Question

Arrange these bonds in order of increasing ionic character: carbon to hydrogen, fluorine to hydrogen, bromine to hydrogen, sodium to chlorine, potassium to fluorine, lithium to chlorine.

Short answer

In order of increasing ionic character, the bonds are: Carbon to Hydrogen, Bromine to Hydrogen, Fluorine to Hydrogen, Lithium to Chlorine, Sodium to Chlorine, and Potassium to Fluorine.

Step-by-step solution

Understand electronegativity

Electronegativity is a measure of the attraction of an atom for the electrons in a chemical bond. The greater an atom's electronegativity, the greater its attraction for bonding electrons.

Determine the electronegativity difference for each bond

Go to the Periodic Table and find the electronegativity values for each atom involved in the bonds. Then, subtract the smaller electronegativity from the larger one for each bond. This will give the electronegativity difference for each one. The differences are Carbon to Hydrogen (2.55-2.20) = 0.35, Fluorine to Hydrogen (3.98-2.20) = 1.78, Bromine to Hydrogen (2.96-2.20) = 0.76, Sodium to Chlorine (3.16-0.93) = 2.23, Potassium to Fluorine (3.98-0.82) = 3.16, Lithium to Chlorine (3.16-0.98) = 2.18

Arrange the bonds in order of increasing electronegativity difference

The bonds with the smallest electronegativity differences have the least ionic character, while those with the largest differences have the most ionic character. Therefore, arrange the bonds in the order from smallest to largest electronegativity difference. It becomes: Carbon to Hydrogen < Bromine to Hydrogen < Fluorine to Hydrogen < Lithium to Chlorine < Sodium to Chlorine < Potassium to Fluorine.

Key concepts

Electronegativity

Electronegativity can be thought of as an atom's ability to attract and hold onto electrons.
In a bond, atoms with higher electronegativity will attract electrons more strongly than those with lower electronegativity.

An Electronegative Example

Consider a bond between hydrogen and chlorine. Chlorine has a much higher electronegativity than hydrogen. It means that in a hydrogen chloride molecule, the shared electrons are more closely associated with the chlorine atom, giving this bond some ionic character.

Measuring Electronegativity

To put this concept into numbers, we use the Pauling scale, where each element is assigned an electronegativity value. Values range from around 0.7 for elements like cesium, which have very low electronegativity, to about 4.0 for elements like fluorine, which has the highest electronegativity on the scale. As the exercise demonstrates, by comparing the electronegativity values of two atoms, students can predict the type of bond they will form.
In summary, electronegativity is a cornerstone of understanding chemical bonding, as it dictates how electrons are distributed in a molecule and, consequently, the molecule's chemical behavior.

Chemical Bonds

Chemical bonds are the physical phenomena of chemical substances being held together by the attraction of atoms to each other through sharing, as well as exchanging, of electrons – or electrostatic forces.

Types of Chemical Bonds

• Ionic bonds – These occur when the difference in electronegativity between two atoms is large, resulting in the transfer of electrons and the formation of ions.
• Covalent bonds – When two atoms have similar electronegativity, they tend to share electrons equally, which makes these bonds have a nonpolar covalent character.
• Polar covalent bonds – When there's a moderate difference in electronegativity, atoms share electrons but not equally. This results in a slight charge separation, or polarity, in the bond.

The ionic character of a bond is directly related to the difference in electronegativity between the two atoms: the greater the difference, the more ionic the bond. Knowing this can help students understand how to arrange bonds based on their ionic character, as in the given exercise, where they look at the differences to determine which bonds have more ionic character than others.

Periodic Table

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties.
Elements are lined up in periods and groups. Periods go from left to right across the table, while groups run up and down the columns.

Understanding Periodic Trends

The periodic table not only provides the atomic mass and electronegativity of elements but also allows us to see trends in these properties across different groups and periods. For instance, electronegativity typically increases from left to right across a period and decreases from top to bottom within a group.
Using the periodic table, students can identify trends that help in solving exercises like determining ionic character from electronegativity differences. Simply locate the elements in question on the table, note their electronegativity, and follow the steps laid out in the exercise. It becomes a tool for understanding deeper chemical concepts by visualizing the relationship among elements.