Download Periodic Trends

PERIODIC TRENDS
CAN STUDYING CHEMISTRY BE TRENDY?
• As you look at the periodic table and focus in on the elements and their characteristics, you
can see there are noticeable patterns (trends) that go across a period (horizontal row) on the
periodic table.
• These quantitative (able to measured with numbers and units) characteristics that follow
distinct patterns across the periodic table are called periodic trends.
• Remember…Mendeleev didn’t get all the fame and fortune for nothing – he was crazy smart!
• The periodic trends that we will be studying are:
• Atomic Radius
• Metallic Trend
• Ionic Radius
• Ionization Energy
• Electron Affinity
• Electronegativity
METALLIC TREND
• If you look at your periodic table, you will notice that the metals are on the
left of the periodic table and the nonmetals are on the right. (With metalloids
in between)
• The metallic character of an element can be defined as how readily an atom
can lose an electron.
• Metallic character increases from right to left and top to bottom.
METALLIC TREND
ATOMIC RADIUS TREND
• The atomic radius of an element is an estimate of the size of an
atom from its nucleus to its outer perimeter.
• Understanding atomic radius will actually help us understand some
of the other periodic trends.
ATOMIC RADIUS TREND
• The Trend of Atomic Radius…
• Atomic radius gets smaller as you move left to right on the periodic
table.
• As you go across a row, you add more protons to the nucleus and more electrons to
the orbits – this means more attraction between the opposing charges and the
orbits are pulled in even closer to the nucleus.
• Atomic radius gets larger as you go top to bottom on the periodic table.
• Each time you go down a spot on one of the columns on the periodic table, you are
adding another orbit – this additional orbit increases the size of the atom.
ATOMIC RADIUS
THE SHIELDING EFFECT
• Reduction in effective nuclear
charge on an electron that is caused
by the repulsive forces of other
electrons between it and the
nucleus
• In an atom with one electron, that
electron experiences the full charge
of the positive nucleus. However, in
an atom with many electrons, the
outer electrons are simultaneously
attracted to the positive nucleus
and repelled by the negatively
charged electrons.
ATOMIC RADIUS TREND
IONIC RADIUS
• Ions are charged atoms, either + or -
• Cations are positive ions
-Cations form when atoms lose electrons
• Anions are negative ions
-Anions form when atoms gain electrons
IONIC RADIUS
CATIONS
VS.
ANIONS
• Cations are smaller than their
parent atoms.
• Anions are larger than their parent
ions
• By losing their valence electrons,
they lose their entire valence shell
• When extra (-) electrons are added,
extra (+) protons are NOT added to
the nucleus
• Cations are formed by the metals on
the left side of the Periodic Table
• Effective nuclear attraction is less
for the increases number of
electrons
IONIC RADIUS
IONIZATION ENERGY
• Energy is needed to remove an electron from an atom
• The energy needed to overcome the attraction of the nuclear
charge and remove an electron (from a gaseous atom) is called the
Ionization Energy
IONIZATION ENERGY TREND
• Ionization energy increases as you go left to right on the periodic table.
• As you go let to right, the radius of the atom is smaller because of the
greater attraction between the protons and electrons. The electrons are
being held more tightly and closely by the nucleus. You have to fight to get
one free.
• Ionization energy gets weaker as you move down a column on the periodic table.
• As you go down a column, you add another orbit so the negative electrons
are further away from the positive protons and the attractive force
between them is not as strong. It’s easier for anyone to come by an rip off
an electron.
IONIZATION ENERGY TREND
MULTIPLE IONIZATION ENERGIES
• The term “multiple ionization energies” refers to the taking of more than one
electron from a gaseous atom.
• The trend here is that it gets a lot tougher to take more and more electrons
from an atom.
• The first electron taken will seem easy compared to the second. The second
electron will be tougher than the first, but, will come away easier than the
third and so on…
• As an electron is taken away, the protons are acting on fewer electrons and
can pull them in even tighter.
ELECTRON AFFINITY
• Electron affinity is the energy released when an electron is added to
a gaseous atom.
• There is no clear pattern for the periodic trend of electron affinity
although there tends to be a general increase in electron affinity as
you go from the left to the right on the periodic table.
• Note that you must spend energy to rip an electron off of an atom
and energy is released, or given off, when an electron in added to an
atom.
ELECTRON AFFINITY TREND
ELECTRONEGATIVITY TREND
• Electronegativity is the relative strength of attraction an atom has
for electrons while it is in a chemical bond.
• Remember that chemical bonds can involve the sharing of pairs of
electrons. The atoms are literally fighting to gain possession of
those electrons – the amount “electron-grabbing muscle” they
have is called electronegativity.
ELECTRONEGATIVITY TREND
• The Trend of Electronegativity…
• Electronegativity increases as you go left to right across the periodic table.
• There are more protons in the atoms as you go across the periodic
table and this means there is more positive charge to attract the
negative electrons.
• Electronegativity decreases as you go down a column on the periodic
table.
• You are adding more orbits so the electrons are further away from the
protons and there is less attractive force to grab the electrons.
ELECTRONEGATIVITY TREND
THE END!