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The Atom

..\Video download\Tsar Bomba
REMASTERED.mp4
In the beginning…

Atoms are the basic building blocks of
matter. The word atom is derived from
the Greek word atomos, which means
indivisible or uncuttable.

The Greeks concluded that matter could
be broken down into particles too small
to be seen. These particles were called
atoms.
How Small is an
Atom?
 The
average size atom (Al) is
about 0.00000003 cm.
 It would take a stack of 50,000
aluminum atoms to equal the
thickness of a sheet of
aluminum foil.
 There
are over
6,000,000,000,000,000,000,000
(6 x 1021) atoms in one drop of
water. It would take you about
100 trillion years to count this
number out.

It would take you 500 years
to count the number of
atoms in a grain of salt.
 If
we stretched a penny until
it covered the entire US,
each of its atoms would be
only 3 cm across!
Atomic Structure
Atomic Structure
 Atoms
have 3 main parts,
called subatomic particles.
Atomic Structure
 Nucleus:
(center of atom)
1. Protons have a positive
(+) charge
 2. Neutrons have no charge,
they are neutral
Atomic Structure (cont’d)
Orbitals: (shells, cloud, flying
around outside)
 3. Electrons have a negative (-)
charge

Atomic Structure
These things are teeeeny
tiny
 The
mass of a proton is
really small, so small in fact,
that scientists created a
whole new unit for it.
 A proton has a mass of 1
atomic mass unit (AMU).
Atomic Mass Unit (AMU)


The unit of
measurement for an
atom is an AMU. It
stands for atomic
mass unit.
One AMU is equal to
the mass of one
proton.
Atomic Mass Unit (AMU)
There are
6 X 1023 or
600,000,000,000,000,
000,000,000 amus in one
gram.
 (Remember that
electrons are 2000
times smaller than one
amu).

A
neutron is actually a little
bigger than a proton, but not
enough to notice the
difference, so we say it also
has a mass of 1 AMU.
 Electrons
are so small, they
don’t have a measurable
mass.
p+
Nucleus Positive
1 amu
Nucleus Neutral
1 amu
Outside
Negative
in
Shells
0 amu
Atomic Number is the Number of
Protons
 All 112 elements are made of atoms.


What makes the elements different?

The atomic number, or number
of protons, determines the element.
Example:

Every gold atom has 79 protons.
Key to the Periodic Table

Elements are organized
on the table according to
their atomic number,
usually found near the top
of the square.
– The atomic number
refers to how many
protons an atom of
that element has.
– For instance, hydrogen
has 1 proton, so it’s
atomic number is 1.
– The atomic number is
unique to that
element. No two
elements have the
same atomic number.
What’s in a square?
Atomic Number
Chemical Symbol
Atomic Mass
Name
State of Matter
“Color of symbol”
Metal, nonmetal or metalloid
“color of box”
Protons?
4
17
27
81
108
13
When is an atom neutral?

An atom is neutral when it has an
equal number of electrons and
protons.
Example:
Helium has 2 protons & 2 electrons
 That means it has 2 + charges & 2 charges.
 They cancel to create no charge.

How Many Electrons?
12
16
36
74
68
Atomic
number also
equals the number of
electrons.
How do you find an atom’s
mass?
What are the only two parts of an atom
that have mass?
 Protons have a mass of 1 amu
 Neutrons have a mass of 1 amu
 Electrons are so teeny they don’t weigh
anything.

Atomic Mass/Mass #
Mass Number = number of protons
+ number of neutrons
 You Try

5
5
6
18
18
22
3
Boron
7
11
3
3
4
6
Think About This!

1. What is heavier, an atom’s nucleus or
the orbitals?
Nucleus
2. What happens to an atom that has an
extra neutron?
It becomes a heavy Isotope
3. What happens to an atom that is
missing an electron?
It becomes a charged ion
Questions...
 What
particles are in the
nucleus?
 Explain why atoms are neutral.
 Why do scientists say that most
of the mass of an atom is
located in the nucleus?
How Do Atoms of Different
Elements Differ?
 Lets
compare a Hydrogen atom
and a Helium atom…
Hydrogen...
 Draw
one proton.
 Draw a circle around the
proton.
 Place one electron on the circle.
 You have just created a
hydrogen atom!
 Hydrogen has no neutrons.
DOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and compounds
are represented by Dots or Crosses to show electrons,
and circles to show the shells. For example;
Hydrogen
Electron (-)
-
H
1
1
Helium
 Draw
two protons and two
neutrons all together.
 Draw an electron orbit around
them.
 Place two electrons on the
orbit.
 You have just created a helium
atom!!!
Helium
Electron
(-)
+
N
N
+
He
2
4
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
Bohr’s Atom
electrons in orbits
nucleus
What is different?
 The
two different elements
have different numbers of
electrons, protons, and
neutrons.
 OK...
Are all atoms of an element
the same?
 Draw
another Hydrogen atom,
but this time add a neutron.
 It is still Hydrogen because it
has only one proton, but it has
more mass in the nucleus.
 It is called an isotope.
What is an Isotope?
 Isotope
- atoms that have the
same number of protons but
have different numbers of
neutrons.
 Some isotopes are radioactive.
 Otherwise they are mostly the
same as the regular atom.
How can you tell one
isotope from another?
 By

their mass numbers.
mass number = protons + neutrons.
 Different
isotopes will have
different mass numbers
because they have different
numbers of neutrons.
Let’s see...
 Hydrogen-1
has 1 proton and 0
neutrons.
 Mass Number = 1
 Hydrogen-2 has 1 proton and 1
neutron.
 Mass Number = 2
Questions…
 List
the charge, location, and
mass of each particle.
 Determine the number of
protons, electrons, and
neutrons in aluminum-27.