Atomic structure

1. The Structure of
the atom (The
discovery of the
sub-atomic
particles)

2. How do you study something that you
cannot see it?
Similar to how you
might study a gift-
wrapped present,
scientists often study
things that cannot be
seen with the naked
eye.

3. Democritus 460 BC
• Greek philosopher proposes the
existence of the atom.
• His Theory:
All atoms:
• Are small hard particles
• Are made of a single material formed into different
shapes and sizes
• Are always moving, and they form different materials by
joining together

4. Aristotle
• He did not think there
was a limit to the number
of times matter could be
divided.
• He thought that all substances were
built up from only four elements.
• Earth Fire
• Water Air

5. John Dalton 1766-1844
• British chemist
• His Theory:
 All substances are made of atoms
that cannot be created, divided, or
destroyed.
 Atoms join with other atoms to make new
substances.
 Atoms of the same element are exactly alike,
and atoms of different elements are different in
mass and size.

6. Dalton’s Model
•Solid Sphere
Model or Bowling
Ball Model
•Proposed by John
Dalton

7. J.J. Thomson
1856-1940
• English chemist and physicist;
discovered 1st subatomic particles.
• His Theory:
• Atoms contain negatively charged
particles called electrons and
positively charged matter.
• Created a model to describe the atom as a sphere
filled with positive matter with negative particles
mixed in
• Referred to it as the plum pudding model

8. J.J. Thomson’s Model
•Plum Pudding
Model or Raisin
Bun Model
•Proposed by J.J.
Thomson

9. Ernest Rutherford
1871-1937
•New Zealand physicist
discovered the nucleus.
•His Theory:
Small, dense, positively charged particle
present in nucleus called a proton
Electrons travel around the nucleus, but
their exact places cannot be described.

10. Rutherford’s Model
•Nuclear
Model
•Proposed by
Ernest
Rutherford

11. Neils Bohr 1913
•Danish physicist; discovered
energy levels.
•His Theory:
Electrons travel around the nucleus in
definite paths and fixed distances.
Electrons can jump from one level to a
path in another level.

12. Bohr’s Model
• In Bohr’s model, electrons
move with constant speed
in fixed orbits around the
nucleus, like planets
around a sun.
• Bohr proposed that electrons
move in paths at certain
distances around the nucleus.
• Electrons can jump from a path
on one level to a path on
another level.

13. Erwin Shrodinger 1924
• Austrian physicist; developed
the electron cloud model.
• His Theory:
The exact path of electrons cannot be
predicted.
The region referred to as the electron cloud,
is an area where electrons can likely be
found.

14. Erwin Shrodinger’s Model
•Electron Cloud
Model
•Proposed by
Erwin
Schrodinger

15. James Chadwick 1932
•English physicist; discovered
neutrons
•His Theory:
Neutrons have no electrical charge.
Neutrons have a mass nearly equal to the
mass of a proton.
Unit of measurement for subatomic
particles is the atomic mass unit (amu).

16. Modern Theory of the Atom
• Atoms are composed of three main subatomic particles: the
electron, proton, and neutron.
• Most of the mass of the atom is concentrated in the nucleus
of the atom.
• The protons and neutrons are located within the nucleus,
while the electrons exist outside of the nucleus.
• In stable atoms, the number of protons is equal to the
number of electrons.

17. Virtually all of an atoms mass is contained
within the dense nucleus. Every atom is
mostly empty space!
Atomic Structure

18. • The type of atom is determined by the
number of protons it has.
• The number of protons in an atom is equal
to the atomic number.
• The sum of the number of protons and
neutrons in a particular atom is called the
atomic mass.
• Valence electrons are the outermost
electrons.

19. Most atoms have this basic structure of 3
particles:
Subatomic
Particle
Symbol Location Charge
Electron e In space surrounding nucleus -1
Proton P Inside the nucleus +1
Neutron N Inside the nucleus 0
Atomic Structure

20. The table below summarizes the properties
of these subatomic particles.
Properties of Subatomic Particles
Particle Symbol
Relative
charge
Relative mass
(mass of proton = 1)
Actual mass
(g)
Electron e– 1– 1/1840 9.11  10–28
Proton p+ 1+ 1 1.67  10–24
Neutron n0 0 1 1.67  10–24

21. Atomic Number
Atomic Number
• The atomic number of an element is the
number of protons in an atom of that element.
• All atoms of any given element have the same
atomic number. Each hydrogen atom has one
proton in its nucleus. Hydrogen is assigned the
atomic number 1.
• Each element has a unique atomic number.

22. Atomic Number and Mass Number
Mass Number
The mass number of an atom is the sum of the
protons and neutrons in the nucleus of that
atom. To find the number of neutrons in an atom,
you need the mass number of the atom and its
atomic number.
The atomic number of aluminum is 13. An atom
of aluminum that has a mass number of 27 has
13 protons and 14 neutrons

23. ATOMICSTRUCTURE
Nucleus
Electron
Orbit
EnergyLevels

24. ATOMIC STRUCTURE
the number of protons in an atom
neutrons in an atom
He
2
4Atomic mass
the number of protons and
Atomic number
number of electrons = number of protons

25. 4
O
16
8
chemical symbol
massnumber
(nucleonnumber)
proton number
(atomic number)
P=E
No. of
protons=no.
of electrons
atomic number (proton number) is thenumber of
protons in anatom.
Eachoxygen atom has8 protons.
Asthe number of electrons is equal to the number of
protons in an atom, eachoxygen atom contains 8
electrons.
Mass=P+N
mass number is the totalnumber
of protons and neutrons in an
atom.
Number of neutrons inthe
oxygen atom is: 16 – 8 =8.
Interpreting ChemicalSymbol

26. Definition ofIsotopes
Isotopes are atoms of the same
element which contains thesame
number of protons but different
number of neutrons.

27. Isotopes
16
8
mass
number
proton
number
Oxygen-17 Oxygen-18
O O O
17 18
8 8
Oxygen-16
n = 8 n =17– 8
= 9
n =18– 8
=10

28. Isotopes
Isotopes have the samechemical
properties but slightly different
physical properties

29. element have theQ. Do all isotopes of the same
same mass?