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CHEM 141 Answers

Answers for Exam 3

QuestionAnswer
How does Valence Bond Theory explain the bonding in diamond? In diamond, each carbon atom uses four sp3 hybrid orbitals to form bonds to four other carbon atoms.
Is 8Be^(4+) --> 1H(+) + 7Li(3+) a chemical or nuclear reaction and why? Nuclear reaction because the nucleus is changing during the reaction.
Consider the bonding within a molecule of H2. Which statement best describes that bonding according to valence bond theory? The bonding electrons are localized in the region of orbital overlap between the two H nuclei.
What must be part of a structure for H-bonding to occur? An H atom must be connect to an O, F, or N atom with at least one lone pair also attached to the O. F, or N atom (the H atom will bond with another lone pair from a different molecule).
What is makes a molecule an isomer? When an molecule has the same number and types of atoms that are connected in the same way?
What is the hybridization if a central atom has 3 single bonds and one lone pair? sp3
Consider a system of two protons moving toward each other. Why does the potential energy of this system initially increase? The protons are moving against the repulsive electrostatic force that exists between them.
How do you fill a molecular orbital diagram? The lower (bonding) orbitals fill up first then the higher (antibonding) orbitals, each antibonding orbital filled will cancel out a bonding orbital.
An element that does not conduct electricity is found to have a melting point of 185 K. Which of the following statements are true for this element? This element exists as discrete atoms or discrete molecules and when this element melts, LDFs are overcome.
Why is fluorine more electronegative than chlorine? Fluorine is smaller than chlorine, so the bonding electrons are closer to the nucleus.
Claim: Butane (CH3CH2CH2CH3) has a higher boiling point than ethane (CH3CH3). What is the evidence and reasoning to support this claim? Butane contains a larger electron cloud and Because butane is more polarizable, the molecules have larger instantaneous dipoles and stronger London Dispersion Forces, requiring more energy to overcome.
What happens when a substance melts? Interactions are broken and energy is absorbed.
Imagine a generic molecule AB2 where A has 4 valence electrons and B has 6 valence electrons. Element A has a valence of 4 and element B has a valence of 2. How many bonds and lone pair electrons are on the central atom A? Two double bonds and no lone pair of electrons.
A central atom has 3 single bonds and one lone pair, what is the electron center geometry? Tetrahedral
Which statement is true about the nitrogen atoms in your body? The nitrogen atoms in your body were produced in fusion reactions in the stars.
Water (H2O, boiling point 100°C) and hydrogen fluoride (HF, boiling point 20°C) have similar molar masses but the boiling point of water is much higher than the boiling point of hydrogen fluoride. Why? Water forms more hydrogen bonding interactions than hydrogen fluoride.
Central atom Y is singly bonded to a Q atom with 3 lone pairs, another Q atom with 3 lone pairs, a Z atom and another Z atom. Element Q is more electronegative than Element Y. Element Y and Element Z have the same electronegativity. Is this atom polar? Polar, because the bond dipoles do not completely cancel leaving the molecule with an overall dipole.
What best explains why metals are ductile? Layers of atoms can move relative to one another because the sea of valence electrons move with them.
An absorption spectrum was collected from a galaxy far from the Earth. Compared to the absorption spectrum of helium collected on Earth, the black lines have the same pattern but are shifted to the red end of the spectrum. What can be inferred? The galaxy contains helium and is moving away from Earth.
Molecule X has a molar mass of 78 g/mol and a melting point of 225 K. Molecule Y has a molar mass of 79 g/mol and a melting point of 190 K. Which of the following statements must be true based on this information? Molecule X has stronger IMFs than Molecule Y.
A central atom is singly bonded to 2 other atoms and has 2 lone pairs, what is the molecule's shape? Bent
Can a single molecule of ethane (CH3CH3) melt? Why or why not? No, a single molecule of ethane cannot be defined as a solid or liquid.
What is true about single bonds? Rotating around a single bond does not break the end-to-end orbital overlap and therefore does not break the bond.
Created by: CRO009
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