Download Atomic - Chemistry R: 4(AE) 5(A,C)

Atoms:
The Building
Blocks of Matter
S.MORRIS 2006
http://www.youtube.com/watch?v=Ki_5a15
gJYg&feature=related
http://www.youtube.com/watch?v=20Nz16
PJaQo&feature=related
ATOMS consist of electrons
orbiting around a nucleus.
ELECTRONS
NUCLEUS contains:
a. PROTON
B. NEUTRON
Nucleons
total # of subatomic particles in the
nucleus of the atom
Atomic Theory
Atoms are incredibly small!
What we know about them is based on
indirect evidence
History of Atomic Theory
Democritus
– 460-371 B.C.
– ancient Greek philosopher
– believed all matter consisted of
extremely small particles that
could not be divided
– atoms, from Greek word
atomos, means “uncut” or
“indivisible”
Aristotle
– believed all matter came from
only four elements—earth, air,
fire and water
John Dalton- an English
schoolteacher
He proposed the ATOMIC THEORY.
John Dalton:
THE ATOMIC THEORY (1808)
1.
All matter is composed of extremely small
particles which cannot be subdivided,
created or destroyed.
2. Atoms of a given element are identical in
physical and chemical properties.
3. Atoms of different elements have different
physical and chemical properties.
4. Atoms of different elements combine in
simple whole-number ratios to form chemical
compounds.
5. In chemical reactions, atoms are combined,
separated, or rearranged, but never created,
destroyed, or changed.
By the late nineteenth century, most
people had accepted Dalton's proposal
of 1808 that matter was made of atoms.
Solid Sphere Model or
Billiard Ball Model
proposed by John Dalton
Dalton- solid sphere reminds
us of a Nilla cracker
http://www.learner.org/resources/se
ries61.html
Problems with Dalton’s Atomic Theory?
1. Matter is composed, indivisible particles
2. All atoms of a particular element are identical
3. Different elements have different atoms
4. Atoms combine in certain whole-number ratios
5. In a chemical reaction, atoms are merely rearranged to form new
compounds; they are not created, destroyed, or changed into
atoms of any other elements.
Scientist: J.J. Thomson
What did he discover: ______________
His Experiment: Cathode Ray Tube
His findings: Electrons are negatively charged
embedded in a positive charge.
J.J.Thomson’s Atomic Model
Plum Pudding Model
Thomson believed that the electrons were like plums
embedded in a positively charged “pudding,” thus it was
called the “plum pudding” model.
J.J. Thomson:
Discovery of the Electron
His Experiment: Cathode Ray Tube
In 1897, J.J. Thomson used a cathode ray tube
to deduce the presence of a negatively charged
particle.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
J.J. Thomson’s cathode ray tube
Thomson knew that rays must have come from the atoms
of the cathode because most of the atoms in the air had
been pumped out of the tube. Because the cathode ray
came from the negatively charged cathode, Thompson
reasoned that the ray was negatively charged.
He observed that when a paddle wheel was
placed in the path of the rays, the wheel
would turn. This observation suggested that
the cathode ray consisted on tiny particles
that were hitting the paddles of the wheel.
His experiments showed the cathode ray
consists of particles that have mass and a
negative charge. These were called _______.
J.J. Thomson’s Model of Atom
was like a chocolate chip cookie!
Enjoy!!
DO NOW:
What was Dalton’s model
of an atom?
Who discovered the
electron? What was his
model called?
Scientist:ERNEST RUTHERFORD
What did he discover: ________________
His experiment: GOLD FOIL EXPERIMENT (1900’s)
His findings:
ERNEST RUTHERFORD
Discovery of the Nucleus
GOLD FOIL EXPERIMENT (1900’s)
Worked with alpha particles (helium nuclei) they have a
positive charge.
HIS EXPERIMENT:
• He fired alpha particles (that are helium nuclei)
at a thin sheet of gold foil.
• Particle hits on the detecting screen (film) were
recorded
• rutherfords_gold_foil_expt.ppt
The above diagram shows
what we would expect
the result of
Rutherford's experiment
to be if the "plum
pudding" model of the
atom is correct.
The above indicates the
actual result. Most of the
alpha particles are only
slightly deflected, as
expected, but occasionally one
is deflected back towards the
source.
