Transcript Periodic Trends

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One
Uno
Ichi
Washid
Periodic Trends
Atomic Size
 Decreases from left to right across a
period.
 More protons as you move across a
period, so greater positive charge on
nucleus.
 More electrons as you move across a
period, so greater negative charge
around nucleus
 Increasing nuclear charge pulls
electrons in highest energy level closer
to nucleus.
Atomic Size
Atomic size increases from top to
bottom within a group
• As atomic # increases within a
column, the number of energy
levels increase.
As Energy Levels Increase
Size Increases
Atomic Size
 Atomic size increases from top
to bottom within a group.
• Shielding effect: The increase in
number of energy levels “shields” or
protects electrons in the highest
occupied energy levels from the
attraction to protons in nucleus.
Trends in Atomic Size
Trends in Ionization Energy
First ionization energy: energy required to
remove the first valence electron from an
atom.
Trends in Ionization Energy
 First Ionization energy decreases from
top to bottom within a group.
• Shielding
Trends in Ionization Energy
 Increases from left to right across a
period.
• Electrons pulled closer to nucleus and held
tighter as protons are added to nucleus and
electrons are added in an energy level.
Ionization Energy
Ionization Energy
Second Ionization Energy
• Energy required to move an electron from an ion
with a 1+ charge.
Third Ionization Energy
• Energy required to remove electron from ion with
2+ charge.
Easy to remove one electron from Group 1A
metal, difficult to remove a second electron.
So, group 1A metals tend to form ions with 1+
charge.
Successive Ionization Energies
Electronegativity
Is the tendency for an atom of an element to
attract electrons from another element in a
compound.
How "greedy" is an element for electrons.
Increases from left to right across a period.
Decrease from top to bottom within a group.
Francium is least electronegative and
fluorine is most electronegative.
Electronegativity increases in
direction of arrows
F
Fr
Reactivity
 How readily an atom reacts
 Reactivity differs metals to non-metals
• Metals are more reactive as atomic
number increases down a column.
o Shielding
• Non-metals are less reactive as atomic
number increases down a column.
 Must consider reactivity separately for
metals and non-metals.
Metals Reactivity
 Metals want to lose an electron to react.
 Therefore reactivity follows decreasing
ionization energy
 Metals reactivity increases down an
column because ionization energy
decreases
 Metals reactivity decreases across a
period because ionization energy
increases.
Non-Metals Reactivity
 Non-metals want to gain electrons to
react.
 Nonmetals reactivity follows increasing
electronegativity.
Non-metals reactivity decreases down a
column.
 Non-metals reactivity increases across
a row
STOP
Ions
Ion: atom or group of atoms with a
positive or negative charge.
Recall: an atom is neutral because it
has equal numbers of protons and
electrons.
Positive and negative ions form when
electrons are transferred between
atoms.
Ions - Positive
Atoms of metals such as Na, tend to become
ions by losing electrons to gain the electron
config. of noble gases, forming a cation.
In a sodium ion, Na+1 the number of electrons
is now 10, like Neon, and is no longer equal
to protons (11).
Since sodium lost an electron and that
electron cloud is no longer there, the atom is
now smaller.
Metals get smaller when they ionize.
Ions - Negative
Atoms of nonmetals, tend to become
ions by gaining one or more electrons to
gain the electron config of noble gases
and forming anions.
Chlorine atoms gain one electron to
have the electron config of Argon.
Since chlorine now has one more
electron, the atom is larger.
Non-metals get bigger when they ionize