Problem 103 - Chemistry: An Atoms-Focused Approach

Question

Which of the binary compounds formed by the following pairs of elements contain polar covalent bonds, and which are considered ionic compounds? a. \(C\) and \(S\) b. Al and Cl c. Cand O d. Ca and O

Step-by-Step Solution

Answer

Answer: The pairs (a) C and S, (b) Al and Cl, and (c) C and O form polar covalent bonds, while the pair (d) Ca and O forms an ionic compound.

Step 1: Determine electronegativity values of each element.

For this step, we will use the periodic table or reference tables to determine the electronegativity values of each element in the given pairs. a. Carbon (C): 2.55 and Sulfur (S): 2.58 b. Aluminum (Al): 1.61 and Chlorine (Cl): 3.16 c. Carbon (C): 2.55 and Oxygen (O): 3.44 d. Calcium (Ca): 1.00 and Oxygen (O): 3.44

Step 2: Calculate electronegativity difference for each pair.

In this step, you have to subtract the electronegativity values to find the difference between them. a. \(|2.55 - 2.58| = 0.03\) b. \(|1.61 - 3.16| = 1.55\) c. \(|2.55 - 3.44| = 0.89\) d. \(|1.00 - 3.44| = 2.44\)

Step 3: Classify the compounds with polar covalent bonds.

Compounds with electronegativity differences greater than 1.7 are considered ionic, while those with smaller differences are considered polar covalent. For each pair, we compare its electronegativity difference with 1.7 and classify accordingly. a. Electronegativity difference = 0.03 < 1.7, so the compound formed by C and S is a polar covalent bond. b. Electronegativity difference = 1.55 < 1.7, so the compound formed by Al and Cl is a polar covalent bond. c. Electronegativity difference = 0.89 < 1.7, so the compound formed by C and O is a polar covalent bond.

Step 4: Identify ionic compounds.

Any remaining compounds with electronegativity differences greater than 1.7 are considered ionic. d. Electronegativity difference = 2.44 > 1.7, so the compound formed by Ca and O is an ionic compound. In conclusion, compounds formed by the pairs (a) C and S, (b) Al and Cl, and (c) C and O contain polar covalent bonds, while the compound formed by the pair (d) Ca and O is considered an ionic compound.

Key Concepts

Polar Covalent Bonds

Polar covalent bonds form when two atoms in a compound share electrons unequally. This occurs when the atoms involved have different electronegativity values but not dramatically different, leaving them below the typical ionic threshold. Electronegativity is a measure of how strongly an atom can attract or hold onto electrons.
When the electronegativity difference between two atoms is less than 1.7, the bond is often considered polar covalent. In such bonds, the atom with the higher electronegativity will attract the shared electrons more, making it slightly negative. The other atom becomes slightly positive as it is deprived of electron sharing to some extent.
The result is a dipole formation, where one end of the molecule is more negative, while the other end is more positive. For example, a compound like carbon monoxide (C and O) has a difference in electronegativity values of 0.89, classifying it as a polar covalent bond.

• The electrons are not equally shared.
• Results in a partial negative charge on one atom, and a partial positive charge on the other.
• Water (H₂O) is a common example of a molecule with polar covalent bonds.

Ionic Compounds

Ionic compounds are formed when there is a complete transfer of electrons from one atom to another. This occurs between atoms that have significantly different electronegativities—usually more than 1.7. Because of this significant electronegativity difference, one atom gains electrons and one loses electrons, resulting in the formation of ions.
The atom with the lower electronegativity loses electrons and becomes a positively charged ion, known as a cation. Conversely, the atom with the higher electronegativity gains those electrons, becoming a negatively charged ion, known as an anion. The resulting compound is held together by the electrostatic attraction between positive and negative ions.
For instance, calcium oxide (Ca and O) is formed via ionic bonding. The electronegativity difference between calcium and oxygen is 2.44. This large difference leads to the complete transfer of electrons from calcium to oxygen.

• Composed of cations and anions.
• Typically formed between metals and non-metals.
• Sodium chloride (NaCl) is a classic example of an ionic compound.

Chemical Bonding

Chemical bonding refers to the process where atoms combine to form molecules by sharing or transferring electrons. This interaction is fundamental in creating the vast array of molecular structures found in both inorganic and organic chemistry.
Chemical bonds hold molecules together, and their types depend on how the electrons are shared or transferred between atomic pairs. There are mainly three types of chemical bonds: covalent, polar covalent, and ionic.
In covalent bonds, atoms share electron pairs equally. When shared unequally, polar covalent bonds form. For ionic bonds, there is a complete transfer of electrons between atoms.
Understanding the principles of electronegativity helps predict the type of bond that will form. It highlights how atomic interactions are not always symmetrical, and this asymmetry can dictate the physical and chemical properties of the compound. Bond strength, melting and boiling points, and conductivity often depend on the type of bonding.

• Depend on electron sharing or transfer.
• Determine the properties and structure of compounds.
• Crucial for understanding chemical reactions and compounds.