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Unit 4: Atoms and the Periodic Table
http://www.sciencewithmrjones.com/handouts.shtml
(with adaptations by J. Stevens)
Vocabulary Term Definition Example
Atom
Building blocks of matter
Proton
Sub-atomic particle with
positive (+) charge; located in
nucleus of atom; determines
identity of element
Neutron
Sub-atomic particle with no
charge, located in the nucleus
of the atom
Electron
Sub-atomic particle with
negative charge; much smaller
than protons and neutrons
Nucleus
Center of atom; made of
protons and neutrons
Valence Electron
Electron found in outermost
shell of an atom; determines
atoms chemical properties
Vocabulary Term Definition Example
Atomic Number
Number of protons in the
nucleus of an atom
Mass number
Protons + neutrons
Atomic Mass
Weighted average of masses
of isotopes of each atom
Isotope
Atom with same # of protons
as other atoms of that element,
but different # of neutrons
Ion
An atom that has gained or lost
one or more electrons; thus
having a + or - charge
Bohr Model Model used to visualize atomic
structure
Lewis Dot
Structure
Used to show number of
valence electrons in an atom
pH scale Scale used to show acidity or
alkalinity of something.
Vocabulary Term Definition Example
Acid Compound which increases H+
ions when dissolved in H2O
Base
Compound which increases
hydroxide ions (OH-) when
dissolved in H2O
Gravitational Force
Attraction of objects due to
their masses and distance;
weakest force
Electromagnetic
Force
Like charges repel and
opposite charges attract;
Holds electrons around the
nucleus
Weak Nuclear
Force
Force responsible for
radioactive decay.
Strong Nuclear
Force
Holds the atomic nucleus
together; Counteracts the
electromagnetic force
Vocabulary Term Definition Example
Periodic Table
Table where elements are
arranged by increasing atomic
number
Group
Vertical (up and down) column of
periodic table; elements in group
share chemical properties (same
# valence electrons)
Period
Horizontal row of elements in
periodic table; = how many
orbitals atoms have
Metals
Good conductors of heat and
electricity; to left of stair step
Non-metals
usually gases or brittle solids at
room temp; are poor conductors;
to right of stair step
Metalloids Have characteristics of metals
and non-metals; make up stair
step
Section 1: Atomic Structure
http://www.sciencewithmrjones.com/handouts.shtml
(with adaptations by J. Stevens)
Key Ideas: • Know the structure of atoms • Explain how sub-atomic particles are different in terms of mass,
electrical charges, and location in the atom • Understand Hydrogen ion concentration in acids and bases, and how
the pH scale measures acids and bases Vocab: • Atom Valence Electron Ion • Proton Atomic Number Bohr Model • Neutron Mass Number Lewis Dot • Electron Atomic Mass pH scale • Nucleus Isotope Acid
Base
How small are atoms?
• http://www.youtube.com/watch?v=yQP4UJ
hNn0I
If they are so small, how do we
know they exist?
Demonstration
• Cutting paper in half….
– Then in half again…. – And again….
– And again…
• How many times do I have to cut to get to
the size of an atom?
You would have to cut the paper in half around thirty-one (31) times to
get to the size of any atom.
http://www.miamisci.org/af/sln/phantom/papercutting.html
Democritus proposes
the 1st atomic theory
460 – 370 BC
History of the Atom - Timeline Antoine Lavoisier
makes a substantial number of contributions
to the field of Chemistry
1766 – 1844
John Dalton proposes his
atomic theory in 1803 1743 – 1794
0
1856 – 1940
J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897
1871 – 1937
Ernest Rutherford performs the Gold Foil
Experiment in 1909
1885 – 1962
Niels Bohr proposes the Bohr Model in
1913
1887 – 1961
Erwin Schrodinger describes
the electron cloud in 1926
1891 – 1974
James Chadwick
discovered the neutron in in 1932
170
0s
180
0s
190
0s
Click on picture for more information
History of the Atom
• For thousands of years, many scientists
have been trying to figure out what makes
up all matter? Of course, its atoms. But
what are they made of? What do they look
like? How do they work?
• After many scientists contributions, and
many experiments, we now have a model
(the Electron Cloud model), that is
supported by all previous evidence
Progression of the Atomic Model
The structure of an atom, according to:
Democritus & John Dalton
J.J. Thomson Ernest Rutherford Neils Bohr Erwin Schrodinger James Chadwick
+ - - - - -
- +
-
-
-
-
-
-
+
-
--
-
-
-
+ Electron Cloud+ Electron Cloud
Image taken from: http://tcc-yr9-
chemistry.wikispaces.com/1-
1+The+Atom
Where are we now?
