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Atomic #
# of protons in an atom Never changes for a given element Therefore, used to always identify
the element
Isotopes
Not all atoms of a particular element are identical
#of neutrons can differ – atomic masses differ
Element with same # of protons and electrons, but different # of neutrons
Two types of isotope notation
1. Symbol notation
2. Hyphen notationPotassium – 39Potassium – 40Potassium – 41
Solve practice problem pg. 101 #14
Average atomic mass
Atomic mass reported on periodic table
Sum of all masses of each isotope x relative abundance of each isotope in decimal form
Pg. 104 #15
Nuclear Decay (Radioactivity)
Unstable nuclei
Subatomic particles
Electron -negatively charged particle found outside the nucleus.
Proton – positively charged subatomic particle found inside the nucleus.
Neutron – Neutrally charged (no charge) subatomic particle found inside the nucleus.
Some Surprises
A neutron is a proton with a captured electron.
A neutron can become a proton by losing that electron.
That electron, when it comes flying out of the nucleus, will be called a beta particle. It’s symbol is the Greek letter β.
Beta radiation
What would happen to the nuclear make-up as a result of beta radiation? Consider: carbon – 14.
+-+ -+
+
+
-+
-+-+
-+-+
++
+
-+ = neutron + = proton
Beta radiation
What would happen to the nuclear make-up as a result of beta radiation? Consider: carbon – 14.
+-+ -+
+
+
-+
-+-+
-+ +
++
+
-+ = neutron + = proton
-
Beta radiation
How many protons does it have now?
What is its mass number?
+-+ -+
+
+
-+
-+-+
-+ +
++
+
-+ = neutron + = proton
Alpha Radiation
An alpha (α) particle is the same as a helium nucleus and is therefore symbolized by: He4
2
-+ = neutron
+-+ -+
+
+
-+
-+-+
-+-+
++
+
+ = proton
+-+
+-+
+-+
+-+ +
-++-++-+
+-+
+-+
+-+
+-+
+-+
+-+
+-+
+-+
+-+
+-+
+-+
Alpha Decay
When an alpha particle is emitted from a nucleus, what is left? Consider Uranium – 238.
23892 U X + He4
2Th23490
Which kind of decay is represented by each change?
I – 130 → Xe – 130 Am-241 → Np-237
Three Kinds of Decay
Alpha – a helium nucleus, cannot penetrate paper.
Beta - an electron which is emitted from the nucleus. Can penetrate paper, but cannot penetrate aluminum foil.
Gamma ray – not a particle. 50% emitted will penetrate 1cm of lead.
