Post on 11-May-2015
Atomic Structure
Unit 7 – Physical Science
Atomic Particles
– Proton
– Neutron
– Electron -
+
N
Protons and Neutrons together are called Nucleons
Atomic Number is the number of Protons
Atomic Mass is Protons and Neutrons together
Proton
• Positively charged particle• Resides in the nucleus• Weighs 1 Atomic Mass Unit (AMU)• Repel other protons• The number of protons determines the
element number.
+
Proton
• Positively charged particle• Resides in the nucleus• Weighs 1 Atomic Mass Unit (AMU)• Repel other protons• The number of protons determines the
element number.+
+
+ +++
Which element would this be?
Proton
• Positively charged particle• Resides in the nucleus• Weighs 1 Atomic Mass Unit (AMU)• Repel other protons• The number of protons determines the
element number.+
+
+ +++
Which element would this be?
Carbon
Too Many Protons
• Protons repel each other due to the electromagnetic force
• If an element has too many protons, it will be unstable and will break apart.
++
Too Many Protons
• This is why all elements over #82 Lead are radioactive!
• In addition, none over #94 Plutonium exist naturally.
++
Neutron
• A Neutron has a neutral charge• Neutrons weigh 1.001 AMU• Resides in the nucleus• It does not affect the elemental or chemical
properties of the atom
N
Neutron
• A Neutron has a neutral charge• Neutrons weigh 1.001 AMU• Resides in the nucleus• It does not affect the elemental or chemical
properties of the atom• It does provide additional nuclear force to
hold the nucleus together
N
Isotopes• Isotopes result from different numbers of
neutrons in an element• Isotopes are chemically the same• They only differ in their mass and their
nuclear stability
N+
+ N
+
+
NN
N
N++ N+
+ N
+
+
NN
N
N++
N N
Carbon-12 C12 Carbon-14 C14
Strong Nuclear Force• The strong nuclear force is the force that holds
the nucleus together.• All Nucleons are attracted to each other.• Because + protons repel each other
(electromagnetic force), the presence of neutrons helps bind the nucleus together.
++
Electromagnetic Force
Strong Nuclear Force
+N
Strong Nuclear Force
NN
Strong Nuclear Force
Atomic Stability• The more protons there are, the more neutrons
are necessary to stabilize the nucleus.• Note that Helium has 2p/2n ratio• Lead has 82p/125n ratio
He2
4Helium
Pb82
207Lead
Atomic Mass• Atomic mass is the average of all isotopes on
Earth together.• To figure out the number of neutrons, just go
Atomic Mass-Atomic # = Neutrons• He 4-2=2 neutrons Pb 207-82 = 125 neutrons
He2
4Helium
Pb82
207Lead
Atomic Stability• The more protons there are, the more neutrons are
necessary to stabilize the nucleus.
Electrons• Electrons are negative particles• Electrons weight 0.001 AMU• They reside outside the nucleus in the electron
cloud• They usually match the number of protons to
make a neutral atom
-
+ -
This is the relative scale
Except the proton should be 10x bigger!
+ -
This is Hydrogen
H1
1Hydrogen
What is a Neutron Anyways?
• OK, so you’ve heard that Neutrons are neutral and weigh 1.001 AMU
• Do you notice any pattern here?
What is a Neutron Anyways?
• Think of a Neutron as a Proton and Electron stuck together.
What is a Neutron Anyways?
• Think of a Neutron as a Proton and Electron stuck together.
N
Beta Decay?• When an isotope has too many neutrons, a
neutron will emit a β-particle
(which is basically an electron)
• This causes the neutron to change from neutral to positive (i.e. a proton).
• This actually changes the element it is!
Beta Decay
K19
40Potassium
N
Beta DecayPotassuim-40 with 19 protons becomes
Calcium-40 with 20 protons!
K19
40Potassium
Ca20
40Calcium
β-
+
What about Electrons?
• Electrons reside outside the nucleus in the electron cloud
Models of ElectronsRutherford Model
Models of ElectronsBohr Model
Energy Levels
Energy Levels• When energy is added, electrons can jump to higher energy
shells.• When that electron returns to its normal state, that energy is
released (often as light). • That is how a fluorescent or neon light works.
Electricity is exciting air molecules
Heisenburg Uncertainty Principal
• Heinsenburg realized it is impossible to knkow both an electrons position and velocity at the same time.
• That is because the moment you detect its position, you have changed its velocity – and vice-versa.
Why the uncertainty?
Why the uncertainty?
you have changed its direction and speed.
You know where it was, but now
Quantum Mechanics• Probability densities• The electrons do not appear
to move in patterns, but simply seem to flash on and off in different locations.
• It is described as being almost like a instantaneous transporter
Models of ElectronsOrbitals