Molecular physics.
Lecturer: Kedruk Yevgeniya
Tel.: +77770206229
Lecture 1.
Molecular physics.
Introduction.
Elements & Atoms
An atom refresher
• Matter is anything that takes up space and has
mass.
• All matter is made of atoms
• Atoms are the building blocks of matter, sort of
how bricks are the building blocks of houses.
An atom refresher
An atom has three parts:
• Proton = positive
• Neutron = no charge
• Electron = negative
 The proton & neutron are
found in the center of the
atom, a place called the
nucleus.
 The electrons orbit the
nucleus.
Picture from
http://education.jlab.org/qa/atom_model_03.gif
What are elements?
• Elements are the
alphabet to the language
of molecules.
• To make molecules, you
must have elements.
• Elements are made of
atoms. While the atoms
may have different
weights and organization,
they are all built in the
same way.
Graphic from http://education.jlab.org/atomtour/fact2.html
More about Elements..
• Elements are the building
blocks of all matter.
• The periodic table is a list of
all of the elements that can
build matter. It’s a little like
the alphabet of chemistry.
• The periodic table tells us
several things…
Periodic Table
Atomic Number:
Number of protons
and it is also the
number of electrons
in an atom of an
element.
Elements Name
Atomic Mass/Weight:
Number of protons +
neutrons.
Element’s Symbol:
An abbreviation for
the element.
8
O
Oxygen
16
Atom Models
• There are two models of the atoms we will be
using in class.
• Bohr Model
• Lewis Dot Structure
Bohr Model
• The Bohr Model shows
all of the particles in the
atom.
• In the center is circles.
Each circle represents a
single neutron or proton.
Protons should have a
plus or P written on
them. Neutrons should
be blank or have an N.
• In a circle around the
nucleus are the
electrons. Electrons
should have a minus
sign or an e.
-
+
+
-
Electrons have special rules….
• You can’t just shove all of the electrons into the
first orbit of an electron.
• Electrons live in something called shells or
energy levels.
• Only so many can be in any certain shell.
Nucleus
1st shell
2nd shell
3rd shell
Adapted from http://www.sciencespot.net/Media/atomsfam.pdf
Electrons have special rules….
• You can’t just shove all of the electrons into the
first orbit of an electron.
• Electrons live in something called shells or
energy levels.
• Only so many can be in any certain shell.
• The electrons in the outer most shell of any
element are called valance electrons.
So let’s try it….
• How to draw a Lithium atom
• First, look at the Periodic Table
• Second, determine the number of
protons (Look @ the atomic number)
• Then determine the number of
neutrons (Atomic mass – atomic
number)
• Then determine the number of
electrons (Look @ the atomic number)
3
Li
Lithium
7
So let’s try it….
Protons = 3
3
-
Li
+
+
+
-
Lithium
-
Electrons = 3
2 in the 1st shell, 1 in the 2nd shell
7
Neutrons = 4
(7-3=4)
Lewis Dot Structure
• The Lewis Dot
Structure is a bit
different from the
Bohr model.
• It only shows the
element symbol
and it’s outer most
electron shell.
-
-
-
+
+ + +
-
-
+ + +
+
-
-
•
• O ••
••
-
Describing a sample of a gas
• 4 variables are needed to completely describe a
sample of a gas:
• Temperature
• Pressure
• Volume
• Amount (number of moles) of gas
Ideal Gas Law
How can you calculate the
amount of a contained gas when the
pressure, volume, and temperature
are specified?
Ideal Gas Law
Suppose you want to calculate the number of moles (n)
of a gas in a fixed volume at a known temperature and
pressure.
• The volume occupied by a gas at a
specified temperature and pressure
depends on the number of particles.
• The number of moles of gas is directly
proportional to the number of particles.
• Moles must be directly proportional to
volume.
Ideal Gas Law
You can introduce moles into the combined gas
law by dividing each side of the equation by n.
• This equation shows that (P  V)/(T  n)
is a constant.
• This constant holds for what are called
ideal gases—gases that conform to the
gas laws.
P1
 V1
T1  n1
=
P2
 V2
T2  n2
Ideal Gas Law
If you know the values for P, V, T, and n for one set of conditions,
you can calculate a value for the ideal gas constant (R).
P
R=
V
Tn
Ideal Gas Law
If you know the values for P, V, T, and n for one set of conditions, you can
calculate a value for the ideal gas constant (R).
• Recall that 1 mol of every gas occupies
22.4 L at STP (101.3 kPa and 273 K).
P
R=
V
Tn
Ideal Gas Law
If you know the values for P, V, T, and n for one set of conditions, you can
calculate a value for the ideal gas constant (R).
• Recall that 1 mol of every gas occupies
22.4 L at STP (101.3 kPa and 273 K).
• Insert the values of P, V, T, and n into
(P  V)/(T  n).
P
V
R=
101.3 kPa  22.4 L
=
Tn
R = 8.31 (L·kPa)/(K·mol)
273 K  1 mol
Ideal Gas Law
•The gas law that includes all four variables—P,
V, T, n—is called the ideal gas law.
PV=nRT
or
PV = nRT
Ideal Gas Law
When the pressure, volume, and
temperature of a contained gas are
known, you can use the ideal gas law
to calculate the number of moles of the
gas.
•How would you rearrange the ideal gas law to
isolate the temperature, T?
nR
A.
PV
C.
T=
T=
nR
PV
B.
nV
T=
PR
nP
D.
T=
RV
•How would you rearrange the ideal gas law to isolate
the temperature, T?
nR
A.
B.
T=
PV
C.
PV
nV
T=
PR
T=
nR
nP
D.
T=
RV
Key Concepts and Key Equation
•When the pressure, volume, and
temperature of a contained gas are known,
you can use the ideal gas law to calculate the
number of moles of the gas.
Real gases differ most from an ideal gas at
low temperatures and high pressures.
Key Equation: ideal gas law
P  V = n  R  T or PV = nRT
Glossary Terms
• ideal gas constant: the constant in the
ideal gas law with the symbol R and
the value 8.31 (L·kPa)/(K·mol)
• ideal gas law: the relationship PV =
nRT, which describes the behavior of
an ideal gas
BIG IDEA
• Kinetic Theory
• Ideal gases conform to the assumptions
of kinetic theory.
• The behavior of ideal gases can be
predicted by the gas laws.
• With the ideal gas law, the number of
moles of a gas in a fixed volume at a
known temperature and pressure can
be calculated.
• Although an ideal gas does not exist,
real gases behave ideally under a
variety of temperature and pressure
conditions.
Thank you for your attention