His observations
1. Most alpha rays passed through with
little or no deflection
2. One in 20,000 were strongly deflected
(every time it was near the center of
the atom)
RUTHERFORD ACTIVITY
HALLWAY
Pennies
Rolled Marbles
Rolled Marbles
Pennies
Equal
Distance
From each
other
1. What was the charge near the center
of the atom?
2. What structure was near the center of
the atom?
3. Why were the alpha particles deflected
so strongly?
Scientist: Niels Bohr, 1913 Danish physicist
What did he discover:Bohr refined
Rutherford's idea by adding that the
electrons were in orbits around the nucleus.
Rather like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.
Bohr’s Atom
1913
electrons in orbits
nucleus
Bohr’s
Atom
HELIUM ATOM
_______
_______
_________
+
_________
N
N
+
-
__________
BOHR MODEL of the ATOM
1.
Electrons revolve around the nucleus in
specific orbits (shells), or energy levels.
PRINCIPAL ENERGY LEVELS
Each of the orbits in the Bohr model of the atom has a fixed
radius.
The greater the radius of an orbit (the farther from the nucleus),
the greater the energy of the electrons in the orbit. The orbits
or shells of the Bohr model are known as principal energy levels.
The main energy level occupied by an electron 1 through 7.
The period an element is found in tells us its energy level.
2. An atom has energy levels. Electrons can
only exist in these energy levels, not in
between.
3. When an atom is in the _____________, the electrons
exist in the energy levels closest to the nucleus.
GROUND STATE:
Click on pic
Electrons in the first energy level have the lowest potential
energy since they are located closest to the nucleus.
4. If an atom receives, energy, the atom becomes excited
and electrons jump to higher energy levels.
EXCITED STATE: an atom with higher potential energy
than in the ground state because electrons have
“jumped” to a higher energy level.
•
•
http://www.crocodile-clips.com/absorb/AC4/sample/LR301_mg.html
Click on bohr increase energy
• http://www.youtube.com/watch?v=vUzTQ
Wn-wfE&feature=related
• Atom song
• http://www.broadeducation.com/htmlDemo
s/AbsorbChem/HistoryAtom/page.htm
• http://www.crocodileclips.com/absorb/AC4/sample/LR301_mg.
html
• Click on bohr increase energy
• http://www.classzone.com/books/earth_sci
ence/terc/content/investigations/es0501/es
0501page03.cfm
• Build an atom
QUANTA (or photons)
One important feature of the Bohr atom is
the idea that electrons can only absorb or
release energy in discrete, specific amounts.
These amounts, or bundles of energy are
called quanta corresponding to differences
in energy levels of the shells.
Spectral lines
•
•
If high voltage is applied to hydrogen gas confined in a gas tube, called
a gas discharge tube, light is emitted. If this light is passed through a
prism, a series of bright lines of distinct colors is produced. Bohr
reasoned that these different colored bands of light were actually
quanta of corresponding energy. These quanta were emitted as
electrons of hydrogen atoms returned from their higher levels in the
excited state to their lower levels in the ground state.
These colors are specific and can be used to identify these metals.
(Flame Tests)
Spectroscopic analysis of the
hydrogen spectrum…
…produces a “bright line” spectrum
•The device designed to
observe the separation of
light into its component colors
(wavelengths) is called a
_________________.
•The series of bright lines produced when excited electrons return
to their original energy levels is called a bright-line spectrum.
•Each element has its own unique set of spectral lines which can
therefore be used to identify the elements presence.
Wave Mechanical Model/
Orbital Model of the Atom
Scientists, influenced by studies of the wave behavior of electrons
replaced the Bohr model with one that describes the motion of
electrons in terms of probability of their positions within the atom.
This model considers the electrons to move freely around the nucleus.
These regions of the most probable location of electrons are known as
________________.
The ______________________ are the most probable locations of
finding a tiny electron in an atom.
The Structure of the Atom
• ORBITALS = 3D region around the nucleus
that indicated the PROBABLE location of an
electron.
• Electrons with higher potential energy occupy
orbitals farther from the nucleus.
• THE FURTHER AN ELECTRON IS FROM THE
NUCLEUS THE GREATER ITS ENERGY!!!
Discoveries about the atom
Dalton
1.
