Transcript File unit 2 atoms

Structure of an Atom
What Is an Atom?

An atom is often referred to as the
building blocks of matter
Atoms are composed of smaller
subatomic particles such as the
proton, neutron, and electron. They
have a nucleus surrounded by an
electron cloud
 Each element is composed of one
type of atom and can not be broken
down into a simpler substance

Inner Structure of an Atom
• Nucleus - Small, dense, positively
charged center of the atom which
contains most of the atom’s mass
• The nucleus contains subatomic
particles have certain
characteristics:
Protons
- positively charged particles in
the nucleus of the atom
Neutrons - particles in the nucleus that
have no charge but contribute to the
atom’s mass
Outer Structure of an Atom
●Electron cloud - an area encircling
the nucleus where electrons are
likely to be found
●The cloud contains energy levels
 electrons are negatively charged
particles located in specific energy levels
energy levels completely surround the
nucleus
there is a specific order for the electrons
to fill the energy levels
Outer Structure of an Atom
●Energy levels completely surround
the nucleus
Maximum
of 2
electrons
Nucleus
Maximum
of 50
electrons
Maximum
of 8
electrons
Maximum
of 18
electrons
Maximum
of 32
electrons
Outer Structure of an Atom
●valence electrons are in the
outermost energy level and are the
electrons involved in bonding
valence is the number of bonds
an atom can form
 an atom is most stable when its
outermost energy level is full
Atom Characteristics
The number of protons in the nucleus is
the atomic number of that atom.
 The number of protons (+) equals the
number of electrons (-)
 The atomic mass is the mass of the
protons plus the mass of the neutrons
Atomic mass is reported in the SI units
atomic mass units (amu)
Protons and neutrons each are given
an amu of 1
Electrons have a mass of nearly zero

An atom recap
An atom has three
parts:
 Proton = positive
 Neutron = no
charge
 Electron =
negative

Picture from
http://education.jlab.org/qa/atom_model_03.gif
• The proton & neutron are found in the center
of the atom, a place called the nucleus.
• The electrons orbit the nucleus.
What are elements?
Elements are the alphabet
to the language of
molecules.
 To make molecules, you
must have elements.
 Elements are made of
atoms. While the atoms
may have different
weights and organization,
they are all built in the
same way.

Decoding Atom Information
# of
protons
Atomic
mass
6
C
carbon
12.0
Atom’s
symbol
Atom’s
name
Decoding Atom Information cont:
# of protons =
# of electrons
6
C
carbon
Atomic mass = #
of protons plus
the # of neutrons
12.0
Atom Models
There are two models of the atoms
we will be using in class.
 Bohr Model
 Lewis Dot Structure

Created by G.Baker
www.thesciencequeen.net
Bohr Model
The Bohr Model shows all of
the particles in the atom.
 In the center is 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.

-
+
+
-
Lewis Dot Structure
The Lewis Dot
Structure is a
bit different
from the Bohr
model.
 It only shows
the element
symbol and
it’s outer most
electron shell.

-
-
-
+
+ + +
-
-
+ + +
+
-
-
•
• O ••
••
-
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.

Nucleus
1st shell
2nd shell
3rd shell
Adapted from http://www.sciencespot.net/Media/atomsfam.pdf
So let’s try it….
What we need to know
-number of protons
-remember our energy levels

Draw an atom of Sodium (Na)
-look at Periodic Table
