Bio 150 Chapter 2

Oxygen has an atomic number of 8 and a mass number of 16. Thus, what is the atomic mass of an oxygen atom?

Approximately 16 daltons

The atomic number of chlorine is 17. The atomic number of magnesium is 12. What is the formula for magnesium chloride?

MgCl2

In what way are elements in the same column of the periodic table the same?

They have the same number of electrons in their valence shell.

Two atoms appear to have the same mass number. These atoms

Must have the same number of protons + neutrons.

The reactivity of an atom arises from

The existence of unpaired electrons in the valence shell.

What bonding or interaction is most likely to occur among a broad array of molecules of various types (polar, nonpolar, hydrophilic, hydrophobic)?

Van der Waal interactions

A group of molecular biologists is trying to synthesize a new artificial compound to mimic the effects of a known hormone that influences sexual behavior. They have turned to you for advice. Which of the following compounds is most likely to mimic the effects of the hormone?

A compound with the same three-dimensional shape as part of the hormone

What is the maximum number of hydrogen atoms that can be covalently bonded in a molecule containing two carbon atoms?

6

In ammonium chloride salt (NH4Cl) the anion is a single chloride ion, Cl. What is the cation of NH4Cl?

NH4, with a charge of +1

An atom has 6 electrons in its outer shell. How many unpaired electrons does it have?

2

Which bond or interaction would be difficult to disrupt when compounds are put into water?

Covalent bond

In the term trace element, the modifier trace means that

The element is required in very small amounts.

An atom with atomic number 12 would have what type of chemical behavior in bonding with other elements?

It would form ions with a +2 charge.

Which of the following statements is false?

Virtually all organisms require the same elements in the same quantities.

Nitrogen (N) is much more electronegative than hydrogen (H). Which of the following statements is correct about the atoms in ammonia (NH3)?

Each hydrogen atom has a partial positive charge; the nitrogen atom has a partial negative charge.

What is the difference between covalent bonds and ionic bonds?

Covalent bonds involve the sharing of electrons between atoms; ionic bonds involve the electrical attraction between atoms.

Carbon-12 is the most common isotope of carbon, and has an atomic mass of 12 daltons. A mole of carbon in naturally occurring coal, however, weighs slightly more than 12 grams. Why?

Some carbon atoms in nature have more neutrons.

Compared with 31P, the radioactive isotope 32P has

One more neutron.

If a salamander relied on hydrogen bonds to cling to surfaces, what type of surface would cause the most problems for this animal?

A surface made with carbon and hydrogen atoms covalently bonded together

Fluorine has an atomic number of 9 and a mass number of 19. How many electrons are needed to complete the valence shell of a fluorine atom?

1

About 25 of the 92 natural elements are known to be essential to life. Which four of these 25 elements make up approximately 96% of living matter?

Carbon, hydrogen, nitrogen, oxygen

Which of the following would be regarded as compounds?

H2O and CH4, but not O2

Which of the following correctly describes any reaction that has reached chemical equilibrium?

The rate of the forward reaction is equal to the rate of the reverse reaction.

Which of the following is not considered to be a weak molecular interaction?

A covalent bond

A covalent bond is likely to be polar when

One of the atoms sharing electrons is much more electronegative than the other atom.

The nucleus of a nitrogen atom contains 7 neutrons and 7 protons. Which of the following is a correct statement concerning nitrogen?

The nitrogen atom has a mass number of 14 and an atomic mass of approximately 14 daltons.

Which of these systems is least likely to be at chemical equilibrium?

A test tube of living cells

The atomic number of nitrogen is 7. Nitrogen-15 is heavier than nitrogen-14 because the atomic nucleus of nitrogen-15 contains how many neutrons?

8

Atoms whose outer electron shells contain 8 electrons tend to

Be both chemically inert and gaseous at room temperature.

Which of the following molecules contains the most polar covalent bond?

H2O

The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound:

H2S

In comparing covalent bonds and ionic bonds, which of the following would you expect?

Covalent bonds and ionic bonds occupy opposite ends of a continuous spectrum, from nearly equal to completely unequal sharing of electrons.

From its atomic number of 15, it is possible to predict that the phosphorus atom has

15 protons and 15 electrons.

Which of the following explains most specifically the attraction of water molecules to one another?

Hydrogen bond

Electrons exist only at fixed levels of potential energy. However, if an atom absorbs sufficient energy, a possible result is that

An electron may move to an electron shell farther away from the nucleus.

A covalent chemical bond is one in which

Outer-shell electrons of two atoms are shared so as to satisfactorily fill the outer electron shells of both atoms.

The atomic number of neon is 10. Therefore, which of the following is most correct about an atom of neon?

It has 8 electrons in its outer electron shell and it is inert.

Phosphorus-32, a radioactive isotope of phosphorus-31 (atomic number 15), undergoes a form of radioactive decay whereby a neutron turns into a proton and emits radiation in the form of an electron. What is the product of such radioactive decay of phosphorus-32?

Sulfur-32 (atomic number 16)

The precise weight of a mole of some pure elements like silicon (Si) can vary slightly from the standard atomic mass, or even from sample to sample. Why?

The element may have multiple stable isotopes, and the isotopic composition may vary from sample to sample.

Van der Waals interactions result when

Electrons are not symmetrically distributed in a molecule.

When two atoms are equally electronegative, they will interact to form

Nonpolar covalent bonds.