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Atoms
What are we going to study about the atom?
•History
•Structure
•Properties
•Forces
Atomic Structure
1. What is an atom composed of?
2. What subparticle(s) are responsible for an
atom’s charge?
3. What subparticle(s) are responsible for an
atom’s mass?
4. Illustrate an atom, identifying the subparticles
and their location within the atom.
Atomic Structure
Subatomic
Particle
symbol
charge Mass (g)
mass
(amu)
proton
p+
+1
1.674 x 10 -24
1
electron
e-
-1
9.11 x 10-28
0
neutron
n0
0
1.675 x 10 -24
1
Distinguishing Atoms
1.Draw the atom below and identify the following:
electrons, protons, neutrons, electron cloud, nucleus,
and energy levels.
2.What distinguishes one element’s atom from another
element’s atom?
education.jlab.org
What distinguishes each element below from one another?
Distinguishing Atoms
Distinguishing Atoms
Atomic number
• The number of protons within an atom’s nucleus.
• An atom’s I.D.
• Atoms of the same element always have the same
number of protons.
• What do you notice about the atomic numbers on
the periodic table?
An Atom’s Mass
Mass number :
• The mass of a single atom.
• Sum of the p+ and n0 within an atom.
• Unit: atomic mass unit (amu)
• The mass number is NOT the same as Atomic Mass
Atomic Structure
Subatomic
Particle
symbol
charge Mass (g)
mass
(amu)
proton
p+
+1
1.674 x 10 -24
1
electron
e-
-1
9.11 x 10-28
0
neutron
n0
0
1.675 x 10 -24
1
Element’s Subatomic Differences
Element
Atomic
Symbol
Atomic
Number
Mass #
(amu)
# of p+
# of n0
# of e-
Neutral Atoms
• Most matter in nature is neutral.
(Doesn’t shock us!)
• This means the atoms making up the matter is
neutral. 
• What are the two charged subatomic particles?
p+ and eFor an atom to be neutral the # of p+ = # of e-.
Elements Quiz
When: Thursday
What: First 20 elements on the periodic table.
Know: symbols and names
Atoms
What are we going to study about the atom?
•History
•Structure
•Properties
•Forces
Isotopes
What is an isotope?
• Atoms of the same element that have different
number of neutrons.
• Also have different number of neutrons.
Common Isotopes of Carbon
C-12
# of p+, n0, e-?
C-13
# of p+, n0, e-?
Atomic Structure
History, Structure and Properties of the Atom
History of the Atom
•Great Thinkers (2,000yrs. Ago)
•Age of Reason and Thought
•Democritus vs. Aristotle view on the
make-up of matter.
Democritus(400b.c.)
Greek Philosopher
1) Observed matter to be
made up of atoms.
2) Atoms are the smallest
form of matter.
3. Atoms cannot be broken
down.
3) The types of atoms in
matter determine its
properties.
Aristotle: Greek Philosopher (300b.c.)
•
Aristotle observed matter to be
made from four things:
air, earth, fire and water.
John Dalton’s Atomic Model
John Dalton’s Atomic Model
• English school teacher
• Proved Democritus atoms
hypothesis using the
scientific method.
• His conclusions produced:
Dalton’s Atomic Theory
Dalton’s Atomic Theory
1. Atoms are the building blocks of all matter.
1. Atoms cannot be subdivided.
2. Each element has the same kind of atoms.
3. In a compound, the different atoms chemically
combine in the same way (fixed composition).
4. Atoms cannot be created or destroyed just
rearranged.
Thomson’s Plum Pudding Model
Thomson’s Cathode Tube Experiment
l-esperimento-piu-bello-della-fisica.bo.imm.c...
Subatomic Particle: Electron
J.J. Thomson (pg. 105)
• 1897 discovered electrons in gas atoms using a
cathode ray tube.
• Determined electrons have a negative charge.
• Electrons have the same charge in all atoms.
Robert Millikan: Determined the mass of the
electron to be very tiny.
J. J Thomson’s Plum Pudding Model
• If atoms are made of electrons how come most
matter does not shock us?
• Atoms must have positive particles, too.
• He proposed the Plum Pudding Atomic Model
•
An atom is
equally made up
of positive and
negative particles.
