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The Magic of Matter

Chemistry for 8th
Grade Science
Warm-up: The word
chemistry means
different things to
different people.
1. In one or two
sentences, summarize
what the word
chemistry means to
you.
2. Draw a picture of what
you think about when
you hear the word
matter.
The Magic of Matter
Part 1: the Structure of
Matter (What is
matter made of?)
TEKS
8.8 (A) describe the structure and
parts of an atom; and
8.8 (B) identify the properties of an
atom including mass and electrical
charge
what really MATTERs here?

Chemistry is the study of matter,
especially its composition, structure,
properties and transformation.
What do you know?
With your learning partner, try and come up
with at least three properties of matter
(general properties that can be applied to
all matter.)

what really MATTERs here?
Some possible answers you may have come
up with are:
 All Matter has mass
 All matter occupies space
 All matter is composed of atoms
 Matter may have charge
what really MATTERs here?

There are many ways
to classify matter.
One way that is useful
is to classify matter as
either Mixtures or
Substances.
Copy this chart into your
notes.
Matter
Heterogeneous Mixtures
Homogenous Matter
(Substances)
Homogenous Mixtures
Pure Substances
Compounds
Elements
what really MATTERs here?


All matter is made up of atoms. An element is a
substance that is composed of only one kind of
atom. There are some 92 naturally occurring
kinds of atoms. They are called the Chemical
Elements.
Note: There are more than 92 elements listed
on the periodic table. The rest are created in
the laboratory by scientists but usually only last
a few seconds.
what really MATTERs here?
Here’s where chemistry simplifies the
universe:


Everything you own, eat, see, touch,
or have heard about, all the beauty
and complexity of the natural world,
is made up only of those 90 distinct
kinds of atoms, put together in
different arrangements!
You see, the world isn’t quite as complicated as you
thought.
If all elements are made of atoms,
what are atoms made of?
 Here
is where chemistry and
physics make the universe even
less complicated, and a LOT
easier to understand.
 All
atoms are made of ONLY three
different parts!!
Atomic Structure
What do you know?
Starting from the center of the atom and
working outwards, what are the three
parts of an atom?

Neutrons – No charge (neutral)
Protons – Positive charge (+)
Electrons – Negative charge (-)
Atomic Structure

Atoms consist of a
nucleus, which is
made of protons and
neutrons, and
electrons which orbit
the nucleus. This
model of the atom is
called the Bohr
model, named after
the physicist Neils
Bohr.
Atomic Facts



The nucleus is very small. If this
classroom were an atom, the nucleus
would be in the center of the room and it
would be the size of a grain of sand!!
Protons and neutrons are about the same
size and are slightly bigger than electrons.
Atoms are made mostly of empty space.
Atomic Structure

The number of protons an atom has
determine what kind of atom it is. The
number of protons is called the Atomic
Number of the atom. All atoms of the
same element have the same number of
protons. (For Example, all carbon atoms
have 6 protons. That’s why they are
carbon atoms.) Atoms are arranged on the
periodic table in order of increasing atomic
number. The higher the atomic number,
the bigger the atom.
Atomic Structure

Electrons orbit the nucleus in energy
levels. An energy level is really just a
specific distance from away from the
nucleus.

Key Point: In a stable atom, there are the same
number of electrons circling the nucleus as there
are protons in the nucleus. That is why stable
atoms do not have charge. Each negative electron
charge is canceled out by a positive proton charge.
What are atoms made of?

Protons - charge of +1, and a
mass of 1 amu

Neutrons - charge of 0, and
a mass of 1 amu

Electrons - charge -1, mass
of 1/2000 amu (call it 0)

Charge - add up the charge
of all the particles in an
atom

Mass - add up the mass of
all the particles in an atom
Bohr model
Practice



What is the mass and charge
of an atom that has 10
protons, 12 neutrons, and 10
electrons?

What is the mass and charge
of an atom with 5 protons, 6
neutrons, and 4 electrons

What is the mass and charge
of an atom with 7 protons, 7
neutrons, and 10 electrons?

Mass: 22
amu,
Charge: 0
Mass: 11
amu,
Charge: 1
Mass: 14
amu,
Charge: -3
The Magic of Matter
Part 2: What Holds Atoms
Together?
Warm-up:
Have you ever fallen down or
stumped your toe? A force acted
on you. There are only a few
kinds of known forces that act
upon matter.
Draw a picture that illustrates as
many kinds of forces as you can
think of.
(Hint: Two of the forces are related
to nouns in TEKS 8.8 B)
TEKS
8.8 (A) describe the structure and
parts of an atom; and
8.8 (B) identify the properties of an
atom including mass and electrical
charge
What Holds Atoms Together?


