Download ATOMS

The building
blocks of all
matter
Today We Will…
Explain the Atomic Theory
 Construct the Bohr Model
 Identify the parts of an Atom
 Identify atomic number, symbol and
mass number.

Atomic - Molecular
Theory of Matter
The Atomic - Molecular
Theory of Matter states
that all matter is
composed of small, fast
moving particles called
atoms. These atoms
can join together to
form molecules.
This theory is really
thousands of individual
theories that provide
evidence for the whole
theory.
Matter
Since the atom is
too small to be seen
even with the most
powerful
microscopes,
scientists rely upon
models to help us to
understand the
atom.
Believe it or not this is a
microscope. Even with the
world’s best microscopes we
cannot clearly see the
structure or behavior of the
atom.
Scientific Models
Scientists create
models to help them
to visualize complex
properties,
structures or
behaviors. Since the
atom is so small,
scientists must
gather Indirect
Evidence to develop
their models.
This is a model of a very
complex molecule made of
many different kinds of atoms.
Each colored ball represents an
atom of a different element.
What should a Model look like?
This is a painting of a young woman
by Pablo Picasso. Does it actually
look like a young woman?
Scientific models
may not always
look like the
actual object. A
model is an
attempt to use
familiar ideas to
describe
unfamiliar things
in a visual way.
Can a Model be Changed?
A model can be changed as new
information is collected.
From the early Greek concept to
the modern atomic theory,
scientists have built upon and
modified existing models of the
atom.
The Bohr Model
Invented by Niels Bohr
 Depicts protons and
neutrons in a nucleus.
 Electrons around the
nucleus in what is
called an electron cloud

Atomic Structure
 Atoms
are composed of 2 regions:
– Nucleus: the center of the atom that
contains the mass of the atom
– Electron Cloud : the region that
surrounds the nucleus that contains most of
the space in the atom
1. ___________________
2._________________
What’s in the nucleus?
The nucleus contains 2 of the 3
subatomic particles.
 Proton: positively charged
subatomic particles


Neutron: neutrally charged
subatomic particles
What’s in the electron cloud?
Electron:
the third subatomic
particle with a negative charge
and relatively no mass.
Why are all Atoms are
Electrically Neutral?
Normally in an atom the
number of electrons
within the electron
cloud is equal to the
number of protons in
the nucleus. The
positive and negative
charges cancel each
other out. Therefore,
the atom is said to be
electrically neutral.
If an atom gains or loses
electrons the atom is no
longer neutral . This can
happen if the atom absorbs or
releases energy The atom is
then called an ION.
IMPORTANT
In all ATOMS the number of
positively charged protons
is always equal to the
number of negatively
charged electrons.
Atomic Number _

Element Symbol


Element Name

Atomic Mass
1
H
Hydrogen
1.008
How do the subatomic particles
balance each other?



In an atom: protons = electrons
If 20 protons are present in an atom
then 20 electrons are there to balance
the overall charge of the atom.
The neutron have neutral charge
therefore they do not have to equal
the number of protons or electrons.
How do we know the number of
subatomic particles in an atom?
 Atomic number: indicates the number of protons in an atom.
– Ex: Hydrogen’s atomic number is 1, so hydrogen has
_______ proton.
– Ex: Carbon’s atomic number is 6 , so carbon has _____
protons.

**The number of protons identifies the atom
– 2 p = _He_______
29 p = __Cu_____
How do we know the number of
subatomic particles in an atom?
 Mass number: the number of
protons and neutrons in the
nucleus.



Ex:Hydrogen can have a mass of
3.
Since it has 1 proton, it must
have 2 neutrons.
**number of neutrons = Mass
# - Atomic #
Determining the number of protons
and neutrons:

Li has a mass # of 7 and an atomic number of 3
– Protons = 3 ( same as the atomic #)
– Neutrons = 7 – 3 = 4 ( Mass # - Atomic #)

Ne has a mass number of 20 and an atomic number of 10.
– Protons = 20
– Neutrons = 10
What about the electrons?
 The electrons are equal to the number of protons.

So electrons = protons = atomic number
– Ex: He has a mass number of 4 and an atomic
number of 2

p = ___2___ n = ___2____ e-= __2____
Determine the number of subatomic
particles in the following:

Cl has a mass number of 35 and an
atomic number of 17
p = 17 n = 18
e- = 17
K
has a mass number of 39 and an
atomic number of 19.
– p = 19 n = 20
e- = 19
How exactly are the particles
arranged?

Bohr Model of the atom:
The 3rd ring
can hold up
to 18 eThe 4th ring
and any after
can hold up to
32 e-
All of the
protons and the
neutrons
The 1st ring can
hold up to 2 eThe 2nd ring can
hold up to 8 e-
What does carbon look like?
Mass # = 12
atomic # = 6
6 p and 6 n live
in the nucleus
p+ = ____
____
no = ____
e- =
Changing Electrons
An
atom that changes the
number of electrons is called
an ion.
The number of protons and
neutrons stays the same.
No change in atomic number
or mass number.
What makes an ion?
 If
the atom loses electrons, the
atom becomes positively
charged.
 If an atom gains electrons, the
atom becomes negatively
charged.
Positive ion
 (4
+) + (3-) = 1+
Negative ion
 (4
+) + (5-) = 1-
Changing Neutrons
Changing
the number of
neutrons in an atom makes an
isotope.
Have the same atomic
number
Have different mass numbers
(number of protons +
neutrons)
Sample Problem 1: For an atom with 15 protons, 16
neutrons, and 18 electrons…
 What
is the atom’s net charge?
 What
is the atomic number of the atom?
What is the mass number?
 This
is an atom of what element?