BSC1010 practice exam 2

Which of the following subatomic particles has appreciable mass and lacks a charge? a. neutron b. element c. electron d. proton e. molecule

a. A neutron weighs about 1.7 × 10-24 grams (has a mass close to 1 dalton), and it is electrically neutral.

The number of protons in an uncharged atom __________. a. equals the number of electrons b. determines the atom's mass number c. equals the number of neutrons d. varies with the different isotopes e. equals the number of electrons in the outer orbital of the atom

a. An uncharged atom has an equal number of protons and electrons.

Some groups of elements react chemically in similar ways. For example, the chemistry of sodium and the chemistry of lithium are similar. The chemistry of chlorine and the chemistry of iodine are also similar. These similarities in chemistry result when different elements have similar __________. a. numbers of outer-shell electrons b. atomic size c. atomic numbers d. total numbers of electrons e. energy per electron

a. Atoms with the same number of electrons in their valence shells exhibit similar chemical behavior or reactivity.

A hydrogen bond __________. a. is a weak chemical bond b. is one in which hydrogen is strongly attracted to a positively charged atom c. .is a function of hydrophobic interactions d. is a strong chemical bond e. is one in which two hydrogen atoms bond to each other

a. In a hydrogen bond the hydrogen has a partial positive charge.

Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons? a. The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge. b. The atomic number of the atom would remain 29, the mass number would be reduced to 62, and the atom would be an anion. c. The atomic number would be reduced to 27, the mass number would remain 64, and the atom would be an anion with a +2 charge. d. The atom would have a double negative charge and be an ion. e. The atomic number would remain 29, the mass number would increase to 66, and the atom would be a cation with a -2 charge.

a. The loss or gain of electrons does not influence the atomic number (number of protons) or the mass number (number of protons plus neutrons) of an atom.

Phosphorus-32 (radioactive) has __________ than phosphorus-35 (normal). a. three fewer neutrons b. three more neutrons c. three fewer protons d. three more protons e. three more atoms

a. The numbers 32 and 35 refer to mass number (number of protons plus neutrons). All the atoms of the same element have the same number of protons, but different isotopes of the same element have different numbers of neutrons. Because 35 - 32 = 3, P-32 has three fewer neutrons than P-35.

What is the role of van der Waals interactions in biological molecules? a. Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules. b. Van der Waals interactions are too weak to be significant. c. Although they are weak bonds, van der Waals interactions involve the sharing of electrons. d. Van der Waals interactions are strong bonds that play a major structural role in holding proteins together. e. Van der Waals interactions are important only in water.

a. Weak bonds are important in the three-dimensional structure of most large biological molecules, and they play a role in molecular interactions.

Which of the following is a trace element? a. nitrogen b. copper c. carbon d. oxygen e. hydrogen

b Copper (Cu) is a trace element. Copper accounts for less than 0.01% of living matter.

Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application? a. the atomic numbers of the atoms involved b. the molecule's shape c. the type of bonding in the molecule d. the number of valence electrons e. the number of double bonds in the molecule

b The molecule would have to have the correct shape to bind to the receptor protein and block it.

What are the four most abundant elements found in living systems? a. nitrogen, carbon, sulfur, and oxygen b. hydrogen, oxygen, nitrogen, and carbon c. magnesium, calcium, iron, and zinc d. hydrogen, oxygen, calcium, and nitrogen e. hydrogen, oxygen, nitrogen, and carbon dioxide

b These four elements make up about 96% of living matter.

Why are radioactive isotopes useful in scientific research? a. because they decay spontaneously and give off energy and subatomic particles b. because they can be used as tracers to follow particular atoms and molecules through metabolic pathways c. because they are difficult to detect in small amounts, but living cells cannot distinguish them from the corresponding stable isotopes d. because they are not readily incorporated into biological reactions e. All of the listed responses are correct.

b.

For most atoms, when is a stable configuration of electrons attained? a. when the atom has moved all its electrons to its outermost shell b. when the atom has eight electrons in its outermost shell c. when the atom has as many protons as neutrons d. when the atom achieves a zero net charge e. None of the listed responses is correct.

b. An atom with a complete valence shell is unreactive.

