This document provides an overview of the history and development of the atomic theory. It discusses early Greek philosophers like Democritus who proposed that all matter is composed of indivisible atoms. Later, scientists like John Dalton developed atomic theory further by proposing that atoms are tiny, indivisible particles that combine to form all substances. The document then outlines evidence for subatomic particles like J.J. Thomson's discovery of electrons and Rutherford's discovery of the nucleus. It defines key subatomic particles like protons, neutrons, and electrons and how they combine to form different atoms and isotopes.

1. INSIDE OUTINSIDE OUT
Module 2:Module 2:

2. What is anWhat is an
Atom?Atom?
What is anWhat is an
Atom?Atom?

3. TIMELINTIMELIN
E OFE OF
ATOMATOM

5. DEMOCRITUSDEMOCRITUS
(460 B.C. – 370 B.C.)(460 B.C. – 370 B.C.)
1.All matter composed of atoms in1.All matter composed of atoms in
void.void.
2.Atoms were indivisible &2.Atoms were indivisible &
indestructible.indestructible.
3.Properties of atom differ in shape,3.Properties of atom differ in shape,
arrangement and sizes.arrangement and sizes.
4.Shape of atom determined4.Shape of atom determined
the substance properties.the substance properties.

7. All matter
is made up
of 4 basic
substance
s.
All matter
is made up
of 4 basic
substance
s.

8. EVIDENCE FOR ATOMSEVIDENCE FOR ATOMS

9. JOHN DALTONJOHN DALTON
(1766 – 1844)(1766 – 1844)
 He developed a theory to explain why theHe developed a theory to explain why the
elements in a compound always join in the sameelements in a compound always join in the same
way.way.
 He proposed explanations for many of the knownHe proposed explanations for many of the known
laws describing the behaviour of matter.laws describing the behaviour of matter.
 Dalton’s theory states “All matter is made up ofDalton’s theory states “All matter is made up of
individual particles called atoms, which cannot beindividual particles called atoms, which cannot be
divided”.divided”.

10. DALTON’S THEORYDALTON’S THEORY
The main points of Dalton’s theory are asThe main points of Dalton’s theory are as
follows.follows.
All matter is composed of tiny, indivisibleAll matter is composed of tiny, indivisible
particles called ATOM.particles called ATOM.
All atoms of an element have identicalAll atoms of an element have identical
properties.properties.
Atoms of two or more elements can combineAtoms of two or more elements can combine
in constant ratios to form new substances.in constant ratios to form new substances.
In chemical reactions, atom join together orIn chemical reactions, atom join together or
separate from each other but not destroyed.separate from each other but not destroyed.

11.  Law of Conservation of Matter
“Atoms are neither created nor destroyed in any chemical
reaction”.
 Law of Conservation of Mass
“Atoms are separate, join or rearrange during a chemical
reaction but remain unchanged. Therefore, there will be
no change in mass. “
 Law of Definite Composition
“Atoms of different elements can physically mix together
of chemically combine with one another in single whole
number ratios to form compounds”.

12.  proposed by
John Dalton in
1804
 this theory
proposed that
matter was
composed of
small, spherical
particles

13. EVIDENCE FOREVIDENCE FOR
SUBATOMIC PARTICLESSUBATOMIC PARTICLES

14. J.J. THOMSONJ.J. THOMSON
1856-19401856-1940
 Discovered electron 1897 –Discovered electron 1897 – Cathode RayCathode Ray
ExperimentExperiment
 ““Plum PuddingPlum Pudding” model 1904” model 1904
Electrons in aElectrons in a soupsoup of positive chargesof positive charges
 DiscoveredDiscovered isotopesisotopes 1913.1913.
 Thomson’s experiments provided the firstThomson’s experiments provided the first
evidence that atoms are made of evenevidence that atoms are made of even
smaller particles.smaller particles.

16. DISCOVERY OF THEDISCOVERY OF THE
NUCLEUSNUCLEUS

17.  Nucleus Theory 1910
 “alpha particle gold-foil”
experiment.
 Rutherford’s model states “All of
an atom’s positive charge is
concentrated in its nucleus.”
 An atom’s mass is mostly in the
nucleus.
 He coined the word “Proton” for
the smallest unit of positive
charge in the nucleus.

