Draw the Lewis structure for carbonyl fluoride, COF2. Describe this molecule’s electron-pair geometry and molecular geometry. What is the hybridisation of the carbon atom? What orbitals overlap to form o and a bonds? (20) 2p 7 2p 2p 2p 2p 2p 2p 2p 2p 2p ENERGY TV TIHTI Tap Tap The highest occupied molecular orbital (the HOMO). 11 025 25 11 25 carbon 025 oxygen orbitals carbon monoxide, CO orbitals Figure 1: The molecular orbitals of carbon monoxide and the HOMO of the molecule. (c) Assume that the energy level diagram for carbon monoxide shown in Figure 1 above can also be applied to the heteronuclear diatomic molecule chlorine monoxide, CIO. (i) Write the electron configuration for CIO (ii) What is the highest energy, occupied molecular orbital (HOMO)? (iii) is the molecule diamagnetic or paramagnetic? (iv) What is the net number of o and a bonds and what is the CIO bond order? (10) (d) Which of the homonuclear, diatomic molecules of second period elements (from Li2 to Ne2) are paramagnetic? Which have a bond order of 1? Which have a bond order of 2? Which diatomic molecule has the highest bond order? (10)
The Correct Answer and Explanation is:
Let’s address each part of the question with correct answers followed by a 300-word detailed explanation.
(b) Carbonyl Fluoride, COF₂
- Lewis Structure:
..
:F–C(=O)–F:
..- Electron-pair geometry: Trigonal planar
- Molecular geometry: Trigonal planar
- Hybridization of Carbon: sp²
- Orbitals involved:
- σ bonds: sp² (C) overlaps with 2p (F or O)
- π bond: 2p (C) overlaps with 2p (O) for the C=O bond
(c) Chlorine Monoxide, ClO
(i) Electron configuration:
Total electrons = Cl (17) + O (8) = 25 electrons
(ii) HOMO:
π*2p (degenerate antibonding orbitals)
(iii) Magnetic character:
Paramagnetic (due to one unpaired electron)
(iv) Net σ and π bonds:
1 σ bond, 1 π bond (but reduced by antibonding)
Bond order = ½ × (bonding e⁻ – antibonding e⁻) = 1.5
(d) Diatomic Molecules from Li₂ to Ne₂
- Paramagnetic: B₂, O₂
- Bond order = 1: Li₂, F₂
- Bond order = 2: Be₂, O₂
- Highest bond order: N₂ (Bond order = 3)
300-Word Explanation:
Carbonyl fluoride (COF₂) is a triatomic molecule composed of one carbon (C), one oxygen (O), and two fluorine (F) atoms. Carbon is the central atom. To draw the Lewis structure, we begin by counting valence electrons: carbon contributes 4, oxygen 6, and each fluorine 7, totaling 24 electrons. Carbon forms a double bond with oxygen and single bonds with each fluorine, completing the octet of all atoms. This arrangement gives COF₂ a trigonal planar shape due to three regions of electron density around the carbon atom. The bond angles are approximately 120°, and carbon is sp² hybridized, forming sigma bonds using its sp² orbitals and a π bond via unhybridized 2p orbitals overlapping with oxygen’s 2p orbitals.
In part (c), chlorine monoxide (ClO) has 25 total valence electrons. Its molecular orbital diagram resembles that of CO. Electrons fill the molecular orbitals following Hund’s rule and the Aufbau principle. The 25th electron enters a π*2p orbital, making it the HOMO. Because it contains an unpaired electron, ClO is paramagnetic. The bond order is calculated as:
$\text{Bond Order} = \frac{1}{2}(13 – 10) = 1.5$
Finally, in part (d), among second-period diatomic molecules:
- Paramagnetic molecules have unpaired electrons: B₂ and O₂.
- Bond order of 1: Li₂ and F₂
- Bond order of 2: Be₂ and O₂
- Highest bond order: N₂ with a bond order of 3, signifying a strong triple bond formed from one sigma and two pi bonds, resulting in a very stable molecule