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CHEM 111 (69)
Lecture

Lattice energy calculated, covalent bonds, bond energy, naming binary covalent compounds, formula/molecular mass

4 Pages
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Department
Chemistry
Course Code
CHEM 111
Professor
Dana Johnson

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4 October Announcements Exam Wednesday Clark building, 7 – 9 pm Same rooms as last time Must know: First 4 periods of the periodic table S block and yellow p block ions (Fig. 2.18 pg. 65) Bold polyatomic ions (Table 2.5, p. 68) Recitations tomorrow All are open for exam preparation (optional) Check class schedule for options Lattice energy calculated Dependent on Coulomb’s Law (again) Energy ≈ (q1* q2) / distance Or, energy ≈ (cation charge * anion charge) / sum of radii Notice gradual difference in energies when charges remain the same Charge difference makes a greater change LiF → 1050 kJ / moles MgO → 3923 kJ / moles Clicker question Which compound has the highest lattice energy? A. LiBr B. NaBr C. KBr D. RbBr E. CsBr All charges are equal, smallest radius Covalent bonds As in ionic bonds, also entail the atom obtaining a full outer shell (octet rule) However, these bonds form by sharing electrons (vs. transferring electrons) Typically, between non-metals Because the octet rule is satisfied only by sharing electrons, covalent compounds form molecules (vs. formula units) Depicting covalent bonds Lewis dot symbols Each atom counts each shared electron toward the octet Shared electrons are “bonding pairs,” typically shown as a line Unshared electrons are “lone pairs” or “nonbonding electrons” Bond order: number of electrons shared between atoms Single bonds (bond order of 1) O 2 C 2 2ouble bonds (bond order = 2) N2 HCN triple bonds
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