The compound CaSO4 ionizes into a calcium ion and a sulfate ion (SO4). Calcium has two electrons in its outer shell. Upon ionization, what would you expect the charge on the sulfate ion to be? a. -4 b. -2 c. -1 d. +1 e. +2

b. By gaining two electrons from calcium, the sulfate ion now has a charge of -2 and calcium has a charge of +2.

A covalent bond is likely to be polar if __________. a. the two atoms sharing electrons are equally electronegative b. one of the atoms sharing electrons is much more electronegative than the other c. the two atoms sharing electrons are of the same element d. it is between two atoms that are both very strong electron acceptors e. it is between two atoms that are both very strong electron donors

b. If one atom is more electronegative than the other, electrons of the bond will not be shared equally, resulting in a polar covalent bond.

A neutral atom of chlorine has an atomic number of 17. It has __________ electrons in its third shell. a. 2 b. 7 c. 8 d. 10 e. 17

b. The first shell holds two electrons and is full; the second shell holds eight electrons and is also full, which leaves seven electrons to occupy the third shell.

An element has eight protons, nine neutrons, and eight electrons. Its atomic number and atomic mass, respectively, are __________. a. 8 and 16 b. 8 and 17 c. 9 and 16 d. 9 and 17 e. 16 and 8

b. The number of protons, eight, gives the atomic number. The atomic mass is the sum of the number of protons and neutrons; thus, 8 + 9 = 17.

Which of the following statements describes a reversible reaction that has reached chemical equilibrium? a. The forward and the reverse reactions have stopped. b. The rate of the reverse reaction equals the rate of the forward reaction. c. The rate of the reverse reaction exceeds the rate of the forward reaction. d. The rate of the forward reaction exceeds the rate of the reverse reaction. e. The concentration of the reactants is equal to the concentration of the products

b. This is the definition of chemical equilibrium.

Consider this statement: Concentrations of trace elements in an environment above what is required by organisms generally have no effect on those organisms. Which of the following is a valid response to this statement? a. True. Only trace element limitation can lead to disease among organisms. b. True. Most organisms have evolved adaptations that allow them to tolerate very high concentrations of trace elements in the environment. c. False. Elevated concentrations of some trace elements such as cobalt and chromium can be toxic. d. False. Elevated concentrations of trace elements such as chromium and phosphorus can be toxic. e. False. Increasing the concentration of trace elements above what is required generally has a beneficial effect on organisms.

c Elevated concentrations of some trace elements are harmful to many forms of life.

Which of the following four statements, if any, is true regarding essential elements and living organisms? a. All organisms require 25 of the 92 naturally occurring elements to survive. b. The elements carbon, hydrogen, nitrogen, and oxygen make up 20-25% of living mass. c. Although all forms of life require iron, other elements are required only by certain species. d. Given their low concentrations in nature, the toxicity of some elements is generally not a factor in the evolution of biological communities. e. All of the listed responses are correct.

c Several of the statements are incorrect.

There are __________ naturally occurring elements. a. 4 b. 25 c. 92 d. 108 e. 238

c There are more than 25 naturally occurring elements, but only 25 of them are known to be essential for human life.

Which of the following statements is true about chemical reactions? a. Only inorganic molecules can participate in chemical reactions. b. They reach chemical equilibrium when the amounts of products and reactants are equal. c. They involve the making and breaking of chemical bonds. d. They may have different numbers of a given atom on each side of the equation arrow. e. They represent the way matter is created and destroyed.

c. Chemical equilibrium is reached when the forward and reverse reaction rates are equal.

In which of the following will isotopes of an element always differ? a. number of protons b. number of electrons c. atomic mass d. atomic number e. None of the listed responses is correct.

c. Atomic mass refers to the number of protons and neutrons in an atom. Atomic forms of an element with the same number of protons (atomic number) but different numbers of neutrons are isotopes of that element.

