Atomic Theory
Standard 2.12
WARM UP:
1. WRITE YOUR OWN STORY
DESCRIBING WHAT AN ATOM IS.
2. LEARN THE NAMES OF
C, Ag, Ne, F, Cr, Fe
3. WRITE DOWN THE ATOMIC
NUMBER OF THE FIRST 12
ELEMENTS AND THEIR SYMBOL.
The Small of It
• This history of the
atomic theory will
provide you with the
tools to draw a model
of the atom and be
able to discuss the
theories leading to
the modern concept
of the atomic model.
EARLY CONCEPT OF MATTER
GREEK MODEL OF ATOM
• FIRE
• AIR • PHLOGISTON-
FORCE
• WATER HOLDING
• EARTH MATTER
• ZOE- LIFE TOGETHER.
FORCE-GREEK • ETHER-
IDEA OF SOUL MYSTICAL
ELEMENT IN
SPACE.
Democritus’ Ideas
• IS IT POSSIBLE TO DIVIDE
MATTER FOREVER INTO
SMALLER AND SMALLER
PIECES?
Democritus’ Ideas
REASONED THAT IT WAS
NOT POSSIBLE. YOU
WOULD REACH A PIECE
WHICH YOU COULD NOT
DIVIDE ANY FURTHER-”
ATOM”
Dalton’s Atomic
Theory 1807
ATOMS: COMPOSE ELEMENTS
CANNOT BE DIVIDED OR
DESTROYED.
DALTONS ATOMIC
THEORY
ATOMS ARE:
- b. THE SAME FOR THE
SAME ELEMENT.
- c. DIFFERENT FOR
DIFFERENT ELEMENTS.
- d. ELEMENTS COMBINE IN
DEFINITE RATIOS TO
MAKE COMPOUNDS.
Thomson’s Pudding
Model 1897
• DISCOVERED NEGATIVELY
CHARGED PARTICLE IN A GAS.
HE DETERMINED THE CHARGE
TO MASS RATIO TO BE
1.76 X 108 COULOMBS PER
GRAM. *
Thomson’s Pudding
Model 1897
• SINCE TOTAL CHARGE ON GAS
IS NEUTRAL ATOM MUST BE
MADE OF NEGATIVE
ELECTRONS.
THESE ARE PRESENT IN A
PUDDINGLIKE POSITIVELY
CHARGED MATRIX OR FIELD.
Thomson Pudding
Model
ELECTRONS ELECTRONS
Millikan’s oil drop
experiment 1909
• Succeeded in determining
charge on electron.
• Charge was 1.60 x 10-19
coulomb for one electron. *
CHALLENGE:
* [Find the mass of an electron
using the charge to mass
data and the charge.]
Rutherford’s Nucleus
Model
• ATOMIC BULLETS SHOWED
AN ATOM WAS EMPTY SPACE
HE DISCOVERED A DENSE POSITIVE
CENTER- NUCLEUS
SUGGESTED ATOM HAD POSITIVE
CENTER WITH ELECTRONS
SCATTERED AROUND IT, LIKE A
SOLAR SYSTEM.
RUTHERFORD’S GOLD FOIL EXPERIMENT
Bohr’s Orbit Model
1913
• ELECTRONS MOVE IN ORBITS
AROUND NUCLEUS
• PROPOSED ENERGY LEVELS
LOCATED AT CERTAIN
DISTANCES FROM NUCLEUS
BASED ON STUDIES OF
HYDROGEN’S SPECTRUM.
BOHR MODEL OF ATOM
Second
Energy
Nucleus Level
First
Energy
level
Wave Model Has It All
• SMALL DENSE POSITIVE
NUCLEUS.
• ELECTRONS MOVING IN
REGIONS AT DISCRETE
DISTANCES FROM THE
NUCLEUS CALLED ENERGY
LEVELS.
WAVE MODEL HAS IT
ALL.
• WAVE MODEL IS A
STATISTICAL MODEL. BASED
ON DEBROGLIE’S ‘MATTER
WAVE’
• ELECTRON WAS A MATTER
WAVE- HAD PROPERTIES OF
BOTH PARTICLE AND A WAVE.
Wave Model Of Atom
LOOKS
LIKE A
FAN MOVING
AIR.
YOU CAN ‘T
SEE THE
BLADE
BECAUSE IT’S
JUST A BLUR!
Heisenberg
uncertainty principle
• IT IS IMPOSSIBLE TO
DETERMINE THE POSITION
AND SPEED OF AN ELECTRON
WITHIN THE ELECTRON
CLOUD.
• LOCATION IS BASED ON
PROBABILITY.
Atomic Structure
What Are The Parts Of An
Atom?
A Picture Of The Atom
• DENSE CLOUD OF
NEGATIVELY CHARGED
ELECTRONS SPINNING
IN ORBITALS AT A
GREAT DISTANCE FROM
A NUCLEUS.
What are the features
of the nucleus?
• NUCLEUS- A DENSE
POSITIVELY CHARGED CORE
WITH PROTONS AND
NEUTRONS.
• MOST OF THE MASS OF THE
ATOM IS IN THE NUCLEUS.
Atoms contain three
fundamental particles.
• 3 PARTICLES IN ATOM
– PROTON
– NEUTRON
– ELECTRON
• PROTON –POSITIVELY CHARGED.
• ELECTRON –NEGATIVELY
CHARGED.
• NEUTRON – NO CHARGE.
Atomic Number
• NUMBER OF PROTONS (p)
=ATOMIC NUMBER
• NUMBER OF ELECTRONS (e)=
NUMBER OF PROTONS.
• p = e , or p +e = 0
Why Is An Atom Electrically
Neutral?
• PROTONS’ ELECTRIC
FIELD
IS JUST STRONG ENOUGH
TO BALANCE THE
ELECTRIC FIELDS OF AN
EQUAL NUMBER OF
SPINNING ELECTRONS
Atomic Neutrality
• The sum of positive charges
and negative charges =0
• EXAMPLE: HYDROGEN (p=1)
• p + e = 0 , 1 + (-1) = 0
Atomic mass
• ATOMIC MASS = AVERAGE
MASS OF ALL ISOTOPES OF THE
ELEMENT TIMES THEIR
PERCENT ABUNDANCE.
• H = 1.0079 amu
• C = 12.011 amu
MASS NUMBER.
• MASS NUMBER = SUM OF
PROTONS AND NEUTRONS IN
NUCLEUS OF ATOM.
• SODIUM – Na MASS NUMBER
(A) = 23 = [11 P + 12 N]
Activity
• FIND THE • FIND THE
ATOMIC NUMBER OF
ELECTRONS FOR
NUMBER FOR:
EACH OF THESE
• HELIUM ATOMS AND
• CHROMIUM WRITE THEIR
SYMBOLS. FIND
• SODIUM THEIR MASS
• URANIUM NUMBERS AND
NEUTRON
NUMBERS.
The Sum Of It
• DEMOCRITUS- • RUTHERFORD-
UNDIVIDED NUCLEUS
ATOMS (SOLAR
SYSTEM)
• DALTON-SOLID
• BOHR- ATOM
ATOMS WITH ENERGY
• THOMSON- LEVELS
ELECTRONS IN • WAVE MODEL
A POSITIVE ELECTRONS IN
FIELD ORBITALS
(ELECTRON
THE END
OF
THE SMALL OF IT