The document discusses the history and development of atomic theory. It covers the following key points: - Greek philosophers first proposed that matter is made of indivisible particles called atoms. Democritus further hypothesized that atoms were tiny, indestructible spheres. - J.J. Thomson's discovery of electrons led to Ernest Rutherford's proposal that atoms have a small, dense nucleus surrounded by electrons. - The arrangement of protons, neutrons, and electrons in atoms, along with their properties, is summarized. The periodic table organizes the elements based on these atomic structures and properties.

1. Atomic Theory

2. Greek Philosophers
•Aristotle
4Elements of matter
-Earth
-Fire
-Air
-Water

3. Matter is made of atoms (cannot be further divided), the word atom
comes from the Greek word “atomos” which means indivisible.
Democritus

4. • Atoms were tiny particles that could not be divided
• John Dalton proposed that an atom is a sphere of
matter that is the same throughout and can’t be seen
by human eyes
• Marble Model

5. • Came up with the idea of the electron negatively charged particle
• Thomson discovered that all atoms contain electrons, which are tiny,
negatively charged particles. Thomson proposed that an atom is a
sphere of positive charge. The electrons are mixed uniformly in the
sphere.
• Cookie Model

6. Ernest Rutherford
• He hypothesized that almost all the mass and all the
positive charge of an atom is concentrated in an extremely
tiny nucleus at the center of the atom.

7. • Thought electrons traveled in fixed paths around the
nucleus called energy levels.

8. Atomic Structure
• Arrangement and number of sub-atomic particles
•Protons
•Neutrons
•Electrons

9. •Center or core of an atom
•Contains 99.9% of the weight of an atom
•Contains protons and neutrons

10. •Positively Charged Sub-atomic particles
•Found in the nucleus
•All protons are a like

11. •Neutrally charged (no charge) sub-atomic particle
•Found in nucleus

12. •They are the negatively charged particles orbiting the
nucleus.
•It is much smaller than the protons and the neutrons .

13. What is the net charge of
the atom ?
• The atom is formed of positively charged proton in the
nucleus and negatively charged electrons in the energy
level ,but they are equal to each other in number ,making
the net charge of the atom “neutral”.
No of positive protons = No of negative electrons

14. • They are charged atoms
• Number of positive protons = Number of negative electrons.
Positive
ion
Negative
ion

15. If the atom lost an electron ,therefore the number of positive protons
are more than the negative electrons making the atom positively
charged
Positive Ion

16. If the atom gained an electron ,therefore the number of negative
electrons
are more than the positive protons making the atom negatively
charged
Negative Ion

17. • Atomic number is the number of Protons in an atom
• All atoms of a particular element have the SAME number of protons (All
Carbon atoms have 6 protons)
• In a neutral atom,
The atomic number =The number of electrons

18. • Also called atomic weight or Mass Number
• Sum weight of protons and neutrons in an atom

19. Calculate the mass number of each of
the following atoms

20. O
8
16
Atomic
number
Mass
number
Symbol
OxygenName
Atomic number= Number of protons= Number of electrons
Mass number= Number of protons + Number of neutrons

21. Calculating Neutrons:
• Mass number = protons + neutrons
so…..
• Neutrons = mass number – protons
What is the number of neutrons of the following atom ?
A
21
45

22. • In 1869 Dimitri Mendeleev was working on a way to
classify elements.
•At the time, more than 60 elements had been
discovered.
•And he arranged the elements according to their
atomic mass
Developing a Periodic Table

23. 100 table The periodic table is
a chart of the
elements arranged
according to their
atomic number in
rows and columns
according to their
physical and chemical
properties.

26. Symbol

27. •The periodic table is a chart of the elements
arranged into rows and columns according to
their physical and chemical properties.
•It can be used to determine the relationships
among the elements.
What is the periodic table?

28. Groups and Periods
- Columns in the periodic table represents “groups”
- There are 18 groups in the periodic table.
- Elements of the same the same group have the same
chemical properties as the all have the same number of
electron/s in the outer most energy levels.

29. - Rows in the periodic table represent “periods”.
- There are 7 periods in the periodic table .
- Elements of the same period have the same number
of energy levels

30. The Periodic Table of Elements

31. Periodic Table
A great deal of information about an element can be gathered
from its position on the period table.
Understanding the organization and plan of the periodic table will
help you obtain basic information about each of the 118 known
elements.

32. Mass Number
Atomic Mass (Mass Number) is the number
…………….
__________
Atom p+ n0 e- Mass #
Oxygen - 8
- 33 42
- 31 15
___ ___ ______
______ ___ ___ ___
______ ___ ______

33. Recall - How are P, N, e- related?
• atomic number = # protons
• # protons = …………….
• # protons + # neutrons = atomic mass
# neutrons = …………….
…………….

34. • How many protons, neutrons and electrons are found in
an atom of Cs?
• _____________
• …………….
• …………….
• Therefore, # Neutrons = …………….
_____________
_____________
55
Cs
133
Example 1

35. Na
Sodium
23
11
___________
___________
___________

36. Example 2
 If an element :Magnesium
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
=_____________
= _____________
= _____________
_____________

37. ATOM
The smallest particle of an element with the same
properties of the element.

38. MOLECULE
The smallest part of a substance made
from more than one atom that binds
together.

39. Let’s Build Some
Molecules

40. Let's start with a couple of Molecules
•Hydrogen Gas H2
H H
•Oxygen Gas O2
O O

41. •Ammonia Gas NH3
H H
H
N
•Water H2O
HH
O

42. Elements
Substance that contains only one kind of atom

43. Compounds-Are substances made of atoms of two or more elements
that are chemically combined.
-The chemical formula of a compound shows the elements
that are in it
-Example:
SiO₂ (sand): It is formed of 1 Silicon atom
2 oxygen atoms

44. -Compounds don’t have the same properties of the
elements forming them
Example:
The ordinary table salt is a compound called NaCl
It is formed of :
1 atom of Sodium and 1 atom of chlorine
Where “Sodium” is a metal

45. • And “Chlorine” is a gas
But when they combine together they give a product of
different properties which is the table salt

46. Howcompoundsareformed?
-Compounds hold together because atoms bond or
attach to one another

47. How atoms can attach or bond with
each other?
They either
Share
electrons
Gain
Or
lose
electrons