The Periodic Table
History
Dmitri Mendeleev (1834-1907)
Mendeleev struggled to find some order
in the 63 elements that were known at that
time. Working with cards that he made showing
the properties of the elements he realized that
there were properties that repeated as the
atomic mass increased. The properties seem
to repeat every 8th element. He formed a table
that showed this observation:
Mendeleev noted patterns in the
combining ratios of elements
Oxygen
•The Elements Lithium (Li), Sodium (na),
and Potassium (K) all bound with oxygen
in the ratio of two atoms per oxygen
atom: R2O
•The Elements Beryllium (Be), Magnesium
(Mg), and Calcium (Ca) all bound with
oxygen in the ratio of one atom per
oxygen atom: RO
•Boron (B) and Aluminum (Al) form R2O3
Oxygen
Oxygen
Oxygen
•Carbon (C) and Silicon (Si) formed RO2
Oxygen
Oxygen
low C
middle C
high C
From the gaps present in his table, Mendeleev
predicted the existence unknown elements which
he called
•eka-silicon
•eka-boron
•eka-aluminum
The elements
•gallium
•scandium
•germanium were found later to fit his predictions
quite well.
There are 8 columns in the
periodic table that repeat
the same number of
valence electrons
From #1 to #116
The Periodic Table is
composed of
Groups…..(18 of these)
And Periods…..(7 of these)
Special Chemical Families
Link to website showing special families of elements
Special Chemical Families
Link to website showing special families of elements
Special Chemical Families
Link to website showing special families of elements
Special Chemical Families
Link to website showing special families of elements
Special Chemical Families
Link to website showing special families of elements
Special Chemical Families
Link to website showing special families of elements
Movie Clip on Metalic trends in table
Click on the Table
to bring up the
website
“Neutral” atom with the same
number of protons as electrons
http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/046_AtomicRadi
Why do the elements get smaller as you
go right even though they are actually getting heavier?
Answer: As they get heavier they have more protons which
pull the oppositely charged electrons IN tighter and tighter.
They get bigger as you go down because
you are adding more layers of electrons.
Metals tend to LOSE electrons
Non-metals tend to GAIN electrons
2s22p6
3s1
1s2
+1
The illustration shows Sodium losing
an electron and becoming positively
charged. It loses the 3s1 electron.
Sodium ions always have a +1 charge
11 protons
11 electrons
17 protons
17 electrons
11 protons
10 electrons
17 protons
18 electrons
Some elements lose or gain two or more
electrons
Oxygen gains 2 electrons
Magnesium
loses 2 electrons
The energy needed to pull an electron off of an atom
2s22p6
1s2
+1
3s1
The purple atoms are the NEUTRAL atoms
The Red atoms are the POSITIVE ions
The Blue atoms are the NEGATIVE ions
How hard does an
atom pull an electron
toward itself?
( also called ELECTRON
AFFINITY)
SUMMARY of some of the trends
in the periodic table
http://wps.prenhall.com/wps/media/objects/476/488316/ch09.html