Download Physical Science: Ch. 10 - Pleasant Hill Elementary School

Physical Science: Ch. 15 & 17
Atomic Structure and the
Periodic Table
Atom - the smallest particle of an
element which has all the properties of
that element
Ex.: each gold atom has the exact same
properties as a gold bar (color, density, melting
point, etc.)
(although this is hard to tell, since a single atom is so small)
• Element - a substance made of only 1 kind of
atom
• All known elements are illustrated on the Periodic
Table
Compounds
• A compound is a combination
of atoms from 2 or more
different elements, in a
definite ratio.
Example: water (H2O) and hydrogen
peroxide (H2O2)
The properties of a compound
may be completely different
from those of the elements
which make it up.
• Sodium, for example, is a very reactive
metal. Chlorine is a poisonous gas.
But combine them together in a 1:1 ratio
and you get …….
• Sodium Chloride………salt.
Chemical and Physical Properties
• Physical properties are properties which
can be easily observed without changing
the chemical make-up of the material.
• Ex.: color, density, melting point, odor
• A physical change is one
where the identity of the
material remains the same,
but physical properties such
as size, shape, or state of
matter may change.
• Ex.: boiling water, breaking a
pencil, melting and reshaping a
metal
• Chemical properties tell how a
substance will react to form
new substances.
• Ex.: flammability, reactivity, corrosiveness
• A chemical change occurs when a
new substance(s) is created from
other substances
• Ex.: rusting, photosynthesis, burning
• Sunny went to the beach and
laid out in the sun for 1 hour,
after which time she had a dark
tan. Was this a chemical
change, a physical change,
both, or neither? Explain.
• Could you chemically combine substances
containing sodium, hydrogen, oxygen, and
chlorine, and end up with one of your
resulting substances containing nitrogen?
• No!
Even though you can create
new substances, you can
only create them from what
you already have. You
cannot end up with the
element nitrogen if you had
none to begin with.
Doh!!
• Alchemists tried to produce gold and
other valuable materials. But with gold
being a pure element, it wasn’t possible.
Law of Conservation of Mass
• In a chemical reaction, mass can neither be
created or destroyed, it can only change
form.
Therefore, the mass of the reactants before the
reaction occurs must be exactly equal to the
mass of the products following the reaction.
• The same thing applies to physical
changes.
mass before = mass after
=
• For example, if a log were placed in a sealed
metal box and set on fire. The products
(smoke, ash, gases, etc.) would have the exact
same mass as the log before it were burnt.
• If the box were sitting on a scale as the log
burned, the weight would not change at all.
• Cletus and Brandine decided to see what
would happen when they mixed baking
soda and vinegar in a bottle and capped the
top with a balloon. As the illustration
shows, the balloon inflated. Wouldn’t this
be a violation of the
Law of Conservation
of Mass, since matter
which was not originally
there was produced?
Why or why not?
The Periodic Table
• The Periodic Table is an arrangement of all
the different elements based on their
chemical and physical properties.
• Elements are arranged by increasing atomic
#'s on the Periodic Table (from left to right)
• Elements in the same group (vertical
column) have similar properties.
• Chemical symbols are used to identify
elements on the Periodic Table.
The symbols consist of 1 or 2 letters, the
first of which is always capitalized.
There are 2 main areas inside an atom:
-The nucleus is the tiny central core of the atom.
It contains protons and neutrons and has a
positive charge.
-The electron cloud is the very large area
surrounding the nucleus. It contains electrons
and has a negative charge.
Atomic Charge
• There are usually the same number of
positively charged protons (p+) in the
nucleus as there are negatively charged
electrons (e-) in the electron cloud.
• These charges cancel out and make the
atom neutral.
Protons & neutrons are located in
the nucleus of the atom
 Protons have a positive charge
 Neutrons have no charge (neutral)
 Both protons and neutrons have a mass of
1 amu (atomic mass unit)
 Almost all of the mass of the atom is
located in the nucleus, even though it is
the smallest part of the atom.
Electrons
• Electrons are negatively charged particles
which are located in the electron cloud (the
area surrounding the nucleus)
• Electrons orbit the nucleus and have
essentially 0 mass.
Atomic number and atomic mass
• An element is identified by it's atomic
# and atomic mass
• Atomic number is simply the # of
protons in the nucleus of an atom
• This number is usually the same as
the # of electrons in the atom
Atomic Mass
• The atomic mass of an element is the mass
of a single atom of the element. This is
determined by adding the # of protons and
neutrons in the atom.
Mass number = # protons + # neutrons
• So...if mass number = # protons + #
neutrons, and the # of protons is just the
atomic #, what would the formula be for
finding the # of neutrons?
• Correct!
Mass number - # protons = # neutrons
Find the # of neutrons in an atom of
Mercury.
• Round 200.59 to 201, subtract the #
of protons (80), the # of neutrons is
121.
• Now, provide the requested info. for
the following elements:
Cadmium
Iron
- atomic #
________________________________________________________________________________________________________________
- atomic mass
_________________________________________________________________________________________________________________
- # protons
_________________________________________________________________________________________________________________
- # electrons
_________________________________________________________________________________________________________________
- # neutrons
- atomic #
- atomic mass
- # protons
- # electrons
- # neutrons
Cadmium
Iron
48
112.411
48
48
64
26
55.845
26
26
30
Isotopes
• An isotope is an atom of an element with
a different number of neutrons than
normal.
• This has a direct effect on the atomic mass
of the atom.
• Ex.: C-12 and C-14 are isotopes of carbon
• Polydactyle cats have a 6th digit on each paw.
They’re still cats, just like an isotope of carbon
is still carbon. They just happen to have a
different number of digits, like C-14 happens to
have 8 neutrons.
• If fingers were
neutrons, this
guy would be
an isotope.
