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Periodic Relationships
Among the Elements
Chapter 8
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Development of the Periodic Table
Dimitri Mendeleev

Arranged the elements by increasing
ATOMIC MASS, he saw a periodic
repetition of properties

Produced the first PERIODIC TABLE – 1871

The table placed elements with similar
properties in the same column

Kept “holes” for undiscovered elements, and
predicted the properties in advance
Development of the Periodic Table
Properties of elements predicted by Mendeleev
Development of the Periodic Table
H. G. Moseley in 1914

Rearranged the elements by
ATOMIC NUMBER

This has become the
MODERN PERIODIC
TABLE
Valence Electrons

valence electrons: electrons available to be
lost, gained, or shared in the formation of
chemical compounds
◦ electrons in the outermost energy level
◦ electrons that are responsible for reactions

Elements in a group have similar properties
because they have the same valence
electron configuration
Inner Core Electrons
• All electrons under the highest energy level
Valence Electron Configuration
Group
1
2
13
14
15
16
17
18
e- configuration
ns1
ns2
ns2np1
ns2np2
ns2np3
ns2np4
ns2np5
ns2np6
Valence electrons
-1
-2
-3
+3
+2
+1
Charges Of Representative Elements
8.2
What ions are isoelectronic with Ne?
an ion that has the same electron configuration
Na+: [Ne]
Al3+: [Ne]
O2-: 1s22s22p6 or [Ne]
F-: 1s22s22p6 or [Ne]
N3-: 1s22s22p6 or [Ne]
Electron Configurations of Transition Metals
When a cation is formed from an atom of a transition
metal, electrons are always removed first from the ns
orbital and then from the (n – 1)d orbitals.
Fe:
[Ar]4s23d6
Fe2+: [Ar]4s03d6 or [Ar]3d6
Fe3+: [Ar]4s03d5 or [Ar]3d5
Mn:
[Ar]4s23d5
Mn2+: [Ar]4s03d5 or [Ar]3d5
Periodic Table Groups
Properties of Metals
• shiny
• conductors of heat
and electricity
• tend to lose electrons
• ductile
– can be stretched
out into a wire
• malleable
–can be hammered
or rolled into
sheets
Properties of Nonmetals
PERIODIC LAW
When elements are arranged in order
of increasing atomic number, their
physical and chemical properties
show a periodic (repeating) pattern.
patterns on the periodic table are
called periodic trends
Atomic Radius
half the distance from center-center of 2
like atoms
Atomic Radii DOWN a Group
As you go down a group another energy
level is added, the atom size gets larger
↓ The number of occupied orbitals between
the nucleus and the outermost energy
level increases
↓
Shielding Effect:
reduction of attraction between positive
nucleus and outer electrons, outer electrons
are not held tight and can move away
Atomic Radius: down group
P
X
Na
X
P P
P
P P
P P
P
P P
P
X
X
X
X
X
X
X
X
X
X
Atomic Radius: down group
P
X
K
X
P P
P
P P
P P
P
P P
P
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Atomic Radii DOWN a Group
↓
DOWN THE GROUP ATOMIC RADIUS
INCREASES
more energy levels,
the larger the size of the atom
Atomic Radii ACROSS a Period
Each atom gains one proton and one
electron in the same energy level
→Each added electron is the same distance
from the nucleus
→As the positive charge increases and
exerts a greater force on the electrons
thereby pulling it closer to the nucleus
→
Atomic Radii ACROSS a Period
Effective nuclear charge (Zeff) :
“positive charge” felt by an electron.
Within a period, every time a proton is added,
the effective nuclear charge (Zeff) increases…
radius decreases
REMEMBER!
PROTONS
are bigger
and stronger!
+
e
+
P
-electrons
are smaller
and weaker!
Atomic Radius: across period
P
X
X
X
X
P P
P
P
P
P P
P P
P
X
X
X
X
X
X
X
Atomic Radii ACROSS a Period
→ACROSS THE
PERIOD ATOMIC RADIUS
DECREASES
greater effective nuclear charge (Zeff),
greater pull on the electrons, smaller radius
Ionic Radii
half the distance from center-center of
2 like ions
Ionic Radius DOWN a Group
↓
As you go down a group another energy
level is added, increasing the size of the
atom.
(just like the atomic radius)
Ionic Radius DOWN the Group
↓
DOWN THE GROUP IONIC RADIUS
INCREASES
more energy levels,
increase in atom size
Ionic Radius ACROSS the Period
Cation: positive ion formed from losing an
electron
