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Atoms and Elements
Chapter 2
Pgs. E34-E49
What are Atoms and Elements?
pgs. E36-E43
Atoms aren’t a New Idea
• Democritus (400 B.C.), a Greek
philosopher, had a theory that matter is
made of tiny particles that can’t be
divided and are too small to see.
• Aristotle also a Greek philosopher didn’t
buy the theory
Neither one based their theories on any
experimental evidence.
Democritus
Aristotle
John Dalton
Early 1800’s
Proposed an
atomic theory
of matter that
was based on
experimental
evidence.
Dalton’s atomic
theory is that
all matter is
made up of
tiny particles
called atoms.
Size of an atom.
Atoms are tiny.
Over five million
atoms could fit
on the head of
a straight pin.
Subatomic Particles
Atoms are teensy weensy; however,
there are even smaller particles on
the inside of the atom.
• nucleus – center of the atom
• proton – positive charged particle
inside of the nucleus
• neutron – a particle inside of the
nucleus with no charge
• electron –a particle outside the
nucleus with a negative charge
Atoms
• Atoms are the smallest unit of an
element that has all the properties
of that element.
Niels Bohr proposed a model
of the structure of an atom
in 1913.
Niels Bohr’s
Atom Structure Model
• Electrons circle the nucleus
• The electrons path is called an
orbit/energy levels
• Low energy electrons orbit close to
the nucleus
• High energy electrons orbit farther
away from the nucleus
Protons and
neutrons have a
mass that is almost
2000 times the
mass of an
electron.
Proton Man
Electron Man
The attraction between the positive
charge of the protons and the negative
charge of the electrons is part of what
holds atoms together.
• If an atom has more protons
than electrons it has a
positive charge.
• If an atom has more
electrons than protons it has
a negative charge.
• An atom that has an equal
amount of protons and
electrons is a neutral atom
An element is a
substance made
up of only one
kind of atom.
Gold is an
element
79 – atomic number = # of protons in one
atom of that
element
Au – chemical symbol
Gold- element name
In your book look at the chart on Pg.
E 41 to see some more common
elements.
Halogen/Salt
Iodine
I
Metal
Platinum
Pt
Gas
Hydrogen
H
Metalloid
Antimony
SB
Molecules
Two or more atoms of the
same kind linked together
form a molecule that is in a
pure state.
Example: Oxygen
O2
A molecule is also formed when two
or more elements are linked
together.
Explore here to view some
molecules”
http://www.worldofmolecules.com/
Properties of Metals
Luster-shiny
Are ductile-able to be hammered thin
Are malleable-can be bent and molded
Conduct electricity and heat
What Are Compounds?
Lesson 2 pgs. E46-E49
Dmitri Mendeleev
• Russian
Chemist
• Organized
elements
into an
orderly table
in 1869.
The Period Table
pgs. E46-E-47
• Elements are arranged in order of atomic
number.
• Elements with similar properties are in
the same column
• Elements on the left side of the table,
except hydrogen, are metals
• Elements on far right are nonmetals.
• Metalloids have properties of both
metals and nonmetals.
Check out these interactive
periodic tables to learn more
about the elements. I liked
the second one better.
http://www.chemicalelements.
com/
http://www.chemsoc.org/visel
ements/pages/pertable_j.htm
Compounds
A substance made of the atoms of
two or more elements.
Use your periodic table on
pgs. E46-E47 to see if you
can match the compounds
and their names
http://www.quia.com/mc/65800.html
How to read a Formula for a compound
1. Chemical formulas are used to describe
the types of atoms and their numbers
in an element or compound.
2. The atoms of each element are
represented by one or two different
letters.
3. When more than one atom of a specific
element is found in a molecule, a
subscript is used to indicate this in the
chemical formula.
2 atoms of
Hydrogen
+
1 atom of
Oxygen
+
H2
+
=
1 molecule
of water
=
O
=
H2O
More Chemical Compounds
Carbon Dioxide > CO2
Ammonia > NH3
Sugar > C6H12O6
Rubbing Alcohol > C3H7OH
Credits
•faculty.washington.edu/smcohen/320/Democritus.jp
g
•www.windows.ucar.edu/people/images/aristotle.gif
•http://web.gc.cuny.edu/ashp/nml/copenhagen/Bohr
.jpg
•nobel.scas.bcit.ca
•http://education.jlab.org/atomtour/proton.gif
•www.csudh.edu/oliver/chemdata/pt100mc.jpg
•http://www.jaysgoldnuggets.com/gold/24pt9gma
us.jpg
•http://www.jergym.hiedu.cz/~canovm/vyhledav/
varianty/mendelej/mendeleev.jpg
•