Lecture 15_Covalent Bonding_Nomenclature_EN

Announcements for October 4 th , 2023 Our objective is to determine how atoms come together to form molecules and ionic compounds • The plan: • Chemical covalent bonds • Nomenclature • Electronegativity Monday reading: Chapter 8, Sections 1 – 3; Chapter 2, Section 8 (Naming ionic compounds – skip polyatomic ions) ; Chapter 3, Sections 3 – 4 Wednesday reading: Chapter 8, Sections 1 – 3; Chapter 2, Section 8 (Naming binary molecular compounds) Friday reading: Chapter 8, Sections 4 – 5 • Homework 5 due Monday, October 9 th by 11:59 PM • Recitation 5 is tomorrow, October 5 th

Atoms “aggregate” to form chemical compounds – gives richness to life Compounds consist of two or more elements that are chemically bonded • Composition occurs with fixed ratio of contributing atoms Liquid water Oxygen gas Hydrogen gas (H 2 O) (H 2 ) (O 2 ) Combustion Electrolysis

Molecules are discrete , independent aggregates of atoms held together by covalent bonds (electron-sharing) Covalent bonds formed between nonmetals – why? ∆? = Energy needed to break H 2 into 2 H atoms Bond length: 74 pm Bond energy: 432 kJ/mol Orbital overlap; electrostatic attraction between valence electrons and nuclei 1 2 3 4 (1) Atoms too far to interact (dissociated) (2) Atoms attracted (3) Most stable covalent bond formed (4) Repulsion between nuclei

Many elements naturally occur as molecular compounds due to chemical bonding H H + Diatomic molecules H H F F + F F O O + O O Cl Cl + Cl Cl Halogens (Group 17) Multiple bonds form between 2 nd period elements N N + N N Br Br I I

From atomic Lewis structures, we can construct Lewis structures for molecules: PH 3 H H H + P H H H P P H H H Many main group elements abide by the “ _________ rule” P: 6 shared e - ’s + 1 unshared lone pair = 8 e - ’s H: 2 shared e - ’s = 2 e - ’s (Closed shell since 1s 2 ) Chemical bonds arise from ________________ e - ’s occur in pairs due to Pauli Exclusion Principle!

Starting from atomic Lewis structures, construct molecular Lewis structures for the following compounds H 2 O BH 3 CH 4 NH 3 1. Atomic Lewis Structure 2. Connect to form bonds

Chemical Nomenclature: A systematic approach to naming chemical compounds (Binary covalent molecules) Molecular compounds – Independent aggregates of nonmetal atoms (Groups 14 – 18) held together by covalent bonds O C O Cl P Cl Cl Cl Cl CO 2 PCl 5 N N O N 2 O CF 4 Greek Greek Count atoms Count atoms NO change Usually lower Group element Base name ≈ 1 st syllable Nitr ogen= Nitr ide Ox ygen= Ox ide C F F F F No ‘mono’ Provide chemical formulas and names for the following:

Write chemical formulas or provide the appropriate chemical name for each (a) Sulfur trioxide (b) Dinitrogen tetroxide (c) P 4 O 6 (d) H 2 O O H H Correct the following names: ?????? ?𝑥𝑖??, ?? 2 ? 3 ?𝑖????𝑖??? ??𝑖?𝑥𝑖??, 𝐴? 2 ? 3 𝑆𝑖?𝑖??? ?𝑉 ?ℎ???𝑖??, 𝑆𝑖?? 4

We can determine molar masses of chemical compounds by summing molar masses of elemental components Ionic compound Molecule Na + Cl - NaCl Sodium chloride Molar mass = sum of contributing molar masses ? ? = ? ?𝑎 + ? 𝐶? ? ? = 22.99?/??? + 35.45?/??? ? ? = 58.44?/??? O C O CO 2 Carbon dioxide ? ? = ? 𝐶 + 2? ? ? ? = 44.01?/??? 1 mole contains 6.022x10 23 formula units of NaCl ? ? = 12.01?/??? + 2(16.00)?/??? In 1 mole of NaCl, how many Na + ions do I have? How many ions? 1 mole contains 6.022x10 23 molecules of CO 2 1 ???? ???? ∙ ? 𝐴 ?. ?. 1 ??? ∙ 1 ?? + 𝑖?? 1 ?. ?. = 6.022𝑥10 23 ?? + 𝑖??? 1 ???? ???? ∙ ? 𝐴 ?. ?. 1 ??? ∙ 2 𝑖??? 1 ?. ?. = 1.204𝑥10 24 𝑖??? (?? + + ?? − ) Remember, mole means counting!

In anticipation of buying a new PS5, Dr. Cirri cheaped out on his wife’s engagement ring by buying a 1.50 carat cubic zirconia stone (zirconium (IV) oxide; $20 vs $10,000 for diamond). Determine the number of formula units and total number of ions in this stone. (1 carat = 0.4 g) 1. What is the molecular formula for the compound? 2. What is the molar mass? 3. What do we know and what do we want? 4. Is that all we want? Avogadro’s number of ZrO 2 formula units contains: Avogadro’s number of Zr +4 ions 2 x Avogadro’s number of O -2 ions

The polarity of chemical covalent bonds is a measure of how unevenly atoms share bonding-pair electrons δ - Homodiatomic molecule (H 2 ) 0 < |δ| < 1 e - pair shared uniformly Heterodiatomic molecule (HF) e - pair mostly on F in bond ( δ =0.41 → ~41% e - transfer) H F Stronger e - tug Z eff 1 ~7 AR (pm) 37 64 IE (kJ/mol) 1311 1681 EA (kJ/mol) -73 -328 Greater tug (pull) on valence e - Atomic properties influence chemical bonding Weaker tug on valence e - Stronger overall e - tug: δ + Uniform e - density _____________ ________________

Electronegativity (EN) is a measure of an atom's ability to attract a shared pair of electrons in a chemical bond EN trend roughly follows IE without exceptions • Greater EN = ______________________ Increasing EN Decreasing EN Most EN atom Least EN atom (4.0 is arbitrary) Metals: Low IE, donate electrons Nonmetals: High IE, share or keep electrons ∆? ?𝑟??.???𝑎???𝑡 = 296 ??/??? ∆? ????𝑟𝑖???𝑡 = 565 ??/??? + EN Scale based on “extra” stabilization energy of polar bonds (covalent + ‘electrostatic’) Polar covalent bonds are intermediate between pure covalent and pure ionic!

Examples of non-polar, polar, or ionic bonding properties Non-polar: Typically, soluble (dissolvable) in organic matter but not in water Polar: Typically, soluble in water Lipid bilayer Styrofoam Δ EN (OH) = 1.4 Ionic: Exist as brittle salts; typically, soluble in water or completely insoluble δ - δ + δ + δ - Protein Ethanol δ - δ + Polar exterior (dissolve in blood) Non-polar Polar Non-polar interior (structure/function) (Cell membranes) Δ EN (CH) = 0.4 Δ EN (NaCl) = 2.1