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The Atom
Concepts to Master
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How big are subatomic particles in
relationship to one another and to the whole
atom?
Where are the subatomic particles located
within the atom?
What are the charges of the subatomic
particles?
Which atomic theory is most current?
Which atomic theory states that electrons
are in clouds?
What is Dalton’s contribution to chemistry?
Who discovered that electrons are
negatively charged?
What was the name of Rutherford’s
experiment why was it so important?
Whose model is like the planetary model?
What are differences between Bohr’s model
and the wave-mechanical model of the
atom?
What is the mass number equal to?
What is the atomic number equal to?
How do you write the symbols for isotopes
of the same element?
How do you calculate atomic mass?
When is an atom neutral?
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Where are valence electrons found?
What do the chemical properties of an
element depend on?
How are ions formed and how are they
written?
How do you write an equation that shows
magnesium losing electrons?
How do you write an equation that shows
phosphorous gaining electrons?
Why do ions form?
Counting subatomic particles for neutral
atoms and ions
How do you draw a Lewis dot diagram for a
neutral atom, a cation, and an anion?
What is the relationship between an
electron’s energy and its distance to the
nucleus?
What do electrons do when they gain
energy?
What do electrons do when they lose
energy?
How can you tell the difference between an
atom in the excited state and an atom in the
ground state?
Recognize an emission spectrum and an
absorption spectrum.
Identify an element based on its spectrum.
Vocab
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Absorption spectrum
Anion
Atom
Atomic mass
Atomic number
Cation
Chemical property
Compound
Continuous spectrum
Dual nature concept
Electromagnetic spectrum
Electron
Electron configuration
Emission spectrum
Excited state
Ground state
Ionic charge
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Ions
Isotope
Mass number
Matter
Neutron
Nucleus
Octet rule
Orbitals
Orbits
Oxidation number
Proton
Subatomic particle
Valence electrons
Valence shell
Labs
• Atomic Structure
• Atomic Mass of Beadrock
• Atomic Spectrum
The Atom
• The smallest component of an element.
– So if there are103 different elements there are
103 different types of atoms.
• Basic unit of all matter.
– Matter is anything that has mass and volume.
Subatomic Particles
• Protons
• Neutrons
• Electrons
Nucleons located in
the Nucleus of an atom
• Mass
– electron mass = 9.10938188 × 10-31 kg
– neutron mass = 1.6749286 × 10-27 kg
– proton mass = 1.67262158 × 10-27 kg
• amu
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Atomic mass unit
1 amu = mass of 1 proton
1 amu = mass of 1 neutron
Easier for scientists to write in terms of amu
• Mass of an electron is approximately 1/1836 of the mass of a
proton or 1/1836 th of an amu.
Proton skyscraper
Electron - Rat at the bottom of the skyscraper
Atomic Structure Theories
• Dalton
– atoms are the basic units of matter
• JJ Thompson
– Plum pudding where the raisin are electrons
• Rutherford
– Atoms are mostly empty space
• Bohr
– Electrons are located in specific orbits around the
nucleus
• Wave Mechanical Model
– Electrons exist in “clouds” around the nucleus
Pg 66-69
Dalton
• Elements are composed of extremely small
particles called atoms.
• All atoms of a given element have identical
properties.
• Compounds are formed when atoms of
different elements combine with one another
in small whole numbers.
• The relative numbers and kinds of atoms are
constant in a given compound.
Dalton’s Elements in 1805
JJ Thompson
1903
• Atom can be divided
into parts. One of
which is an electron.
• These are negatively
charged particles
embedded in a
positively charged
atom.
• Raisins embedded in
plum pudding
Rutherford
1909
• An atom contains a
dense positively
charged nucleus.
• The rest of the atom
is mostly empty space
where the electrons
are.
• Determined this
theory after
performing the goldfoil experiment.
Rutherford’s Gold-foil Experiment
•Rutherford directed alpha particles (radioactive source) which are
positively charged and smaller than atoms at a thin piece of gold foil.
•He expected all the alpha particles to pass through (detected by the
fluorescent screen) with just a few being slightly defected.
Rutherford’s Gold-foil Experiment
Results:
1. Most of the particles did go straight through (atoms are mostly empty space).
2. A few were slightly deflected. BUT, some were GREATLY deflected. They
were strongly repelled by a dense, positive, central core and bounced back
Bohr
1913
• Electrons are located in specific orbits around the
nucleus.
