Chemistry Unit 3 Flashcards

Questions and Answers

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion

What basic fact determines molecular shapes?

Electron pairs repel each other.

What is the electronic geometry of NH3 (ammonia)?

Tetrahedral

Under what condition is the electronic arrangement the same as the molecular shape?

When there are no lone pairs of electrons on the central atom. Signup and view all the answers

What is the molecular geometry of ammonia (NH3)?

Trigonal pyramidal Signup and view all the answers

Why is the bond angle of H2O less than 109.5˚?

The repulsion between lone pairs of electrons is greater than the repulsion between bonding pairs. Signup and view all the answers

What is the arrangement of atoms around the central atom in a molecule with five covalent bonds and no lone pairs?

Trigonal bipyramidal Signup and view all the answers

True or False: All non-polar molecules have non-polar bonds.

False Signup and view all the answers

Which molecular geometry is possible with 0, 3, or 4 lone pairs?

Linear Signup and view all the answers

Consider this molecule: HCN (with C as the central atom). The electronic geometry of this molecule is . The molecular geometry of this molecule is . This molecule is . There are/is lone pair(s) total within the molecule.

linear; linear; polar; one Signup and view all the answers

Consider this molecule: SCl4. The electronic geometry of this molecule is . The molecular geometry of this molecule is . This molecule is . There are/is lone pair(s) on the central atom and there are/is __ lone pair(s) total within the molecule.

trigonal bipyramidal; see-saw; polar; one; one Signup and view all the answers

The Valence Bond theory describes the bonds in molecules as arising from the of atomic orbitals centered on the atoms in the molecule. However, to achieve the correct geometries, it must often use new orbitals that result from the mixing of some number of pure atomic orbitals.

overlap; hybrid Signup and view all the answers

What type of geometry do new hybridized atomic orbitals occupy around the atom?

Electronic geometry Signup and view all the answers

How many other atoms can a central atom that is sp3 hybridized bind?

4 Signup and view all the answers

How many pi bonds can a central atom that is sp2 hybridized form with a neighboring atom that has a p orbital?

1 Signup and view all the answers

What describes the bonds that exist between the two nitrogen atoms in the molecule N2?

One sigma bond and two pi bonds Signup and view all the answers

What is the hybridization of the second carbon atom in H2CCCH2?

sp Signup and view all the answers

What is the hybridization of the central atom if it has five regions of high electron density with one being a lone pair?

sp3d Signup and view all the answers

What is the hybridization of Sb in the molecule SbCl5^2-?

sp3d2 Signup and view all the answers

Identify the orbitals used by the bolded atom in acetone (CH3COCH3).

sp3 Signup and view all the answers

Using molecular orbital theory, we can calculate quantitatively the energy of a molecule as a function of the __________ between the two nuclei.

distance Signup and view all the answers

Such calculations for the diatomic molecule would yield information about __________.

bond length and bond energy Signup and view all the answers

MOs (molecular orbitals) that are lower in energy than their corresponding AOs (atomic orbitals) are called . MOs that are higher in energy than their corresponding AO's are called . If the MOs have identical energy (or very similar energy) to the AOs, we label them as __.

bonding; anti-bonding; non-bonding Signup and view all the answers

What type of interference is responsible for sigma bonding?

Constructive Signup and view all the answers

What are nodes?

Places of zero electron density between atoms Signup and view all the answers

What is the bond order of methane (CH4)?

4 Signup and view all the answers

What can non-bonding orbitals be thought of as?

Lone pairs Signup and view all the answers

What are the molecular orbital configurations for O2, O2-, and O2-- and their respective bond orders?

2, 1.5, 1 Signup and view all the answers

If you find a molecule absorbs wavelengths of 205 nm, 280 nm, and 310 nm, which corresponds to the HOMO-LUMO energy gap?

310 nm Signup and view all the answers

What would you likely guess about an unknown molecular substance?

Diamagnetic Signup and view all the answers

What is MO theory better at describing than VB theory?

Delocalization Signup and view all the answers

What forces does every molecule have?

