Download Atomic number

Contributors to Atomic Theory
What was the journey mankind took
To come up with this!?
Proceed with caution
•
The next couple classes will be the most
difficult (conceptually) in the course. Do
not get discouraged. It all makes sense
once you get through it.
Ancient Greece
• Natural
Philosophers tried to
understand Nature
and what everything
is made of, but they
did not do lab
experiments –
they only used logic.
Ancient Greece
– Believed that all
matter was made
from 4 elements:
air, earth, fire,
and water
Fire!
Fire led to the discovery of metals like
copper and iron
Fire led to other discoveries like
building bricks
and making soap
Before you know it chemistry was
everywhere
Democritus
Earliest contributor
Greek
Philosopher
Said that atoms are the smallest
building block of matter.
Coined the term.
460 – 370 BC
“atomos” is Greek for
indivisible
Was known as the laughing philosopher,
even unto death.
ATOM
Alchemy and the Middle Ages
• Even though the idea of ATOMS was
discovered in ancient Greek times, the
idea was rejected, because
nobody
could prove anything
experimentally.
• People continued to believe that all Matter
was made from: earth, air, water, fire.
• Alchemists believed that since
everything is made from 4 elements,
then you could make gold by combining
the elements in a special way.
• For over 1,000 years they tried to make
gold.
THE ALCHEMIST
• Alchemists did NOT turn metals into gold,
but they did learn a lot about how to do
chemical reactions.
• Also, they created a lot of lab equipment
and ideas that chemists would use to
make important discoveries.
Antoine Lavoisier
French chemist during the French Revolution
Father of
1743 - 1794
Modern Chemistry
Calculated the relative masses of then
known elements using Closed containers
Introduced the
Was beheaded
in 1794
TAX
Law of conservation of mass
Joseph Proust
Noted that
Water always contains
11% Hydrogen and
89% Oxygen
E.g.: Water is always 2 H’s for every O
hence:!
1754 - 1826
Developed the Law of Multiple
Proportions:
When 2 elements form
more than one compound,
the elements are always
in small, whole number ratios.
H2O
2
2.1
Law of Multiple Proportions
• CO
and CO2
H2O and H2O2
1g C
1.33g O for
CO
1g C
2.66g O for
CO2
John Dalton
Integrated ideas to introduce the
Theory that all matter contains atoms
5 Postulates of this Theory:
1. All matter is composed of atoms.
2. All atoms of the same element are identical.
3. A chemical reaction rearranges atoms in the
reactants to form products
4. Atoms are not divided, created, or destroyed.
5. Atoms unite in simple ratios to form compounds,
which are 2 or more elements chemically combined.
Dalton was colorblind, and to this day,
“Daltonism” means colorblindness.
1766 - 1844
16 H
+
8O
8 H 2O
2.1
What is the Scientific Method?
• It is the steps someone takes to identify a
question, develop a hypothesis, design and
carry out steps or procedures to test the
hypothesis, and document observations
and findings to share with someone else.
• In other words, it’s a way to solve a
problem.
The Scientific Method (Lyrical Life Science) audio clip
Scientists develop a
question, gather
information and form an
hypothesis.
A key to experiments is
observing what happens and
writing it down.
• Gathering information or
data and documenting it so
it is readable and makes
sense to others is really
important.
Once a scientist completes an
experiment, they often repeat
it to see if they get the same
findings and results.
• This is really what we call
verification, or checking
things out to make sure
everything was valid and
will happen again and
again.
The steps of the Scientific
Method are:
•
•
•
•
•
•
•
Question
Research
Hypothesis
Procedure/Method
Data
Observations
Conclusion
The Scientific Method (Lyrical Life Science) audio
clip
JJ Thomson
Discovered the
Electron,
using the
Cathode Ray Tube Experiment
1856 - 1940
He was able to calculate
ratio of electric charge
to mass of the cathode ray
“Plum Pudding” Model was developed and acclaimed.