All matter is composed
Of extremely small particles which
cannot be subdivided, created or
destroyed.
2. Atoms of a given element are
identical in physical and chemical
properties.
3. Atoms of different elements have
different physical and chemical
properties.
4. Atoms of different elements
combine in simple whole-number
ratios to form chemical compounds.
5. In chemical reactions, atoms are
combined, separated, or rearranged,
but never created, destroyed, or
changed.
JJ Thomson
What did he
discover: Electron
His Experiment:
Cathode Ray Tube
His findings:
Electrons are
negatively charged
embedded in a
positive charge.
Rutherford
What did he
discover: The Nucleus
His experiment:
GOLD FOIL
EXPERIMENT (1900’s)
His findings:
The atom is mostly
empty space.
The nucleus is small.
The nucleus is dense.
The nucleus is
positively charged
Niels Bohr
•Electrons revolve around the nucleus
in specific orbits, or energy levels.
• An atom has energy levels.
Electrons can only exist in these
energy levels, not in between.
•When an atom is in the ground state,
the electrons exist in the energy
levels closest to the nucleus.
•GROUND STATE: the lowest energy
state of an atom; the electrons
occupy energy levels closest to the
nucleus.
•If an atom receives, energy, the
atom becomes excited and electrons
jump to higher energy levels.
•EXCITED STATE: an atom with
higher potential energy than in the
ground state because electrons have
“jumped” to a higher energy level.
Solid
Sphere
Model
Wave
Mechanical
Model/
Orbital
model
This model
suggested that
electrons could be
considered waves
confined to the
space around a
nucleus.
Electron cloudsregions where
electrons are
likely to be found
Subatomic Particles
Particle
Electron
Proton
Neutron
Charge
Mass (amu)
Location
Particle
symbol
Mass of atoms are measured in
Atomic Mass Units!
1 amu = 1/12 mass the Carbon-12
The Atomic
Scale
 Most of the mass of the
atom is in the _________
(protons and neutrons)
 _________ are found
outside of the nucleus (the
electron cloud)
 Most of the volume of the
atom is ___________
Atomic Number
•The number of _________ in the
nucleus of each atom of that element.
•Identifies the element.
•Every element has a different atomic
number.
•Atomic number also equals the number
of electrons in the neutral atom
6C
Element
Oxygen
Phosphorus
Gold
# of protons
Atomic #
Mass Number
•Number of ________ and
_________ in the nucleus of an
isotope.
Mass # = p+ + n0
Element
p+
Oxygen 33
Phosphorus
n0
e- Mass #
If the number of ELECTRONS
EQUALS the number of PROTONS, the ATOM
is electrically ______________.
# electron = # protons
In an atom the # electrons = # protons
The charge of an atom is neutral.
How to find # of neutrons?
# Neutrons =Mass # - Atomic #
12
6
C
FIND THE NUMBER OF NEUTRONS IN THE FOLLOWING:
1.
2.
3.
4.
5.
6.
Sodium
Calcium
Nitrogen
Iron
Argon
Lithium
HYDROGEN
• Hydrogen is the simplest of all atoms
• All hydrogen atoms have only 1 proton
and one electron.
• Like many other elements, hydrogen
atoms can have different numbers of
neutrons.
PROTIUM
• 99.9885% of all hydrogen atoms have
1 proton and 0 neutrons in their
nucleus.
DEUTERIUM
• 0.0115% of hydrogen atoms have 1
proton and 1 neutron in their nucleus.
TRITIUM
• Very small amounts of hydrogen atoms
have 1 proton and 2 neutrons in their
nucleus.
• Tritium is radioactive.
• All hydrogen atoms have only 1 proton
and 1 electron.
Isotopes
Isotopes- elements with the same number of protons
and electrons, BUT different numbers of neutrons.
So the ATOMIC NUMBER IS THE ______________
the MASS NUMBER IS ____________________
Elements occur in nature as mixtures of isotopes.
How are these atoms different
from each other how are they
the same?
Isotope
Hydrogen–1
(protium)
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium)
Protons Electrons Neutrons Nucleus
Isotopes &
Their Uses
Bone scans with
radioactive
technetium-99.
Isotopes & Their Uses
The tritium content of ground water is used to
discover the source of the water, for example,
in municipal water or the source of the steam
from a volcano.