Goldstein’s Cathode Tube Experiment
chemed.chem.purdue.edu
reich-chemistry.wikispaces.com
He discovered protons using a cathode ray tube.
Observe particles moving in the opposite direction.
Subatomic Particles: Protons
• 1886 Eugen Goldstein observed particles
traveling in the opposite direction of the
cathode rays(electrons).
• He knew these particles must be (+) charged.
They were called protons.
• Protons charge is the same for all atoms
• Protons have a significant mass compared to
the electron.
Rutherford’s Model of the Atom
green-planet-solar-energy.com
Rutherford’s Gold Foil Experiment
Rutherford’s Conclusion
•Most of the atom is empty space.
•Small dense region composed of
(+) charged particles.
(Nucleus)
Rutherford’s Nuclear Atom Model
Subatomic Particle: Neutron
•What keeps the protons within the nucleus ?
(Like particles repel each other)
•1932 - James Chadwick discovers that the
nucleus also has neutral particles present. He
called them neutrons.
Chadwick’s Experiments: Neutron
nobelprize.org
Bohr’s Model of the Atom
http://micro.magnet.fsu.edu/
Bohr’s Model of the Atom
http://micro.magnet.fsu.edu/
Current Atomic Model
Erwin Schrodinger
blogs.stsci.edu
Current Atomic Model
Erwin Schrodinger
blogs.stsci.edu
science.howstuffworks.com
Current Atomic Model
Erwin Schrodinger
blogs.stsci.edu
Types of electron paths around nucleus
Bell Ringer
1. Compare the different views Aristotle and
Democritus had about what matter was made of.
2. Which Greek philosopher was correct ?
3. Which later scientist proved his view?
Bell Ringer:
4. a. Identify and explain this Atomic Model?
b. Who concluded this atomic model?
Bell Ringer
5. Look at the following experiment below.
a. What was this experiment called?
b. Who developed this experiment?
c. Did his experiment prove or disprove the
Plum Pudding Model?
Rutherford’s Conclusion
•Most of the atom was empty space.
•Small dense region composed of
(+) charged particles. (nuclues)
Rutherford’s Atomic Model
Rutherford’s Nuclear Atom Model
Subatomic Particle: Neutron
•What keeps the protons within the nucleus ?
(Like particles repel each other)
•1932 - James Chadwick discovers the nucleus
also has neutral particles present. He called
them neutrons.
•Neutrons have a significant mass like protons.
Modern Atomic Model
Properties of Subatomic Particles
Atomic
Subparticles
Electron
Charge
(- charge)
mass (g)
9.11 x 10 -28
Proton
(+ charge)
1.674 x10-24
Neutron
(neutral)
1.675 x10-24
mass (amu)
subparticle’s
contribution
to atom
Neutral Atoms
Subatomic Masses (amu)
Subatomic
Particle
symbol
charge
Mass (g)
(g)
mass (amu)
proton
P+
+1
1.674 x 10 -24
1
electron
e-
-1
9.11 x 10-28
0
neutron
n0
0
1.675 x 10 -24
1
Atom’s Subatomic Particles
Problem B: A cesium (Cs) atom has a mass of
133 amu and an atomic number of 55. How
many p+, e-, and n0 are there?
Problem C: An iron atom has an atomic number
of 26 and consists of 30 neutrons.
a. How many p+ and e- are there?
b.What is iron’s mass number (amu)?
Atomic Subparticles
Isotopes
• Isotopes= atoms with different number of
neutrons in their nucleus.
• Elements can have several isotopes.
Ex. Carbon C-12 and C-14 (mass #)
• Mass # changes. (varied # neutrons)
• Atomic # stays the same (# of protons).
Element’s Isotopes
• Oxygen has three isotopes. They are O-16,
O-17, and O-18.
1. What is the mass number for each isotope of
oxygen in amu?
2. What is the atomic number for each isotope of
oxygen?
3. What is the number of p+, n0, and e- for each
isotope of Oxygen ?
Atomic Mass
Element’s average mass
• Atomic mass= the weighted average mass of
all the element’s isotopes present within a
naturally occuring sample of matter.
• Calculate Atomic Mass of an Element
1. Multiply the mass # of each isotope by its
natural abundance ( common occurance) in
decimal form.
