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Atoms and the Periodic Table
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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 total mass of all the
protons, neutrons and electrons in an
individual atom.
Since electrons have so little mass, the
atomic mass is approximately equal
to the sum of the number of protons
and neutrons- the nucleons.
Molecule: Two or more
ATOMS bonded
together.
Examples:
Water = H2O
Oxygen = O2
Compound:Two or
more different
ELEMENTS bonded
together.
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.
Ions will NOT have a net
charge of zero, but will
be either positive or
negative
Isotope: Atoms that
have the same
number of protons but
different number of
neutrons. They are
the SAME element!
Notation that indicates nucleon number
(approx = atomic mass) as well as atomic number
Number of nucleons
= protons + neutrons
Approx. atomic mass
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.
Radioactive
Elements
Some elements are unstable, especially if they’re
really massive, and spontaneously fall apart or
decay and thereby lose energy.
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 decay transforms the atom’s nucleus so
that it is either in a different state of energy or it has
different nucleons (transmutation) and is therefore a
different element.
Transmutation:
Radioactive Elements
They will continue to
decay until they are
stable (non-radioactive),
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.
The individual rows are called Periods.
The individual columns are called
Groups
Elements in the same group have the
same number of valence electrons and
will react, bond, behave, in similar ways.
Metals 




How to remember??
In the alphabet……
“M” comes before “N”
Non metals
e-
Metals have “free electrons” (in their outer shell)
that’s how they conduct electricity
Metals can DONATE those electrons
Nonmetals can ACCEPT those electrons.
Group 1 donates 1, Group 2 donates 2, etc.
Group 17 (VIIA) accepts 1, Group 16 accepts 2, etc.
Think of those electrons flowing like electricity flows
from the metals over to the nonmetals
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.
Group 17 is called the Halogens.
And, in this group, the element Fluorine has
the highest “electronegativity” – the ability
to accept electrons
A Halide is a binary compound of which one
part is a halogen.
Examples: KCl and AgBr
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? (acidity or alkalinity)
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
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 is one reason water is 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.
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
As the pressure increases,
A. the solubility of a gas in a liquid
increases.
B. the solubility of a gas in a liquid
decreases.
C. the solubility of a solid in a liquid
increases.
D. the solubility of a solid in a liquid
decreases.
Ionic
Bonds
Atoms will bond together in order to have a stable
valence shell.
One atom may give up an electron to another atom
so that they both have stable valence shells.
Since one atom lost an electron and the other
gained an electron, they are both now IONS.
This called an ionic bond.
36
Ionic Bonds
For TAKS, you must know how to write the
chemical formula after the ionic bond has
formed.
Example: what is the chemical formula for
Aluminum Hydroxide formed when
Al+3 is bonded 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 in a closed system, the total mass of
the reactants before a reaction is equal to
the total mass of the products 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 chemical
reaction as there is after the reaction.
# of atoms of each element before a reaction
=
# of atoms of each element after a reaction
That’s where balancing equations is important.
Density
One characteristic of matter is DENSITY
Density = mass / volume
Unit: kg / m3 or g / cm3
The density of water is 1000 kg / m3
Or 1 g / cm3
An object will float in a liquid if its density is
less than that of the liquid.
BuoyancyArchimedes Principle
An object immersed in a
fluid is buoyed up with
a force that is equal to
the weight of the
displaced fluid.
That’s why you seem to
weigh less in a
swimming pool that
you actually do!
Apparent Weight =
Actual Weight – Buoyant Force
In this example, the stone weighs 48 N
out of water and 38 N submerged in
water.
What was the buoyant force?
How much did the displaced water
weigh?
Buoyant Force =
Weight of displaced fluid
But buoyancy applies to air as well as water!
It is what gives a lifting force to hot air balloons.
The weight of the air displaced to make room for the
balloon is pushing upward on the balloon!
Archimedes' Principle explains why steel ships
float when solid steel spheres do not float.
Because of all the air in the hull, the overall
density is less than that of water, therefore, it
floats- the buoyant force equals the weight
as the ship floats on the surface of the
ocean.
Fluids in Motion
Fluids include both
liquids and gases.
Viscosity: the
resistance to flow
Honey is more viscous
than water.