Download Discovering and understanding patterns in the PT Periodic Trends

Discovering and understanding patterns in the P.T.
Objective: To discover the periodic trends of
certain physical properties of elements related
to their position on the Periodic Table of
Elements.
Background: The Periodic Table is arranged
according to the Periodic Law. Periodic Law
states that when elements are arranged in
order of increasing atomic number, their
physical and chemical properties show a
periodic pattern. You will discover this by
examining the changes in properties of
elements on the Periodic Table.
Background, (cont.)
The properties included in this lesson are:
Atomic Radius
The Atomic radius is the distance from the
center of the atom’s nucleus to the outermost
electron
Atomic Radius and Ionic Radius
Why is there a difference in radius size between
the Na/Mg elements and the [Na]+1/ [Mg]+2 ions?
Ionization Energy
Ionization energy is the energy needed to
remove one of it’s electrons. Think of this as
how tightly the atom is holding on to its’
electrons. If it holds on tight, Ionization
energy is high, and conversely, if ionization
energy is low, the atom will give up an
electron easily.
First ionization energy is the energy required to
remove the first electron. Successive ionization
energies are those required to remove
additional electrons from an atom.
Electronegativity
Electronegativity has to do with an atom's
ability to attract electrons when it bonds
with another atom. In common terms it’s
electron greediness!
Electron Affinity
The energy change that occurs when an atom
gains an extra electron and becomes an anion.
For example, the electron affinity for Fluorine
is –228 kJ/mol. Why is the number negative?
Fluorine does not need energy to gain an
electron, there is sufficient energy available
within the fluorine atom to accept the electron
and so it releases the extra energy!
Valence
This is a number indicating the number of
electrons which will be gained or lost when it
bonds to another atom (also called its oxidation #).
When an atom gains or loses electrons it is
called an ion.
Negative ion (gains e-’s) = anion
Positive ion (loses e-’s) = cation “Plussy Cat”
6 Periodic Trends
The Final word
That’s just another way of saying we’re not
done yet and you better remember this!
Periodic Trends
A periodic trend is a property that changes
predictably as you move across a period and
down a Family in the periodic Table.
Atomic Radius The size of the atom measured from
the center of the nucleus to the outer
most electron.
Periodic Trends
Atomic Radius
As you move from left to right across a
period atomic radius decreases since we are
adding more protons and electrons. As
these particles are added, the attractive
force between the particles increases and the
electrons get pulled closer to the nucleus and
the atom gets smaller.
As you move from top to bottom of a family
you are also adding electron orbitals and the
atom gets bigger.
Valence Valence is a number indicating the
atoms’ tendency to gain or lose e-’s
during the bonding process
+1
0
+2
Periodic Trends
Valence Varies
+3 +4 -3 -2 -1
Valence
As a general rule, valence shows a pattern in
families 1A-8A. This pattern exists because
of each of the elements desire to have a full
octet thus looking like a noble gas.
When you consider the transition metals,
the pattern no longer exists.
Electronegativity The property of an atom which
describes its ability to attract e-’s
in a chemical bond.
Periodic Trends
Electronegativity
Electronegativity is directly related to atomic
radius and ionization energy. As we move
across the period the atomic radius decreases
and since the electrons are closer to the nucleus,
they are held very tightly and require large
amounts of ionization energy in order to remove
an electron. The tendency for atoms with high
electronegativity is to hold very tightly to the
electrons within a bond. As we move down a
Family there is a decrease again partially due to
a radii increase.
Ionization Energy The energy required to remove e-’s
creating an cation.
Periodic Trends
Ionization energy
Ionization energy is directly related to atomic
radius. As we move across the period the
atomic radius decreases and since the electrons
are closer to the nucleus, they are held very
tightly and require large amounts of ionization
energy in order to remove an electron. As we
move down a family the atoms radius increases
so therefore it doesn’t require as much energy
to remove an outer electron.
Electron Affinity The energy change that occurs
when an atom gains an e- and
become a anion.
Periodic Trends
Electron Affinity
Electron Affinity is the measure of an atom’s
attraction for an additional electron. As a
general rule, the atoms of nonmetals electron
affinity (except for the Noble gases), are more
negative than for metals. In other words,
nonmetals tend to have a higher affinity for
electrons than do metals.
This is in part due to both their position in the
table and the size of their radii.
Metallic Properties Included are elements that are
soft solids at room temp, having
the property to conduct electricity
& have magnetic attraction.
Periodic Trends
Nonmetals
Metals
Metallic Properties
Metallic properties include, being soft solids
at room temperature (with the exception of
mercury), conductors of heat and electricity,
being attracted to a magnet, malleable and
ductile, high melting points with high luster
and shine.
Each of the 6 trends described are properties that
change in a predictable manner as you move across a
period and down a Family in the periodic Table.
We will now complete a reciprocal
teaching & learning activity to
help your learn these Trends.