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PERIODIC TABLE
OBJECTIVE 1—DEVELOPMENT OF
THE PERIODIC TABLE
I. ORIGINAL PT
A. Dmitri Mendeleev—mid 1800s—
Russian
B. arranged 63 known elements in
order of increasing atomic mass
C. found that elements had similar
physical and chemical properties –
arranged columns
D. Certain groups had the same
reactivity (# of valence e-, but these
hadn’t been discovered yet!)
Valence Electrons – The outer
electrons, in the highest energy
orbital(s)
E. concluded that elements had
periodic properties
(3 elements discovered in his lifetime
had properties that he predicted)
II. MODERN PT
A. Several elements appeared to be out
of place
B. Rutherford 1908 discovered the
nucleus containing proton & neutron
A. Shortly after that, (50 yrs after
DM) Henry Moseley determined the
atomic # of elements by using X rays
III. ARRANGEMENT OF PT
A. Groups (families)—vertical
columns
1. all elements in a family have
same # of valence e “A” group elements only
2. similar but not identical
properties in some families
 alkali metals, halogens, noble
gases
B.
Periods—horizontal rows
1. all elements in a period have the
same # of quantum energy levels
2. properties change drastically
but there is a pattern (periodic or
repeating pattern)
a. 1st element is a very active
solid metal
b. last element is a very inactive
gas
There are 92 naturally occurring
elements and several synthetic
elements.
OBJECTIVE 2—PERIODIC
PROPERTIES/TRENDS
Can obtain information about an element from
its location in the PT
Certain properties vary in a periodic way from
left to right
1. Reactivity
a. Metals—lose electrons easily;
will react with water to corrode
easily
b. Non-metals—gain electrons
easily
2.Metallic properties- how easily
the atom loses electrons
Going from left to right across the
period elements change from metals
to metalloids and finally nonmetallic elements. Down a group,
elements become more metallic.
3. Nuclear Charge- As proton
number increases across a period
and down a group, the positive
charge of the nucleus increases as
well.
4.
Shielding effect- the reduction of
the attractive force from the nuclear
charge. The effect results from the
addition of quantum energy levels.
The inner electrons shield the
outermost electrons from the positive
attraction of the nucleus. MAKES
THE VALENCE ELECTRONS
EASIER TO TAKE.
5. Atomic Size/Atomic Radius
a. ½ the distance between the
nuclei of 2 atoms of the same
element when they are combined.
b. Atomic size decreases from left
to right and increases top to bottom
c. As atomic # increases across a
period, # of protons increase and
electrons are added to the outer
level
d. the increase in neg. electrons and
the increase in pos. protons cause an
increased attraction between
particles
e. Electrons are pulled closer to the
nucleus causing atomic size to
decrease within a period
6. Electron affinity— the energy
change that occurs when an
electron is acquired by a neutral
atom 
starting at left of each period and
going to the right affinity increases
7. Ionization energy- the energy
required to overcome the nuclear
charge and remove an electron
from an atom that is by itself
8. Electronegativity- the tendency
for the atoms of the element to
attract electrons when they are
chemically bonded to atoms of
another element
Octet rule – Atoms react
and gain or lose electrons to
obtain the electron
configuration (valence
electrons) of noble gases.
Usually 8.