Electron Configuration and
Periodic Properties/Trends
Chapter 5
Section 3
Pgs. 140-154
There is a correlation between
the arrangement of elements in
the periodic table and their
electron configuration
This P.T. is color coded by main energy level…
Concepts to know about…
•
•
•
•
Atomic radius
Ionization energy
Electronegativity
Valence electron
• Be able to compare
periodic trends of
main group elements
and explain why
these trends occur
• “Main” group
elements do not
include the transition
metals or rare Earth
metals.
Atomic Radius…
• One half of the
distance between two
nuclei of the identical
atoms that are
bonded together
Atomic radius trends…
• Across Periods…
– Smaller atoms across a
period (left to right)
– Caused by increasing
positive charge of the
nucleus pulling in the
electrons
• Down Groups/Families...
– Atoms increase in size
down a group/family
– because higher main
energy levels are being
filled as you down a group
Ions...
• Ions are… A single atom or a group of
bonded atoms that have an overall
positive or negative charge
• Na+ Cl- Cr3+
• Polyatomic ions: OH- CO32- CN• Ionization is any process that results in the
formation of an ion
• How do ions form???
– Loss or gain of electrons!!!
Ions...
• Cation = positive ion = electrons have
been removed
• Anion = negative ion = electrons have
been added
Ionization energy...
• Energy needed to remove one electron
from a neutral atom is the first ionization
energy ( symbolized as IE1 )
• Second ionization energy, third ionization
energy remove electrons from an ion too.
• Second ionization energy is always larger
than first. Third larger than second…
Ionization energy trends…
• Across Periods…
– Ionization energy
increases across a
period due to
increases nuclear
charge (# of protons
w/in nucleus)
– If electrons are
closer to the nucleus
they are harder to
remove away...
• Down Groups
– Decreases down a
group because the
higher main energy
levels are further from
nucleus
– Electrons that are
farther away from
nucleus can be
removed more easily...
Ionization energy Trends
Valence Electrons…
• Valence Electrons are available to be lost,
gained or shared when forming chemical
compounds
• Valence electrons are the electrons found in
the outermost S and P orbitals only!!
– there are always a maximum of 8 v.e. (S holds 2
and P holds 6)
1
•Atoms in the same columns have the same
number of valence electrons.
2
•Helium only has 2 valence
electrons (not 8 like the rest
8
3 4 5 6 7
of the noble gases)
15
Electronegativity…
• Is a measure of the ability of an atom in a
chemical compound to attract electrons
– Essentially to pull electrons away from the
other atom(s)
• Valence electrons hold compounds
together
• Uneven electrical charge is important in
compound formation and other chemical
properties
Electronegativity
• Across Periods…
– Increases across
periods
– Fluorine is the most
electronegative
• Down Groups/Families
– Decreases or stay same
down a group
• Noble gases do not form
compounds so are not
assigned
electronegativity
numbers
Electronegativity Trends