Passage I

Figure 1 is a simplified periodic table that gives the atomic number, symbol, name, and electronegativity (EN) of 21 elements. Rows of elements are called periods. Columns of elements are called groups.

Figure 1 adapted from Nivaldo J. Tro, Chemistry: A Molecular Approach, 2nd ed.©2011 by Pearson Education, Inc.

The greater the EN of an element, the more strongly an atom of that element attracts electrons to itself in a chemical bond. The greater the absolute value of the differ­ence between the ENs of 2 elements, | EN₁ - EN₂ |, the more polar is the bond between atoms of the elements. Figure 2 gives, for each of 6 compounds, | EN₁ - EN₂ | and the bond energy at 298 K (the energy needed to break all the bonds in 1 mole of a compound at 298 K).

Figure 2 adapted from James G. Speight, Lange's Handbook of Chemistry, 16th ed. ©2005 by McGraw-Hill, Inc.