Transcript Ionization Energy and Electron Affinity

Ionization Energy and
Electron Affinity
Section 7.4-7.5
Objectives
• Examine periodic trends in ionization
energy
• Examine periodic trends in electron
affinity
Key Terms
• Ionization energy
• Electron Affinity
Ionization Energy
• Ease at which electrons can be removed
from an atom or ion
• First ionization energy, I1, is the energy
required to remove the first electron from
neutral atom
• Second ionization energy, I2, is the energy
required to remove the second electron from
a +1 ion
• Greater the I, the more difficult to remove
the electron
Trends of Ionization Energy
• I1< I2 < I3 < I4
• With each removal, the ion becomes more
positive
• Strengthens nucleus’s hold on its electrons
• Sharp increase in I when inner-shell
electrons are removed
• Table 7.2 on page 271
Periodic Trends in I1
• Within rows, I1 increases with atomic
number
• Slight irregularities
• Within columns, I1 decreases with
increasing atomic number
• Representative elements show larger
range of I1 values than transition metals
• Transitions slowly increase across rows
Factors Affecting Trends
• More energy is needed to remove an
electron as:
• Effective Nuclear Charge increases
• Atomic Radius decreases
Irregularities
• I does not always increases across rows
• Decrease from Be to B
Be: [He] 2s2
B: [He]2s2 2p1
• The most easily removed electron in B is that in
the 2p orbital, higher in energy than the 2s
electrons in Be
• 2p electron of B needs less energy for total
removal than does the 2s electron of Be
Irregularities
• O is lower than N
• N: [He]2s2 2p3
• O: [He]2s2 2p4
• Important difference in the way electrons are
distributed
• Hund’s rule: 3 e- in the 2p orbitals of a nitrogen atom
all have the same spin, but e- are paired in one of the 2p
orbitals of oxygen
• Electrons try to stay as far apart as possible to minimize
repulsion
• Force of repulsion between these electrons is minimized
to some extent by pairing electrons
• Slightly easier to remove an electron
Electron Affinities
• Energy change that occurs when electron
are added to a gaseous atom
• Measure of the attraction of an atom to an
electron
• Negative values (energy is released during
process)
• kJ/mol
• More negative affinity = greater attraction
Trends in Affinities
• Not as evident as that of ionization
energy
• Halogens have the greatest affinities (1 eshy of a filled p subshell)
• Noble gases have affinities of 0
• Group 2A and 5A have very little affinity
Electron Affinities (kJ/mol)
Putting it all together
Homework
• 7.35, 7.42, 7.44, and 7.46 on page 294