Download In an atom

Learning Goal #3: Discriminate between the relative size, charge,
position, and number of protons, neutrons, and electrons of different
elements.
MATTER UNIT
WHAT IS AN ATOM?

Atom: the smallest unit of matter
that retains the identity of the
substance
SIZE OF THE ATOM



http://learn.genetics.utah.edu/content/begin/cells/scale/
The nucleus has a diameter 10,000 times smaller than the atom. The
great amount of empty space in an atom can be illustrated by the
following analogy.
Imagine the nucleus to be the size of a golf ball. Then on this scale the
first electron shell would be about one kilometer from the golf ball, the
second shell about four kilometers, the third nine kilometers and so on.
If you find that hard to visualize then try this. The period at the end of
this sentence, (depending on your monitor and the font you are using), is
probably about 1/2 a millimeter in diameter. If that period represents
the nucleus then the electrons in the first shell would be orbiting with a
diameter about 50 meters around you. in fact, the actual diameter of an
atom is very small and it would require some two hundred million of
them side by side to form a line a centimeter long.
ATOMIC STRUCTURE

Atoms are composed of 2 regions:
 Nucleus:
the center of the atom that
contains the mass of the atom
 Electron cloud: region that surrounds
the nucleus that contains most of the
space in the atom
Electron
Cloud
Nucleus
ATOMIC STRUCTURE
The nucleus contains 2 of the 3
subatomic particles:
Protons: positively charged
subatomic particles
Neutrons: neutrally charged
subatomic particles
The 3rd subatomic particle
resides outside of the nucleus in
the electron cloud
Electron: the subatomic
particle with a negative
charge and relatively no mass
Atomic Particles
Particle
Charge Mass #
Location
symbol
Electron
-1
0
Electron
cloud
e-
Proton
+1
1
Nucleus
p+
0
1
Nucleus
n0
Neutron
HOW DO THESE PARTICLES
INTERACT?
Protons and neutrons are in the tiny
positively charged nucleus accounting for
most of the mass of the atom
 The negatively charged electrons are small
and have a relatively small mass but occupy
a large volume of space outside the
nucleus

HOW DO THE SUBATOMIC
PARTICLES BALANCE EACH OTHER?

In an atom:
 The
# of protons = The # of electrons
 If
20 protons are present in an atom then 20
electrons are there to balance the overall
charge of the atom—atoms are neutral
 The
neutrons have no charge; therefore
they do not have to equal the number of
protons or electrons
THE NUMBER OF
PROTONS
IDENTIFIES THE
ATOM.
An atom with 6 protons = Carbon
 An atom with 8 protons = Oxygen
 An atom with 20 protons = Calcium

ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
Number of electrons = Number of protons
Number of neutrons = Atomic mass – Number of protons
DETERMINING THE NUMBER
OF PROTONS AND NEUTRONS

Li has a mass number of 7 and an
atomic number of 3
 Protons
= 3 (same as atomic #)
 Neutrons= 7-3 = 4 (mass # - atomic #)

Ne has a mass number of 20 and an
atomic number of 10
 Protons
= 10
 Neutrons = 20 - 10= 10
WHAT ABOUT THE ELECTRONS?

The electrons are equal to the
number of protons
 So

e- = p = atomic #
Ex: He has a mass # of 4 and an
atomic # of 2
 p+
 no
=2
=2
 e- = 2
DETERMINE THE NUMBER OF
SUBATOMIC PARTICLES IN
THE FOLLOWING:

Cl has a mass # of 35 and an atomic #
of 17
 p+

= 17,
no = 18,
e- = 17
K has a mass # of 39 and an atomic #
of 19
 P+
= 19,
no = 20
e- = 19
HOW EXACTLY ARE THE
PARTICLES ARRANGED?

Bohr Model of the atom:
All of the
protons and
the neutrons
The 3rd ring
can hold up
to 8 eThe 4th ring
and any after
can hold up to
18 e-
The 1st ring can
hold up to 2 eThe 2nd ring can
hold up to 8 e-
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
WHAT DOES CARBON LOOK
LIKE?
Mass # = 12
atomic # = 6
6 p and 6 n live
in the nucleus
p+ = 6
no = 6
e- = 6
PRACTICE BOHR DIAGRAMS
A unit created to describe atoms
because the gram and kilogram are too
large to use to define an atom.
 1amu = 1.66 x 10-24g
 .00000000000000000000000166g



Listed on the periodic
table as the atomic
mass.
The average mass of
all of the isotopes of
an atom.
Element
amu
Hydrogen
1.008
Carbon
12.01
Nitrogen
14.01
Oxygen
16.00
Sodium
22.99
Aluminum
26.98
1 atom = 1 amu
 Example

› 1 atom of carbon = 12.001 amu of carbon
› 3 atoms of carbon = 36.003 amu of carbon
› 3.00 X 1020 amu =2.50 x 1019 atoms of carbon
The unit all chemists use in describing
numbers of atoms.
 Defined as the number equal to the
number of carbon atoms in 12.01 grams
of carbon.
 A sample of on element with a mass
equal to that element’s average atomic
mass expressed in grams contains 1 mol
of atoms.

6.022 X 1023
 One mole of
something consists
of 6.022 X 1023 units
of that substance.

› One mole of eggs is
6.022 X
1023 of
eggs.
Elements
# of
atoms
Mass of
sample
(g)
Aluminum
6.022 X 1023
26.98
Gold
6.022 X 1023
196.97
Iron
6.022 X 1023
55.85
Sulfur
6.022 X 1023
32.07
Boron
6.022 X 1023
10.81
Xenon
6.022 X 1023
131.3

The mass of one mole of a substance.
› The sum of all the
masses of the atoms
in a compound.
CH4
C - 1x12.01=12.01
H – 4x1.008=4.032
Total = 16.04g