Download Atoms, Elements, Compounds, and Mixtures

Atoms, Elements,
Compounds, and Mixtures
Structure of the Atom
 Atoms are the smallest
 All atoms share the same
particles into which matter can
basic structure. Over the
be divided and still maintain its
years, scientists have
characteristics.
designed many different
models for this structure.
 Atoms are the building blocks
of the universe. There are 92  Each one was the best
different kinds of atoms that
model at the time, but as
occur naturally, although more
new evidence was
are man-made.
discovered, the models were
revised to fit it.
 These building blocks can be
joined together to create all of  Scientists will probably revise
the different kinds of matter we
the current model as more
can observe.
evidence becomes available.
What’s inside of an
atom?
?
Early Atomic Models
 The Greek scientist Democritus was the
first person to say that all matter is made of
atoms, but he also said that atoms are
indivisible.
All mater is made
of atoms, and
atoms of an
element are alike.
Different elements
have different
atoms.
+
=
“Atoms are
indivisible.”
- Democritus
 In the early 1800’s, the English scientist
John Dalton developed his Atomic Theory of
Matter. It said four things: (1) All matter is
made of atoms. (2) Atoms of an element are
alike. (3) Atoms of different elements are
different. (4) Atoms of different elements join
together to make compounds.
Atoms join to make compounds. - John Dalton
In the late 1800’s, J. J. Thomson
discovered that atoms were made of smaller
particles. He discovered the electron and
devised the “Plum Pudding” model of the
atom.
Positivelycharged matrix
Negativelycharged
electron
- J. J.
Thomson
Recent Atomic Models
 In the early 1900’s, scientists
discovered the positively-charged proton.
In 1911, Rutherford discovered the nucleus
of the atom, where protons are located.
Atoms are mostly empty space.
Electrons
orbit the
nucleus.
- Niels Bohr
Positively-charged
protons are in the
nucleus.
- Rutherford
 Niels Bohr changed Rutherford’s model in
1913. Bohr said that electrons move around the
nucleus in fixed energy levels. Electrons can
move from one energy level to another. Bohr’s
model has been called the “Solar System” model
of the atom.
Negative electron cloud
 The current model of atomic structure is
called the “electron cloud” model.
Electrons move within an energy level in
an ever-changing path, not a fixed orbit.
Neutrons bond with protons in the nucleus.
Neutral neutrons are
in nucleus with
positive protons.
- Electron Cloud
Model
Atomic Number and Mass Number
 All atoms of an element have the  Atoms of the same element may
same number of protons, and
have different numbers of
different elements have different
neutrons. Atoms with extra or
numbers of protons in their
missing neutrons are called
atoms.
isotopes.
 The atomic number of an atom is
 An atom’s mass number is the
the number of protons it has. If
number of protons plus neutrons.
the atom is neutral, the atomic
number is also the number of
 Different isotopes of an element
electrons.
have different mass numbers.
Atomic number of this
neutral atom = 6.
This means that it
has 6 protons and 6
electrons.
Mass number of this neutral
atom is 14. This is the sum of
the protons plus neutrons.
Since there are 6 protons,
there must be 14 - 6 = 8
neutrons.
Elements
 An element is matter that is made of
 Chemical symbols are
only one kind of atom. All of the
abbreviations for the names of
atoms of an element are alike. There
elements. You can also use a
are 92 naturally occurring elements.
chemical symbol to represent
one atom of an element.
 Elements can be identified by their
properties. Some properties are color,  Chemical symbols are the
texture, density, malleability, ductility,
same all over the world, no
ability to dissolve in water, and ability
matter what language is
to conduct heat or electricity.
spoken. The first letter is
always capitalized, and if there
 At room temperature, most elements
is a second letter it is never
are solids, although a few are liquids
capitalized.
and some are gases.
H
Na
Chemical symbol for the
element Hydrogen, a
flammable gas.
Chemical symbol for the
element Sodium, used in
sodium vapor lamps.
Chemical symbol for the
element Chlorine, used in
bleach and water treatment.
Cl
O
Chemical symbol for the
element Oxygen, needed for
life.
Compounds
 The atoms of most elements are 
very reactive. They chemically
join together with atoms of other
elements to form compounds.
 The properties of compounds are
different than the properties of the
elements that make the
compound.

 When elements join to make
compounds, they always join in
the same proportion. H2O is
water, not HO or H3O !
H is symbol
for Hydrogen
H2O
Subscript 2
means that there
are 2 Hydrogen
atoms
Water molecule
O is symbol for
Oxygen
No subscript
means one
Oxygen atom
Compounds are separated into two
groups, depending on how their
atoms are joined: (1) Molecular
compounds are made of atoms that
share electrons. (2) Ionic compounds
are made of atoms that gain or lose
electrons.
Chemical formulas represent
compounds. They show the kind and
number or atoms in the compound.
N is symbol
for Nitrogen
NH3
No subscript
means one
Nitrogen
atom
H is symbol for
Hydrogen
Subscript 3
means there
are 3
Hydrogen
atoms
Ammonia
Molecule
Mixtures
 Mixtures are made when there
are at least two different kinds of
atoms that are in the same
place but are not chemically
combined.
 A mixture can be made with any
proportion of ingredients, but a
compound must be made in
only one certain way.
 Components of a mixture keep
their own properties, but those
of a compound do not.
 Components of a mixture are
not chemically combined, so
they can be separated by
physical means.
This coffee is a
mixture.
This cake is a
mixture.
This basket of fruit
is also a mixture.
Types of Mixtures
 A homogeneous mixture is the
same throughout. All parts of the
mixture have the same proportion
of ingredients.
 A heterogeneous mixture is
different in different parts. Different
regions of this kind of mixture have
different proportions of the
ingredients.
 An alloy is a homogeneous mixture
of metals.
 All solutions are homogeneous
mixtures.
This cookie is
heterogeneous.
Soft drinks are
homogeneous
mixtures.
The alloy these keys are
made of is a
homogeneous mixture.
The crayons in the pail
make a
heterogeneous
mixture.
The milk is
homogeneous.
The gelatin mold is a
heterogeneous mixture.