Transcript Chapter 3 notes

Chapter 3
Atomic Structure
The Structure Of the Atom
Particle mass
charge location
Proton 1 AMU
+1
in nucleus
Neutron 1 AMU
0
in nucleus
Electron 0 AMU
-1 outside nucleus
Atomic number – number of protons in the
nucleus, It determines which element an
atom is
A neutral atom has the same number
of protons as electrons
Example: atomic # 12 – magnesium has
12 protons and 12 electrons
An atom can gain or lose electrons to
become an ion
Ions have a charge and are very different
than the atoms that they used to be
Na is a very reactive metal.
http://www5.wittenberg.edu/academics/che
m/fac_staff/dmcdowell/alkalishow.html
Na+ ion is part of table salt and is
necessary for life.
Isotopes
Atoms of an element all have the same
number of protons and electrons;
however, they can have different
number of neutrons.
Isotopes – atoms of the same element
that differ in their number of neutrons.
Isotopes of an element have the same
chemical properties (differ only in mass).
Isotopes of Hydrogen
Isotopes of Carbon
Isotopic Notation
http://preparatorychemistry.com/Bishop_Is
otope_Notation.htm
# of neutrons = mass # - # of protons
1 AMU = exactly 1/12 the mass of one
atom of C-12
The mass of an element given on the
chart is an average of the isotopes of
that element found in nature.
Some isotopes are stable and some are
not.
If an atom has the wrong number of
neutrons it will be unstable (see page 113)
Also, if an atom has too many protons
(more than 83) it will be unstable.
Unstable atoms are radioactive and break
down (nuclear decay)
They eventually change to a stable
element
Stability of Isotopes
Half life – the time it takes for one
half of a sample of a radioactive
element to change.
If you start with 4 grams of uranium, after
one half-life you will have only 2 grams of
uranium. The rest will be changed to
another element.
If you start with 4 grams of uranium, how
much will be left after 4 half lives?
Types of Radioactive Decay
Name
Identity
Charge Penetration
Alpha particle He nuclei
+2 stopped by paper
Beta particle
electron
-1 stopped by clothing
Gamma ray, high energy light 0
thick lead used
Nuclear Decay of Uranium
Emitting alpha and gamma particles
Decay of I-131
emitting beta particle
Decay of Rb-81
Electron capture
Assignment: page 122 &123
questions 3-13, 15-21