Charge is a property of matter. Most
matter has no charge because most
matter has an even number of protons (+)
and electrons (-). However, matter can
acquire charge by gaining or loosing
electrons.
Particles of the same charge repel each
other, and particles of opposite charge
attract each other. This is called the
electromagnetic force.
What Holds Atoms Together?
 The
electromagnetic force is a
strong force – a million million
million million times stronger than
gravity!!!
 …but, it only acts over short
distances.
What Holds Atoms Together?


The electromagnetic force is what makes
electrons orbit the nucleus. The negative
electrons are attracted to the positive
protons. The electron’s velocity keeps it
moving around the nucleus instead of
crashing into it.
But Wait!!! If like charges repel each
other, how can you have so many positive
protons in the nucleus without the
electromagnetic force blowing the nucleus
apart?
What Holds Atoms Together?


Answer: There is a force stronger than
the electromagnetic force. It is called the
Strong Nuclear Force.
This force only works over very short
distances. You must force protons
incredibly close together for the strong
nuclear force to engage and overpower
the repelling force. Neutrons also exert
strong nuclear forces and this acts like
glue to hold the nucleus together.
What Holds Atoms Together?


Because the electromagnetic force is so
strong, it requires intense pressure and
temperatures to overpower it and force
protons close enough together for the
strong nuclear force to take hold. In fact,
it requires temperatures in the tens of
millions of degrees!!!!
Where can you find temperatures and
pressures such as these?
Where Do Atoms Come From?
Surprisingly,
temperatures in the tens
of millions of degrees are
common in nature. Can
you think of where?
Where Do Atoms Come From


On the insides of
stars!
Atoms are made on
the insides of stars.
Stars are giant
nuclear reactors,
fusing hydrogen
atoms together to
make the heavier
elements.
Where Do Atoms Come From

When giant stars die,
they explode in what
is called a Supernova.
When this occurs, the
star sends all the
heavy elements it has
created out into
space. This is where
all atoms (except
Hydrogen and
Helium) come from.
Where Do Atoms Come From


Hydrogen atoms are as old as the
universe. They have been around since
the Big Bang. Great clouds of hydrogen
condense in space, drawn together by
gravity. These clouds are called Nebulas.
Gravity is a weak force, but it acts over
enormous distances and pulls matter
together.
Where Do Atoms Come From


As clouds of hydrogen atoms get bigger
and more dense, the atoms start bumping
into each other more and getting hotter.
Eventually, the nebula gets so dense and
hot that when hydrogen atoms bump into
each other, they fuse together to form a
Helium atom. This sets off a fusion
reaction, and a new star turns on.
Nebula with new stars
Important Point!!!



There is no difference between two
Hydrogen atoms held together by nuclear
forces and a Helium atom. They are the
same thing!
H (atomic #1) + H (atomic #1) = He (atomic
#2)
He (atomic #2) + He (atomic #2) + enough
neutrons to hold the nucleus together = Be
(atomic # 4)
You are the star!



Now you try!
Fuse 40 helium atoms together with
enough neutrons to hold the nucleus
together and what new element do you
make?
You are given the choice of either adding
one proton to your new element or
subtracting one proton. Which would you
choose to do and why?
The Biggest Idea


Except for hydrogen and helium, all the
atoms in the universe were made in now
dead stars. Everything we see and know,
from the gasoline in our cars to the
uranium in our warheads to the gold in
our banks and the carbon in our DNA,
even we ourselves, are made of Star
Stuff.
It is no surprise that we stare up in
wonder at the stars in the night sky. We
are their children.
Estimate the area of the yellow
circles
Hints:
The box is
10 cm on a
side
There are
100 red
dots
Use the dots to estimate the
size of the yellow circles





Notice, the dots are evenly distributed in
the area
So you can expect the proportion of dots on
yellow circles to be the same as the
proportion of area of yellow circles
# dots in yellow / total # dots EQUALS
total area of yellow / total area
23 dots / 100 dots = area of yellow / 100
cm2
Area of yellow dots ~ 23 cm2
That’s how the radius of an
atomic nucleus was first
measured!


