existence of chocolate chip electrons and cookie model : protons •Introduces

Atoms are the concept of solid spheres the nucleus made-up of a J.J. Thomson solid positive  c.1850 mass (or core) with tiny negative particles embedded in the positive core.

Does not explain the existence of electrons outside the nucleus •

•Does

not talk

about neutrons therefore can't explain radioactivity and the existence of isotopes

• Does

Famous Gold Leaf Experiment

E.  Rutherford

c. 1905 •

proves that the nucleus is positive and the electrons are outside the nucleus.

not place electrons in definite energy levels around the nucleus •Doesn't

First real modern view of the atom

include neutrons in the nucleus

Proposes that the atom is really mostly

•

Electrons in Definite  energy  Levels around the nucleus

It does not explain the shapes of molecules or other abnormalities Fully explains that result ionic and form unevenly covalent bonding shared pairs of electrons Explains the role of valence electrons in bonding

Used atomic spectra to prove that (Neils Bohr) electrons are Bohr-  Places electrons placed in Rutherford in definite energy definite c. 1920 levels orbitals around the 2 e- in the first nucleus. 8 e- in the second 8 e- in the third

•

Quantum Mechanical Model

Modern Theory Many Scientists Contributed. So some of the more famous are: •Schroedinger •Einstein •Luis De Broglie •Max Planck •Frank Hertz •Maxwell •Fermi

or Electron  Cloud Model The analogy here is that of a "beehive" where the bees are the electrons moving around the nucleus in a "cloud" of energy levels.

Advanced Theories wi the behaviour of atoms and their chemical and physical properties in forming new compounds.

Selected properties of the three basic Subatomic Particles Name

Charge

Mas (amu) Mass (g)

Electrons

-1

5.4 x 10 -4

9.1095 x 10 -28

1.00

1.6725 x 10 -24

1.00

1.6750 x 10 -24

Proton Neutron

+1 0

Calculate the number of protons, neutrons, and electrons in each of the ff:  a.  b.

32

23

 c.

19

 d.

35

S16 Na11

F9 Cl17

Isotopes and Atomic Mass Mass no. 1. 35 Chlorine 37

Isotopic Mass

2. Oxygen

15.9949 amu 99.76 16.9991 amu 0.04 17.9992 amu

16 17 18

% Abundance

34.969 amu 75.53 36.966 amu 24.47

0.20

Ave. At. Mass 35.458

15.9993

PERIOD

SCIENTIST

5th Cent.

DEMOCRITUS

MATTER IS COMPOSED OF ATOMOS

1803

JOHN DALTON

ATOMIC THEORY BASED ON THE NATURE OF MATTER

1830

MICHAEL FARADAY

EFFECTS OF ELECTRICITY ON MATTER RESULTED TO THE DISCOVERY OF SUB ATOMIC PARTICLES

ATOMIC THEORY

PERIOD

SCIENTIST

1880

WILLIAM CROOKES

1896

EUGEN GOLDSTEIN

1897

JOSEPH JOHN THOMSON

ATOMIC THEORY STUDIED ATOMIC STRUCTURE USING THE ELECTRIC DISCHARGE THROUGH GASES DISCOVERED NEW PARTICLES CALLED CANAL RAYS NOW CALLED IONS AN ATOM COULD BE THOUGHT OF A UNIFORM, POSITIVE SPHERE OF MATTER IN WHICH ELECTRON ARE EMBEDED.

PERIOD SCIENTIST

1909

1913

ATOMIC THEORY

ALPHA SCATERRING EXPERIMENT DISCOVERED RUTHERFORD NUCLEUS AS A CENTRAL PART OF ATOM & DISCOVERED FUNDAMENTAL PARTICLE CALLED PROTON. NEILS BOHR PROPOSED THAT AN ATOM IS A MINIATURE SOLAR SYSTEM IN WHICH PLANETARY ELECTRONS REVOLVE AROUND THE SUN WHICH IS NUCLEUS AND ELECTRON HAS A DEFINITE ORBIT KNOWN AS THE ENERGY LEVELS

ERNEST

PERIOD

SCIENTIST

ATOMIC THEORY

1916

ARNOLD

LOWER ENERGY ELECTRON REVOLVED IN CIRCULAR PATH AND HIGHER ENERGY ELECTRON FOLLOW AN ELLIPTICAL PATH AROUND THE NUCLEUS. INTRODUCE THE QUANTUM THEORY.HE POSTULATED THAT RADIANT ENERGY IS EMMITTED BY ATOMS & MOLECULES IN SMALL DISCRETE AMOUNTS (QUANTA)

SOMMERFIELD

1900

MAX PLANK

PERIOD

SCIENTIST

ATOMIC THEORY

1924

LOIUS DE BROGLIE

ELECTRON HAS DUAL PROPERTIES THAT OF A PARTICLE AND A WAVE.

1924

ERWIN

MECHANICAL CALCULATION OF THE ENERGY OF EACH ELECTRON.THIS MODEL SHOWS THAT ELECTRON OCCUPIES VARIOUS ENERGY LEVELS AND SUB LEVELS AND ORBITALS, THE HISHEST PROBABILITY OF LOCATING AN ELECTRON IS FOUND.

SCHRODINGER

PERIOD SCIENTIST

ATOMIC THEORY

1926

HEISENBERG

UNCERTAINTY PRINCIPLE STATES THAT IT IS IMPOSSIBLE TO DETERMINE SIMULTANEOUSLY THE EXACT POSITION AND THE EXACT MOMENTUM OF A BODY AS SMALL AS AN ELECTRON.

1932

JAMES CHADWICK

HE PROVIDED EXPERIMENTAL EVIDENCE ON THE PRESENCE OF NEUTRONS IN THE NUCLEUS.BOMBARDMENT OF Be WITH ALPHA PARTICLES.