Cathode Ray Tube
2.2
Goldstein- Modified Cathode Ray
Tube
• Goldstein used a perforated cathode. A "ray" is produced in the
holes in the cathode and travels in a direction opposite to the
“cathode rays," which are streams of electrons. Goldstein called
these positive rays canal rays because it looks like they are passing
through a canal. In 1907 a study revealed that the particles making
up the ray were not all the same mass. The lightest ones, formed
when there was some Hydrogen gas in the tube, were calculated to
be about 1837 times as massive as an electron. They were protons.
Robert Millikan
1868 – 1953
Discovered the.
Charge of an electron,
using an oil drop experiment
http://www.dlt.ncssm.edu/flashdownloads/structure/OilDropExperiment.ex
Subatomic Particles
• Proton – Charge +1, mass = 1.67 x 10 -24g
• Electron - Charge -1, mass = 9.11x10-28 g
• Neutron – Charge 0, mass = 1.67 x 10-24g
JJ Thomson Chocolate Chip
Cookie Model or Plum Pudding
Model
Ernest Rutherford
Discovered the
NUCLEUS
1871 - 1937
What’s happening up close:
He is also credited with
The discovery of the proton
(1908 Nobel Prize in Chemistry)
 particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron (-)
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
2.2
Rutherford’s Model of
the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
“If the atom is the Houston Astrodome, then
the nucleus is a marble on the 50-yard line.”
2.2
James Chadwick
Discovered the.
NEUTRONS
1891 - 1974
Parts of the Atom
Proton
Goldstein
Modified Cathode rays
Discovered by ____________________ using ________________
The # of protons always =# of electrons in a neutral atom
Mass = 1 amu
So what is a proton made of……….
Protons are made of 3 quarks:
“New realistic quark model”
two “up” and one “down”
of the proton
THEN…
Neutron
Be and alpha particles
James Chadwick
Discovered by __________________ using _____________________.
Mass number- Atomic number =
# of Neutrons
Mass = 1 amu
Neutrons are made
e.g.: How many neutrons are in Co – 59?
of three quarks:
One “up” and two “down”
Mass # = 59
# protons = 27
59 – 27 = 32 neutrons
Electron
Cathode Ray Tube
JJ Thomson
Discovered by _________________ using _____________________.
Mass of an electron:
9.11 X 10-28 grams,
Essentially 0 amu.
Comparing proton to electron masses:
One
proton
Calculating the # electrons:
= # protons in a neutral atom.
# protons - charge if not neutral.
Eg: Mg +2 has
10 electrons
=
1,860
electrons!
Nucleus
Ernest Rutherford
Gold Atoms and Gold Foil Experiment
Discovered by ________________ using ___________________.
Contains most of the atom’s mass
Accounts for next to nothing of its volume.
DO YOU UNDERSTAND?
• How many protons, neutrons, and
electrons in the following:
Fe – 85
p=
n=
e=
Gold
p=
n=
e=
S 2p=
n=
e=
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different
numbers of neutrons(mass numbers) in their nuclei
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
U
(T)
How many protons and neutrons in each isotope?
1 proton, 0 neutrons
1 proton, 1 neutron
1 proton, 2 neutrons
Do You Understand Isotopes?
How many protons, neutrons, and electrons are
14
in 6 C ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are
11
in 6 C ?
6 protons, 5 (11 - 6) neutrons, 6 electrons
Do You Understand Ions?
How many protons and electrons are in
27 3+
13 Al
?
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in
78 234 Al
34 protons, 36 (34 + 2) electrons
?
Quantum Theory and the
Electronic Structure of Atoms
Chapter 2.2 and some of Ch 7
Niels Bohr
Danish physicist. He placed each electron
in a specific energy level.
1885 - 1962
With Rutherford, developed the
Nucleated model of the atom
positive
negative
Adding Electrons to the Model
Materials, when rubbed, can develop a charge
difference. This electricity is called “cathode rays”
when passed through an evacuated tube.
These rays have a small mass and are negative.
Thompson noted that these negative subatomic
particles were a fundamental part of all atoms.
1) Dalton’s “Billiard ball” model (1800-1900)
Atoms are solid and indivisible.
2) Thompson “Plum pudding” model (1900)
Negative electrons in a positive framework.
