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 notation Potassium – 39 Potassium – 40 Potassium – 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 – = neutron + = proton

Beta radiation  What would happen to the nuclear make-up as a result of beta radiation? Consider: carbon – = 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: He 4242

-+ = neutron = proton

Alpha Decay  When an alpha particle is emitted from a nucleus, what is left? Consider Uranium – U X + He 4242 Th

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.