• Each electron must contain a certain amount of energy
to stay in its orbit. The further the electron is from the
nucleus, the more energy it contains.
Planetary
Model
Pg 80-82
Wave – Mechanical Model
• Previously matter was
considered a particle and
energy was considered a
wave.
• This current model predicts
that matter and energy can
act like waves or particles –
Dual Nature Concept
• In this model (aka - the
electron cloud model), the
electrons are in orbitals,
which are defined as regions
of the most probable electron
location.
Pg 82-85 (2.9-2.10)
Bohr’s Model versus the
Wave – Mechanical Model
• The difference is in the description of
electron location around the nucleus.
• Bohr suggested well defined, fixed orbits.
• The wave-mechanical model shows
electrons located around the nucleus in
orbitals.
• An orbital is a region in which an electron
with a certain amount of energy is most
likely to be located (like a cloud).
• Rutherford’s Ghost – 2:30 min
• http://www.youtube.com/watch?v=ic5Q3_W7
q7w&feature=related
• Electron in motion – wave mechanical model
– 1 min – notice electrons don’t stay in a
single path, more of a vibration cloud
• http://www.youtube.com/watch?v=32uEvwxN
JvE&feature=related
The Nucleus
• Contains both protons and neutrons
– Similar in size
– Protons are positively charged
– Neutrons are not charged, they’re neutral
– So overall charge of the nucleus is POSITIVE
Pg 70-75 (2.5-2.6)
Atomic Number
• Equals the number of
protons in an atoms
nucleus.
• It identifies the element.
• It NEVER changes unless
the element has changed.
• All atoms of Lithium will
have 3 Protons.
Nucleus of atom like
Nucleus inside of cell
• Both contain
information that is
critical for
identification
– Cell nucleus
contains DNA that
identifies the
functions of that cell.
– Atomic nucleus
contains a certain
number of protons
that identifies the
element and its
properties.
Mass Number
• Equals the number of
Protons + Neutrons in
the nucleus.
• Does NOT identify the
element.
• Li : mass # = 7
• The # of neutrons an the
nucleus can change thus
mass # can change.
Isotopes
• Atoms of the same protons but with a
different number of neutrons.
• The number of protons does NOT change.
Isotopes
3 H
1
=
3
H1
3
=H =
H-3
12
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6C
13
6C
14
6C
The Element is __________
The number 6 refers to the # of ________
The numbers 12,13,14 refer to the # of _______
How many protons and neutrons are in the first
isotope?
• How many protons and neutrons are in the
second isotope?
• How many protons and neutrons are in the third
isotope?
Atomic mass
• Decimal
• Average of all the isotopes that occur in
nature.
C-12
C-13
C-14
Calculating Atomic Mass
• Of all the naturally occurring Copper, 30.8% are
atoms of Copper-65 and 69.2% of copper-63.
What is the atomic mass of Cu?
• Step 1 - convert percentages into decimals
30.8/100 = .308
69.2/100 = .692
• Step 2 – Calculate the contribution of each
isotope to the atomic mass by multiplying the
decimal percentage by the mass # for each
isotope.
0.308 x 65 AMU = 20.2 AMU
0.692 x 63 AMU = 43.596 AMU
• Step 3 – Add them together to get the
weighted average for the atomic mass.
20.2 AMU
+ 43.596 AMU
63.796 AMU
Uranium
Isotope
Atomic
#
Mass
#
# of
# of
# of
Protons Neutrons Electrons
U-235
235
0.7
92U
U-238
238
% found
in
NATURE
99.3
92U
Calculate ATOMIC MASS
Boron
Isotope
Atomic
#
Mass
#
# of
# of
# of
Protons Neutrons Electrons
B-10
10
19.9
5B
B-11
11
% found
in
NATURE
80.1
5B
Calculate ATOMIC MASS
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Discovering the elements
Handout is Introduction to the elements
36 min from intro to size of atoms segment
http://player.discoveryeducation.com/index.cfm?
guidAssetId=2113C4B6-CECB-42E5-B8E41244EB5EC32F&blnFromSearch=1
Physical Science Series: Atomic Structure and
the Periodic Table
11 min from intro thru electron segment
Handout is atomic structure
http://player.discoveryeducation.com/index.cfm?
guidAssetId=298799C9-686A-461A-A060851A721FB678&blnFromSearch=1
Electrons 101
• Found in energy levels around the nucleus
(orbitals according to the wave-mechanical
model)
• Negatively charged
• Very, Very, Very small
• When atoms are neutral (no charge), protons =
electrons, Na0.
