Periodic Trends
I. History
II. Vocabulary
A. group
B. period
C. nuclear charge
D. shielding effect
E. effective nuclear charge
F. electron repulsions
G. ionization energy
H. electronegativity
I. electron affinity
III. Trends
A. properties of metals, nonmetals and metalloids
B. atomic radius
C. ionic radius
D. ionization energy
E. electronegativity
F. chemical reactivity
G. Allotropes
Resources: brief video about trends
I.
I. History
II.
Vocabulary
A.
group: vertical column representing number of valence electrons in an atom
B.
period: horizontal row representing PEL and energy progression of electrons in atoms
C.
nuclear charge: the positive charge in the nucleus
D.
shielding effect: the blocking of the attraction between the nucleus (+) and valence

electrons by interior electrons
E.
effective nuclear charge: Z eff = Z - S
eff
F.
electron repulsions: the repulsion of electrons within the same PEL
G.
ionization energy: the amount of energy required to remove the most loosely bound electron.
H.
electronegativity: the ability of an atom to attract electrons
I.
electron affinity: the negative ion equivalent to ionization energies. The amount of energy released when an atom gains an electron.
III.
Trends:

A.
Properties of:
1.
metals: ductile(can be drawn into wires) malleable(can be pounded into shape) good conductors of heat and electricity relatively high mp's (all but 1 solid at STP) shiny metallic luster low IE and low electronegativity strong electrostatic attractions holding them together(like IMF's)
2.
nonmetals:
3.
metalloids:
B.
Atomic Radius

1.
down a group: atomic radius will increase because of a.
greater number of occupied PEL's b.
increased shielding effect c.
less effective nuclear charge
2.
across a period: atomic radius will decrease because of a.
greater effective nuclear charge
C.
Ionic Radius "babysitting" [parents(protons) watching kids(electrons)]

1.
cations will be SMALLER than the parent atoms because the loss of electrons a.
reduces the number of occupied PEL's b.
increases the effective nuclear charge
2.
anions will be LARGER than parent atoms
D.
Ionization Energy:
1.
First- the trend in 1st ionization energies is that it increases up and to the right. It is increasingly difficult to remove an electron that is 1)within interior PEL's and 2) with an atom with a strong effective nuclear charge.

2.
Second, Third, etc. - It is also possible to remove additional electrons but each is successively harder and harder to remove. When you finally begin removing electrons from the octet notice the remarkable jump in IE required. This pattern is useful in determining an atom's group number.
E.
Electronegativity
Def: The ability to attract electrons. (caused by the electrostatic pull of an atoms nucleus)
1. E-neg values are based on an arbitrary scale from 0-4, 4 being
Fluorine, the "king of electronegativity"
2. Electronegativity values are very helpful when determining
the type of bonds which will exist between different atoms in
a compound.

F.
Chemical Reactivity:
There are two trends in reactivity because there are two different types of elements (metals and nonmetals). We have already established that metals typically lose electrons whereas nonmetals,
Group 18 excluded, tend to gain. All of these interactions occur to establish a stable electron configuration, ie. full octet / nearest noble gas.
1.
2.
metals reactivity

3.
nonmetals reactivity
G.
Allotropes:
Def: elements that exist in two or more different forms
1.
Because of their different bonding allotropes of the same element have DIFFERENT physical and chemical properties
2.
Allotropes are found in Groups IVA, VA, VIA (14,15,16) respectively. a.
IVA- carbon (Weblink)
(1) diamond
(2) graphite
(3) amorphous (coal)

b.
VA- phosphorus
(1) white
(2) red c.
VIA-oxygen
(1) O
2
-oxygen
(2) O
3
- ozone