 Dimitri Mendeleev
 Creating first periodic
chart in 1869.
 Was able to accurately
predict the existence
and mass of several
unknown elements.
 First known example of
periodic “law”
 Atomic radius – half
the distance between
two nuclei of the same
element.
 Group Trends – atoms get bigger as
they go down a family because they are
adding more energy levels
Periodic Trend – atoms get smaller
as you go across the period from
left to right.
 adding the electrons in the same energy level and the
nuclear charge is increasing (More ++++++’s).
 This pulls the valence (outer) electrons in closer to the
atom. This effect is less as we move across the period
due to electron shielding.
 Valance electrons do not
“feel” the full pull of the
positive charge of the nucleus
 Zeff = # of protons - # of
non-valance electrons.
 Calculate Zeff for the
following elements:
 Na, Mg, Si, S, Ar
 Ionization Energy - The energy required to remove
an electron from an element
 X  X+ + e Ions - charged atoms resulting from addition or loss
of valence electrons.
 Cations – atoms that lose electrons and become (+)
charged
 Anions – atoms that gain electrons and become (–)
charged.
 More than one electron can be removed.
 Each ionization energy is labeled by the number of the
electron that is being removed : 1st, 2nd, and 3rd
ionization energies.
 As each electron is removed the ionization energy
increases. This happens because you are removing
electrons from a positive ion after the first electron is
removed.
 Measure of the energy change when an electron is
acquired by a neutral atom.
X + e-
Xˉ
 “Opposite” of Ionization Energy (not mathematically)
 Halogens gain electrons readily
 Noble gases and alkili earth metals do not gain electrons
Complete Table
Figure 5-10 p 149
 Group trends : they get larger as you go down a
family - more energy levels
 Periodic trends:
 Cations – smaller than the atoms because they lose
electrons and they get smaller as you lose more electrons
 Anions – larger than the atoms because they gain
electrons and they get smaller as they gain fewer
electrons
Figure 5-19 , page 149
 Electronegativity is the
attraction for a pair of
electrons by an element in
a shared bond.
 Fluorine has the highest
electronegativity.
 Cesium (francium) has the
lowest electronegativity.
 Group trends –
attraction decreases
down a family
 Periodic trends –
increase as the atoms
get smaller across the
period
Figure 5-20 p151
Electron Affinity Increases