Dispersion Signup and view all the answers

For which of the following molecules will dipole-dipole interactions be important? A. CO2 B. SO2 C. O2 D. O3

O3 Signup and view all the answers

Which of the following molecules can be involved in hydrogen bonding? H2, HF, CH4, CH3OH

HF Signup and view all the answers

Which would you expect to have the lowest vapor pressure at room temperature?

CH4 Signup and view all the answers

Substances A and B are similar in size and weight, but substance A is more volatile than substance B. What can be true based on this information? (Select all that apply)

Substance A has a higher vapor pressure than substance B. Signup and view all the answers

Rank the liquids in order of increasing viscosity at 25°C: I. C6H6 II. CH3CH2OH III. CH2OHCHOHCH2OH IV. CH2OHCH2OH V. H2O

I < V < II < IV < III Signup and view all the answers

What holds covalent solids together?

Covalent bonds Signup and view all the answers

If a soluble ionic compound is made into an aqueous solution, what is usually observed?

Conduct current Signup and view all the answers

What kind of materials conduct heat and electricity well in the solid state?

Metals bonding with metals Signup and view all the answers

How would you classify the solid quartz (SiO2) which has a relatively high melting point?

Network Signup and view all the answers

Which type of crystalline solid is typically the most malleable?

Metallic Signup and view all the answers

Study Notes

VSEPR Theory and Molecular Geometry

VSEPR stands for Valence Shell Electron Pair Repulsion, where electron pairs repel each other, determining molecular shapes.
NH3 has a tetrahedral electronic geometry but a trigonal pyramidal molecular geometry due to one lone pair on the nitrogen atom.
H2O has a bond angle less than 109.5˚ because lone pair repulsion is greater than bonding pair repulsion.
The arrangement for a central atom bonded to five atoms (with no lone pairs) is trigonal bipyramidal.

Molecular Geometry Concepts

Non-polar molecules can have polar bonds, making the statement that all non-polar molecules have non-polar bonds false.
A linear molecular geometry can occur with 0, 3, or 4 lone pairs on the central atom.
For HCN, both electronic and molecular geometries are linear, and the molecule is polar with one lone pair.

Hybridization and Bonding

Valence Bond theory states that bonds arise from the overlap of atomic orbitals and often require hybrid orbitals for correct geometries.
sp³ hybridization allows a central atom to bond with up to four other atoms.
A sp² central atom can form one pi bond with a neighboring atom with a p orbital.
N₂ involves one sigma bond and two pi bonds between the nitrogen atoms, with each nitrogen being sp hybridized.

Molecular Orbital Theory

Molecular orbitals (MOs) are classified as bonding, anti-bonding, or non-bonding depending on their energy relative to atomic orbitals.
Sigma bonds result from constructive interference and are located "on axis" between two nuclei.
Nodes represent regions of zero electron density in molecular interactions.
For the molecules O2, O2-, and O22-, the bond orders are 2, 1.5, and 1, respectively.

Intermolecular Forces

All molecules exhibit dispersion forces, and dipole-dipole interactions are significant in polar molecules like SO2 and O3.
Hydrogen bonding occurs in HF and CH3OH, significant due to the strong interactions involving H and highly electronegative atoms.
Compounds like CCl4 and CO2 are characterized by having only dispersion forces.

Vapor Pressure and Surface Tension

CH4 has the lowest vapor pressure at room temperature, indicating stronger intermolecular forces in other substances.
Higher volatility correlates with lower boiling points and weaker intermolecular forces.
Surface tension phenomena include a piece of aluminum foil floating and water beading on a windshield.

Types of Solids

Covalent solids, such as quartz (SiO2), are held together by covalent bonds and exhibit high melting points.
Metallic solids are typically the most malleable due to the nature of metallic bonding.
Ionic compounds in aqueous solutions conduct electricity, indicating the presence of free-moving ions.

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Test your knowledge with these flashcards covering key concepts from Chemistry Unit 3. Explore important terms like VSEPR theory and molecular shapes, and understand how electron pairs influence molecular geometry. Perfect for students preparing for exams or wanting to strengthen their understanding of molecular structure.