Download Atoms

Atoms, Elements &
Molecules
The Building Blocks of the
Physical Universe.
Atoms
Atoms are the absolute smallest units that make up
matter.
Atoms are so small that we cannot see them with our
bare eyes, they are so small that we can’t even see
them with a light microscope.
An element is a substance made from only one type of
atom.
Two or more atoms combined together makes a
molecule.
Protons, Neutrons and
Electrons
An atom has three parts:
 Proton = positive
 Neutron = neutral, meaning they have no charge
 Electron = negative
The proton & neutron are found in the center of the
atom, a place called the nucleus.
The electrons orbit the nucleus.
What Does an Atom Look Like?
The Atom Continued -
Graphic from http://education.jlab.org/atomtour/fact2.html
Elements
Over time, scientist began to realize that every
different atom makes a different element. For
example atoms of a certain kind make up carbon and
atoms of another kind make up hydrogen.
The number of protons in an atom determines what
element it will be.
A long time ago people learned that it is impossible to
turn one kind of atom into another.
What are elements?
 Elements are made of
atoms. While atoms may
have different masses and
the number of parts, they
are all built in the same way.
 Elements
are to
molecules
as the
alphabet is
to words.
 Elements are
necessary if
you want to
make
molecules.
Report on Development of the Atom
Work together with classmates
at your table.
Obtain:
Choose one of the
following scientists:
 Grade 7 Textbook (208-209)
 Democritus
 OER Textbook (17-22)
 Dalton
Select a scientist
Write a short report on your
scientist, using the textbooks as
your sources. Use a separate
piece of paper and include the
names of your group.
 Thomson
 Rutherford
 Bohr
History
Because atoms are so
incredibly small,
scientists have had to
make new tools and
technology to be able to
study them. This has led
to generations of
scientists discovering
more and more about
atoms.
Early Greek
Theories
• 430 B.C. - Democritus thought
matter could not be divided
indefinitely. He called these
indivisible pieces atomos.
• 350 B.C - Aristotle rejected this
idea and modified an earlier theory
that matter was made of four
“elements”: earth, fire, water, air.
• Aristotle was wrong. However,
his theory persisted for 2000
years.
John Dalton
It wasn’t until the 1800s that the
next scientist John Dalton brought
back the idea of an atom.
However, rather than just make
theories about the idea he did
experiments to try to learn more.
He said that all matter is made of
atoms and atoms of a single
element are identical and that
different atoms combine to make
molecules.
Dalton (con’t)
Dalton was the first scientist to create a
model of the atom. Models are used to
represent what scientists think atoms look
like, or how they move. However, models
don’t always perfectly show all the parts of
what it is they represent.
“Billiard Ball” Model
Billiard Ball
Model
Atoms
cannot be
subdivided,
created, or
destroyed.
History - Thomson
In 1897, Thomson showed that
cathode rays were composed
of previously unknown
negatively charged particles.
Thus he is credited with the
discovery and identification of
the electron; and with the
discovery of the first subatomic
particle.
Joseph J. Thomson
Plum Pudding Model
Plum Pudding
Model (1897)
History - Rutherford
Geiger–Marsden experiment,
which demonstrated the
nuclear nature of atoms by
deflecting alpha particles
passing through thin gold foil.
A very small positive charged
nucleus, containing most of
the atom's mass, was orbited
by low-mass electrons.
Planetary Model (1911)
Ernest Rutherford
Planetary Model
(1911)
Positive
charged
nucleus with
orbiting
electrons
.
History - Bohr
A negatively charged electron,
confined to an atomic orbital,
orbits a small, positively
charged nucleus.
He introduced the idea that an
electron could drop from a
higher-energy orbit to a lower
one, thus emitting a quantum
of energy.
Niels Bohr
Bohr Model
Bohr Model
(1913)
Depicts the atom as
a small, positively
charged nucleus
surrounded by
electrons that travel
in circular orbits
around the nucleus.
Electron Cloud Model
Today we use the Electron Cloud Model. It looks a lot
like Bohr’s model, the protons and neutrons stay in
the nucleus and the electrons are in different levels
around the nucleus.
The Electron Cloud model says that the electrons
move around randomly and don’t always stay in the
same place. Electrons move like waves but stay in
the same orbital.
Progression of the
Atomic Model
-
-
-
-
-
+
++
-
-
-
--
The structure of an atom, according to:
-+
Electron
Electron Cloud
Cloud
Democritus
James
Neils
Chadwick
Bohr&
J.J.
Thomson
Ernest
Erwin
Schrodinger
Rutherford
John Dalton
Periodic Table of
Elements
To better organize
the elements, or
different types of
atoms, Dimitri
Mendeleev created
a periodic table of
elements (1869)
… Elements ...
• Elements build all
matter in the universe.
• All the elements of
matter make up the
Periodic Table. You
could call it the alphabet
of chemistry.
• The Periodic Table
provides several items
of information, like …
Periodic Table of Elements
- Continued
The number above each element symbol or letter is
its atomic number. The atomic number = the number
of protons in the nucleus. Example:
Hydrogen 1
Oxygen 8
Carbon 6
Nitrogen 7
Iron 26
The number below each element symbol or letter is its
atomic mass. The atomic mass = number of protons
plus neutrons in its nucleus.
The number of electrons is usually equal to the
number of protons in an atom.
Electrons have special rules …
• You can’t just shove
all of the electrons
into the first orbit of
an electron.
• Electrons live in
something called
shells or energy
levels.
• Only so many can be
in any certain shell.
Electron Shell Configuration
• Electrons live in something called shells or energy levels.
• Only a certain number of electrons can be in any certain shell.
• The electrons in the outer most shell of any element are called
valance electrons.
Nucleus
1st shell
2nd shell
3rd shell
Adapted from http://www.sciencespot.net/Media/atomsfam.pdf
And now let’s try ...
How to draw a Lithium atom:
First – Examine the
Periodic Table
Second – Determine the
number of protons
(Atomic Number)
Third – Determine the
number of neutrons
(Atomic Mass – Atomic
Number)
Fourth – Determine the
number of electrons
(Refer to Atomic Number)
__
___
______
__
Current Atomic Model
The current atomic (Bohr)
model shows all of the
particles in the atom.
In the center are circles.
Each circle represents a
single neutron or proton.
Protons should have a plus
(+) or P written on them.
Neutrons should be blank or
have an N.
In a circle around the
nucleus are the electrons.
Electrons should have a
minus sign (-) or an e.
+
+
-
Draw a Model:
Protons = 3
3
Li
Lithium
7
Neutrons = 4
Electrons = 3
2 in the 1st shell, 1
in the 2nd shell
(7-3=4)