Transcript Periodic Trends - PearsonGreatPath

THE PERIODIC LAW
Dimitri Mendeleev was the first scientist to
publish an organized periodic table of the
known elements.
 He was perpetually in trouble with the Russian
government and the Russian Orthodox Church,
but he was brilliant never-the-less.

THE PERIODIC LAW

Mendeleev even went out on a limb and
predicted the properties of 2 at the time
undiscovered elements.
Mendeleev, for instance, predicted the
discovery of germanium (which he called ekasilicon) as an element with an atomic weight
between that of zinc and arsenic, but with
chemical properties similar to those of silicon.
Mendeleev, for instance, predicted the
discovery of germanium (which he called ekasilicon) as an element with an atomic weight
between that of zinc and arsenic, but with
chemical properties similar to those of silicon.
(Same properties = Same group/Family = 4A)
THE PERIODIC LAW
Mendeleev understood the ‘Periodic Law’ which
states:
 PERIODIC LAW - When arranged by increasing
atomic number, the chemical elements display
a regular and repeating pattern of chemical
and physical properties.
 (Everything in 1A had the SAME properties)

Periodic Law: (repeating pattern)
Same number of valence electrons
= same properties = same group/family
Atoms with similar properties appear in groups
or families (vertical columns) on the periodic
table.
 They are similar because they all have the
same number of valence (outer shell) electrons,
which governs their chemical behavior.

METALS, NONMETALS, METALLOIDS
METALS
Metals are lustrous
(shiny), malleable,
ductile, and are good
conductors of heat and
electricity.
 They are mostly solids
at room temp.
 What is one exception?

NONMETALS
Nonmetals are the
opposite.
 They are dull, brittle,
nonconductors
(insulators).
 Some are solid, but
many are gases, and
Bromine is a liquid.

METALLOIDS


Have some
characteristics of
metals, some of
nonmetals.
For instance, silicon
looks shiny, but is
brittle and fairly poor
conductor.
METALLOIDS
Metalloids, aka semimetals are just that.
 They have characteristics
of both metals and
nonmetals.
 They are shiny but brittle.
 And they are
semiconductors.
 What is our most important
semiconductor?

Which element is more NON-Metallic?
Which element is the MOST metallic?
Francium
PERIODIC TRENDS
There are several important atomic
characteristics that show predictable trends
that you should know.
 The first and most important is atomic radius.
 Radius is the distance from the center of the
nucleus to the “edge” of the electron cloud.

COVALENT RADIUS

Two Br atoms bonded together are 2.86
angstroms apart. So, the radius of each atom
is 1.43 Å.
Nucleus
2.86 Å
1.43 Å
1.43 Å
Li – 2, 1
Period 2 = E2
Na – 2,8, 1
Period 3 = E3
Atomic radius increase down a group
K – 2,8,8, 1
Period 4 = E4
What do you think will happen
to the radius across a period?
Rb – 2,8,18,8, 1
Period 5 = E5
 Increases
ATOMIC RADIUS
Largest
Radius
 Increases
Smallest
Radius
ATOMIC RADIUS
4P+ 5P+ 6P+ 7P+ 8P+ 9P+
-
+
-
++
+
-
++
+ ++
+
-
Effective
Nuclear
Same
Energy
Level
(2)
–
More
Charge (Z)
positive
greater
pull
Effective nuclear
chargeprotons
is the pullthat
an electron
onfrom
electrons
 smaller
radius
(negative) “feels”
the nucleus
(positive).
ATOMIC RADIUS
 Moving across a period, each
element gains one proton
-  A more positive nucleus (more
+
protons) has a greater pull on
++
the electron cloud.
++
+
 The nucleus is more positive
+ ++
+
and the electron cloud is more
negative.
Effective
 The increased attraction pulls
Nuclear
the cloud in closer, making
Charge (Z)
atoms smaller as we move
from left to right across a
period.
 More Energy Levels
ATOMIC RADIUS
 Fewer Protons = Less Pull
Smallest
Radius
Largest
Radius
NOTES = (Draw the box below)
TRENDS FOR ATOMIC RADIUS
Smallest Radius
Largest Radius
Which Element has the larger atomic radii?
IONIZATION ENERGY
This is the second important periodic trend.
 If an electron is given enough energy (in the
form of a photon) to overcome the effective
nuclear charge holding the electron in the
cloud, it can leave the atom completely.
 The atom has been “ionized” or charged.
 The number of protons and electrons is no
longer equal.

IONIZATION ENERGY
Ionization energy - The energy required to
remove an electron from an atom .
(measured in kilojoules, kJ)
 -- Larger atom = Lower ionization energy

The larger the atom is, the further away the
valence electrons are, the easier its
electrons are to remove.
 Ionization energy and atomic radius are
inversely proportional.
 Ionization energy is always endothermic,
that is energy is added to the atom to
remove the electron.

IONIZATION ENERGY
What is the trend?
IONIZATION
ENERGY
Larger atom =
Lower Ionization Energy
Effective nuclear
charge
is
the
pull
that
an
electron
(negative) “feels” from the nucleus (positive)
In the same energy level (period), FEWER
protons  Weaker pull  Valence Electrons
further from the nucleus  Larger Atom 
Lower Ionization Energy need to remove an
electron..
3. TREND IN IONIZATION POTENTIAL
NOTES = (Draw the box below)
TRENDS FOR IONIZATION ENERGY
Highest
Lowest
Which Element has the greater Ionization Energy?
ELECTRON AFFINITY
What does the word ‘affinity’ mean?
 Electron affinity is the energy change that
occurs when an atom gains an electron (also
measured in kJ).
 Where ionization energy is always endothermic
(energy IN), electron affinity is usually
exothermic (energy OUT), but not always.

TRENDS IN ELECTRON AFFINITY
Electron Affinity - The energy release when an
electron is added to an atom.
--An affinity (attraction) of ADDITIONAL electrons
(same period) More protons  More Effective
Nuclear Charge  Great pull on electrons  Greater
affinity (attraction) of additional electrons.
4P+ 5P+ 6P+ 7P+ 8P+ 9P+
NOTES = (Draw the box below)
TRENDS FOR ELECTRON AFFINITY
Highest
Lowest
ELECTRONEGATIVITY

Electronegativity - a measure of an atom’s
attraction for another atom’s shared
electrons. (covalently bonded electrons)
Highest
Lowest
Which Element has the greater Electronegativity?
OVERALL REACTIVITY
This ties all the previous trends together
in one package.
 However, we must treat metals and
nonmetals separately.
 The most reactive metals are the largest
since they are the best electron givers.
 The most reactive nonmetals are the
smallest ones, the best electron takers.

OVERALL REACTIVITY
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