Quarks
• A quark is a fundamental particle which makes up
protons and neutrons.
• Quarks are detected and identified by accelerating
protons to very high speeds, colliding them
together, and then looking at their component
parts.
• So why does it matter
what these particles are
made of, or how many
protons are located
where?
Electron Shells
• The electron cloud is a large area, however,
the electrons in the electron cloud are not
randomly scattered here and there.
• If you were to slice an atom in half, there are
certain areas surrounding the nucleus where
you are more likely to find electrons located.
• Think of it like this, if you had a handful of bb’s
and dropped them all on the floor, they would
fall and scatter out. But they wouldn’t
necessarily scatter randomly. There will likely
be a greater concentration of bb’s that end up
close to where they were dropped from, and
fewer and fewer the farther you move out from
that area.
• That’s similar to how the electrons are
spread out around the nucleus. Therefore,
the area closest to the nucleus in the
diagram appears darker, because there is a
greater electron concentration there.
• Why do you think the electrons are
more likely to be concentrated close to
the nucleus?
• These areas where the electrons are
located around the nucleus are called
electron shells (or energy levels).
• An electron shell diagram is simply a
diagram showing where in the electron
cloud the electrons are most likely to be
found.
• Think of the levels like a Gobstopper, with
several different hard candy areas
(electron shells) surrounding the center
(nucleus).
• Each shell can hold a certain # of electrons.
Where the electrons are located is important
because the location helps determine how 1
atom will react with other atoms.
Electron Shells
You could also think of it like the inside of a stadium.
It is divided into different seating levels as you move
outward from the field. Likewise, there are different
electron levels (shells) as you move outward from the
nucleus.
Just like in a stadium, the levels closest to the
nucleus (field) will fill up first. Then, once a
level is full the next level out will start to fill up.
The further out you move, the more electrons
(people) can fit into each level (even though
the concentration ,may be less)
Electron Shells
• In the electron cloud, the first level out from
the nucleus can hold 2 electrons, the next
level can hold 8, the 3rd level holds 18, the
4th - 32, and 5th - 50.
• The number of electrons in the outermost
shell is called the outer shell electrons.
• To draw an electron shell diagram, first find the
# of electrons for an element. Let's use
Bromine (Br) for an example.
• Bromine has an atomic # of 35, so it has 35
electrons. So let's start filling up the electron
shells until all 35 of the electrons are accounted
for.
• The first level can hold 2 e-, so you put 2
of the 35 in there (33 left)
• The second level can hold 8, so in goes 8
(25 left).
The 3rd level can hold 18, which will leave you with
7. Even though the 4th level can hold 32, it doesn't
have to be filled up, just stick in however many you
have left, which in this case is seven. (2 + 8 + 18 +
7 = 35)
• So the distribution of electrons in the electron
cloud would look something like this.
(note: the nucleus is greatly exaggerated in size, therefore the
electron concentration around the nucleus does not appear as
dense as it actually is)
• However, realizing that not all of my students
have the artistic ability that I do (and to save
time and space), the diagram can be drawn
as shown below.
Now, try one on your own.
Draw the electron shell diagram for Calcium.
• This should be what you got.
• The # of electrons located in the outer most shell
for a given element ( 10 for calcium, 7 for
bromine, and so on) will determine how an atom
of that element will react with other atoms. But
we'll get into that in a later chapter.
Element
Oxygen
Neon
Tellurium
Barium-141
Plutonium
Mercury
Sodium
Silver
Radon-217
Chemical
Symbol
Atomic #
Atomic
Mass
# protons
#
neutrons
# electrons
Atomic #
Atomic
Mass
# protons
# neutrons
# electrons
O
8
15.999
8
8
8
Neon
Ne
10
20.180
10
10
10
Tellurium
Te
52
127.60
52
76
52
Barium
Ba
56
137.327
56
81
56
Plutonium
Pu
94
244
94
150
94
Mercury
Hg
80
200.59
80
121
80
Sodium
Na
11
22.990
11
12
11
Silver
Ag
47
107.868
47
61
47
Radon
Rn
86
222
86
136
86
Element
Chemical
Symbol
Oxygen
• Name 3 different elements which all have 3
outer shell electrons.
• How many neutrons would the isotope
C-14 have?
• How many electrons would it take to fill the first
4 electron shells? Which element would
accomplish that?
• U-235 and U-238 are two common isotopes of
uranium. Provide the following information for
each of these elements:
• # of protons, neutrons, and electrons
• Atomic mass
Identify the following elements:
• Has an atomic mass of 107.8682
• Has 22 electrons
• Has 10 neutrons
• Lightest element which is a liquid at room
temperature
• What is unusual about Iodine and
Tellurium?
Answers
• Silver
• Titanium
• Fluorine or Neon
• Bromine
• Iodine has a larger atomic number but a
smaller atomic mass
• You are given a plastic bucket containing 4 different
materials: iron filings, sand, salt, and very small
plastic chips. The 4 materials all have about the
same sized pieces and are thoroughly mixed together
in equal amounts. Explain what you could do, step
by step, to separate the 4 materials based on their
different physical properties. Note: Picking out the
separate materials piece by piece is not acceptable.
• Physical properties are properties which can be easily observed or
measured without changing the chemical make-up of the material.
Ex.: color, density, melting point, odor
• Nitrogen (78%) and oxygen (21%) are the 2 main
gases which make up the air that we breathe.
Based on this, and information from the Periodic
Table, explain why it is often harder to breathe at
higher elevations (like Denver) than it is at lower
elevations.
• Also explain why higher
elevation locations are
often favored for training
by endurance athletes.
• Provide the following information for argon:
-# of protons, neutrons, and electrons
-# of outer shell electrons
-group # and period #
-2 elements with similar properties as argon