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General Chemistry Principles, Patterns, and Applications, 2011

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ion. The electron affinity (EA) of an element is the energy change that occurs when an electron is<br />

added to a gaseous atom to give an anion. In general, elements with the most negative electron affinities<br />

(the highest affinity for an added electron) are those with the smallest size <strong>and</strong> highest ionization energies<br />

<strong>and</strong> are located in the upper right corner of the periodic table. The electronegativity (χ) of an element is<br />

the relative ability of an atom to attract electrons to itself in a chemical compound <strong>and</strong> increases<br />

diagonally from the lower left of the periodic table to the upper right. The Pauling electronegativity scale<br />

is based on measurements of the strengths of covalent bonds between different atoms, whereas the<br />

Mulliken electronegativity of an element is the average of its first ionization energy <strong>and</strong> the absolute value<br />

of its electron affinity. Elements with a high electronegativity are generally nonmetals <strong>and</strong> electrical<br />

insulators <strong>and</strong> tend to behave as oxidants in chemical reactions. Conversely, elements with a low<br />

electronegativity are generally metals <strong>and</strong> good electrical conductors <strong>and</strong> tend to behave as reductants in<br />

chemical reactions.<br />

K E Y T A K E A W A Y<br />

<br />

<strong>General</strong>ly, the first ionization energy <strong>and</strong> electronegativity values increase diagonally<br />

from the lower left of the periodic table to the upper right, <strong>and</strong> electron affinities<br />

become more negative across a row.<br />

C O N C E PTUAL P R OBLEMS<br />

1. Identify each statement as either true or false <strong>and</strong> explain your reasoning.<br />

a. Ionization energies increase with atomic radius.<br />

b. Ionization energies decrease down a group.<br />

c. Ionization energies increase with an increase in the magnitude of the electron affinity.<br />

d. Ionization energies decrease diagonally across the periodic table from He to Cs.<br />

e. Ionization energies depend on electron configuration.<br />

f. Ionization energies decrease across a row.<br />

2. Based on electronic configurations, explain why the first ionization energies of the group 16 elements are<br />

lower than those of the group 15 elements, which is contrary to the general trend.<br />

3. The first through third ionization energies do not vary greatly across the lanthanides. Why? How does the<br />

effective nuclear charge experienced by the ns electron change when going from left to right (with increasing<br />

atomic number) in this series?<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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