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Atoms and the Periodic Table
• A neutron walks into a bar; he asks the
bartender, 'How much for a beer?' The
bartender looks at him, and says 'For you,
no charge.'
Two atoms bump into each other. One
says 'I think I lost an electron!' The other
asks, 'Are you sure?', to which the first
replies, 'I'm positive.'
Atom: the smallest particle of an
element. Everything is made of
atoms
Proton: positive particle in the
nucleus
Neutron: neutral particle in the
nucleus
Electron: tiny negative charge
outside the nucleus
Atoms are mostly….
… empty space!
Element: a substance made of only
one kind of atom, cannot be
chemically or physically separated
into other substances.
Atomic number: the number of
protons in an atom. All
elements are identified by their
atomic number.
For example, any element with 6
protons is Carbon, regardless
of how many neutrons (or
electrons) it has
Atomic mass: the sum of the
number of protons and
neutrons.
Molecule: Two or more
ATOMS bonded
together.
Examples:
Water = H2O
Oxygen = O2
Compound:Two or more
different ELEMENTS
bonded together.
Which of these is a molecule but not a
compound?
A) Ar
B) NaCl
C) H2SO4
D) H2
Homogenous mixture: substances are evenly
distributed so that one part of the mixture can’t be
distinguished from another.
Example: stirring cream into your coffee
heterogenous mixture: substances are not evenly
distributed and can be distinguished from
another.
Example: soil, oil and vinegar
Ion: an atom or
molecule that has a
positive or negative
electric charge
because its number of
protons is not equal to
its number of
electrons.
Isotope: Atoms that
have the same
number of protons but
different number of
neutrons. They are
the SAME element!
Writing the elements to show
atomic mass and number
Atomic mass
= protons + neutrons
4
2 He
Atomic number = protons
14
6C
12
6C
This is “Carbon-14”. How many neutrons does it have?
This is “Carbon-12”. How many neutrons does it have?
Carbon-14 and Carbon-12 are different ????? of Carbon.
Chemical Formula: A description that uses
numbers and symbols of elements to describe a
molecule.
H2O
NaCl
CaCl2
Periodic Table: A chart that lists the elements by
atomic number and electron arrangement.
Use your periodic table!
What’s the atomic number of Cobalt?
What’s its atomic mass?
How many protons does Calcium have?
What element has 17 protons and 18
neutrons?
What is its atomic number?
What is its atomic mass?
Radioactive
Elements
Some elements are unstable, especially if they’re
really massive, and spontaneously fall apart or
decay.
Why would nucleii tend to fall apart?? (Think about
what protons do to each other)
These unstable elements are called RADIOACTIVE.
All elements with more than 83 protons are
RADIOACTIVE.
Radioactive Elements
They will continue to
decay until they are
stable (nonradioactive), even if it
takes years.
The amount of time it
takes until half of the
atoms in a radioactive
sample have decayed
is called its
HALF-LIFE.
Number of radioactive atoms
A radioactive sample has 1000 atoms.
The graph shows the number of
radioactive atoms remaining as a
function of time.
What is the HALF-LIFE of this sample?
A) 50 years
B) 80 years C) 150
years
D) 400 years
B) 80 years
Time in years
The individual columns are called
GROUPS.
Elements in the same GROUP react in
similar ways!
Which elements will behave in similar ways?
Ca Br O
F
Which are in the same GROUP??
Br and F
Metals 




How to remember??
In the alphabet……
“M” comes before “N”
Non metals
Which of the following are metals:
Calcium, Sulfur, Cobalt, Boron, Aluminum
Metals: Calcium, Cobalt, Aluminum
e-
Metals have “free electrons” (in their outer shell)
that can move around- that’s how they conduct
electricity
Metals can DONATE those electrons
Nonmetals will ACCEPT those electrons.
Think of those electrons flowing like electricity
flows from the metals over to the nonmetals
Don’t react with anything! 
Which element will accept electrons?
Al
S
K
Ne
Well, Ne is the furthest to the right, but….. The
last column is special- these are the inert or
noble gases. They are completely unreactive,
because their outer shell is full.
So the right answer is…..
Sulfur
The ability to accept electrons is called
electronegativity.
Which elements MOST readily accept
electrons?
The group of elements that only need ONE
more electron to fill their outermost shell.
Which group needs only ONE more electron to fill its outer shell??
Group 17
Group 17 is called the Halogens.
And, in this group, the element Fluorine has
the highest “electronegativity” – the ability
to accept electrons
Which element most readily accepts electrons?
Zn
N
F
As
Nitrogen, Arsenic and Fluorine all will accept
electrons, but Fluorine has the highest
electronegativity!
Acids and Bases
pH scale identifies acids and bases with a
number:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Acids  Neutral  Bases
How to remember???
In the alphabet, “A” is before “B”
Basic substances will turn
litmus paper BLUE
Acidic substances will turn
litmus paper RED.
Examples of acids:
hydrochloric acid, lemon
juice, vinegar
Examples of bases:
ammonia, soap, baking
soda (often bases are
slippery stuff!)
