Questions and Answers
What is an incomplete octet?
Another significant exception to the octet rule involves those elements that tend to form.
Which pair of atoms forms the most polar bond?
Which pair of atoms forms a nonpolar covalent bond?
What is the formal charge equation?
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What is the formal charge of nitrogen in a Lewis structure?
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What geometry corresponds to four electron groups around a central atom?
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What geometry corresponds to two electron groups around a central atom?
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What geometry corresponds to a central atom with 4 bonds and 1 lone pair?
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Predict the relative bond angles in CCl4 and H2O.
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Which molecule is polar?
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What is ΔE for the surroundings if a chemical system produces 170 kJ of heat and does 20 kJ of work?
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Which sample is most likely to undergo the smallest change in temperature upon the absorption of 100 kJ of heat?
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What is the empirical formula of the compound with the molecular formula C12H8?
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Which substance is an ionic compound?
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Which gas sample has the greatest volume at STP?
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Study Notes
Incomplete Octet
- Incomplete octet refers to elements that do not follow the octet rule and form molecules with fewer than eight electrons in their valence shell.
Polarity of Bonds
- A bond is more polar with a greater electronegativity difference; the bond between carbon and fluorine (C-F) is the most polar due to fluorine's high electronegativity.
- Nonpolar covalent bonds exhibit negligible electronegativity differences, such as in C-I bonds.
Formal Charge
- The formal charge can be calculated using the formula:
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of valence electrons − (lone pairs + # of bonds).
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- In Lewis structures, a formal charge of zero is ideal, reflecting stable electron arrangements.
Molecular Geometry
- Tetrahedral geometry features four electron groups around the central atom, while linear geometry corresponds to two electron groups.
- Seesaw geometry arises from four bonds and one lone pair, typically observed in SF4.
- H2O has a smaller bond angle compared to CCl4 due to the presence of lone pairs in H2O affecting bond angle size.
Polarity of Molecules
- SF2 is polar with a bent geometry, resulting from electronegative atoms creating polar bonds that do not cancel out.
Heat and Work in Chemical Systems
- In a scenario where a system expels heat and does work, the overall energy change (ΔE) for the surroundings is calculated by integrating heat (q) and work (w).
Heat Absorption and Temperature Change
- The temperature change upon absorbing heat depends on the mass and specific heat capacity of the material; larger masses or higher specific heat capacities yield smaller temperature changes.
Volume and Work
- The volume change in a gas system can be determined using work equations; expansion against pressure can be calculated using work equations involving volume differences.
Isotopes and Atomic Mass
- Potassium has three isotopes with different natural abundances; calculating its atomic mass involves taking a weighted average using these abundances.
- Moles of an element can be determined by dividing the number of atoms by Avogadro's number.
Matter Classification
- Matter may be classified by its state (solid, liquid, gas) or composition (element, compound, mixture).
Changes in Atomic Count
- The conversion of carats to grams and then applying atomic mass will determine the number of carbon atoms in a diamond.
Thermodynamics and Conservation Laws
- Antoine Lavoisier's law of conservation of mass indicates that mass is conserved during chemical reactions.
- John Dalton’s atomic theory revolutionized the understanding of matter being composed of indivisible atoms.
Electron Configuration and Quantum Numbers
- Fluorine's electrons are most shielded in 2p orbitals, demonstrating valence electrons' susceptibility to nuclear charge.
- 3d orbital electron configurations adhere to specific quantum number rules.
Lattice Energy and Ionic Compounds
- Lattice energy varies with ionic charge and radius; compounds with higher ionic charges generally have greater lattice energies.
Empirical vs. Molecular Formulas
- The empirical formula of a compound presents the simplest integer ratio, while the molecular formula reflects the actual number of atoms present.
- Ionic compounds consist of metals and nonmetals, while molecular compounds are typically formed from nonmetals.
Gas Volumes and Ideal Conditions
- At standard temperature and pressure (STP), gases with lower molar masses contain more moles per weight, thus occupying greater volumes.
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Test your knowledge of key chemistry concepts with these final exam flashcards. Covering topics like incomplete octets and polar bonds, these cards are designed to help you prepare effectively for your chemistry exam.