Atomic Mass
Atomic mass is the average mass of all the
naturally isotopes of that element.
Carbon = 12.011
Isotope
Symbol Composition
of the
nucleus
12C
Carbon-12
6 protons
6 neutrons
13C
Carbon-13
6 protons
7 neutrons
14C
Carbon-14
6 protons
8 neutrons
% Abundance
in nature
98.89%
1.11%
<0.01%
ATOMIC STRUCTURE
Atomic mass
Atomic number
4
2
He
number of electrons = number of ________
SUMMARY
Atomic Number = number of protons in the
nucleus of an atom
Mass Number = number of protons and neutrons
in the nucleus of an isotope
Atomic Mass= weighted average of the masses
of the existing isotopes of an element
Isotopes = same number of protons, different
number of neutrons
Same atomic number, different atomic mass
Ions
Are created when an atom loses of gains one
or more electrons, it acquires a charge
http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-ions.shtml
Charge of Ion =
More electrons than protons =
More protons than electrons =
12
6
C +1
# of protons 
# of electrons 
Total charge 
PRACTICE IONS
Ion
Li
+1
Ni
+2
Pb
+2
Ca
+2
Cs
+1
# protons
# neutrons # electrons
Chemical
Symbol
Number of
protons
I
Number of
electrons
Number of
neutrons
Atom or Ion?
53
35
36
11
55
45
12
atom
78
atom
Zr
atom
12
14
50
Br
12
69
atom
45
atom
Ce
atom
1
2
27
25
32
84
80
125
Sc
Pb
78
73
68
108
Ni
atom
50
71
atom
HOW TO CALCULATE ATOMIC MASS:
Boron exists as 2 isotopes
B-10
or
B-11
B
% Abundance
19.78%
B
80.22%
B-10
10
5
B-11
11
5
How to calculate Atomic Mass:
STEP 1: Take the Mass # (in amu)
of each element and multiply by its
Percent Abundance
STEP 2: Add all of these values
together
STEP 3: Divide by 100
Atomic Mass of Boron
STEP 1: 10 x 19.78 = 197.8
11 x 80.22 = 882.42
STEP 2: 197.8 + 882.42
STEP 3:
1080.22
100
= 1080.22
= 10.802 amu
Calculate the Atomic Mass of Chlorine:
% Abundance
Chlorine – 35
75.53
Chlorine – 37
24.47
Calculate the Atomic Mass of Silicon:
% Abundance
Si – 28
92.21
Si – 29
4.70
Si – 30
3.09
Calculate the Atomic Mass of Oxygen:
% Abundance
O-16
99.762
O-17
0.038
O-18
0.200
ELECTRON CONFIGURATION
1. Shows arrangement of electrons
2. Each atom has a distinct electron configuration.
3. In an atom the number of electrons must equal the atomic number.
4.
Principal Energy
Levels
Maximum # of
Electrons in Energy
Level
1
2
3
4
5
5.The ground state Electron Configuration is found on the periodic table in
the lower left hand corner of each box.
6. Electrons generally occupy energy levels in sequence, beginning with
those of lowest energy.
7. No more than eight electrons occupy the outermost principal energy
level (except that the 1st can only hold two).
Element
Al
K
C
Electron Configuration
Explanation
The configuration listed on the periodic
table is the
ground state electron configuration.
Element
He
O
Na
F
Si
Mg
Br
Ground State Electron Configuration
EXCITED ELECTRON
CONFIGURATIONS:
• When an atom is excited, electrons
jump to a higher sublevel or energy
levels.
• An example of a transition from a
ground state electron configuration to
an excited state electron configuration
would be:
Classify the following as ground state electron
configurations or excited state electron configurations.
Element
ground state electron configurations or
excited state electron configuration
1-2
2-8-7-3
2-8-7
2-7-4
2-7-1
2-8-1
2-8-7-2
Element
Ground State
Electron
Configuration
Ion
Ion’s Electron
Configuration
Na
Na
+
Mg
Mg
+2
Fe
Fe
+3
Al
Al
+3
Li
Li
+1
Valence Electrons
Electrons that occupy the valence energy level
Valence Electrons= found in outer most energy level
Na 2-8-1
Cl 2-8-7
Atoms can have a maximum of 8 valence electrons
(with the exception of Hydrogen and Helium)
Lewis Dot Diagrams
(Electron Dot Diagrams)
• Represent the arrangement of
electrons around the nucleus.
