Classify the bond between these pairs of elements as principally ionic or principally covalent (use Table 11.5): (a) sodium and oxygen (b) nitrogen and hydrogen (c) oxygen and hydrogen (d) phosphorus and chlorine

Understanding the difference between ionic and covalent bonds is fundamental in chemistry. An ionic bond is a type of chemical bond where one atom donates an electron to another, resulting in the formation of positively and negatively charged ions that attract each other. This type of bond typically occurs between a metal, which tends to lose electrons, and a nonmetal, which tends to gain electrons.

On the other hand, a covalent bond is when two atoms share one or more pairs of electrons. This form of bonding commonly occurs between two nonmetals, which both have a similar tendency to attract electrons. The shared electrons occupy the space between the atoms, effectively 'gluing' them together to form a molecule.

For example, sodium (a metal) and oxygen (a nonmetal), create an ionic bond as sodium donates its outer electron to oxygen. Conversely, nitrogen and hydrogen, being both nonmetals, form a covalent bond as they share their electrons.

Electronegativity is a measure of an atom's ability to attract and hold onto electrons when forming a chemical bond. It plays a crucial role in determining the type of bond two atoms will form. On the Pauling scale, which is commonly used to measure electronegativity, values generally range from about 0.7 to 4.0.

The larger the difference in electronegativity between two atoms, the more ionic the bond will be. Typically, a difference greater than 1.7 indicates an ionic bond, as seen between sodium (low electronegativity) and oxygen (high electronegativity). A smaller difference points towards a covalent bond. For example, the bond between oxygen and hydrogen is polar covalent because the difference in their electronegativity values is significant but not enough to make the bond ionic.

The periodic table is more than just a list of elements; it's a map of chemical properties. Tracking down the position of an element on the table can give insight into its bonding behavior. Metals, found on the left and center of the periodic table, tend to form ionic bonds due to their lower electronegativity. Nonmetals, located on the right side, are predisposed to form covalent bonds because of their higher electronegativity and tendency to share electrons.

When determining the type of bond, it's important to locate each element in the periodic table. This helps in predicting how an element will interact with others during bond formation. For instance, phosphorus and chlorine are both nonmetals making a covalent bond their mode of chemical combination.