But we’re getting ahead of ourselves…
Let’s start with a few basic ideas…
Democritus of Abderra




Lived in Greece, from about 460 B.C. to 370
B.C.
Along with Leucippus, was first to suggest
that all matter is made of microscopic
atoms
Reached that conclusion using ONLY logic…
never conducted any experiments to check
the idea
(also first to realize the Milky Way was
made of millions of separate stars)
John Dalton



Experimented with reacting gases
Example: Observed that water could be
broken down into hydrogen and
oxygen… but their masses were not
equal. 18 grams of water would give 2
grams of hydrogen and 16 grams of
oxygen. And NEVER any other gas!
This, and many other observations with
other gases, led to:
Dalton’s Atomic theory
1.
2.
3.
4.
5.
6.
Elements are made of very tiny particles called
atoms
All atoms of a given element are identical
Atoms of different elements have different
properties, including mass and chemical
reactivity
Atoms aren’t changed by chemical reactions;
they are merely rearranged into new
combinations
Compounds are formed when atoms of different
elements combine
Compounds are defined by the number and
This theory could be falsified by:




Some examples:
Breaking water down into two elements
other than hydrogen and oxygen
Finding atoms of an element that have
some dissimilar properties
Observing a chemical reaction that
changes the atoms involved
What about the structure of the
atoms themselves?


Dalton knew atoms
existed and how they
combined to make
compounds, but he had
no evidence concerning
their
So
hestructure
picked the simplest possible
structure: tiny, hard spheres
J.J. Thomson (1897)



Discovered the electron
Conducted experiments in
which a gas produced
electrons
Concluded that atoms are
positively charged spheres
that contain removable
electrons
Ernest Rutherford (1911)




Bounced alpha particles off
of atomic nucleus
Realized that positive part
of atom must be tiny, less
than 1/10,000th of the
volume!
Did not have information
about electron location
Discovered the proton in
1918
Niels Bohr (1913)

Used observations
that each element
will emit particular
frequencies of light
to suggest that
electrons only exist
in precisely defined
orbits
Erwin Schrodinger (1926)



Louis de Broglie showed
that a moving particle
could be treated,
mathematically, as a wave
Schrodinger used that
result to work with
electrons in atoms as
probability waves.
This led to much more
precise predictions of the
light emitted by atoms
James Chadwick (1932)


Identified where the
extra mass in atoms
came from.
There is another
particle in the nucleus
- the neutron. It has
the same mass as a
proton, but is
electrically neutral.
The Magic of Matter

Part 4: Where the Real
Magic Lies – Electrons
and Change
Warm-up- Short Writing:
Based on what you know
about the
electromagnetic force,
describe why electrons
space themselves out
around the nucleus
instead of grouping
tightly around it.
TEKS
8.8 (B) identify the properties of an atom
including mass and electrical charge
8.9 (A) demonstrate that substances may
react to form new substances
Bonding Basics



Sodium (Na, atomic number 11) is a soft
metal that is highly reactive. It explodes
on contact with water.
Chlorine (Cl, atomic number 17) is a
poisonous, corrosive, green gas used to
kill soldiers in WW1.
What happens when these dangerous
elements are placed in a reaction vessel
together?
When Na is placed into a cylinder filled
with Cl, a violent reaction occurs giving
off large amounts of heat.
Bonding Basics
The result is a crystalline substance which is dissolved in
our seas and in our veins. It is essential for life. It makes
food taste better. We call it table salt.
Bonding Basics
 How
can it be that a metal and
gas can combine to produce an
eatable solid? The answer is that
a chemical reaction has taken
place to create a new substance
with new properties. That means
that chemical bonds have broken
and reformed in a different
arrangement.
Chemistry’s Big Question
Where are the
Electrons?
To understand how atoms
bond together, we must
understand electrons.
Electron Configurations

An atom has from 1 to
Electrons circle the 7 energy levels
nucleus of the
atom in clouds that
are a specific
distance from the
nucleus. These are
called energy
levels. Electrons
always fill the
lowest energy
Electron Configurations




The horizontal rows of the periodic table
are called Periods. They are numbered
from 1 to 7. The period an atom is in
tells how many energy levels it has.
Each energy level can hold only a
certain number of electrons.
Level 1 = 2 electrons, Level 2 = 8 electrons,
Level 3 = 18 electron, Level 4 = 32 electrons
Bonding Basics

Earlier, we said that atoms normally
have no charge because they have
equal numbers of protons and
electrons. However, atoms can gain
or loose electrons. The only place
this electron change can happen is in
the outer most energy level.
Electrons in the outer energy level
are called the valence electrons.
Bonding Basics
Key Point!
The vertical columns of the periodic
table are called Families or Groups.
The are numbered across the top of
the periodic table. Elements in
the same family behave
similarly because they have
the same number of valence
electrons.
Bonding Basics


The elements in group 8A, on the far right
side of the periodic table, all have full
outer energy levels. They are called the
Noble Gasses.
They are happy having full outer energy levels.
They won’t take any more electrons from any
other atoms, and they aren’t giving any of theirs
away. Therefore, these atoms do not react
readily with other atoms, or with each other.
Bonding Basics
 How
Noble
Gasses see
themselves.
Bonding Basics

Like some people, atoms have a goal.
 Atoms
want to have FULL
outer energy levels!

