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BIO 140 Human Biology I - Questions and Solutions

Chemical Bonds - Solutions

Review Questions

1. Which of the following is a molecule, but not a compound?

  1. H2O
  2. 2H
  3. H2
  4. H+
2. A molecule of ammonia contains one atom of nitrogen and three atoms of hydrogen. These are linked with ________.
  1. ionic bonds
  2. nonpolar covalent bonds
  3. polar covalent bonds
  4. hydrogen bonds
3. When an atom donates an electron to another atom, it becomes
  1. an ion
  2. an anion
  3. nonpolar
  4. all of the above
4. A substance formed of crystals of equal numbers of cations and anions held together by ionic bonds is called a(n) ________.
  1. noble gas
  2. salt
  3. electrolyte
  4. dipole
5. Which of the following statements about chemical bonds is true?
  1. Covalent bonds are stronger than ionic bonds.
  2. Hydrogen bonds occur between two atoms of hydrogen.
  3. Bonding readily occurs between nonpolar and polar molecules.
  4. A molecule of water is unlikely to bond with an ion.

 

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Critical Thinking Questions

1. Explain why CH4 is one of the most common molecules found in nature. Are the bonds between the atoms ionic or covalent?

Solution: A carbon atom has four electrons in its valence shell. According to the octet rule, it will readily participate in chemical reactions that result in its valence shell having eight electrons. Hydrogen, with one electron, will complete its valence shell with two. Electron sharing between an atom of carbon and four atoms of hydrogen meets the requirements of all atoms. The bonds are covalent because the electrons are shared: although hydrogen often participates in ionic bonds, carbon does not because it is highly unlikely to donate or accept four electrons.

2. In a hurry one day, you merely rinse your lunch dishes with water. As you are drying your salad bowl, you notice that it still has an oily film. Why was the water alone not effective in cleaning the bowl?

Solution: Water is a polar molecule. It has a region of weakly positive charge and a region of weakly negative charge. These regions are attracted to ions as well as to other polar molecules. Oils are nonpolar, and are repelled by water.

3. Could two atoms of oxygen engage in ionic bonding? Why or why not?

Solution: Identical atoms have identical electronegativity and cannot form ionic bonds. Oxygen, for example, has six electrons in its valence shell. Neither donating nor accepting the valence shell electrons of the other will result in the oxygen atoms completing their valence shells. Two atoms of the same element always form covalent bonds.

 

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OpenStax, Chemical Bonds. OpenStax CNX. Feb 28, 2018 http://cnx.org/contents/2c60e072-7665-49b9-a2c9-2736b72b533c@5. © Feb 28, 2018 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License 4.0 license.