Download Atoms and the Periodic Table

th
8
Grade Science
Democritus
 Around 430 B.C.
(2437 years ago)
the Greek
philosopher first
proposed the idea
that all matter is
formed from
atoms.
Dalton’s Atomic Theory
 English chemist that first
described many of the
characteristics of atoms.
Continued…
Dalton’s Atomic Theory
1. All elements are
composed of atoms that
cannot be divided.
Continued…
Dalton’s Atomic Theory
2. All atoms of the same
element are exactly alike
and have the same mass.
Atoms of different elements
are different and have
different masses.
Continued…
Dalton’s Atomic Theory
3. An atom of one element
cannot be changed into an
atom of a different element.
Atoms cannot be created
or destroyed in any
chemical change, only
rearranged.
Dalton’s Atomic Theory
4. Every compound is
composed of atoms of
different elements
combined in a specific
ratio.
• All matter is made of one or
more elements.
Elements are pure
substances that cannot be
broken down by any
chemical or physical means.
• The atom is the smallest
particle of an element.
Draw this:
• Atoms are composed of 3
subatomic particles called
protons, neutrons and electrons.
• The center of the atom is called
the nucleus. It contains protons
and neutrons.
• Circling around the nucleus is 1 or
more electrons.
• Atoms are different from each
other because each element’s
atoms have different #s of the
subatomic particles.
Now create a chart that looks like this:
Proton
Neutron
Electron
• The electron is found moving
around the outside of the
nucleus.
• The electron has a (-) electric
charge.
• The has a mass of 0.0005
amu. (The mass of the
electron is so small compared
to the proton and neutron that
it is ignored.)
e
• Protons are located in the center core of
the atom called the nucleus.
• Protons have a positive electric charge
(+1)
• Protons (p1) have a mass of 1 amu
(atomic mass units).
• Protons are found in the center core
of the atom called the nucleus.
• Protons have a positive electric
charge(+).
• Protons (p+) have a mass of 1 atomic
mass unit (amu).
Structure / Parts of the
Helium Atom
Electron
Neutron
Proton
• Neutrons are also located in the
nucleus.
• Neutrons are electrically neutral.
They do not have a charge.
• Neutrons (n0) have a mass of 1 amu.
AMU = protons +
neutrons + electrons
The periodic table gives the
following information about
each element and its atoms.
• Atomic Number
• Atomic Mass
• Element
Symbol
Sample Periodic Table
• The symbol is an abbreviation
for the name of each element.
It’s either 1 or 2 letters with
the 1st letter capitalized.
• The atomic number is the
smaller of the 2 numbers.
This number tells us the
number of protons and
electrons in the atom.
• The atomic mass # is the
sum of the protons,
neutrons, and electrons.
• This number is used to find
the number of neutrons.
• Finding the Neutrons =
Atomic mass (rounded) –
atomic number
Mass – Protons = Neutrons
Practice
 1. Use the periodic table to
determine the number of
protons, neutrons, electrons,
and chemical name for the
following:
a. N
b. Na
c. Te
This is a Bohr model for the atoms
of the element carbon.
Nucleus
Shell 2
Shell 1
Electron Placement
•
e
are not all the same
distance from the
nucleus.
Electron Placement
•
e
are placed in shells
(energy levels) which are
located at different
distances from the nucleus.
• The shell closest to the
st
nucleus is the 1 shell and
can hold a max of 2 e-.
• Shell no. 2 can hold a max
of 8 e .
• Valence shells (outermost)
can hold a max of 8 e .
Element
Protons Neutron
and
Electrons
Carbon
6
6
Oxygen
8
8
Two atoms are isotopes
of one another when they
have the same # of p+ but
0
different #s of n .
Atom
Name
Protons Neutrons
Carbon 12
6
6
Carbon 14
6
8
Example of Isotopes
Neutron
Proton
Standard
Hydrogen
Hydrogen
Isotope
• An atom is (0) when
# of e- = # of p+.
The atom does not have
an overall charge.
• An atom becomes an ion
when it either gains or
loses an e . There is no
longer a balance between
p+ and e- and the atom is
now either positively or
negatively charged.
• 18 vertical columns called
groups or families.
• Elements in each group, have
similar properties and
characteristics.
• Elements in horizontal rows
called periods.
• The periodic table
is divided into three
different regions.
• The three regions
are the metals,
semimetals/
metalloids, and the
nonmetals
including the noble
gases.
Metals = green, Semimetals = purple,
Nonmetals = yellow/orange,
Noble Gases = Blue
Semimetals/
Noble (Inert) Gases
• Physical properties: hardness,
shininess, malleability, and
ductility.
• Malleable material can be
pounded into shapes.
• Ductile material can be pulled
out or drawn into a long wire.
• Metals are good conductors
of heat and electricity. Most
are also magnetic as well.
• Located on the left of the
zigzag line in the periodic
table.
• Why were gold and silver
mad when they went to
school together?
• Because they were in
different periods!
• Lack properties of metals.
• Right of the zigzag line in periodic
table.
• Noble gases (inert gases) located in
family 18. They are stable and are
not reactive with other elements.
Other elements want to be like them
and have their outer shell full.
• Elements that form the zigzag line in the
periodic table.
• Most chemists agree on 6 or 7 metalloids
depending on which source you use.
• Semimetals/metalloids have some
properties of metals and some properties
of nonmetals.
• One of the most important properties of
semimetals/nonmetals is their varying
ability to conduct electricity.
 I asked the guy sitting next to me if he
had any Sodium Hypobromite…
 He said NaBrO
 Q: What is the show cesium and iodine
love watching together?
 A: CsI
 Your teacher - Making bad chemistry
jokes since 1992, because all the good
ones Argon!
 Silver walks up to Gold in a bar and says,
"AU, get outta here!"
 I would like to apologize for not adding
more jokes... but I only update them....
periodically!
• When a (0) atom gains 1 or
more e-, it now has more (-)
e- than (+) p+. This type of
ion now has a (-) overall
charge and is called an
anion.
• A (0) oxygen atom will often
gain 2 e- to become more
stable. The anion now has
a charge of – 2. There are 2
more e- than there are p+.
Oxygen Anion
Gained
Electron
8 Protons and 10 Electrons = - 2 charge
Gained Electron
• Some people say that anions are
negative.
• I don’t think anions are negative,
they're just misunderstood!
• Q: What did one ion say to the
other?
• I’ve got my ion you!
• When a (0) atom loses 1 or more
e-, it now has more (+) p+ than it
does (-) e-. Cation = (+) charged
ion.
• A (0) lithium atom will often lose
an e- to become more stable.
The cation will have a charge of
+ 1.
Lithium Cation
Electron lost
3 Protons and 2 Electrons = +1 charge
Nitrogen 14 and Nitrogen 15
atoms are used in research.
Answer the following questions.
• What are these two atoms called?
• List the number of p+, e-, and n0
for each atom.
• A neutral magnesium atom loses
two electrons. What is it’s
charge?
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