Chapter 2 - Small Molecules and the Chemistry of Life

• What is the charge and mass of electrons?

  Electrons have a negligible mass and a negative charge.
• What are the charges and masses of protons and neutrons?

  Protons have mass and a positive charge; neutrons have mass and no charge.
• What defines an element?


  An element is a pure substance containing only one kind of atom.
• How is the atomic number defined?

  The atomic number is defined as the number of protons in an atom.
• What is the mass of one proton or one neutron in atomic mass units (amu)?

  1 atomic mass unit (amu) or 1 dalton.
• What is the mass of one electron in grams?

  9 × 10^–28 grams.
• How do the number of protons and electrons affect an element's behavior in chemical reactions?

  The number of protons and electrons determines how an element behaves in chemical reactions.
• What percentage of the 92 elements are considered essential to life?

  About 20–25% of the 92 elements are essential to life.
• What are the bulk elements that make up 96% of living matter?

  Carbon, hydrogen, oxygen, and nitrogen.
• What are trace elements and how are they characterized?

  Trace elements are required in only minute quantities.
• What is the mass number of an atom?

  The mass number is the number of protons plus the number of neutrons.
• What is the mass number of an atom equal to in daltons?

  The mass number is equal to the mass of the atom in daltons.
• What are isotopes?


  Isotopes are forms of an element with different numbers of neutrons and thus different mass numbers.
• What is atomic weight?

  Atomic weight is the average of mass numbers of isotopes in their normally occurring proportions.
• What is the atomic weight of hydrogen?

  1. 0079.
• What are radioisotopes?


  Radioisotopes are unstable isotopes that give off energy in the form of radiation from the nucleus.
• What is radioactive decay?

  Radioactive decay is the transformation of an atom that sometimes results in a change in the number of protons.
• How can radiation from radioisotopes be used?

  Radiation can be used to detect the presence of radioisotopes and can be incorporated into molecules to act as a tag or label.
• What is a molecule?


  A molecule is a stable association of atoms.
• What are the uses of radioisotopes in research and medicine?

  Radioisotopes are useful in research and in medicine, but radiation can damage cells and tissues.
• How does the number of electrons affect atomic interactions?

  The number of electrons determines how atoms will interact in chemical reactions.
• What describes the locations of electrons?

  Locations of electrons are described by orbitals.
• What is an orbital?


  An orbital is a region where an electron is found at least 90% of the time.
• How many electrons can orbitals hold?

  Orbitals can be occupied by two electrons.
• What are electron shells?

  Electron shells are series of orbitals or energy levels.
• How many electrons can the first shell hold?

  The first shell can hold 2 electrons.
• How many electrons can the second shell hold?

  The second shell can hold 8 electrons.
• What determines the reactivity of an atom?

  The outermost electron shell (valence shell) determines how the atom behaves.
• What happens if the outermost shell is full?

  If the outermost shell is full, the atom is stable and won’t react with other atoms.
• What characterizes reactive atoms?

  Reactive atoms have unpaired electrons in their outermost shell.
• What is the octet rule?

  The octet rule is the tendency of atoms to form stable molecules resulting in 8 electrons in their outermost shells.
• How do atoms achieve a full outermost shell according to the octet rule?

  Atoms try to complete their outermost shell by transferring or receiving (sharing) electrons.
• What happens to atoms that transfer electrons during a chemical reaction?

  Atoms that transfer their electrons become positive ions.
• What happens to atoms that receive electrons during a chemical reaction?

  Atoms that receive electrons become negative ions.
• What characterizes elements with a complete valence shell?

  Elements with a complete valence shell are chemically inert.
• What are the review questions related to an atom with 9 electrons?

  • Valence electron: 1
  • Transfer or receive electrons: Transfer
  • Electrons it receives: 0
  • Bonds it can make: 1
  • Ion upon reaction: a) Positive
• What are the review questions related to an atom with 4 electrons?

  • Valence electron: 4
  • Transfer or receive electrons: Transfer
  • Electrons it can transfer: 4
  • Bonds it can make: 4
  • Ion upon reaction: a) Positive
• What are the review questions related to oxygen's proton number of 8?

  • Electrons on oxygen's valence shell: 6
  • Bonds oxygen can make: 2
• What is a chemical bond?

  A chemical bond is the attractive force that links atoms together to form molecules.
• What are covalent bonds?

  Covalent bonds are formed when atoms share one or more pairs of electrons.