2. Add all the isotopes products together.
Atomic Mass
(Element’s average mass)
• Carbon (C) has two isotopes:
Carbon-12 has a natural abundance = 98.89%
Carbon-13 has a natural abundance = 1.11%
Carbon’s atomic mass=
(12 x 0.9889) + ( 13x0.0111) = 12.011 amu
= 12 amu (2 sig. figures)
Atomic Mass Unit (amu)
• Scientist needed an easier value to describe an
atom’s mass #.
• Use a reference isotope as a standard.
• Carbon-12 was chosen as the reference isotope
because of its natural abundance and strong
stability.
• Carbon’s atomic mass unit = 12 amu
• Atomic mass unit (amu)= 1/12 the mass of a
Carbon-12 atom.
• Compare atom’s mass with Carbon
Periodic Table
• Atomic # = The elements are arranged in
numerical order based on the number of
protons present within their atom.
• Metal vs. Non-metal vs. Metalloids
• Periods vs. Groups
Periodic Table:
Metals
• Metals are the majority of elements on the
periodic table.
• They are every thing left of the metalloids.
• Some metals are extremely reactive and some
don’t react easily.
• Transition metals are elements that form a
bridge between the elements on the left and
right sides of the periodic table.
Periodic Table: Non-metals
• Non-metals are elements that are poor
conductors of heat and electric current.
• Because non metals have low boiling points,
many non metals are gases at room
temperature.
• Fun fact-All the gases in the periodic table are
non metals
Periodic Table: Metalloids
• Metalloids are elements with properties that fall
between those of metals and non-metals.
• Metals are good conductors of electric current and
non-metals are poor conductors of electric current.
• Metalloids ability to conduct electric current varies
with temperature.
• Examples of metalloids:
– Boron, silicon, germanium, arsenic, antimony, polonium,
and astatine.
Periodic Table:
Periods (rows)
Periodic Table:
Groups
• Each column in the periodic table;;
• The elements of the group have similar properties &
Electron configurations;;
• The electron configuration determines its chemical
properties;;
• Properties of elements repeat in a predictable way
when atomic numbers are used to arrange elements
into groups;;
• The pattern of repeating properties is the periodic
law;;
An Element’s Isotopes
• Isotopes= atoms with different number of
neutrons in their nucleus.
• Elements can have several isotopes
• Mass # changes. (varied # neutrons)
• Atomic # stays the same (# of protons)
• Chemical properties of an element’s
isotopes are the same because their # of
protons and electrons are the same.
Atomic Mass
Element’s average mass
• Atomic mass= average mass of all the
naturally occurring isotopes of an element.
• Multiply the mass number of each isotope by
its natural abundance (decimal form) and
then add all the isotopes products together.
Atomic Mass
(Element’s average mass)
• Carbon (C) has two stable isotopes:
Carbon-12 has a natural abundance = 98.89%
Carbon-13 has a natural abundance = 1.11%
Carbon’s atomic mass=
(12 x 0.9889) +13x0.0111) = 12.011 amu
Bell Ringer: 9/9/09
• 1. What is an isotope?
• 2. How many isotopes did Kandium have?
• 3. Did each of Kandium’s isotope have the same
mass?
• 4. What two values did you need to calculate
Kandium’s atomic mass?
• 5. After you calculated Kandium’s atomic mass
what other value did you need to determine its
atomic composition (p+,e-, n0)
Element’s Atomic Mass
• Element’s atomic mass = average mass
calculated from its isotopes.
• Isotopes : mass # (amu) and relative abundance
Ex. Calculate Nitrogen’s atomic mass:
Nitrogen-14 has a natural abundance 99.63%
Nitrogen-15 has a natural abundance 0.37%
Calculating Kandium’s
Atomic Mass
•
•
•
•
M&M –
ReesiumSkittliumKa atomic mass=
Kandium Lab
• Realistically, we can determine an
element’s isotopes mass(g) by using a mass
spectrometer.
• Proton = 1.67x10^-24 g
• Neutron =1.67x10^-24g
• Electron = 9.11x10^-28g (very insignificant)
• Mass # in grams for an atom is important
information but values are not easy to work
with .