• Watch “The existence of quarks”
– Existence of Quarks
• Watch “A boy and his atoms”
– http://www.research.ibm.com/articles/madewit
hatoms.shtml#fbid=Kt4Y4qGwgbx
• Scanning Tunneling Microscope
– http://www.youtube.com/watch?feature=playe
r_embedded&v=rNf-A3m6HVo
The Building Blocks of Matter: Atoms
+
+
+
+
+
+ +
-
-
-
-
- -
-
- +
Matter
• Anything that has mass and takes up space (volume) – Examples:
• A brick has mass and takes up space • A desk has mass and takes up space • A pencil has mass and takes up space • Air has mass and takes up space
All of the above examples are considered matter because they have mass and take up space. Can you think of anything
that would not be considered matter?
What are atoms made of?
• Smallest possible unit into which matter can be divided, while still maintaining its properties.
• Made up of: – protons – neutrons – electrons
• The solar system is commonly used as an analogy to describe the structure of an atom
For example, what is the smallest possible unit
into which a long essay can be divided and still have some meaning?
+
- + +
+
-
-
- -
+
Atoms are so small that…
• it would take a stack of about 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil from your kitchen.
• if you could enlarge a penny until it was as wide as the US, each of its atoms would be only about 3 cm in diameter – about the size of a ping-pong ball
• a human hair is about 1 million carbon atoms wide.
• a typical human cell contains roughly 1 trillion atoms.
• a speck of dust might contain 3x1012 (3 trillion) atoms.
• it would take you around 500 years to count the number of atoms in a grain of salt.
www.deckersfoods.com
C-C-C-C-C-… + 999,995 more
1 trillion atoms
. Is made of approximately 3 trillion atoms
Just one of these grains
Protons (+)
• Positively charged particles, in the nucleus
• # protons = atomic number • Contribute to the atomic
mass • # protons = to # of
electrons (in a neutral atom) • Help identify the atom (could
be considered an atom’s DNA) +
+
+ + +
+ + +
-
-
-
-
- -
-
- +
Neutrons • Neutral particles;
have no electric charge
• In the nucleus • Contribute to the
atomic mass • Found by
subtracting the number of protons from the mass number
• Mass number – protons= neutrons
+
+ +
+
+ + +
-
-
-
-
- -
-
- +
Electrons (-)
• Negatively charged particles • Found outside the nucleus of
the atom, in the electron orbits/levels;
• each orbit/level can hold a maximum number of electrons ( 1st = 2, 2nd = 8, 3rd = 8 or 18, etc…)
• Move so rapidly around the nucleus that they create an electron cloud
• Mass is insignificant when compared to protons and neutrons (smallest)
• = to number of protons (in a neutral atom)
• Involved in the formation of chemical bonds
-
+
+ +
+
+ + +
-
-
-
-
- -
-
- +
Valence Electrons • Number of electrons in the outside orbital of the
atom
• Electrons that can be gained, lost or shared in chemical reactions and chemical bonding
• How many valence electrons does this atom have?
• What element is this atom?
http://images.tutorvista.com/content/structure-atom/valence-
electron-of-atom.jpeg
Bohr Model
• Even though this model is not correct, we use it to easily visualize what is happening with protons, neutrons and electrons.
• How do we
know that this
model is
Nitrogen?
http://www.britannica.com/EBchecked/topic/71700/Bohr
-atomic-model
Lewis Dot Structure
• Lewis Dot Structure shows the number of valence electrons for atoms.
• How many valence electrons does this atom of Nitrogen have?
• How many total electrons does it have? http://rayschemworld.pbworks.com/f/1349966207/NitrogenLewis
Dot.GIF
Hydrogen (H) Atom
• Notice the one electron in the first orbital
+
- +
-
= 1
= 0
= 1
How many more
electrons can fit in
the 1st orbital/ level?
Oxygen (O) Atom
• Notice the two electrons in the first orbital/level and the six in the second
+
+
+
+
+
+ +
-
-
-
-
- -
-
- +
+
-
= 8
= 8
= 8
How many more
electrons can fit in the 2nd orbital/ level?
Sodium (Na) Atom
• Notice the two electrons in the first orbital/level, eight in the second, and one in the third
+
+
+
+
+
+ +
-
-
-
-
- -
-
- +
-
-
-
+
-
= 11
= 12
= 11
The Atom’s “Center”
• Protons and neutrons are grouped together to form the “center” or nucleus of an atom.
-
+ + +
Notice that the electrons are not apart of the nucleus
-
-
QUARKS
• Particles that make up protons and neutrons
• Existence of Quarks
Notice the smaller
particles that make
up this neutron
after you take a
closer look.
+
Notice the smaller
particles that make
up this proton
after you take a
closer look.
What do you notice about the number of quarks in the neutron and proton?