Full energy levels are more stable, and
atoms are all about stability.
Bonding Basics

The key to understanding chemistry:
Atoms will loose or gain
electrons in order to have the
Key Point!
same number of valence
electrons as the Noble Gas
closest to them on the Periodic
Table.
That’s all you need to know to
predict most chemical reactions.
Bonding Basics

The Noble Gasses have 8 electrons in their outer
most energy levels. Since all atoms want to be
like the Noble Gas closest to them, we can say
that atoms will gain or loose electrons in order
to have an octet (8) of valence electrons. This
is called the Octet Rule.

There are exceptions: H and He have only one
energy level that can only hold 2 electrons. Also
the Transitions Metals in Groups 3B-12B do not
follow the rule. You’ll find out why when you
take Chemistry in high school.
Bonding Basics


Example #1
Na, atomic #11, is in Group 1A. It has
one valence electron in its outer shell.
The Noble Gas it is closest to is Neon,
atomic #10. Na must loose one electron
to have the same number of electrons as
Neon, and that is what Na does in most
reaction.
Bonding Basics


Example #2:
Chlorine , atomic #17, is in group 7A. It
has 7 valence electrons in its outer shell.
Argon, atomic # 18 is the closest gas to
Chlorine, so chlorine must gain 1 electron
to be like Argon. That is what chlorine
does in most reactions.
Decide
Now you try!
if the following atoms will gain or loose
electrons in a chemical reaction, and how many:
Potassium (K, #19)
Phosphorous (P, #15)
Magnesium (Mg, #12)
Loose 1 electron
Gain 3 electrons
Loose 2 electrons
The Magic of Matter
Part 5: Kinds of Bonds
– Stealing and
Sharing Electrons
Warm-up:
Draw a model of an
atom with an atomic
number of 7, a mass
of 14, and a charge of
-2.

Ions



Atoms which have gained or lost
electrons are called Ions. Ions are
just atoms with charge.
An atom which looses electrons will have a
positive (+) charge. These are called cations.
An atom which gains electrons will have a
negative (-) charge. These are called anions.
Kinds of Bonds



Atoms can gain or loose electrons to
complete their octets in two ways:
1. They can trade electrons with other
atoms. Bonds formed in this way are
called Ionic Bonds.
2. They can share electrons with other
atoms. Bonds formed in this way are
called Covalent Bonds.
Ionic Bonds



1. Metal atom looses
an electron(s) and
becomes positively
charged.
2. Non-metal atom
gains those electrons
and becomes
negatively charged.
3. The two ions have
opposite charge and
are attracted to each
other by the
electromagnetic force.
Properties of Ionic Substances





Form Between metals and non-metals.
Usually forms high melting point solids.
Ionic substances are usually brittle and
cleave easily.
Dissolve easily in water
Conduct electricity in solution.
Covalent Bonds


Atoms share one or more electrons to fill
their outer energy level.
Covalent Bonds form between two nonmetals. (Elements to the right of the zigzag line on the periodic table.)
Covalent Bonding



No ions are
formed in
covalent bonding.
No atoms gain or
loose electrons.
Atoms simply
share valence
electrons so that
they have full
outer energy
levels.
Hydrogen Molecule
Note that
electrons
actually exist
inside electron
clouds. We
cannot say
exactly where
the electrons
are, only where
they are most
likely to be at
any given time.
Properties of Covalent
Substances




Many are gasses or liquids
There are some covalent solids, but they
generally have low boiling points.
Do not conduct electricity
Do not dissolve easily in water.
Water is a special covalent
molecule.
Polar Covalent Bonds


Oxygen has a
stronger pull on
electrons than
Hydrogen, so the
electrons spend more
time around Oxygen,
making that region
slightly negative.
The Hydrogen region
becomes slightly
positive.
Hydrogen Bonds

The slightly negative region of water near
the Oxygen can be electrostatically
attracted to the slightly positive hydrogen
region of another water molecule. This is
called a Hydrogen Bond. Hydrogen bonds
are weak bonds that are easy to form and
break. They are of high importance in
biology!
Hydrogen Bonds in H2O
Hydrogen bonds give water its unique
properties.
Hydrogen Bonds in Water
Hydrogen Bonds in Proteins
Hydrogen bonds often give structure to
biological compounds.
Hydrogen Bonds in DNA
Why do you suppose…

We stated that Hydrogen
bonds are very weak
bonds, easy to form and
break. Yet, the DNA
strands of the double
Helix are held together by
Hydrogen bonds. Can you
think of any functional
reason why hydrogen
bonds are a good choice
for this purpose?
Chemical Reactions
Warm-Up:
On a sheet of paper,
draw a picture of a
chemical reaction that
happens in your daily
life, or write down
three things you think
of when you think
about chemical
reactions.