• Can be gained or lost from the outer most
energy level
– Valence electrons are found in the valence shell.
– These are responsible for most chemical reactions
and in the formation of compounds.
– Every atom wants 8 valence electrons (unless it has
only 1 energy level, then it wants only 2).
Valence Electrons
In general, the number of valence electrons
affects the chemical properties of an element.
Valence electron # = Group # of the periodic table.
unless it has only 1 energy level, then it wants only 2
In an effort to achieve an octet
atoms becomes charged and
IONS are formed.
Ion Types - Cations
• Sodium has 3 orbits (Bohr Model)
• The third orbit has 1 electron.
• To be more stable
– give away the only electron it has in the
third orbit
– receive 7 more electrons from another
atom in order for it to have 8 electrons on
the outer orbit.
– Both processes would have sodium
ending up with 8 electrons on its outer
orbit.
– Giving away 1 electron is easier than
receiving 7 electrons.
• Sodium will lose 1 electron which
means that it now has 10 electrons
and 11 protons.
• It has 1 less electron than
proton so it’s charge is +1.
• Na --> Na+1 + 1e
Cats are +
Ion Types - Anions
• Oxygen has 2 orbits (Bohr Model).
• The second orbit has 6 electrons.
• To be more stable
– give away all the 6 electrons on the
second orbit
– receive 2 more electrons from another
atom.
– Both processes will lead to oxygen
having 8 electrons on its outer orbit.
– receiving 2 more electrons from another
atoms is easier than giving away all its 6
electrons.
• Oxygen will receive 2 more electrons
which means it now has 10 electrons
and 8 protons.
• It has 2 more electrons than
protons so it’s charge is -2.
• O + 2e --> O-2
+2e
IONS
Oxidation Number
Ionic Charge = Oxidation Number
ION
Na+
Mg+2
ClO-2
H+
S-2
Fe+3
Cu+1
Oxidation Number
Na and Cl
Na
(Metal)
# of valence electrons?
How many will be lost
or gained to achieve an
octet?
Ion type
Oxidation #
Cl
(non-Metal)
Ca and Cl
Ca
(Metal)
# of valence
electrons?
How many will be
lost or gained to
achieve an octet?
Ion Type
Oxidation #
Cl
(non-Metal)
Al and O
Al
(Metal)
# of valence
electrons?
How many will be lost
or gained to achieve
an octet?
Ion Type
Oxidation #
O
(non-Metal)
Counting Subatomic Particles
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• As-3
Number of protons = a
– Number of protons = 33
Number of electrons = b
– Number of electrons = a
Number of neutrons = c
– Number of neutrons = 42
Atomic number = 83
– Atomic number = b
Mass # = 209
– Mass # = c
Atomic Mass = Mass #
Counting Subatomic Particles
• Os+4
• Te+6
– Number of protons = a
– Number of protons = 52
– Number of electrons = b
– Number of electrons = a
– Number of neutrons = 114
– Number of neutrons = b
– Atomic number = 76
– Atomic number = c
– Mass # = c
– Mass # = 128
Atomic Mass = Mass #
• http://player.discoveryeducation.com/index
.cfm?guidAssetId=AE2C7A14-611A-485786F266933E4C286A&blnFromSearch=1&produ
ctcode=US
• How boron ions form – 2 min
Lewis Dot Diagrams
• Show only Valence Electrons for the element.
• Steps for drawing them
– Write the elemental symbols for the atoms
S
– Fill in the electrons
• If more than 2, place 1 electrons at each side of the element
symbol and then double up as needed.
• If there are 2 valence electrons, place both of them on the
same side of the element symbol.
Ca
Atoms versus Ions
O
vs
-2
O
Mg
vs
Mg+2
P
vs
P-3
Lewis Dot Diagrams
• Cations have NO electrons in the
outermost orbital.
+1
Cs
• Anions have 8 in the outermost orbital.
-1
I
Which diagrams show a
full valence shell?