3) The Rutherford model (around 1910)
Atoms are mostly empty space.
Negative electrons orbit a positive nucleus.
Bohr Model
• In 1913, Niels Bohr placed
each electron in a specific
energy level.
• He proposed that electrons
move in definite orbits
around the nucleus, much
like planets circle the sun.
These orbits, or energy
levels, are located at certain
distances from the nucleus
Bohr - Rutherford diagrams
• To draw the diagram you must know the # of
protons, neutrons, and electrons (2,8,8 filling
order)
• Draw protons (p) and (n) in circle (“nucleus”)
• Draw electrons around in shells
He
Li
Li shorthand
p+
2
2 n0
3 p+
4 n0
3 p+
4 n0
2e– 1e–
Draw Be, B, Al and shorthand diagrams for O, Na
Be
B
Al
4 p+
5 n°
O
5 p+
6 n°
13 p+
14 n°
Na
8 p+ 2e– 6e–
8 n°
11 p+ 2e– 8e– 1e–
12 n°
Atomic Models
Note electron
cloud
More Models of Atoms
Note electron cloud
Note
electron
cloud
Maxwell (1873), proposed that visible light consists of
electromagnetic waves.
Electromagnetic
radiation is the emission
and transmission of energy
in the form of
electromagnetic waves.
Speed of light (c) in vacuum = 3.00 x 108 m/s
All electromagnetic radiation
lxn=c
7.1
Properties of Waves
Wavelength (l) is the distance between identical points on
successive waves.(peak to peak)(crest to crest)
Amplitude is the vertical distance from the midline of a
wave to the peak or trough.
7.1
Formula relating them:
c = speed of light = 3.00 x 108 m/s
l = “lambda” = wavelength in meters
u = “nu” frequency in Hertz (Hz)
 What is the frequency of an e-mag
that is 2.45 x 10-8 meters? __________
What kind of e-mag wave is it? ____________
7.1
Properties of Waves
Frequency (n) is the number of waves that pass through a
particular point in 1 second (Hz = 1 cycle/s).
The speed (c) of the wave = l x n
7.1
A photon has a frequency of 6.0 x 104 Hz. Convert
this frequency into wavelength (nm). Does this frequency
fall in the visible region?
l
lxn=c
n
l = c/n
l = 3.00 x 108 m/s / 6.0 x 104 Hz
l = 5.0 x 103 m
l = 5.0 x 1012 nm
Radio wave
7.1
Mystery #1, “Black Body Problem”
Solved by Planck in 1900
Energy (light) is emitted or
absorbed in discrete units
(quantum).
E=hxn
Planck’s constant (h)
h = 6.63 x 10-34 J•s
7.1
When copper is bombarded with high-energy electrons,
X rays are emitted. Calculate the energy (in joules)
associated with the photons if the wavelength of the X
rays is 0.154 nm.
E=hxn
E=hxc/l
E = 6.63 x 10-34 (J•s) x 3.00 x 10 8 (m/s) / 0.154 x 10-9 (m)
E = 1.29 x 10 -15 J
7.2
If we had a piece of K metal and it took 4 x 10 -15 J to eject
electrons from it.
Would red or blue light have enough energy to do this?
Blue light has a wavelength of 435 nm.
Red light has a wavelength 660 nm.
Each color represents a certain amount of energy.
7.1
7.3
Bohr Model of the Atom
Electrons move around the nucleus
in rigid paths, or orbits.
SODIUM - 23
You can excite an electron to a higher orbit by absorbing
a specific amount, or “quantum” of energy.
As you can see, after it absorbs energy,
the e- falls back down, emitting energy.
Line Emission Spectrum of Hydrogen Atoms
7.3
Bohr’s Model of
the Atom (1913)
1. e- can only have specific
(quantized) energy
values
2. light is emitted as emoves from one energy
level to a lower energy
level
En = -RH (
1
n2
)
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J
7.3
E = hn
E = hn
Which electron is losing the most energy?
