Transcript C-4 Atomic Structure

C-4 Atomic Structure
The nucleus and the moving
electrons.
Law of Definite Proportions
• Specific substances always contain
the same elements in the same ratio
by mass.
• Ex. Water is made up of about 2
grams of hydrogen to 16 grams of
oxygen. Therefore we come up with
the formula for water to be H2O.
Law of Multiple Proportions
• The ratio of masses of one
element that combine with a
constant mass of another element
can be expressed in small whole
numbers. The ratio of hydrogen
to oxygen can be different in 2
different compounds.
• Ex. Water = H2O and Hydrogen
peroxide = H2O2.
Atomic Mass
• The proton and neutron are
essentially equal in mass while the
electron is considerable less.
• electron = 9.10953 X 10-28 g
• proton = 1.67265 X 10-24 g
• neutron = 1.67495 X 10-24 g
• Notice the mass of an electron is
about 1800 times lighter than a
proton or neutron.
• The orbiting of electrons around
the nucleus is much like a
satellite orbiting the earth.
• Electrons are continuously giving
off energy thus should slow down
and be pulled in by the nucleus
and the + charge: Just as a
satellite would be pulled into the
earth if it lost energy and slowed
down.
• Electrons never collapse
into the nucleus even
though they are
continuously giving off
energy.
Electromagnetic Radiation
The energy given off by
electrons is called
electromagnetic radiation.
• This energy is not coming off
continuously but in spurts.
• Once the energy comes off it
travels at the speed of light.
(c)
•
c=300,000,000 m/sec
When the energy spurts out it
travels in all directions and is
analogous to ripples in water
when a rock is dropped in
water.
• Therefore we can say that
electromagnetic radiation
(energy) comes off in waves.
• The longer the time between
emissions of EMR from electrons
the further the waves are apart.
The distance between 2
successive waves is called the
energy’s wavelength.
• The more frequently an
electron emits energy, the
higher the number of waves
that come off each second.
The # of waves emitted per
second is called frequency.
• The larger the frequency of emission
of energy, the closer the waves are to
each other or in other words the
smaller the wavelength.
• The product of the wavelength and
frequency is always a constant and
that constant has been found to be
the speed of light. “ wavelength X
frequency = c”
•
lambda X f = c
• The greater the frequency of energy
emission, the more energy you’ll be
bombarded with each second.
Therefore, the frequency determines
the amount of energy coming off an
electron.
• Planck was the first to determine the
equation for energy and frequency.
•
E = h x f
( h is a
constant)
Photons
• Let’s take a closer look at these
waves of energy that are being
emitted by electrons.
• The energy coming off is in
packets or quanta so that waves
would look like:
• These little packets of energy
are called photons.
• These photons eventually hit
some form of matter and are
absorbed thus giving the
matter more energy.
• This energy is absorbed on the
atomic level of the matter (in the
electrons) and thus these atoms
have more energy.
• An atom which has absorbed
energy in this way is called an
excited atom.
• When excited atoms radiate
energy, the radiation must be
given off in photons.
Types of E.M.R.
• We have already decided that EMR
can have different frequencies of
emission.
• The difference in frequencies
determines the type of EMR.
• Types of EMR: x-rays, ultraviolet,
infrared, radio, visible, etc.
• Your eyes are sensitive to certain
frequencies of EMR.---light.
Spectra of Atoms
• Different elements are excited
differently when energy is
added and thus emit energy
differently also.
• This fact can be used to
identify the elements.
• Know the spectrum p.96
Radiation
• There are 3 forms of radiation with the
first 2 being comprised of particles.
– 1. alpha particle-is a helium nucleus
made up of 2 protons and 2 neutrons.
– 2. beta particle-is a high speed electron
from a radioactive nuclei.
– 3. gamma rays-very high energy x-rays
The Hydrogen Atom and the
Quantum Theory
• The electrons travel in many
different orbits around the
nucleus. The smallest of these
orbits is called the ground
state.
• The further out an electron
travels the more energy it has.
• Therefore, an electron at
ground state has the lowest
amount of energy.
• An electron needs to gain
energy to move to an outer
orbit, it gives off energy
when it moves into a closer
orbit.
Atomic Mass
• The proton and neutron are
essentially equal in mass while the
electron is considerable less.
• electron = 9.10953 X 10-28 g
• proton = 1.67265 X 10-24 g
• neutron = 1.67495 X 10-24 g
• Notice the mass of an electron is
about 1800 times lighter than a
proton or neutron.
Average Atomic Mass
• Not all atoms of the same
element have the same mass.
They have a mass that is close to
an average for that element.
• The average mass is calculated
by taking the masses for all the
isotopes of an element and their
relative amount of existence.
• Ex. Hydrogen has an atomic
mass of 1.00797 amu that is
based on 2 isotopes,
deuterium-2amu and
protium-1amu.
• Read & Work the sample on
p.103