18. Alpha Particle Experiment

19. SUBATOMICSUBATOMIC
PARTICLESPARTICLES

20.  Every Atom has a core called a nucleus.Every Atom has a core called a nucleus.
 The Nucleus is largest part of an atomThe Nucleus is largest part of an atom
(about 99.9% of it’s mass)(about 99.9% of it’s mass)
 Within the nucleus are very small particlesWithin the nucleus are very small particles
called protons and neutronscalled protons and neutrons
 Electrons are in an orbit around theElectrons are in an orbit around the
nucleusnucleus

21.  Discovered by Eugen Goldstein, AnodeDiscovered by Eugen Goldstein, Anode
RaysRays
 Protons are the positively chargedProtons are the positively charged
particles found inside the nucleus of anparticles found inside the nucleus of an
atomatom
 Every element has a unique atomic #.Every element has a unique atomic #.
This # is the amount of protons inside thatThis # is the amount of protons inside that
elements nucleus.elements nucleus.
Example:Example:
Oxygen has an atomic # of 8. How manyOxygen has an atomic # of 8. How many
protons does it have?protons does it have?

22.  Negatively charged particles found orbitingNegatively charged particles found orbiting
around the nucleusaround the nucleus
 Electrons are very small; only aboutElectrons are very small; only about
1/2000th the mass of a proton or neutron1/2000th the mass of a proton or neutron
 Electrons can move between atoms whichElectrons can move between atoms which
causes bonds; this is how newcauses bonds; this is how new
compounds are formed.compounds are formed.

23.  Discovered by James ChadwickDiscovered by James Chadwick
 Neutrons are the other particle foundNeutrons are the other particle found
inside the nucleus of an atominside the nucleus of an atom
 Neutrons have no chargeNeutrons have no charge
 Atoms of a same element may not carryAtoms of a same element may not carry
the same number of neutrons.the same number of neutrons.

26. SHORTHAND NOTATION
Element A Z P N e Charge
Lithium 7 3 3 4 2 +1

27.  Atoms that have the same number ofAtoms that have the same number of
protons, but have different numbers ofprotons, but have different numbers of
neutrons.neutrons.
Examples:Examples:
+
-
+
-
+
-
Hydrogen (Protium) Hydrogen (Deuterium) Hydrogen (Tritium)

29. SEATWORKSEATWORK
ELEMENT charge A Z P N e
Boron 0
Nitrogen 0
Fluorine -1
Neon 0
Magnesium +2
Aluminum +3
Silicon 0
Sulfur 0
Potassium +2
Carbon -2

30. SCIENCE IDEASSCIENCE IDEAS
 Atom is regarded as the smallest, basic unit of matter.Atom is regarded as the smallest, basic unit of matter.
Even if it is the basic unit of matter, it is still composed ofEven if it is the basic unit of matter, it is still composed of
parts.parts.
 The parts are the electrons (-), protons (+), and neutronsThe parts are the electrons (-), protons (+), and neutrons
(0).(0).
 An atom has equal number of protons and electrons. ThisAn atom has equal number of protons and electrons. This
makes the atom neutral.makes the atom neutral.
 ••Protons and neutrons are relatively heavier thanProtons and neutrons are relatively heavier than
electrons. They compose the nucleus and collectivelyelectrons. They compose the nucleus and collectively
called ascalled as nucleonsnucleons. The mass of an atom is mainly. The mass of an atom is mainly
determined by the mass of the nucleus.determined by the mass of the nucleus.

31. SCIENCE IDEAS:SCIENCE IDEAS:
 Several models have tried to show how the subatomic particles areSeveral models have tried to show how the subatomic particles are
arranged in an atom. Thus far, the accepted model places the protonsarranged in an atom. Thus far, the accepted model places the protons
and neutrons in the center of the atom; or the so-called,and neutrons in the center of the atom; or the so-called, nucleusnucleus. Moving. Moving
rapidly around the nucleus are the electrons.rapidly around the nucleus are the electrons.
 Atomic number, or the number of protons of an atom distinguishes anAtomic number, or the number of protons of an atom distinguishes an
element from the others. This number is the same for all atoms of aelement from the others. This number is the same for all atoms of a
particular element.particular element.
 While the number of protons is fixed for an atom of an element, theWhile the number of protons is fixed for an atom of an element, the
number of neutrons may vary. Atoms having the same number ofnumber of neutrons may vary. Atoms having the same number of
protons but different number of neutrons are referred as isotopes. Theprotons but different number of neutrons are referred as isotopes. The
isotopes are identified through their mass number which is the sum ofisotopes are identified through their mass number which is the sum of
the number of protons and the number of neutrons in an atom.the number of protons and the number of neutrons in an atom.
 Information on the subatomic composition of an element may beInformation on the subatomic composition of an element may be
represented through shorthand notations.represented through shorthand notations.