PERIODIC TRENDS!!
VALENCE ELECTRONS

Valence electrons: Electrons in the highest
energy level
 These
electrons are the ones that bond!!
 The group A # matches how many valence
electrons
VALENCE ELECTRONS
Group #
# of valence electrons
1 or 1A
1
2 or 2A
2
13 or 3A
3
14 or 4A
4
15 or 5A
5
16 or 6A
6
17 or 7A
7
18 or 8A
8
Group 13-18. # of valence electrons equal to group number - 10
YOU CAN PREDICT THE CHARGE OF THE IONS
Octet rule: atoms will gain or lose electrons to
have a full energy level (8 electrons)
 Period number responds to how many energy
levels an atom has

PREDICTING CHARGES OF IONS
ION SIZE TRENDS

ION: an atom that lost or gained electrons
 Cation:
metal atom that loses e- (+)
 Anion: nonmetal atom that gain e- (-)
ALL CATS HAVE PAWS (AND ARE MEAN)
(cation is positive: metals)
PERIODIC TRENDS

There are 4 trends of the periodic table you will
need to know
Ionic Size
 Atomic Size



Electronegativity

Ionization Energy
Need to know how AND why they trend the way
they do.
1. IONIC SIZE TRENDS

Cations are smaller than their neutral atoms
 Because

they lost an electron and energy level
Anions are larger than their neutral atoms
 Because
another)
they gain electrons (which repulse one
IONIC SIZE EXAMPLE
Ex
1: Which is larger?
Mg
or Mg2+
Ans:
Ex
Mg
2: Which is larger?
S
or S2-
Ans:
S2-
2. ATOMIC SIZE

The size of the atom
2. ATOMIC SIZE

Atomic size increases as you move:
 from
right to left in a period
 from top to bottom in a group
 Francium has the largest size
Fr
ATOMIC SIZE REASON

Going from Left to Right
 Gets
smaller because you add more protons to
nucleus and then pull in the electrons

Going Down
 Gets
larger because you add energies
ATOMIC SIZE EXAMPLE
Ex.
1: Arrange the following
elements in order of their
decreasing size.
P(15),
Ans:
Mg(12), S(16)
Mg,P, S
3. ELECTRONEGATIVITY TRENDS

Electronegativity is a measure of the ability of
an atom to attract electrons from another atom
ELECTRONEGATIVITY TRENDS
Electronegativity increases as you move:
 from left to right across a period
 from bottom to top in a group
 Fluorine (9) is the most electronegative
element

F
ELECTRONEGATIVITY REASON
Electronegativity is opposite of atomic size,
because the smaller the atom…the more
electrons are attracted to the nucleus
TRENDS IN ELECTRONEGATIVITY
Why are the noble gases not on
here??!
ELECTRONEGATIVITY EXAMPLE
Arrange
the following in order of
their increasing electronegativity.

Rb(37), I(53), Sn(50)
Ans:
Rb, Sn, I
4. IONIZATION ENERGY TRENDS

The ionization energy is the energy needed to
remove an electron from a gaseous atom.
 The
higher ionization energy, the harder it is to pull
off electrons
IONIZATION ENERGY TRENDS

Ionization energy increases as you move:
 from
left to right across a period
 from bottom to top in a group

Helium (2) has the highest ionization energy
He
IONIZATION ENERGY

Reason: The smaller the atom, the closer
electrons are to nucleus so higher the
ionization energy
IONIZATION ENERGY EXAMPLE
Arrange
the following in order of
increasing ionization energy.
He(2),
Ans:
Xe(54), Ar(18)
Xe, Ar, He
PERIODIC TRENDS SUMMARY
METAL REACTIVITY TRENDS

Metal reactivity increases as you move:
 right
to left across a period
 top to bottom in a group

Francium (87) is the most reactive metal
Fr
NON-METAL REACTIVITY TRENDS

Non-metal reactivity increases as you move:
 left
to right across a period
 bottom to top in a group

Fluorine (9) is the most reactive non-metal
F
REACTIVITY EXAMPLES
Ex.
1: Which is more reactive?
Fe(26)
Ans:
Ex.
or Co(27)
Fe
2: Which is less reactive?
Cl(17)
Ans:
or F(9)
Cl