Question

Using the table of electronegativity values (Table 11.5), indicate which element is more positive and which is more negative in these compounds: (a) \(\mathrm{HCl}\) (b) \(\mathrm{SO}_{2}\) (c) \(\mathrm{CCl}_{4}\) (d) IBr (e) CsI (f) \(\mathrm{OF}_{2}\)

Short answer

For the compounds listed: (a) H is positive, Cl is negative; (b) S is positive, O is negative; (c) C is positive, Cl is negative; (d) I is positive, Br is negative; (e) Cs is positive, I is negative; (f) O is positive, F is negative.

Step-by-step solution

Review Electronegativity

Consult Table 11.5 for the electronegativity values of the elements involved in the compounds. Electronegativity indicates an atom's ability to attract and hold electrons. A higher electronegativity value means the element is more negative.

Compare Electronegativity for HCl

Look at the electronegativity values for Hydrogen and Chlorine. Chlorine has a higher electronegativity than Hydrogen, making it more negative and Hydrogen more positive.

Compare Electronegativity for SO2

Sulfur and Oxygen are the elements in SO2. Oxygen has a higher electronegativity; therefore, it is more negative and Sulfur is more positive.

Compare Electronegativity for CCl4

Compare Carbon and Chlorine electronegativity values. Chlorine is more electronegative, making it more negative, and Carbon will be more positive in CCl4.

Compare Electronegativity for IBr

For the Iodine and Bromine pair, Bromine is more electronegative, hence more negative, whereas Iodine is more positive.

Compare Electronegativity for CsI

Cesium and Iodine are compared. Iodine being more electronegative is more negative, making Cesium the more positive element.

Compare Electronegativity for OF2

Compare the electronegativity of Oxygen and Fluorine. Fluorine is the most electronegative element, so it's more negative than Oxygen, making Oxygen more positive in OF2.

Key concepts

Understanding Chemical Bonding

Chemical bonding lies at the heart of understanding how atoms combine to form compounds. Essentially, it's the process where atoms connect by sharing or transferring electrons. There are three primary types of chemical bonds: ionic, covalent, and metallic bonds.

• Ionic Bonding: This occurs when atoms with significantly different electronegativity values transfer electrons, resulting in positively and negatively charged ions. For instance, in sodium chloride (NaCl), the sodium atom donates an electron to chlorine, creating ions that are held together by electrostatic forces.
• Covalent Bonding: When atoms with similar electronegativity share electrons, it forms a covalent bond. Take water (H₂O) for example: the oxygen atom shares electrons with two hydrogen atoms, binding them together.
• Metallic Bonding: Found in metals, this bond involves the communal sharing of electrons among a lattice of metal atoms, giving metals their characteristic properties such as conductivity and flexibility.

Electronegativity plays a crucial role in understanding these bonds, as differences in this value dictate the polarity of the bond. Recognizing how atoms bond and interact enables us to predict a molecule's properties and behavior.

Exploring Molecular Polarity

Molecular polarity is the distribution of electrical charge over the molecules. It arises due to the differences in electronegativity between bonded atoms. When electronegativity values are similar, the shared electrons are distributed evenly, resulting in nonpolar bonds. Conversely, if the difference is substantial, the electrons tend to be closer to the more electronegative atom, creating polar bonds and thereby, polar molecules.

For example, in carbon dioxide (CO₂), the oxygen is more electronegative than the carbon, pulling the shared electrons towards itself. However, the molecule is linear, causing the polarities to cancel out, making CO₂ a nonpolar molecule. Whereas in water (H₂O), the bent shape with oxygen at the vertex means that the polarity does not cancel out, making water a polar molecule. Understanding the concept of molecular polarity is vital for deciphering the solubility, boiling and melting points, and even the reactivity of substances.

Periodic Table Trends and Electronegativity

The periodic table is not just a chart of elements; it's a map of chemical properties and trends, including electronegativity. This value typically increases from left to right within a period and decreases down a group. These trends help us predict how atoms will interact and form bonds.

For example, elements on the right side of the periodic table (excluding noble gases) like fluorine have higher electronegativities and are great at attracting electrons. Contrastingly, elements on the left side, such as cesium, have lower electronegativities and readily lose electrons to form positive ions.

The understanding of these trends helps us deduce why iodine is more electronegative than cesium (CsI), or why fluorine (F) is more electronegative than oxygen (O), as seen in OF₂. Recognizing these patterns is fundamental for students as they tackle various problems in chemistry, particularly when predicting molecule behavior and the types of bonds formed.