1,001 Chemistry Practice Problems For Dummies (2014)

Part I. The Questions

Chapter 8. Molecular Geometry

The difference in the electronegativity between two atoms is an indicator of the polarity of the bond between the elements. The difference ranges from 0 to about 3, and the bond ranges from nonpolar to polar to ionic.

The position of an element on the periodic table indicates the number of valence electrons on an atom. The key to a Lewis dot diagram is the sum of the valence electrons of all atoms in a species plus electrons indicated by the charge on an anion (negative ion) or minus electrons indicated by the charge on a cation (positive ion). A correct diagram must indicate all of these electrons. The bonds and lone pairs around an atom in a Lewis dot diagram indicate the shape and polarity of the species.

The Problems You’ll Work On

In this chapter, you work with molecular geometry in the following ways:

check Counting electrons in Lewis dot diagrams

check Predicting bond types based on electronegativity values

check Recognizing molecular shapes

check Identifying polarity in bonds and molecules

Note: For access to the periodic table, see the Appendix.

What to Watch Out For

Remember the following when working on molecular geometry:

check The Lewis structure must account for all valence electrons plus or minus electrons gained or lost to form ions.

check Know the basic geometries and which geometries are inherently polar.

check The bond between two different atoms is likely to be polar. Some bonds are so polar they’re ionic.

check The farther apart two nonmetals are on the periodic table, the more polar the bond. Hydrogen is an exception; its electronegativity falls between boron’s and carbon’s on the periodic table.

check Predicting the correct molecular shape relies on having a correct Lewis structure. Second-period elements never have more than an octet of electrons.

Valence Electrons

481–490 Answer the following questions concerning valence electrons.

481. How many electrons are in the Lewis dot diagram of a boron atom?

482. How many electrons are in the Lewis dot diagram of a barium atom?

483. How many electrons are in the Lewis dot diagram of a chlorine atom?

484. How many electrons are in the Lewis dot diagram of an O2– ion?

485. How many electrons are in the Lewis dot diagram of a sodium ion?

486. Which group on the periodic table contains atoms that have the following Lewis dot diagram?

9781118549322-un0801.eps

487. Which group on the periodic table contains atoms that have the following Lewis dot diagram?

9781118549322-un0802.eps

488. Which group on the periodic table contains atoms that have the following Lewis dot diagram?

9781118549322-un0803.eps

489. Which group on the periodic table contains atoms that have the following Lewis dot diagram?

9781118549322-un0804.eps

490. Which group on the periodic table contains atoms that have the following Lewis dot diagram?

9781118549322-un0805.eps

Predicting Bond Types

491–501 Predict the type of bond.

491. What is the name for a measure of an atom’s strength to attract a bonding pair of electrons?

492. What kind of bond forms between elements with the same or nearly the same electronegativity?

493. What kind of bond forms between elements when the electronegativity difference is moderate?

494. For the representative elements, metals are expected to have a __________ (lower/higher) electronegativity, and nonmetals are expected to have a __________ (lower/higher) electronegativity.

495. Based on their relative electronegativity values, what type of bond will form between carbon and bromine?

496. Based on their relative electronegativity values, what type of bond will form between carbon and fluorine?

497. Based on their relative electronegativity values, what type of bond will form between chlorine and fluorine?

498. Based on their relative electronegativity values, what type of bond will form between boron and hydrogen?

499. Based on their relative electronegativity values, what type of bond will form between carbon and hydrogen?

500. Based on their relative electronegativity values, what type of bond will form between phosphorus and fluorine?

501. Arrange the following bonds in order of increasing polarity.

Si–Cl, S–Cl, O–S

Basic Molecular Shapes

502–521 The following questions cover basic molecular shapes.

502. What term best describes the shape of the following molecule?

9781118549322-un0806.eps

503. What term best describes the shape of the following molecule?

9781118549322-un0807.eps

504. What term best describes the shape of the following molecule?

9781118549322-un0808.eps

505. What term best describes the shape of the following molecule?

9781118549322-un0809.eps

506. What term best describes the shape of the following molecule?

9781118549322-un0810.eps

507. What term best describes the shape of the following molecule?

9781118549322-un0811.eps

508. What molecular shape has bond angles that are approximately 180°?

509. What molecular shape has bond angles that are approximately 120°?

510. What molecular shape has bond angles that are approximately 109.5°?

511. What is the molecular shape of boron trichloride, BCl3?

512. What is the molecular shape of bromine, Br2?

513. What is the molecular shape of methane, CH4?

514. What is the molecular shape of water, H2O?

515. What is the molecular shape of ammonia, NH3?

516. What is the molecular shape of carbon ­dioxide, CO2?

517. Why does water, H2O, have a bent molecular shape?

518. Why does nitrogen trifluoride, NF3, have a trigonal pyramidal molecular shape?

519. Why does carbon dioxide, CO2, have a linear molecular shape?

520. Why does carbon tetrachloride, CCl4, have a tetrahedral molecular shape?

521. Why does boron trifluoride, BF3, have a ­trigonal planar molecular shape?

Exceptional Molecular Shapes

522–536 The following questions deal with exceptional molecular shapes.

522. What term best describes the following molecular shape?

9781118549322-un0812.eps

523. What term best describes the following molecular shape?

9781118549322-un0813.eps

524. What term best describes the following molecular shape?

9781118549322-un0814.eps

525. What term best describes the following molecular shape?

9781118549322-un0815.eps

526. What term best describes the following molecular shape?

9781118549322-un0816.eps

527. What term best describes the following molecular shape?

9781118549322-un0817.eps

528. What molecular shape has bond angles between atoms that are 90°, 120°, and 180°?

529. Which molecular shape has 109.5° bond angles?

530. What is the molecular shape of sulfur tetrafluoride, SF4?

531. What is the molecular shape of phosphorus pentachloride, PCl5?

532. What is the molecular shape of bromine pentafluoride, BrF5?

533. What is the molecular shape of sulfur hexafluoride, SF6?

534. What is the molecular shape of xenon tetrafluoride, XeF4?

535. What is the molecular shape of chlorine ­trifluoride, ClF3?

536. What are the electron geometry and the molecular shape of xenon difluoride?

Polarity of Molecules

537–545 These questions deal with the polarity of molecules.

537. What do you need to know about a molecule to determine its polarity?

538. H2 contains a __________ (nonpolar/polar) bond and is a __________ (nonpolar/polar) molecule.

539. HCl contains a __________ (nonpolar/polar) bond and is a __________ (nonpolar/polar) molecule.

540. CClcontains __________ (nonpolar/polar) bonds and is a __________ (nonpolar/polar) molecule.

541. NH3 contains __________ (nonpolar/polar) bonds and is a __________ (nonpolar/polar) molecule.

542. SeCl4 contains __________ (nonpolar/polar) bonds and is a __________ (nonpolar/polar) molecule.

543. XeO4 contains __________ (nonpolar/polar) bonds and is a __________ (nonpolar/polar) molecule.

544. ICl3 contains __________ (nonpolar/polar) bonds and is a __________ (nonpolar/polar) molecule.

545. Which of the following molecules are polar?

CO2, OF2, BF3, NBr3, PCl3, KrF4, SnH4, IF5