Atomic Mass Unit (amu)
• Compare atom’s mass with carbon.
• Ex. If Helium has a mass of 4 amu how does it
compare with Carbons mass in amu?
• Amu = 1/12 C, 4(1/12) = 1/3x mass of C
• Ex. If Sulfur has a mass of 32 amu, how does
it compare with Carbon mass in amu.
• Amu = 1/12 C
32/12 = 2.67x mass of C
Atom Composition
• If we know the atomic mass and the atomic
number we can determine the atom’s
composition : # of e•
# of p+
•
# of n0
Atomic Composition
Shorthand
• Shorthand method of atomic composition:
Carbon-12 has an atomic # of 6
Ex. Oxygen-16 has an atomic # of 8
Ex. Silicon-28 has an atomic # of 14
Periodic Table
• The periodic table is arranged in numerical
order by an atom’s atomic #.
• What is an atom’s atomic #?
• Why are the elements arranged this way?
Atom’s chemical nature is dependent upon its
charged particles :
Atom’s protons remain conserved with most
reactions because present within nucleus.
The # of electrons (electron cloud) will
fluctuate with most reactions
Periodic Table Trends
• Organizing atoms based on atomic #
establishes trends:
• Period= The horizontal rows within a periodic
table. The atoms in each row share a pattern
of properties.
• Group= The vertical columns of the periodic
table. Atoms in each group share similar
physical and chemical properties.
•What is the total # of atoms making up the Kandium sample? Record in table.
Bell Ringer
(9/10/09)
1. How are elements arranged in the periodic table?
2.What does period and group refer to on the
periodic table?
3.Identify which subparticles exist in the nucleus and
the electron cloud.
4.Which two subparticles affect the chemical nature
of atoms?
5.What subparticle determines the mass of the atom?
6.Which subparticle is also the atomic #?
Objectives
• I can determine the atomic composition of atoms when I
know the atomic mass and atomic #.
• I can recognize that the periodic table is organized by an
element’s atomic number.
• I can divide the elements in the periodic table into periods
and groups.
• I can identify and distinguish between metals, nonmetals,
and metalloids on the periodic table.
• I can determine if an atom is neutral or has an overall
charge based on the # of electrons present within the
atom.
Periodic Table Trends
• Organizing atoms based on atomic #
establishes trends:
• Period= The horizontal rows within a periodic
table. The atoms in each row share a pattern
of properties.
• Group= The vertical columns of the periodic
table. Atoms in each group share similar
physical and chemical properties.
Periodic Table
Elements can be classified into 3 groups:
I. Metals= good conductors of electricity and heat.
II.Non-metals= primary make-up of life.
Synthetic (man-made) materials.
Poor conductors of electricity and heat.
III Metalloids = properties of metals and non-metals.
Neutral Atom
• What are the two charged subatomic particles that
make-up an atom?
• Neutral atoms: # protons = # of electrons
• What happens if they are not balanced?
Charged Atom
Atoms become charged when they gain or loose
electrons. This would affect the atom’s balance
between # of p+ and # of e-.
• Charged atoms are called ions.
Ion Types
• Ions = charged atoms
• Two types of Ions
1. Anion= An atom that has gained one or more
electrons.
What charge would an anion have?
• Non-metal ions can be anions.
Ex. What are some examples of anions?
Anions
Ex. Fluorine (F) atomic # = 9
Neutral Fluorine: F
Anion
Ex. Phosphorous (P) atomic # is 15.
Neutral Phosphorous:P
Ion Types
• Cations= An atom that looses one or more
electrons.
What charge would a cation have?
• Metals can be cations.
What are some examples of cations?
Cation
• Ex. Potassium (K) atomic # = 19
• Neutral Potassium: K
Cation
• Ex. Iron (Fe) atomic # = 26
Neutral Iron: Fe
Mass # vs. Atomic Mass
• Mass # = # of protons and # of neutrons in an
atom.
• Atomic Mass = The average mass for an element.
It is determined by taking in account all the isotopes
that make-up an element. You must know the
isotopes relative abundance and mass # to
calculate the atomic mass of the element.
-Atomic mass = observed on the periodic table.