How do you know if it’s an acid or
base?
Acids have H+
Bases very often have OH(“hydroxide”)
How to remember???
In the alphabet, “H” comes before
“O”, just like “acids” come before
“bases
A substance has a pH of 8. What is it likely
to contain more of?
O2 K
H+ OHA pH of 8 means…..
It’s a BASE so….
It contains …..
OH-
Water
Think of water as an H+ bonded with an OH-.
H2O (two hydrogen, one oxygen)
Equal acid and base. Therefore….
Pure water is neutral with a pH of
7
Which makes water very important…
Some things dissolve better in acids.
Some things dissolve better in bases.
Water is a universal solvent.
Base,
Acid, H+
OHH
O
H
Rather like the Earth has a North Pole and a South
Pole, water is POLAR, with a more “acid / +” pole and
a more “base / -” pole.
That’s why it’s called a UNIVERSAL SOLVENT.
This is how water easily breaks apart ionic
compounds. It surrounds both negative
and positive ions and breaks apart ionic
solids.
One reason water is an effective solvent is
that ita. Contains the acid, H+
b. Can evaporate easily
c. Is a polar molecule
d. Contains the base, OHThe correct answer is “c”.
Physical vs Chemical Changes
Ice melting
Iron rusting
Food digesting in your stomach
Wood burning
Body decomposing
Sugar dissolving
Which of these describes a pollution-producing
process that involves only a physical change?
a) Coal with a high sulfur content is burned,
producing gases that cause acid rain.
b) Chlorofluorocarbons are released, changing
ozone in the upper atmosphere into oxygen.
c) Hot wastewater is discharged into a lake.
d) Nitrogen oxide emissions combine with water
vapor, producing nitric acid.
The correct answer is “c”
Solubility of a solid in a liquid
a measure of how much solute will dissolve
into the solvent
Temperature will affect solubility- the
solubility will be INCREASED as the
temperature is increased.
Stirring will increase solubility.
Molecular or Particle Size will affect the
solubility. The larger the molecule or
particle the less soluble the substance will
be. So smashing something into smaller
pieces makes it dissolve better.
Solubility of a gas in a liquid
Think of carbonation in your soft
drink!
Pressure will affect solubility of a gas in a
liquid. As the outside pressure goes up, the
solubility (staying dissolved) will go up.
For example: the CO2 (fizzies) stays dissolved
in your coke because it’s bottled under high
pressure.
Once you open the lid, the bubbles began to
escape. Higher pressure increases solubility.
Temperature affects the solubility. Cokes lose
their fizziness faster as the temperature
increases.
Colder temperature increases solubility.
Decompression sickness can happen in these
situations:
-A diver ascends too quickly from a dive
-An unpressurized aircraft goes too high.
-The cabin pressurization system of a high-flying aircraft
fails.
-Divers flying in any aircraft shortly after diving.
-An astronaut exits a space vehicle to perform a spacewalk.
These situations cause inert gases, generally nitrogen,
which are normally dissolved in body fluids and
tissues, to come out of physical solution (“outgas”)
and form gas bubbles.
If nitrogen is forced to come out of solution too quickly,
bubbles form in parts of the body causing the signs
and symptoms of the "bends" which can be itching
skin and rashes, joint pain, sensory system failure,
paralysis, and death.
As a scuba diver goes deeper underwater,
the diver must be aware that the
increased pressure affects the human
body by increasing thea) body’s temperature
b) Amount of dissolved gases in the body
c) Amount of suspended solids in the body
d) Concentration of minerals in the body
The correct answer is “b”
All of these can affect the rate at which a
solid dissolves in water except
A) Decreasing air pressure
B) Stirring the water
C) Increasing the temperature of the water
D) Using larger crystals of the solid
The correct answer is A, decreasing the
pressure in the air above the water won’t
affect the rate the solid dissolves
Bonding
Ions will bond to form neutral molecules.
What’s the chemical formula for Aluminum
Hydroxide formed when
Al+3 bonds with OH- ?
Just “cross-multiple” the numbers!
Al(OH)3
Let’s try some:
Zn2+ and Cl
ZnCl2
Al3+ and SO42Al2(SO4)3
Ca1+ and CO31CaCO3
Fe3+ and SO42Fe2(SO4)3
NH4+ and PO43(NH4)3PO4
Conservation of Mass
According to the law of conservation of
mass, the total mass before a reaction is
equal to the total mass after the reaction.
Total mass before = total mass after
Conservation of Mass
For example: In this reaction, how much zinc
was present in the zinc carbonate?
64 g Calcium + 192 g Zinc Carbonate  152 g Calcium carbonate + ?? g Zinc
Think of the  as an =
64 + 192 = 152 + ??
There was 104 g of Zinc
3 g of CaCl2 reacted with 2 g of Na3PO4
the products were 1 g of Ca3(PO4)2 and
table salt- NaCl.
How many grams of NaCl were produced?
In a similar way, there is the same number of
atoms of each element before a reaction as
there is after a reaction.
# of atoms of each element before a reaction
=
# of atoms of each element after a reaction
That’s where balancing equations is important.