Download Periodic Trends (Section 6.3).

Periodic Trends
Section 6.3
Objectives:
AOD C.3.1 Define atomic radii, ionization
energy, electronegativity, and energy levels.
AOD C.3.2 Recognize periodic trends of
elements, including the number of valence
electrons, atomic size, and reactivity.
Atomic Radius
• Def: The distance between an atom’s
nucleus and its valence electrons.
• Size of the atom varies from substance to
substance
Trends within Periods
• Atomic radius INCREASES as you move
to the left across a period.
– Due to decreased nuclear charge (total
charge in the nucleus --- which would be
based on WHAT?)
– Decreased nuclear charge has less pull on
the outermost (highest energy, valence)
electrons so they can move further away
from each other (and the nucleus).
Trends within Groups
• Atomic radius INCREASES as you move
down a group.
• Nuclear charge increases, but as
electrons are added to higher energy
levels, they are further from the pull of the
nuclear protons, AND they are “shielded”
by the electrons between them and the
nucleus.
• Summary: Increases left and down!
Examples
• Which element has the smallest atomic
radius? Largest atomic radius?
Iodine (I)
Bromine (Br)
Fluorine (F)
Chlorine (Cl)
• Fluorine
• Iodine
Ionic Radius
• Ion: an atom that gains or loses electrons
• When atoms lose electrons they form
positive ions and become smaller.
– The electron lost will always be a valence
electron.
– Loss of valence electrons may leave an
empty outer orbital which results in a smaller
radius. (Example: Na+1)
– Even if the orbital is not emptied, repulsion
between fewer electrons decreases allowing
them to be pulled closer to the nucleus.
Ionic Radius, continued….….
• When atoms GAIN electrons they form
negative ions and they always become
larger.
– The addition of an electron to an atom
increases the repulsion between the
valence electrons, forcing them to move
farther apart (Example: O-2).
– The result is a larger radius.
Ionic Radius within Periods
• Size of the positive ions gradually
increases from right to left across a
period.
• The size of the much larger negative ions
also gradually increases from right to left,
until you reach the smaller positive ions.
• Ionic radius GENERALLY INCREASES to
the left across periods.
Ionic Radius within Groups
• As you move down a group an ion’s outer
electrons are in higher principal energy
levels resulting in a gradual increase in
ionic size.
• Ionic radius INCREASES as you move
down a group.
• Summary: Increases left and down.
Ionization Energy
• Def: the energy required to remove an
electron from an atom in the gaseous
state
• “How strongly an atom’s nucleus holds
on to its valence electrons”
• High IE indicates atom has a strong hold
on its electrons
• Low IE indicates an atom loses its outer
electron more.easily
Ionization Energy
• Energy required to remove the 1st electron
is the first ionization energy.
• Energy required to remove the 2nd
electron is the second ionization energy.
• 1st IE is ALWAYS highest.
Ionization Energy within Periods
• INCREASES as you move from left to
right across a period
• The increased nuclear charge of each
successive element produces an
increased hold on the valence electrons,
as they are all in the same principal
energy level.
Ionization Energy within Groups
• INCREASES as you move up a group
because the valence electrons are closer
to the nucleus.
• Summary: Increases up and right.
Octet Rule
• Atoms tend to gain, lose, or share
electrons in order to acquire a full set of
eight valence electrons (resembling which
elements?).
• Elements on the right side of the periodic
table (nonmetals) tend to gain electrons in
order to acquire the 8 valence electrons,
forming negative ions)
• Elements on the left side of the periodic
table (metals) tend to lose electrons and
form positive ions.
Electronegativity of an Element
• Indicates the relative ability of an atom to
attract electrons in a chemical bond.
• Noble Gases are not assigned values
• Fluorine is the most electronegative
element.
• Fr & Cs are the least.
• In a chemical bond the atom with the
greater electronegativity more strongly
attracts the shared electrons.
Electronegativity Trends within
Periods & Groups
• INCREASES as you move up a group and
across a period (up and right).
• The lowest electronegativities are found
at the lower left side
• Highest are found at the upper right side
Example Problems
• Which element has the highest
electronegativity? Lowest?
•
•
•
•
•
•
•
N- Nitrogen
P- Phosphorus
As-Arsenic
Sb-Antimony
Bi- bismuth
N=highest
Bi= Lowest
Homework Problems
• Pg. 175
• #56, 57, 59, 62, 63, 65-67