Transcript Periodic Trends - Alamo Heights Independent School District

Periodic Trends, Cont.
Shielding
Ion Size
Ionization Energy
Electronegativity
Chemistry Riddle
Q: What is a robber’s least favorite
element?
A: Copper!!!
Shielding
• The electrons in the outside energy level
are blocked from the pull of the nucleus
by all the inner electrons.
• The shielding does not change as you
add electrons to the same energy level.
• The shielding increases when you move
to the next highest energy level.
ShieldingTrends
Shielding is constant
Shielding increases
Ion Size
 To form ions, atoms may gain or lose
electrons.
 If an atom loses electrons, a positive ion
is formed called a cation.
– Metals tend to lose electrons.
 This cation is smaller than the atom from
which it formed.
– It now has fewer occupied energy
levels.
Ion Size
 When an atom gains electrons, a negative
ion is formed called an anion.
– Nonmetals tend to gain electrons.
 This anion is larger than the atom from
which it was formed.
 The period and group trends for ions are
the same as atomic radius….except in the
period trend when you cross the metalnonmetal dividing line.
Ion Size Period Trend
Li1+
B3+
Be2+
N3-
O2-
F1-
C4+
Cations—Atoms that
have lost electrons to
become positively
charged.
Anions—Atoms that have
gained electrons to
become negatively
charged.
Smaller than the
original, but showing
the same trend in size.
Larger than the
original, but showing
the same trend in size.
Ionization Energy
• The amount of energy required to
completely remove an electron from an
atom.
• Removing one electron makes a +1 ion
• The energy required to remove the
outermost electron is called the first
ionization energy.
• Also known as…IE
Ionization Energy Trends
• As you go across a period…
• The electrons are closer to the
positive nucleus and therefore harder
to pull off.
• The harder it is to pull off the electron,
the higher the ionization energy.
Ionization Energy Trends
• As you go down a group…
• The electrons are farther away from the
positive nucleus and therefore easier to
pull off.
• There are more electrons shielding the
outer electrons from the positive nucleus,
making them easier to pull off.
• The easier it is to pull off the electron, the
lower the ionization energy.
Ionization Energy Trends
(Generally) Increases
Decreases
Ionization Energy Graph
Electronegativity
• The tendency for an atom to attract electrons
to itself when it is chemically combined with
another element.
• Measures how fair an atom shares electrons.
• Large electronegativity means it pulls the
electron toward it strongly.
• Fluorine is the most electronegative element
Electronegativity Trends
Increases
F
Decreases
Noble
Gases
are not
electronegative.
Fluorine is the most
electronegative element.
Chemistry Riddle
Give this flask to Mel and tell him
to put it away where no one can
find it.
What is it?
It’s formaldehyde!!