Transcript 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:
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Atomic Radius
Ionization Energy
Electron Affinity
Electronegativity
Atomic Radius
 The atomic radius of an element is an estimate of the
size of an atom from its nucleus to its outer perimeter.
 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.
 Understanding atomic radius will actually help us
understand some of the other periodic trends.
Atomic Radius
Ionization Energy
 The trend of ionization energy deals with ions – atoms that have lost or
gained electrons. (Anions are negative ions; cations are positive ions).
 Ionization energy is the energy needed to remove an electron from a
gaseous atom.
 The Trend of Ionization Energy…
 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.
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.
Ionization Energy
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
Electronegativity
 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.
 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
THE END