2. ATOMIC STRUCTUREATOMIC STRUCTURE
Learning objectives:Learning objectives:
1.1. To know about the fundamental particles of matter.To know about the fundamental particles of matter.
2.2. To know about the subatomic particles.To know about the subatomic particles.
3.3. To know about the classical and modernTo know about the classical and modern
postulates and theories about the structure ofpostulates and theories about the structure of
atom.atom.
4. 1.2 The difference between the1.2 The difference between the
Three states of matterThree states of matter
1.1. In gases the fundamental particlesIn gases the fundamental particles
are found to be most loosely heldare found to be most loosely held
due to the presence of very weakdue to the presence of very weak
force of attractionforce of attraction
2.2. In liquids the fundamental particlesIn liquids the fundamental particles
are found to be loosely held due toare found to be loosely held due to
the presence of some weak force ofthe presence of some weak force of
attraction.attraction.
3. In solids the fundamental particles3. In solids the fundamental particles
are found to be tightly held due toare found to be tightly held due to
the presence some strong force ofthe presence some strong force of
attraction.attraction.
Note:
The word fundamental particles denotes atoms or molecules. In element it denotes
atoms, while in compounds it denotes molecules.
LiquidsLiquids
GasesGases
SolidsSolids
5. 1.3 What are the fundamental1.3 What are the fundamental
particles of matter (atoms)?particles of matter (atoms)?
An atom is the smallest fundamentalAn atom is the smallest fundamental
particle of an element that can existparticle of an element that can exist
independently and retain all itsindependently and retain all its
chemical properties.chemical properties.
In other words atoms are buildingIn other words atoms are building
blocks of all the three forms of theblocks of all the three forms of the
matters.matters.
Democritus
6. 1.4 Four Element Theory1.4 Four Element Theory
Plato was an atomistPlato was an atomist
Thought all matter wasThought all matter was
composed of 4composed of 4
elements:elements:
– Earth (cool, heavy)Earth (cool, heavy)
– Water (wet)Water (wet)
– Fire (hot)Fire (hot)
– Air (light)Air (light)
– Ether (close to heaven)Ether (close to heaven)
‘MATTER’
FIRE
EARTHAIR
WATER
Hot
Wet
Cold
Dry
Relation of the four elements and the four qualities
plato
7. AnaxagorasAnaxagoras (Greek, born 500 B.C.)
–Suggested every substance had its own kind of “seedsseeds” that clustered together to
make the substance, much as our atoms cluster to make molecules.
1.6 Some Early Ideas on Matter1.6 Some Early Ideas on Matter
EmpedoclesEmpedocles (Greek, born in Sicily, 490 B.C.)
–Suggested there were only four basic seeds – earth, air, fire, and water– earth, air, fire, and water. The
elementary substances (atoms to us) combined in various ways to make
everything.
DemocritusDemocritus (Thracian, born 470 B.C.)
–Actually proposed the word atomproposed the word atom (indivisible) because he believed that all
matter consisted of such tiny units with voids between, an idea quite similar to
our own beliefs. It was rejected by Aristotle and thus lost for 2000 years.
AristotleAristotle (Greek, born 384 B.C.)
–Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements– heat, cold, dryness, moisture – as basic elements
which combined as shown in the diagram (previous page).
Hot + dry made fire; hot + wet made air, and so on.
8. The GreeksThe Greeks
History of the AtomHistory of the Atom
Not the history of atom,Not the history of atom,
but the idea of the atombut the idea of the atom
In 400 B.C the GreeksIn 400 B.C the Greeks
tried to understandtried to understand
matter (chemicals) andmatter (chemicals) and
broke them down intobroke them down into
earth, wind, fire, and air.earth, wind, fire, and air.
Democritus and LeucippusDemocritus and Leucippus
Greek philosophersGreek philosophers
∼∼
Leucippus
Democritus
9. Greek Model
• Greek philosopher
• Idea of ‘democracy’
• Idea of ‘atomos’
– Atom= ‘indivisible’
– ‘Atom’ is derived M
• No experiments to support
idea
• Continuous vs. discontinuous
theory of matter
Democritus’s model of atom
No protons, electrons, or neutrons
Solid and INDESTRUCTABLE
Democritus
“To understand the very large,
we must understand the very small.”
10. Alchemy
• After that chemistry was
ruled by alchemy.
• They believed that that
could take any cheap
metals and turn them into
gold.
• Alchemists were almost
like magicians.
– elixirs, physical immortality
11. Alchemy
. . . . .. . . .. . .. ..
GOLD SILVER COPPER IRON SAND
Alchemical symbols for
substances…
transmutation: changing one substance into anot
her
In ordinary chemistry, we cannot transmute elements.
∆
12. 1.4 Dalton’s Atomic theory
Postulates of Dalton’s Atomic theory:
• All matter consist of tiny particles.
• Atoms are indestructible and unchangeable.
• Elements are characterized by the mass of
their atoms
• When elements react, their atoms combine in
simple numerical ratio.
• When elements react their atoms sometimes combine in more
simple whole
number ratio.
John Dalton
13. Atom
1.5 Dalton’s model of the atom
A. Atom has no
nucleus.
B. Atom is solid and
Indivisible.
14. 1.5 Thomson model of the atom.
(Plum-pudding model)
In 1910 William Thomson proposed
the Plum-Pudding model.
-- Negative charged electrons were
Embedded Into a positively charged
electron cloud.
J.J. Thomson
+
- -
- -
-
- -
Positively charged
nucleus
Negatively-charged
electrons
15. 1.6 Rutherford model of an Atom
(The modern view of the atom was developed by Ernest Rutherford)
1. In the early twentieth century, Rutherford showed that most
of an atom’s mass is concentrated in small positively
charged region called the nucleus.
2. Atom is almost empty.
3. Nucleus has positive charge.
4. Electron float around Nucleus.
Ernest Rutherford
16. Bohr model of an atom
(planetary model)
After Rutherford’s discovery Neils Bohr proposed that
electrons travel in definite Orbits around the nucleus.
Particles in the atom.
Electrons- Negative charge.
Located out side the nucleus.
Proton- positive charge.
Located inside the nucleus.
Neutron- positive charge
Located inside the nucleus.
Neils Bohr
18. Daltons Atomic Theory
• Dalton stated that
elements consisted of tiny
particles called atoms
• He also called the
elements pure
substances because all
atoms of an element
were identical and that in
particular they had the
same mass.
