Download Chapter 5 - King Fahd University of Petroleum and Minerals

KING FAHD UNIVERSITY OF
PETROLEUM AND MINERALS
PYP 001
Fall 2012 (Term 121)
Chapter 5
The Atom
5.2: Improvements to the
Atomic Model
Rutherford Theory: failed in describing the position
of electrons in an atom.
Bohr’s Atomic Model,
 Electrons revolve around the nucleus at orbits with
fixed orbits energy level with fixed distance from the
nucleolus.
 Electrons could not exist between energy levels.
 Electrons don’t loose energy while travelling in the
same energy level.
Planck’s theory: Energy exists in tiny packets.
• What happen when Electron absorbs a certain
amount of energy?
5.2: Improvements to the Atomic Model
Fig 5.8
5.2: Improvements to the Atomic Model
Fig 5.9
Emission Line Spectrum:
The narrow slits of light that released when
exciting Hydrogen gas by high electric voltage.
5.2: Improvements to the Atomic Model
Bohr’s Evidence
• Hydrogen Spectrum was experimental evidence
that supports his atomic model.
• The amount of energy released from the electron
while coming back
to lower energy
level determines
the wavelength of
emitted light.
5.2: Improvements to the Atomic Model
Principal Energy Levels and Sublevels
Bohr suggested that :
• The principal energy levels may have sublevels
( s, p, d and f ).
•
The number of energy sublevels depends on the
principal energy level.
 1st principal energy level has one sublevel , 1s
 2nd principal energy level has two sublevels , 2s and
2p.
 3rd principal energy level has three sublevels , 3s, 3p
and 3d.
 4th principal energy level has four sublevel , 4s,
4p,4d and 4f
5.2: Improvements to the Atomic Model
Energy Sublevel
Number of electrons
(e)
s
p
d
f
2
6
10
14
5.2: Improvements to the Atomic Model
Chadwick’s Contributions, 1932
• One final problem remained, "short of the actual
mass of an atom”
• Neutrons : particles inside the nucleolus with no
electric charge.
• Mass of Neutrons
is slightly greater
than the mass of
protons. ( 1.6749
x 10-24 g)
5.2: Improvements to the Atomic Model
Modern Atomic Theory
Heisenberg, 1927
• Its impossible to know both the exact position and
exact velocity of an electron in the same time.
• Electron Cloud: the region around the nucleus in
which the electrons are likely to exist at any
specific time.
5.3: Properties of Subatomic
Particles.
Subatomic Particles
Particle
Symbol
Location
Charge
electron
e-
Outside nucleolus
-1
proton
p
Inside nucleolus
+1
neutron
n
Inside nucleolus
0
5.3: Properties of Subatomic Particles.
Atomic Size:
• Described in a very small unit “nanometer” , 10-9.
• AVG Atom diameter is about 0.2 nm.
• We can get an image of an atoms through a device
called : scanning tunneling microscope.
5.3: Properties of Subatomic Particles.
Atomic Number:
• The number of protons in the nucleolus is known
as “atomic number”.
• Every element has a unique atomic number.
• Example: atomic number for Au is 79, He is 2.
Isotopes :
• Atoms of the same element that have a different
number of neutrons in their nuclei are called
“isotopes”.
• “H” has two stable isotopes protium ( 1p, 0 n) and
deuterium (1p, 1n), one unstable isotope tritium
(1p, 2n).
5.3: Properties of Subatomic Particles.
5.3: Properties of Subatomic Particles.
Mass Number
• The total number of protons and neutrons in the
nucleus of an atom is called “mass number”.
• Atomic notation :
Mass number
 Fluorine
Atomic number
•
Number of p =
• Number of e =
• Number of N=
• Also you can write it as ( Fluorine-19).
5.3: Properties of Subatomic Particles.
Atomic Mass:
• (amu) : atomic mass unit is the unit that used to
describe atomic masses.
• 1 amu= 1/12 of the mass of carbon-12 atom.
• The atomic mass of an element is the weighted
average of all naturally occurring isotopes.
• Example: calculating atomic mass of Carbon:
 C-12 : 12.00000 amu x ( 98.89%) = 11.87 amu
 C-13 : 13.00335 amu x ( 1.11%) = 0.144 amu.
 Total = 11.87+0.144 = 12.01 amu
Summary:
• 5.2: Improvements to the Atomic Model
• Bohr proposed a model of the atom that suggested that
electrons orbit the nucleolus in discreet energy levels.
• Chadwick discovered the neutron, which is a subatomic
particle that is eclectically neutral.
• Acceding to the modern theory of the atom the specific
locations of electrons can’t determined. Instead a region
in which they are likely to exist, called an electron cloud,
can be described.
• .
Summary:
• 5.3: Properties of Subatomic Particles.
• Protons, neutrons, and electrons are described as
subatomic particles. Protons and neutrons make up the
nucleus of an atom. Electrons are located outside the
nucleus.
• The atomic number of an atom is the number of protons
in the nucleus.
• The sum of the numbers of protons and neutrons in an
atom’s nucleus is the atom’s mass number.
• Two atoms of the same element with different numbers of
neutrons are known as isotopes. Each isotope exists
naturally in a different abundance, so the atomic mass of
an element is calculated as weighted average.