Sub-Atomic Particles Weight Comparison
(protons, neutrons, electrons)
Neutron = 1.6749286 x10-27 kg Proton = 1.6726231 x10-27 kg Electron = 9.1093897 x10-31 kg
+
- +
- - - -
- - -
- -
- -
-
-
-
-
-
-
- - - - -
- - -
- -
- -
-
-
-
-
-
-
1836 electrons = 1 proton 1839 electrons = 1 neutron
How do you think the mass of a neutron compares to that of a proton?
1 neutron ≈ 1 proton
Sub-atomic Particles Size Comparison
(protons, neutrons, electrons, & quarks)
Size in atoms
Size in meters
(m)
Atom
1 10-10
Nucleus __1__
10,000 10-14
Proton or Neutron
___1___
100,000 10-15
Electron or Quark
_____1____
100,000,000 10-18
(at largest)
+
+
+
+
+
+ +
-
-
-
-
- -
-
- +
Atomic Number-same as the number of protons
• The number of protons in the nucleus of an atom
+ + +
-
-
-
What would be the atomic number of this
atom?
http://www.chemicalelements.com/bohr/b0003.gif
Mass Number (protons + neutrons)
• Tells us the number of protons and neutrons in an atom’s nucleus
• Expressed in Atomic Mass Units (amu) – Each proton or neutron has a mass of 1 amu
+ + +
-
-
- What would be the mass
number of this atom?
+ 3
4
3 protons + 4 neutrons = a mass number of 7 amu
Why did we not account for the electrons when calculating the
mass number?
Let’s Practice Building Atoms
What are the atomic and mass numbers (amu) for the following atoms?
Atoms Protons Neutrons Electrons
Carbon 6 6 6
Beryllium 4 5 4
Oxygen 8 8 8
Lithium 3 4 3
Sodium 11 12 11
Average Atomic Mass
• The weighted average of the masses of all the naturally occurring isotopes of an element (forms of an element with different number of neutrons)
• The average considers the percent abundance of each isotope in nature • Found on the periodic table of elements • Example
+
-
+
-
+ -
Hydrogen (Protium) Mass # = 1 amu
Hydrogen (Deuterium) Mass # = 2 amu
Hydrogen (Tritium) Mass # = 3 amu
If you simply average the three, 2 amu (1 amu + 2 amu + 3 amu/3) would be the atomic mass, but since 99.9% of the Hydrogen is Protium, the atomic mass is around 1 amu (.999 x 1 amu)
What would be the atomic mass (≈) of Hydrogen if these three isotopes were found in the following percentages (99.9, 0.015, 0) respectively?
Symbol = O2+
Ion
• Atom that does not have the same number of electrons and protons, resulting in either a + or – charge
• If I gain electrons, I get a negative charge (more electrons than protons)
• If I lose electrons I get a positive charge (more protons than electrons)
+
+
+
+
+
+ +
-
-
-
-
- -
-
- +
-
Now that this atom of oxygen just gained an electron, it is no longer neutral or an atom. It is now
considered an ion (anion). This ion has more electrons (9) than protons (8).
+
-
= 8
= 8
= 8 9 6
Symbol = O1-
Now that three electrons were lost, the number of electrons (6) and protons (8) is still unbalanced;
therefore, it is still an ion, but now it is specifically referred to as a cation.
Currently, this atom of oxygen is neutral because it has an equal
number of electrons (8) and protons (8). Symbol = O
Building Ions
Build the following ions, and determine their atomic and mass numbers.
Ions Protons Neutrons Electrons
Carbon (C³¯) 6 6 9
Hydrogen (H¹+) 1 0 0
Oxygen (O²¯) 8 8 10
Lithium (Li³+) 3 4 0
Sodium (Na¹¯) 11 12 12
Be aware that the atomic and mass numbers are not impacted by the loss or gain of electrons.
Acids and bases The pH scale – potential hydrogen
http://fergusonfoundation.org/lessons/glossary_images/ph_scale.jpg
Acids and Bases • Acid
– Releases a hydrogen
ion (H+) when it
dissolves in water.
– 0 to 7= acids
strong weak
– Examples: lemon
juice, hydrochloric acid
(in our stomachs)
– Taste sour, burns
nose, sticky
• Base
– Removes H+ ions from
a solution
– 7 to 14= basic
weak strong
– Examples: household
cleaners
– Taste bitter, usually no
smell, slippery
***pH of 7 is neutral – neither acid or base, like water
Section 2: FORCES IN THE ATOM
Key Ideas: • Understand the magnitude and range of the four
fundamental forces
• Recognize the effect of each force on the structure of matter
Vocab:
• Gravitational Force
• Electromagnetic Force
• Strong Nuclear Force
• Weak Nuclear Force
Section 2: FORCES IN THE ATOM
• Gravitational Force
• Electromagnetic Force
• Weak Nuclear Force
• Strong Nuclear Force
• Nature of Forces
Gravitational Force
• Attraction of objects due to their masses and distance
• The amount of gravity between objects depends on their masses and the distance between them
• Weakest Force
Do you think this force plays a significant role in holding the atom together?