• Electrons are the DOTS.
• Nucleus is the symbol.
• ONLY REPRESENT VALENCE
ELECTRONS!!
• Fill one side first, then one on each
side before you pair electrons.
Lewis Dot Diagrams
(Electron Dot Diagrams)
Na
B
O
Mg
Cl
Ne
Si
H
N
THE END
Law of Conservation of Mass
Mass is neither
created nor destroyed
during chemical or
physical reactions.
Total mass of reactants
=
Total mass of products
Antoine Lavoisier
Electromagnetic radiation propagates
through space as a wave moving at
the speed of light.
c = 
C = speed of light, a constant (3.00 x 108 m/s)
 = frequency, in units of hertz (hz, sec-1)
 = wavelength, in meters
The energy (E ) of electromagnetic
radiation is directly proportional to the
frequency () of the radiation.
E = h
E = Energy, in units of Joules (kg·m2/s2)
h = Planck’s constant (6.626 x 10-34 J·s)
 = frequency, in units of hertz (hz, sec-1)
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Rutherford’s Gold Foil
Experiment
Rutherford’s Work
Atomic Models: J.J. Thompson
Passed electricity
through an uncharged
gas
– The gas gave off rays to
show it was
NEGATIVELY charged
– How?
– Negative charges must
come from inside the
atom!
Electrons!
Some Modern
Cathode Ray Tubes
•
•
Chemistry Class Atom Model Project
•
Build a Bhor atom model of neon using materials of your choice. Your model must be a free-hanging, three-dimensional structure with
protons, neutrons, electrons, and electron energy levels clearly visible. Hint: this drawing represents a Bohr diagram of a carbon atom.
Assignment: This is an individual project - each student is to build their own atom model outside of class using scrap material available
at home. Materials must be non-perishable and appropriate for classroom display. Project Deadline:
Scoring: Your atom model will score points based on the following:
NO atom models will be accepted after the project deadline.
A detailed diagram accompanies the model to act as a key to the parts.
The model demonstrates pride in workmanship.
The following parts must be shown:
•
•
•
•
•
–
–
–
–
correct number of protons
correct number of neutrons
correct number of electrons
correct arrangement of electron energy levels
•
•
•
0 points
40 points
20 points
•
•
•
•
•
10 points
10 points
10 points
10 points
Total of 100 Points
•
• Dalton "proved" his theory with a number of
assumptions, each of which is either factually
wrong or was used in a logically inconsistent
manner. Nonetheless opposition from critics
such as Mach, who never believed in atoms,
was largely ignored. Throughout the nineteenth
century atomism became an idea that came to
dominate thought in a number of fields, including
political science, sociology, psychology, biology
and more.
•
•
•
•
•
•
•
Bohr's Model
Neils Bohr knew about all of these facts, and in the early part of the century was collaborating with
Rutherford. He also knew about the existence of line spectra from chemical elements; a document
on this topic may be found here. He was struggling to make sense of all of this. As was common
with Bohr when confronted with a puzzle, this struggle was nearly all-consuming.
Then in 1913 Bohr, by accident, stumbled across Balmer's numerology for the hydrogen
spectrum, and in a flash came up with a workable model of the atom. The model asserts that:
The planetary model is correct.
When an electron is in an "allowed" orbit it does not radiate. Thus the model simply throws out
classical electromagnetic theory. Technical note: an allowed orbit is one in which the electron
mass times its speed times the radius of the orbit is equal to a positive integer n times Planck's
constant divided by 2 pi. The integer n can be 1, 2, 3, 17, 108, etc. In fact, there are an infinite
number of allowed orbits corresponding to the infinite number of positive integers.
When an electron absorbs energy from incident electromagnetic radiation, it "quantum jumps" into
a higher energy allowed state. This higher energy state corresponds to an allowed orbit with a
higher value of the integer n.
When an electron is in a higher energy state, it can quantum jump into a lower energy state, one
with a smaller value of n, emitting all of its energy as a single photon of electromagnetic energy.
Bohr atom