7.3
ni = 3
ni = 3
ni = 2
nf = 2
Ephoton = DE = Ef - Ei
1
Ef = -RH ( 2
nf
1
Ei = -RH ( 2
ni
1
DE = RH( 2
ni
)
)
1
n2f
)
nnf f==11
7.3
How the Bohr Model fits into this:
n = 4 to n = 1: e-mag wave
with a l of 97 nm
1 nm = 1 x 10-9 m
n = 3 to n = 1: 103 nm
n = 2 to n = 1: 122 nm
Note: ALL e- going to n = 1
emit Unltraviolet Light
All e- going to n = 2 emit
Visible light.
All e- going to n = 3 emit
infrared light
Eg: What wavelength of light is emitted as
when n = 3 goes to n = 2? What color is
this?
656 nm
RED
CHApTER 7
Bohr’s Model
Ground vs Excited State
• An atom is considered “excited” if its
electron(s) have absorbed enough
energy to jump to another energy
level
• Energy absorbed must be a
SPECIFIC amount (quanta or photon
of energy)
• Specific Energy is released when it
loses its source of energy (flame,
electricity)
Ground vs Excited State
• Because a specific energy is released, it has
a specific frequency (E=h*u), and therefore a
specific wavelength (c=λ*u), and therefore a
specific color of light.
• Prism or spectroscopes simply separate
those different lights so we see them
individually
• Different atoms require different energies for
electrons to “jump” so this explains why they
give off different colors
Forefathers of Quantum Mechanics

Max
Planck
– Father of Quantum Mechanics
discovered that matter gains or lose
energy in distinct “quanta”, or packets.
Louis DeBroglie

Matter may have the properties of waves.
1858 - 1947
In other words: Matter = Energy?!
1892 - 1987
Louis de Broglie
• Asked the question “How can electrons stay
in a fixed orbit?”
• Negative charges should change this if they
get close to other negative charges(like
charges repel)
• Brought up the idea that electrons (e-) act
both like particles, but also like energy waves
• All energy waves have a specific wavelength
(λ)
Louis de Broglie
• If e- are like waves, this would mean
they also have a specific wave length
• If they have a specific wave length,
then they also have a specific
frequency
• If they have both a specific frequency
and a specific wavelength then they
must be in a specific “orbit” around the
nucleus
The Wave Nature of Matter
•
•
•
•
•
Louis de Broglie (1924) suggested that
electrons are also waves (not particles)
This can be difficult to comprehend:
normally we perceive objects as solid.
The reason objects seem solid is because
they have a small wave length…
According to De Broglie: l = h/mv
All that really matters is that mass is on the
bottom, so as mass gets large, l gets small
small m
large m
Louis de Broglie
• Problem is, how do we prove if
an e- is actually in that specific
area?????
• In comes Erwin Schrödinger
Erwin Schrödinger
• Came up with a big equation that predicts
where an e- was
• Equation only works with certain energies,
which means there are only a few numbers
for energy that will work for the e- of each
atom
• Because e- are moving so fast, are so small,
and move like a wave, this only predicts the
general area where the e- can be found
An electron can easily be seen
as both matter and energy!
Erwin Schrodinger
proved the electron was a wave (form of energy)
1887 - 1961
quantum mechanical model of the atom
Schrödinger’s Equation
• If your interested
Werner Heisenberg
• Expanded on Schrödinger work
• Heisenberg Uncertainty Principle – We cannot
know the position and speed of an electron
simultaneously.
• An electron can never be precisely located, but
can only have a probability that it is somewhere
in a specific area…
• In other words, the best we can do is say that
we are 95% confident that this specific e- is in
the back half of the atom at this time…or
something like this
It is impossible to ever see an electron.
Why not?
Heisenberg’s Uncertainty Principle
“It is impossible to know both the position and momentum
of an object at the same time.”
They are going too fast to see their position
They are so small, a photon of light hitting them will
change their position and momentum.
1901 - 1976
In comes the
Quantum Model
• Improvement over Bohr’s Model – it
works for more than just Hydrogen
atoms
• Nucleus is the same – protons and
neutrons stuck in the middle
• Orbits (where e- are found)
– 3-D areas of probability
– a specific e- is likely to be in this area 90%
of the time
– Orbits are arranged around the nucleus