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2.03 – General Trends on the Periodic Table
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Groups
o columns on the Periodic Table
o 18 of them
o also known as Families
o The elements often have very similar properties within a group.
o In the previous lesson, you’ve seen how the electron structure ends up being
very similar for elements in the same group.
Period
o rows on the Periodic Table
o 7 of them
Trends
o There are many properties that change gradually as you go down a group or
across a period.
o There are exceptions to these, but the general trend usually holds for many of
these.
Trends summarized from
http://www.geocities.com/capecanaveral/lab/4097/chem/chap4/periodictrends.html
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Atomic Size or Atomic radius
o Period : Decreases as you move from left to right across a period
 The more protons in the nucleus pull the electrons in that Period’s energy
level tighter. This decreases the size.
o Group: Increases as you move down a group
 As you move down a group, you increase the number of energy levels.
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Electronegativity
o How hard an atom “pulls” on electrons
o Period: Increases as you move from left to right across a period.
 The nonmetals on the right side have close to full outer energy levels and
pull very hard to fill up the valence shell or the outermost energy level.
o Group: Decreases as you move down a group.
 “Elements near the top of the period table have few electrons to begin
with; every electron is a big deal. They have a stronger desire to acquire
more electrons.”
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Ionization energy
o Amount of energy needed to remove electrons in the outermost energy level
o Period: Increases as you move from left to right across a period.
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“Elements on the right of the chart want to take others atom's electron
(not given them up) because they are close to achieving the octet. The
means it will require more energy to remove the outer most electron.
Elements on the left of the chart would prefer to give up their electrons
so it is easy to remove them, requiring less energy (low ionization
energy).”
o Group: Decreases as you move down a group.
 “The shielding affect makes it easier to remove the outer most electrons
from those atoms that have many electrons (those near the bottom of
the chart).”
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Reactivity
o Reactivity refers to how likely or vigorously an atom is to react with other
substances.
 This is usually determined by how easily electrons can be removed
(ionization energy) and how badly they want to take other atom's
electrons (electronegativity) because it is the transfer/interaction of
electrons that is the basis of chemical reactions.
o Reactivity of Metals
 Period: Decreases as you go from left to right across a period.
 Group: Reactivity increases as you go down a group
 The farther to the left and down the periodic chart you go, the
easier it is for electrons to be given or taken away, resulting in
higher reactivity.
o Reactivity of Nonmetals
 Period: Increases as you go from the left to the right across a period.
 Group: Reactivity decreases as you go down the group.
 The farther right and up you go on the periodic table, the higher
the electronegativity, resulting in a more vigorous exchange of
electron.
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Ionic radius of Positive ions (Metals)
o Ionic radius of a metal is smaller than the atomic radius.
 “Generally, metals lose electrons to achieve the octet. This creates a
larger positive charge in the nucleus than the negative charge in the
electron cloud, causing the electron cloud to be drawn a little closer to
the nucleus as an ion.”
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Ionic radius of Negative ions (Nonmetals)
o Ionic radius of a nonmetal is larger than the atomic radius.
o “Generally, non-metals loose electrons to achieve the octet. This creates a larger
negative charge in the electron cloud than positive charge in the nucleus, causing
the electron cloud to 'puff out' a little bit as an ion.”
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Melting Point
o Metals – generally decreases as you go down a group
o Nonmetals – generally increases as you go down a group