Transcript Periodic Table Trends

Periodic Table Trends
(1) Atomic Radius
• As one goes from left to right across a
period, the atomic radii decreases.
• Reason: All the elements in a period have
the same principal quantum number. As
atomic number increases, so does the
attraction between the electrons and the
nucleus, and the attraction pulls the
electrons in.
Atomic Radius Continued
• As one goes down a group, the atomic
radii increases.
• Reason: The principal quantum number
increases (each new period represents a
new energy level), therefore the size of the
electron cloud increases.
(2) Ionization Energy
• The removal of an electron is known as
ionization (the formation of a positive ion).
The energy required to remove an electron
from an atom is called ionization energy.
The further the outermost electron is from
the nucleus, the less energy it takes to
remove it.
Ionization energy continued.
• From left to right across a period,
ionization energy increases.
• Reason: As you go from left to right
across a period, the atomic radius
decreases as the nuclear charge
increases. Thus, the valence electrons
are more strongly attracted to the nucleus
and more energy is needed to remove an
electron from the atom.
Ionization energy continued
• From top to bottom of a group, the ionization
energy decreases.
• Reason: As you go down a column, the atomic
radius increases, therefore, the distance
between the valence electrons and the nucleus
increases. In addition, the shielding effect by the
inner electrons increases (they block the
attraction of the nucleus for outer electrons),
therefore lowering ionization energy.
(3) Electron Affinity
• Electron affinity is a measure of the
tendency of an atom to gain electrons (a
measure of the attraction of an atom for
electrons).
Electron affinity continued
• From left to right across a period, electron
affinity increases.
• Reason: The increased nuclear charge of
each successive element increases the
attraction for electrons.
Electron affinity continued
• As you go down a column, electron affinity
decreases.
• Reason: As you go down a column, the
atoms become larger. As a result, the
nucleus is farther away from the surface
and attracts the outer electrons less
strongly.
(4) Electronegativity
• Electronegativity is the tendency for an
atom to attract electrons to itself when it is
chemically combined with another
element.
Electronegativity continued
• As one goes from left to right across a
period, electronegativity increases.
• As one goes down a group,
electronegativity decreases.
(5) Metallic Character
• Chemical properties associated with those
elements classed as metals. These
properties arise from the element's ability
to lose electrons.
Metallic character continued
• As one goes from left to right across a
period, metallic character decreases.
• As one goes down a group, metallic
character increases.