Electromagnetic Force
• Like charges repel and opposite charges attract
• Holds electrons around the nucleus
• Gravity and Electromagnetism
-
+
+
+
- -
Notice how the particles with the same charge move apart and
the particles with different charges
move together.
Why are neutrons not pictured above?
Strong Force • Holds the atomic nucleus
together
• Counteracts the electromagnetic force
• Weak and Strong Nuclear Forces
• How does a particle accelerator work?
• Particle Accelerator
If you need help remembering strong force, just think of…
+ +
+ +
Notice how the electromagnetic force causes the protons to repel each other but, the strong force
holds them together.
Would an atom have a nucleus if the strong force did not exist?
-
n
Weak Nuclear Force
• This force plays a key role in the possible change of sub-atomic particles. – For example, a neutron
can change into a proton(+) and an electron(-)
• The force responsible for radioactive decay. – Radioactive decay
process in which the nucleus of a radioactive (unstable) atom releases nuclear radiation.
+
If you need help remembering
weak force, just think of…
Notice how the original particle changes to something
new.
Section 3: The Periodic Table
Key Ideas • Relate the properties of atoms and their
position in the periodic table to the arrangement of their electrons
Vocab • Periodic Table
• Group
• Period
• Metal
• Non-Metal
• Metalloids
What is the periodic table of elements?
http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm
What is the periodic table of elements?
Table where elements are organized by increasing
atomic number (or number of protons)
Nova Interactive Periodic Table
First Organizers
• Dmitri Mendeleev (late 1800’s), Russian chemist • Organizes first periodic table
based on atomic mass, but some elements are out of order
• Henry G.J. Moseley (1913), British chemist • Arranged elements by atomic
number, which is what we use today
• Student of Rutherford
How is the periodic table actually organized?
• Groups:
• Vertical columns of elements with similar properties
• Numbered 1 – 18
• Elements in same group, have the same number of
electrons in outer energy level (valence electrons)
• Example: Every element in group 1, has 1 electron in its
outer shell, every element in group 2, has 2 electrons in its
outer shell, and so on (excluding transition metals)
http://www.chem4kids.com/files/art/elem_pertable3.gif
Valence Electrons
• Electrons in the last “shell” or energy level of an atom
• Important because:
• Determine an elements ability to “bond” with another
element
• Chemical properties depend almost entirely on the
configuration of the outer electron shell (reactivity,
flammability, etc.)
How is the periodic table actually organized?
• Periods
• Horizontal rows of elements that contain increasing
numbers of protons and electrons
• Numbered 1 – 7
• Each row in a period ends when an outer energy level is
filled
• Example: Every element in the top row has 1 orbital for its
electrons, 2nd row has two orbitals and so on
http://www.chem4kids.com/files/art/elem_pertable2.gif
How is the periodic table actually organized?
Categorized by:
Alkali
Alkaline Earth
Transition Metals
Basic metal
Semi metal
Non-metal
Halogens
Noble Gas
Lanthanide (rare-earth) -
radioactive
Actinides (rare-earth) -
radioactive
http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm
3 Main categories
http://www1.whsd.net/courses/J0078/Periodic__Table/periodic_table.JPG
Metals, Non-metals and Metalloids (Semi-
Metals)
Metals • Good conductors of heat and electricity • All but Mercury are solid at room temp • ***Metals are located to the left of the stair step • Alkali Metals – (Group 1) are the most reactive of all
metals; don’t occur in nature in their element form • Alkaline Earth Metals – (Group 2) shiny, ductile and
malleable; combine readily with other elements • Transition Metals – (Group 3 – 12) most familiar metals
because they often occur in nature uncombined • Inner Transition Metals
• Lanthanide Series – elements with atomic # 58-71 • Actinide Series – elements with atomic # 90 - 103
Non-Metals
Elements that are: • usually gases or brittle solids at room temp, • are poor conductors • ***located to the right of the stair step • Noble gases – (Group 18) exist as isolated atoms. They
are all stable because the outer energy level is filled.
Metalloids
• ***Elements that make up the stair step • Have metallic and non-metallic properties (share
characteristics with metals and non-metals) • Part of the mixed groups (groups 13, 14, 15, 16 and 17) –
which contain metals, non-metals and metalloids
How to read the periodic table
http://d1jqu7g1y74ds1.cloudfront.net/wp-
content/uploads/2010/02/c-atom_e.gif
www.nittygrittyscience.blogspot.com/
Watch “Hunting the Elements” with worksheet
