University:
Boston University
Course:
CAS CH 641 | Physical Organic Chemistry
Academic year:

2023
Views:

431

Pages:

15
Author:

Cali Bowman

[TP] Which molecule is more polar? (χH = 2.1, χB = 2.04, χN = 3.04, χF = 3.98) 1. NH3 (trigonal pyramid) 2. BF3 (trigonal planar) 3. Polarity is the same Electronegativity Formal charge assumes electrons between atoms are shared equally. Unless two connected atoms are identical, sharing always favors one atom. Electronegativity is a relative measure the tendency of an atom to attract electrons shared with another atom in a covalent bond. Electronegativity, χ (Greek letter chi, like in “ kite”) Electronegativity is a relative measure the tendency of an atom to attract electrons shared with another atom in a covalent bond. Electronegativity, χ Electronegativity is a relative measure the tendency of an atom to attract electrons shared with another atom in a covalent bond. Bond polarity The greater the electronegativity difference of two covalently bonded atoms, the more unequal the sharing of the electrons forming the covalent bond. BrI: 2.96 − 2.66 = 0.30, covalent HCl: 3.16 − 2.1 = 1.0, polar covalent NaCl: 3.16 − 0.93 = 2.23, ionic Please keep in mind that these definitions are qualitative, since sharing is always unequal unless the bonded atoms are identical. [TP] Which bond is more polar? (χH = 2.1, χB = 2.04, χN = 3.04, χF = 3.98) 1. N−H 2. B−F 3. Polarity is the same Predicting molecular geometries How atoms are arranged in three dimensions around their central atom is determined by the steric number (SN) the central atom. SN = attached atoms + lone pairs SN = attached atoms + lone pairs What is SN of C in CO2 ? SN = 2: Two attached atoms and zero lone pairs What is the SN of O in H2 O? SN = 4: Two attached atoms and two lone pairs What is the SN of N in NO− 2? SN = 3: Two attached atoms and one lone pair SN = attached atoms + lone pairs What is the SN of B in BF3 ? SN = 3: Three attached atoms and zero lone pairs What is SN of S in SF4 ? SN = 5: Four attached atoms and one lone pair What is the SN of S in SF6 ? SN = 6: Six attached atoms and zero lone pairs Predicting molecular geometries: SN = 2 What is SN of C in CO2 ? SN = 2: Two attached atoms and zero lone pairs Shape is linear, bond angle is 180° Predicting molecular geometries: SN = 3 What is the SN of N in NO− 2? SN = 3: Two attached atoms and one lone pair Shape is bent, bond angle a bit less than 120° Predicting molecular geometries: SN = 4 What is the SN of O in H2 O? SN = 4: Two attached atoms and two lone pairs Shape is bent, bond angle a little less than 109.5° Predicting molecular geometries: SN = 5 What is SN of S in SF4 ? SN = 5: Four attached atoms and one lone pair Shape is seesaw, bond angles are a little less than 180°, 120°, and 90° Predicting molecular geometries: SN = 6 What is the SN of S in SF6 ? SN = 6: Six attached atoms and zero lone pairs Shape is octahedral, bond angles are 90° [TP] What is the molecular shape of ClF3? 1. 2. 3. 4. 5. 6. 7. 8. Linear Trigonal planar Tetrahedral Trigonal pyramidal Bent Seesaw T-shaped None of these