Chapter 6
The Periodic Table
S
Valence Electrons
S These are electrons in the outermost shell (or energy level) for a
particular atom.
S They are the ONLY electrons that are involved in chemical bonding
and chemistry.
S Valence electrons can be
S Lost
S Gained
S Shared
S Every atom always wants to have 8 of them. 8 is called an “octet.”
That’s the “octet rule.”
Lewis Structures
http://www.ausetute.com.au/lewisstr.html
S A Lewis structure can have a maximum of 8 dots.
S You put one dot on each side of the symbol (top, bottom,
left and right), until each side has a dot.
S Then you can start pairing them up, until every side has 2
dots.
S When every side has two dots, you can’t put any more dots
on the structure. If you need to, you did something
wrong.
Exceptions to the Rules for
electron configurations
S Copper and Chromium do not follow the rules. By not following the
rules, copper and chromium form a more stable configuration than
would be predicted by the rules.
S A half full set of p or d orbitals is a stable configuration. A full set
of p or d orbitals is even MORE stable.
S This is why the Nobel gases are completely unreactive. They have a
full set of valence electrons and don’t want or need yours.
S It also explains WHY Zinc only has a charge of +2, but we’ll get to
that in just a second.
Shorthand electron
configurations
S Use the NOBEL GAS which precedes the element.
S Remove the electron configuration for the Nobel gas from
your configuration and replace it with [NG] where NG =
the symbol for the specific Noble gas.
S Let’s do a few examples…
The Periodic Law
S When you arrange the elements in order of increasing atomic
number, there is a periodic repetition of chemical and physical
properties.
S Write that into your notes in YOUR OWN WORDS.
Metals and Nonmetals and
Metalloids…oh my!
S Metals
S Nonmetals
S Metalloids (B, Si, Ge, As, Sb, Te, Po)
Alkali Metals
S Sodium and potassium and all the rest of the elements in
that group are alkali metals.
S The alkali metals all have one valence electron. That
similarity is what makes them behave the same chemically.
S They are very reactive. Reactivity is highest on the outer
edges of the table and elements get less reactive the closer
they are to the center of the table. Lithium is the least
reactive alkali metal and reactivity increases as you go down
the group.
Alkaline Earth Metals
& Halogens
S Group IIA or Group 2 are called “the alkaline earth
metals.” They have 2 valence electrons.
S Group VIIA or Group 17 are called “the halogens.” The
halogens all have 7 valence electrons, and like the alkali
metals, they are very reactive (fluorine is most reactive and
reactivity decreases as you go down the group).
S Iron is one of the least reactive elements known. It can take
literally years for it to react.
Noble Gases
S The noble gases are very stable. They are unreactive
because they are so stable.
S The noble gases all have 8 valence electrons. Helium is an
exception in that it only has 2.
S The noble gases are gases at STP
S STP = Standard Temperature and Pressure
Representative Element &
Transition Metals.
S The representative elements are the Group A elements.
S The representative elements always behave the same. And any one
member of the group is “representative” of all the other members in its
group.
S The representative elements are all the elements in the s and p blocks.
S The transition metals are the Group B elements.
S They behave differently at different times. They do not always act the
same.
S The f block is the Lanthanides (top row) and Actinides (bottom row).
S These are also called the “inner transition metals.”
Representative Element &
Transition Metals.
SLet’s Label the
Periodic Table.
Periodic Trends
S Atomic Radius
S Decreases from left to right in period (because of
increased shielding)
S Increases as you go down a group (because you are
going to higher energy levels, which are further away
from the nucleus).
S Ionic Radius
S Same as atomic radius
S Big change in size between groups 14 and 15, where
you shift from positive ions to negative ions.
What is an Angstom (Å)
http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/ATRADIID.DIR_PICT0003.gif
S
Even the largest atoms are very small. The diameter of a uranium atom is only about
0.345 nanometers. 2,898,550,725 uranium atoms could fit on a METER stick!!
S
A special unit is sometimes used to describe lengths at the atomic level, such as atomic
radius or atomic diameter. Note the trend as you go across a row and down a column.
S
That is the Angstrom. We use a Å to represent Angstroms (if you want to type that it’s
shift-alt-A on a Mac and control-shift-2, shift-A on a bogus, inferior, Windows or Vista
based machine).
Angstoms (Å)
http://upload.wikimedia.org/wikipedia/commons/1/11/Hydrogen_Atom.jpg
S Even the largest atoms are very
small. The diameter of a
uranium atom is only about 0.345
nanometers.
S 0.345 nm = 3.45Å
S 1nm = 10Å
S 1Å = 1 x 10-10 meters
S A hydrogen atom is the smallest
atom. H has a diameter of only
0.74Å. About 13.5 TRILLION
hydrogen atoms could fit onto the
edge of a meter stick.
2 more Periodic Trends
S Ionization Energy
S Increases from left to right in period (OPPOSITE from
atomic radius and ionic radius)
S Decreases as you go down a group (because it gets easier
to remove the electron the further away it is from the
nucleus.
S Electronegativity (how strong an atom attracts
electrons to itself).
S Same as ionization energy in terms of trends.
S DRAW ARROWS on your periodic table to
represent trends!
Allotropes
http://chemistry.about.com/od/periodictableelements/ig/Element-Photo-Gallery.--98
S Allotropes =
different forms of
the same element.
Different structures
with different
properties.
S Diamond and
graphite are both
forms of carbon.
S Oxygen (O2) and
ozone (O3) are
both allotropes of
oxygen.
l
Diamond and graphite
are both allotropes of
carbon.
Remember Distillation?
/activity/distil.htm
S Distillation can
be used to
separate a

mixture of liquids
based on boiling
points.
S This is a
distillation setup.
Organic Flavor
S Carbon can bond and form long chains
S Like in soap molecules
S Carbon can form rings
S Like in sugar molecule
S Carbon can form huge networks of carbon atoms
S Like in diamonds
S Carbon is always bonded to 4 things. Carbons unique size (atomic
radius) and electronegativity (we’ll get to that in a minute) means that it
can form very strong COVALENT bonds between itself and H and O
and N and other atoms (that means electrons are SHARED).
The End
What’s Next….
For Advanced…we still have Chapter 25 to do for Unit 2
For Chemistry…see you in Unit 3 (Chapter 7)
S