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					     Chapter 4

Compounds and Mixtures
Matter is sorted just like you would sort
things in your life. Matter is divided into 3
groups.

Elements: made of only one kind of atom.

Compounds: made up of atoms of two or
more elements that are chemically
combined. The elements are combined in a
mixed ratio.

Example: Salt is made up of 1 atom of
sodium and 1 atom of chlorine.
Mixture: made of two or more kinds
of matter that are physically
combined or mixed together. There
can be any amount of matter in the
mixture.

Example: Salad, sugar and
cinnamon, salt and sugar.
Elements and Compounds have similar
characteristics. If you have a sample of an element,
another sample of the exact same element has the
exact same properties. Same with a compounds. If
you have a sample of a certain compound, the exact
same compound in a different sample will have the
exact same properties.

Examples: Sugar that you use in your cookies when
you bake is the same sugar that makes up candy.
Because elements and
compounds have similar
characteristics, they are called

substances: any element or
compound.
Elements combine with other elements to
become compounds.

What is a compound?
Substance made up of two or more
elements that are chemically combined

Example: hydrogen and oxygen are both
elements that are gases but when they
combine they make WATER!!
What are some common
     compounds?
Properties of compounds are very
different then the properties of the
elements that make them up. Some
elements may be very dangerous but
when they combine to make a compound
they are not.

Example: sodium explodes when added
to water. Chlorine is a poisonous gas.
When they combine, they make table
salt.
Most compounds are made of
molecules: the smallest part of a
substance that has all the same properties
of that substance. It can be made of a
single atom or a lot of atoms.

Example: Molecule of lead is one atom
of lead. A molecule of sucrose is 45
atoms.
Compounds are made through a chemical
change. The elements form chemical bonds
between the atoms. A chemical bond is the force
of attraction the holds atoms in a molecule
together. A chemical change can also change a
compound back into an element. To do this, the
chemical bonds have to be broken. Heating is
one of the ways that this is done.

Examples: As you know the chemical formula
for sugar is C6H12O6. Well when you heat sugar
it melts. If you heat the melted sugar long
enough the oxygen and hydrogen will break
away from the carbon and become gases. The
carbon will remain in the test tube.
Another way to break apart bonds
are through electricity.
What is a mixture?
Two or more substances that have been
PHYSICALLY combined.

What are some examples of a mixture?
Salad, sugar and cinnamon, salt water,
sugar and water.
There are two kinds of mixtures.
Even mixtures and uneven mixtures.
Think about a salt water mixture.
There are even amounts of salt and
water. Salt is still salt and water is
still water but they are so evenly
distributed that they look all the
same. They do have all of their own
properties.
Now think of a salad. This is an
example of an uneven mixture. In
this mixture, each item in the
mixture has all of its own properties.
So a tomato is still a tomato and
lettuce is still lettuce.
Knowing the difference properties of the
items in a mixture can help you to
separate them. This is because parts of a
mixture are not chemically combined.
This means that you can separate them
by their physical properties. In the salad,
the tomatoes can be picked out manually.
How do you think that you would
separate the salt water mixture?

You would have to boil the
water. When you boil water, the
water evaporates and all the you
would be left with is the salt.
Other mixtures can be separated by
filtering.

Example: Sand and water can be
separated through filtering. You would
use a funnel with filter paper to pour the
mixture through. The water would go
through the filter paper and the sand
would not.
So how exactly are mixtures
different than compounds?
• Compounds are combines chemically
  where mixtures are combine
  physically.
• You can separate a mixture manually
  by their physical means but a
  compound you have to separate
  chemically with heat or with
  electricity.
What are iron fillings?

Small sliver or shavings of the
element iron.
What is sulfur?

An element on the periodic table
that is not a metal. It is a
yellowish substance.
How would you separate this
mixture?

You would separate it by using a
magnet. The iron is a metal and
all metals are attracted to a
magnet. The sulfur is not a metal
so it is not attracted to a magnet.
How are compounds made?
Form as a result of a chemical change.
Made of two or more elements that are
chemically combined.

Examples: Molecules of salt are
combined by a chemical change.
Sodium atoms form bonds with chlorine
atoms to produce salt molecules.
Can iron and sulfur combine
chemically also?

 Yes they can…it is called iron
sulfide. It forms when iron
fillings and sulfur are mixed then
heated.
There are many differences between
mixtures and compounds. A mixture
has no definite chemical
composition. Each item contains its
own properties in a mixture. A
mixture can be separated by physical
means.
A compound has a definite chemical
composition. Elements lose their
physical properties when they
become chemically combined. They
cannot be separated by physical
means.
Ionic Bonding

Chemical bonds are formed through
the use of valence electrons.
Valence electrons: electrons in the
outmost energy level of an atom.
The outermost energy level
contains up to 8 valence
electrons; except for hydrogen
and helium: their outermost
energy level only contain up to 2
valence electrons.
All the atoms of all the elements
have valence electrons. Atoms with
fewer that 8 valence electrons form
bonds with other atoms. Atoms can
either gain electrons, lose electrons
or share electrons. When they do
this…it makes them more stable.
What is all matter made of?

ATOMS!!!!
What are the smaller particles that make
up an atom and what are their charges?

Proton: positive charge in the nucleus

Neutron: no charge in the nucleus

Electron: negative charge surrounding
the nucleus
What makes an atom neutral?

The number of protons and
electrons are the same in every
atom.
When chemical bonds are formed,
nonmetals are going to gain
electrons. Metals are going to lose
electrons. When this happens the
number of protons is going to be
different than the number of
electrons and the atoms becomes
electrically charged.
What is an ion?

Atom with an electrical charge.
A neutral atom that gains electrons
becomes a negative ion. A neutral atom
that loses electrons becomes a positive
ion.
Why does this happen?

  This happens because if an atom loses
 electrons, then the nucleus has a
 greater number of protons than
 electrons meaning the nucleus has a
 greater positive charge. When an atom
 gains electrons, there will be greater
 negative charge outside of the nucleus
 then a positive charge inside the
 nucleus because there are now more
 electrons in the atom than protons.
Compounds are held together by
chemical bonds.

What is an ionic bond? A bond
formed between atoms that have
gained or lost electrons.
   What are ionic compounds?

• Compounds held together by ionic bonds.
• Not made of molecules
• Made up instead by one or more positive
  ions and one or more negative ions.
• All ionic compounds have similar properties
• One property is that they become crystals.
• Have high melting points
• Conduct electricity when they are melted.
Covalent Bonding

As you have noticed with the periodic
table, not all the elements have their
outermost energy levels full. Because of
this, atoms are either going to gain, lose
or share electrons. The electrons are
going to come from other atoms that also
have incomplete outermost energy
levels.
How are ionic compounds
formed?

When atoms gain one or more
electrons and other atom loses
one or more electrons. Opposites
attract making an ionic
compound.
Elements also form compounds
when they share electrons. When
atoms bond this way, the bond is
called a covalent bond.
Covalent compounds:
compounds whose atoms share
electrons in covalent bonds.

Water is an example of a
covalent bond.
Here is what it looks like:
So what are the differences between ionic
and covalent bonds?
Atoms in Ionic Bonds gain or lose
electrons. Atoms in covalent bond share
electrons. This means that the atoms do
not become positively or negatively
charged. The atoms remain neutral.

You can use electron dot diagrams to show
how covalent bonds form and how
electrons are shared.

				
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