Atoms : To be neutral or charged
• Neutral atom = # p+ is equal to # e• Ions (charged atoms) = change in # of ea. Cation (+ charge) = # of e- is less than in the
neutral atom. Ex. Metals (Na +)
# of e- = subtracting the charge from # of p+
b. Anion = # of e- are more than in the neutral
atom. Ex. Nonmetals. (F-)
# of e- = adding the charge to # of p+
Neutral or Not
1. Beryllium : Be 2+
2. Sulfur: S
3. Sulfur: S 2-
d) the larger the atom the weaker the strong
force is --> larger atoms tend to decay
(nuclear decay)
e) also, atoms with certain numbers of protons
tend to decay--if they have the same number
of protons and neutrons they tend to be more
stable--different numbers--more unstable
5) 4 forces in nature
a) strong force
b) weak force
c) electrical force
d) gravitational force
6) Usages of Nuclear Chemistry
a) production of power
b) killing bacteria in food products
7) Radiation-Radioactivity
a) radiation is electrically charged particles
or waves emitted by an energy source or
decaying atoms.
b) radioactivity - is radiation from an
unstable atom that is splitting or
undergoing decay. There are three types of
radioactive materials
* Alpha radiation - harmful if inhaled or
otherwise enter the body - can be stopped
by clothes, skin or a sheet of paper.
Some producers of alpha particles are
among the longest lasting waves
* beta particles - more penetrating power
than alpha but most serious when inhaled
or ingested -- tend to concentrate in certain
body parts, such as bone -can cause serious
health problems with minimal exposure
* gamma radiation-- highest energy levels similar to x-rays, can penetrate the body
Types of Radiation
• 1. Alpha Radiation : an alpha particle emitted from radioactive
nuclei, consists of 2 protons and 2 neutrons, but no electrons
• Not very harmful
• Large atoms are not very stable and need to decrease mass
• What is the charge and mass of an alpha particle?
• +2 and 4amu
• Example
• 22688Ra → 22286Rn + 42He
•
Radium
Radon
Alpha Particle
Types of Radiation
• Beta Radiation: fast moving electron emitted from a
radioactive element called a Beta Particle.
• Can cause serious health problems especially in bones
• Atoms want to have a 1 : 1 neutron to proton ratio
• Beta emission is used to decrease the neutron to proton ratio.
• What is the charge and mass on a beta particle?
• -1 and 0
• 146C → 147N + 0-1β
Types of Radiation
• Gamma Radiation: Gamma rays are released
from radioactive nuclei.
• Gamma rays have no mass or charge.
• Gamma rays are very harmful and have a very
high energy
* Effects of radioactive particles on biological
systems --can alter cellular function
particularly DNA--carries the cells genetic
code-causing birth defects-can create
mutated forms of cells that can cause
cancerous growths
8) Fusion-Fission
a) fusion uniting of nuclei of two light
elements to form heavier nucleus- example
b) fission - a heavy nuclide splits into two or
more intermediate- sized fragments when hit
in a particular way by a neutron --utilized by
nuclear power plants --to make nuclear bombs
Periodic Table Trends
• Organizing atoms based on atomic #
establishes trends:
• Period= The horizontal rows within a periodic
table. The atoms in each row share a pattern
of properties.
• Group= The vertical columns of the periodic
table. Atoms in each group share similar
physical and chemical properties.
Elements in a Period (row)
• The mass of an atom increases as you go from
left to right across any period.
Metals, Non-metals, and Metalloids
• Metals= shiny, good conductors of electricity and
heat, malleable, and ductile.
(primarily solids)
• Non-metals = poor conductors of electricity,
sometimes transparent, neither malleable nor
ductile, brittle.
(solids, liquids and gases)
Metalloids= Weak conductors of electricity, useful
semi-conductors. They can exhibit metal and
nonmetal properties.
Postulate 4 is actually the Law of
Definite Proportions,
by Joseph Louis Proust in 1797.
a) a given chemical compound always
contains the same proportion by mass of its
constituent elements or...
b) the relative amount of each element in a
particular compound is always the same,
regardless of preparation or source.
Assignment: Illustrate the following Atomic Models
•Dalton’s Atomic Model
•Thomson’s Plum Pudding Model
• Rutherford’s Nuclear Model
• Modern Atomic Model.
Thomson’s Plum Pudding Model