Chemical Reactions
When you hear the phrase
“Chemical Reaction,” what do
you think of?




Explosions?
Acids dissolving doors?
Glowing liquids?
Purple clouds?
Changes in Matter




We can classify changes in matter as
either physical or chemical changes.
Physical changes only change the shape
or state of an object.
Chemical changes rearrange atoms
among molecules.
Can you think of some examples of
each?
Physical






Crushing ice
Melting ice
Boiling water
Bending a piece of
metal
Separating iron
filings and sulfur
powder
Melting iron and tin,
mixing, and letting
the mixture cool
Chemical



Using a battery to
break water into
hydrogen and
oxygen gas
Burning a piece of
wood
Heating iron
filings and sulfur
until they bond,
making pig iron
Bonding and Energy





Chemical reactions are the
rearrangement of atoms
What do you have to do in order to
rearrange atoms?
You have to break their bonds!
It takes energy to break bonds.
How can we give a molecule energy it
can use to break a bond?
Giving Molecules Energy






Slam other molecules into it (heating)
Like when you bake a cake…
Pull them apart with an electric field or
hit them with electrons (electricity)
Like when you put wires from a battery
in water to make hydrogen and oxygen
Hit them with light
Like when your dentist uses a UV light
to set a polymer filling
Getting Energy from Molecules





Of course, you can get energy from
molecules, too.
That’s why we burn gasoline in our cars
- to get the energy to turn the wheels
Heat - the new molecules are moving
more quickly
Electricity - the molecules get rid of
electrons (like in a battery!)
Light - like in a glowstick
Exothermic Reaction

If molecules release more energy than
they absorb, the reaction is exothermic.
Sodium and Water
Endothermic Reaction

If molecules take in more energy than
they release, the reaction is
endothermic.
Endo or Exo?
You mix two substances together, and…
 … they heat up.
 Exothermic
 … they cool down.
 Endothermic
 … they glow.
 Exothermic
 … nothing happens until you shine light
on them.
 Endothermic
Chemical Equations



“Methane gas combines with oxygen
gas to produce carbon dioxide and
water”
That’s quite a mouthful, eh?
There’s a shorter way to write that
CH4 + O2
methane
oxygen
 CO2 + H2O
carbon dioxide and water
combines with to produce
Types of Reactions

synthesis - two different elements
combine together to form one
compound
 Fe

(II) + O  FeO (rust!)
Decomposition - one compound is
broken into its two individual elements
 H2O
 2H + O
Types of Reactions (cont.)

single displacement - a lone element
replaces some part of a compound.
 2Li

+ 2H2O  2LiOH + H2
double replacement - atoms in
compounds switch partners
 BaBr2
+ K2SO4  2KBr + BaSO4
Conservation of Atoms




Conservation means, in science, “keep
the same” or “the same everywhere”
It really means, “there’s no such thing
as a free lunch”
When you have a chemical reaction, the
atoms IN must be the same as the
atoms OUT. The atoms must come
from somewhere!
Are atoms conserved in this reaction?
 CH4
+ O2  CO2 + H2O
CH4 + O2  CO2 + H2O







C - Carbon
1 goes in… 1 comes out
H - Hydrogen
4 go in… 2 come out (??)
O - Oxygen
2 go in… 3 come out (??)
Nope, the atoms aren’t conserved.
Balancing Equations

Balancing equations is adjusting the
numbers of each molecule until there’s
the same number of each atom on each
side.
+ O2  CO2 + H2O
 Hrm… what if I had TWO
oxygen molecules on the left?
 CH4 + 2 O2  CO2 + H2O
 C - 1, H - 4, O - 4 on the left
 C - 1, H - 2, O - 3 on the right
 CH4
Balancing Equations (cont.)


Closer… I need 2 more H and 1 more
O on the right.
How about another water molecule?
+ 2 O2  CO2 + 2 H2O
 C - 1, H - 4, O - 4 on the left
 C - 1, H - 4, O - 4 on the right
 It is balanced!
 CH4
Balancing Equations (practice)
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
If I mix aluminum (Al) and sulfur (S)
together, what compound will they
make?
Hrm… Al has an oxidation of 3+, S has
an oxidation of 2-…
2 Al + 3 S  Al2S3