Download Atomic Structure

Atomic
Structure
Unit 3
Atomic Structure
• If a nucleus were the size of baseball, a
baseball would be the over 3000 miles
high.
• Nucleus- positive center of atom
– makes up 99.9% of the atom’s mass.
• Electron cloud- contains negatively
charged e-.
– takes up virtually the entire volume of the
atom.
Atomic Particles
Charge
Proton
Electron
Neutron
+1
-1
0
mass (amu)
Location
1
Nucleus
1/1836
e- cloud
1
Nucleus
Atomic Particles (Cont.)
• atomic number: # of protons.
• Protons identify the element. If the
# of protons changes, the element
changes.
• Since all atoms are neutral, the:
# of e- = # of p+
Atomic Particles (Cont.)
• Atomic Mass (mass number) = #
protons + # neutrons.
Atomic Mass
Atomic #
# of Neutrons
electron
neutron
proton
12
C
6
Atomic Mass
Atomic #
Mass Number
Mass number is the number of protons and
neutrons in the nucleus of an isotope.
Mass # = p+ + n0
Nuclide
p+
n0
e-
Mass #
Oxygen - 18
8
10
8
18
Arsenic - 75
33
42
33
75
Phosphorus - 31
15
16
15
31
Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com
Relative Atomic Mass
• Masses of atoms expressed in grams
are very small.
• For this reason, we use relative
mass.
– The standard used by scientists to
govern units of atomic mass is carbon12 atom. It has been arbitrarily
assigned a mass of exactly 12 atomic
mass units (amu).
Relative Atomic Mass (Cont)
• The hydrogen-1 atom has an atomic
mass of about 1/12 that of carbon12 atom, or about 1amu.
• An oxygen-16 atom has about
16/12(or 4/3) the mass of carbon-12
atom…and so on
Isotopes
• Isotopes are alternate forms of an
element. They have the same
number of protons but different
numbers of neutrons and thus,
different masses.
12
C
6
Atom
14
C
6
Isotope
1
2
H
H
1
1
Atom
Isotope
3
H
1
Isotope
Isotopes (Cont.)
• If the atomic mass
on the periodic
table matches the
mass of your
example, it is an
atom. If not, it is
an Isotope.
• Many Isotopes are
radioactive forms
of an element.
Isotopes
Let’s Practice
25Mg
12
31P
15
235
U
92
# protons =
What is it?
# electrons =
# neutrons =
12
12
13
# protons =
15
What is it?
# electrons =
# neutrons =
15
16
An Atom!
# protons =
92 What is it?
92
143 An Isotope!
# electrons =
# neutrons =
An Isotope!
Ions
• When the number of electrons
changes, the ‘atom’ now has a
charge and is called an Ion.
• A Cation has more protons than
electrons and is a positively charged
ion: Na+1, Ca+2
• An Anion has more electrons than
protons and is a negatively charged
ion: O-2, Cl-1
Ions are Important
Heart cell rhythm depends on the opening and
closing of a complex series of valves on the cell
membrane, called ion channels. Some valves let
certain ions ike potassium (K+) flow out, others let
different ions like sodium (Na+) flow in. There
are also pumps that actively move ions one
direction or another.
Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com
Let’s Practice
40Ca+2
20
# protons =
80Br
35
-1
27Al+3
13
What is it?
# electrons =
# neutrons =
20
18
20
# protons =
35
What is it?
# electrons =
# neutrons =
36
45
# protons =
13 What is it?
10
14 A Cation!
# electrons =
# neutrons =
A Cation!
An Anion!
Ions (Cont.)
• A Polyatomic Ion is an ion made of
different elements bound together.
They can be positive or negative but
are mostly negative.
• Ex: NH4+1; NO2-1; SO4-2; PO4-3.
• Atoms acquire this charge by gaining
or losing electrons from their outermost level = valence electrons.
Ions (Cont.)
• Why would an atom do this?
Because… Atoms with a full
valence shell are more stable.
• The first level holds up to 2 electrons
and all others hold 8.
8
8
2
P
N
Perhaps one of you gentlemen would mind telling me just
what is outside the window that you find so attractive!
Atoms & Ions
More Atomic Theory
• Protons, neutrons and electrons are
known to be separated into even
smaller particles.
• “Quark” is the term of all the other
particles located in the nucleus of an
atom. Some types of quarks
combine to form a proton. Other
types combine to form a neutron.
The Quark…
Oops…wrong Quark!
About Quarks…
Protons and neutrons are
NOT fundamental particles.
Protons are made of
two “up” quarks and
one “down” quark.
Neutrons are made of
one “up” quark and
two “down” quarks.
Quarks are held together
by “gluons”
Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com
Build an Atom
• http://www.pbs.org/wgbh/aso/tr
yit/atom/#
The
average
atomic
mass
can
be
•••The
Average
average
atomic
atomic
mass
mass
is
the
of
an
weighted
• Three isotopes of argon occur in nature
calculated
multiplying
the mass
atomic
element
average
depends
of
the
atomic
on
both
masses
the
the
[(35.97amu
x by
0.337)+(37.96amu
xofthe
Ar-36, Ar-38,
and
Ar-40.
Calculate
mass
each
isotope
itsofto
relative
average
atomic
mass
of by
argon
two
.063)+(39.96amu
x 99.600)]/100
= of
and
naturally
theofrelative
occurring
abundance
isotopes
ofeach
an
decimal
places,
given thein
following
abundance(expressed
decimalrelative
the
element
element’s
isotopes.
OR
atomicand
masses
and the
abundances
of each of
form)
adding
results.
[(35.97amu x 0.00337)+(37.96amu x
the isotopes .
.00063)+(39.96amu x .99600)] =
• Ar-36(35.97 amu;0.337%),
39.94amu
• Ar-38(37.96 amu; .063%, and
• Ar-40(39.96 amu;99.600%)
3 Laws of Atomic Theory
• Law of Definite Composition ─ a
compound contains the same
elements in exactly the same
proportions by mass regardless of
the size of the sample or source of
the compound
• Example: teaspoon and a cup of
sugar both are composed of 42.1 %
carbon, 51.4% Oxygen & 6.5%
Hydrogen
Law of Definite Composition
CO molecules are always composed of 1 carbon
and 1 oxygen. CO2 molecules are always
composed of 1 carbon and 2 oxygens
Law of Conservation of Mass
• When two or more elements react to
produce a compound, the total mass
of the compound is the same as the
sum of the masses of the individual
elements.
• Matter and mass is neither created
nor destroyed.
Law of Multiple Proportions
• This applies to different compounds
made from the same element; the
mass ratio for one of the elements
that combines with a fixed mass of
the other element can be expressed
in a small whole number ratio.
Law of Multiple Proportions
Radioactivity
• Atoms that “break down” are said to
be radioactive.
• There are eight other naturally
radioactive elements: polonium,
astatine, radon, francium, radium,
actinium, thorium and protactinium.
• All other man-made elements
heavier than uranium are radioactive
as well.