+1
Ag
+2
Zn
Electrons 102
• Each electron in an atom has its own distinct
amount of energy.
– depending on their orbital
• Electrons in orbitals closer to the nucleus have less energy
and are more stable
• Electrons in orbitals further from the nucleus have more
energy and are less stable
• When all electrons in an atom are in their lowest
possible energy level, the atom is at its ground
state.
– The number of electrons found in each orbital when
an atom is at the ground state can be found on the
periodic table.
– This is the atoms electron configuration.
Pg 76-79 (2.7-2.8)
Phosphorus (P): 2-8-5
Ground State
• P has 3 orbitals
• The first orbital closest to
the nucleus contains 2
electrons.
• The second contains 8.
• The third contains 5.
• P has 5 valence electrons
(the # of electrons in the
outermost shell)
2-8-5 is the P atom’s electron configuration
Iron (Fe): 2-8-14-2
Ground State
• Fe has 4 orbitals
• The first orbital closest to
the nucleus contains 2
electrons.
• The second contains 8.
• The third contains 14.
• The fourth contains 2
• Fe has 2 valence
electrons (the # of
electrons in the outermost
shell)
2-8-14-2 is the Fe atom’s electron configuration
Electrons ABSORB energy to
become EXCITED
• When an electron in an atom
gains a specific amount of
energy, the electron becomes
excited and jumps to a higher
energy level (orbital).
– The energy can come from outside
sources like heat, light, electricity.
– Copper is absorbing energy from a
Bunsen burner flame.
Phosphorus (P): 2-7-6
Excited State
• The ground state configuration changes.
• But the total number of electrons stays the
same.
• Ground state = 2-8-5
– Total electrons = 15
• Excited State = 2-7-6
– Total electrons = 15
Iron (Fe): 2-8-13-3
Excited State
• Ground state = 2-8-14-2
– Total electrons = 26
• Excited State = 2-8-13-3
– Total electrons = 26
Electrons EMIT energy to go back
to the Ground State
• After jumping to a higher
level, the electron will very
quickly return to its original
level.
– The energy they previously
absorbed is now released as
infrared, ultraviolet, or visible
light.
– This emitted energy can be
used to identify an element.
– Copper emits blue light as its
electrons return to the ground
state.
Electricity
Ground State
The amount of
energy absorbed
Absorption
of energy
=
Excited State
the amount of
energy emitted
Electromagnetic Spectrum
• The energy released as the electron returns to the
ground state has a certain wavelength.
• Every electron within an atom has a specific energy
which when released will correspond with a specific
wavelength.
Conservation of Energy
Energy can not be created or destroyed
(but it can change form)
SO
The amount of
energy absorbed
by the electron
=
The amount of
energy emitted
by the electron
Electric Pickle Demo
Atomic Spectrum
• Elements can be identified by the
wavelengths of energy that each of their
electrons absorbs or emits.
– Emission spectrum
– Absorption spectrum
http://jersey.uoregon.edu/vlab/elements/Elements.html
Types of Spectrum
Continuous
Emission
Absorption
Which element is it?
Na
Ne
Fe
C
Unknown
Are these emission or
absorption spectrum?
IONS and Electron Configuration
+2
Lewis Dot Diagram
Mg
Mg
+2
Electron Configuration
2-8-2
2-8
IONS and Electron Configuration
Element
Br
Al
Sc
Sr
N
Cs
Atom electron
configuration
[Kr]
Ion electron
configuration
(top ox # on
periodic table)
IONS and Electron Configuration
Element
Atom electron
configuration
Br
Al
Sr
N
Cs
2-8-18-7
2-8-3
[Kr]-8-2
2-5
[Xe] - 1
Ion electron
configuration
(top ox # on
periodic table)
[2-8-18-8]-1
[2-8]+3
[{Kr}-8]+2
[2-5-3]-3
[2-8-18-18-8]+1
IONS and Electron Configuration
+2
Lewis Dot Diagram
Mg
Mg
+2
Electron Configuration
2-8-2
2-8
Check
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P-3
Number of protons = a
Number of electrons = 18
Number of neutrons = b
Atomic number = c
Mass number = 31
• a = __________
• b = _________
• c = _________
•Give the electron configuration for sulfur in ground state and the excited state:
2-8-6
2-7-7