→ A cation is always smaller than the
original atom
→The more electrons lost the more
protons available to attract a smaller
number of electrons.
Ionic Radius
P
X
Na +
P P
P
P P
P P
P
P P
P
X
X
X
X
X
X
X
X
X
X
X
Ionic Radius ACROSS the Period
→ACROSS THE
PERIOD IONIC RADIUS
DECREASES
greater pull on electrons,
the shorter the radius
Ionic Radius ACROSS the Period
Anion: negative ion formed from gaining an
electron
→ A anion is always larger than the original
atom
→The more electrons gained, the less
protons available to attract a larger
number of electrons.
Ionic Radius
P
X
-F
P P
P
P P
P P
P
P P
P
X
X
X
X
X
X
X
X
X
X
Ionic Radius ACROSS the Period
→ACROSS THE
PERIOD IONIC RADIUS
DECREASES
As electrons are added the atom gets
Larger from right to left,
General trend from left to right is decreasing
8.3
Ionization Energy
amount of energy needed to
remove an electron from an atom
Multiple Ionization Energies
I1 + X (g)
X+(g) + e-
I1 first ionization energy
I2 + X (g)
X2+(g) + e-
I2 second ionization energy
I3 + X (g)
X3+(g) + e-
I3 third ionization energy
I1 < I2 < I3
Ionization Energy DOWN a Group
↓
As you go down a group atoms become
larger, electrons are farther from the
nucleus and more easily removed
↓
The more electrons in an atom between
the nucleus and valence shell, the greater
the shielding effect
Ionization Energy DOWN a Group
↓
DOWN THE GROUP IONIZATION ENERGY
DECREASES
greater distance from the nucleus,
greater shielding effect
(less energy needed to remove)
Ionization Energy ACROSS a Period
→As
atomic radius decreases there is a
greater attraction between protons and
electrons. (effective nuclear charge)
→The stronger the attraction, the more
energy needed to remove an electron.
→The more electrons present, the more
energy required to remove them all to
become STABLE
Ionization Energy ACROSS a Period
→ACROSS THE
PERIOD IONIZATION ENERGY
INCREASES
more electrons on an energy level,
more energy required to remove them
Electronegativity
tendency for an atom to attract electrons
It is a “tug of war” between the two
.
atoms of a bond
:
.
H . F
:
:
Which is the more electronegative element?
Electronegativity
DOWN the Group
↓
The farther away from the nucleus, the
greater the shielding effect
↓
The larger the atom, the less likely it is to
accept more electrons.
Electronegativity
DOWN the Group
↓
DOWN THE GROUP ELECTRONEGATIVITY
DECREASES
farther the distance from the nucleus,
lower ability to attract electrons
Electronegativity
ACROSS the Period
→As
you go across a period atomic radius
decreases because there is a greater
attraction between protons and electrons
→Metals
do not attract electrons.
→Non-metals do attract electrons.
Electronegativity
ACROSS the Period
→ACROSS THE
PERIOD ELECTRONEGATIVITY
INCREASES
greater effective nuclear charge,
greater ability to add electrons
Electron Affinity
the negative of the energy change that
occurs when an electron is accepted by
an atom in the gaseous state to form an
anion.
Increases with ability to attract and hold
an electron
Electron Affinity
A large positive value means the anion is
very stable
X (g) + e-
X-(g)
F (g) + e-
X-(g)
DH = -328 kJ/mol
EA = +328 kJ/mol
O (g) + e-
O-(g)
DH = -141 kJ/mol
EA = +141 kJ/mol
Electron Affinity
DOWN the Group
Down a group, the energy released
becomes less negative so electron affinity
is smaller
↓ The larger the atom the less effective
nuclear charge and the more difficult to
accept electrons
↓
↓
Metals want to lose electrons.
Electron Affinity
DOWN the Group
↓
DOWN THE GROUP ELECTRON AFFINITY
DECREASES
farther the distance from the nucleus,
forms poor anions
Electron Affinity
ACROSS the Period
→Across
the period the energy released
becomes more negative, making electron
affinity more positive
→As effective nuclear charge gets stronger,
it is easier to attract an electron.
→Non-metals
want to attract electrons to
become stable
Electron Affinity
ACROSS the Period
→ACROSS THE
PERIOD ELECTRON AFFINITY
INCREASES
greater effective nuclear charge,
easily forms anions
Other Trends
Reactivity of Metals Video 1
Reactivity of Metals Video 2
Increasing reactivity
METAL REACTIVITY
Increasing reactivity
NONMETAL REACTIVITY