The chemical characteristics or reactivity of an element depend mostly on the __________. a. number of electron shells present in the atoms b. degree to which it has more or fewer electrons than protons c. number of electrons in its outermost shell d. number of protons plus the number of neutrons e. mean energy level of its electrons

c. Only electrons are directly involved in the interactions between atoms, and the number of electrons in the outermost shell determines the chemical behavior or reactivity of an atom.

A particular carbon isotope has an atomic number of 6 and an atomic mass of 14. The respective number of neutrons, protons, and electrons that this carbon isotope has is __________. a. 6, 6, and 8 b. 8, 6, and 8 c. 8, 6, and 6 d. 8, 6, and 4 e. 6, 8, and 6

c. The atomic number, 6, is equal to the number of protons. Therefore, the number of electrons in an electrically neutral atom would also be 6. The number of neutrons must be 8 because the atomic mass is 14 (14 - 6 = 8).

Consider a hypothetical atom with an atomic number of 4 and a net charge of +1. How many neutrons does this ion have? a. one b. three c. four d. The answer cannot be determined from the information provided. e. None of the listed responses is correct.

d. All the atoms of an element have the same number of protons, but some atoms have different numbers of neutrons than other atoms of the same element; therefore, the atoms have different mass numbers. Without the mass number (number of protons + neutrons), it is not possible to determine the number of neutrons.

How many electrons would be present in the valence shell of a sulfur atom (atomic number 16, mass number 32)? a. one electron b. two electrons c. four electrons d. six electrons e. eight electrons

d. An atom of sulfur would have 16 electrons, with 2 electrons in the innermost electron shell, 8 electrons in the next electron shell, and 6 electrons in the outermost or valence shell.

When the proton number and electron number are unequal, the atom or molecule __________. a. gains or loses a proton b. becomes part of a molecule c. gains or loses a neutron d. is an ion e. forms a covalent bond with another atom

d. Covalent bonding does not result from an excess or deficiency of electrons but rather from a sharing of pairs of electrons.

The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium? ) a. an atom with 20 protons, 20 neutrons, and 18 electrons b. an atom with 21 protons, 20 neutrons, and 21 electrons c. an atom with 21 protons, 21 neutrons, and 21 electrons d. an atom with 20 protons, 21 neutrons, and 20 electrons e. All of the listed responses are correct.

d. Isotopes of an element have the same number of protons but different numbers of neutrons.

An uncharged atom of nitrogen (atomic number = 7) has __________. a. seven protons and seven neutrons b. seven neutrons c. seven valence electrons d. seven protons and seven electrons e. seven neutrons and seven electrons

d. The atomic number is the number of protons, and this equals the number of electrons in an electrically neutral (uncharged) atom.

Which of the following molecules has the shape of a completed tetrahedron? a. hydrogen gas (H2) b. water (H2O) c. glucose (C6H12O6) d. methane (CH4) e. oxygen gas (O2)

d. The nucleus of the carbon atom is at the center of the tetrahedron, with its four covalent bonds radiating to the hydrogen nuclei at the corners of the tetrahedron.

When do hydrogen bonds occur? a. when a molecule with a low molecular weight is bonded to a molecule with a high molecular weight b. when two atoms achieve stable electron configurations by sharing electrons with each other c. when a molecule with partial charges contacts a molecule without partial charges d. when partial opposite charges on molecules come close enough to attract each other e. None of the listed responses is correct.

d. in a hydrogen bond, both atoms have a partial charge, but of opposite sign.

Which of the following has negligible mass? a. atom b. element c. proton d. neutron e. electron

e Because the mass of an electron is only about 1/2,000 that of a proton or neutron, electrons are not considered when computing atomic mass.

Consider this statement: Oxygen is not a greenhouse gas; therefore, gases containing oxygen—such as ozone, nitrous oxide, and carbon dioxide—are not greenhouse gases either. Which of the following is a valid response to this statement? a. False. Oxygen is a special case because of its reactivity and electronegativity. b. True. Compounds display emergent properties that are very similar to those of the elements that form them. c. True. It is impossible for a gas containing oxygen to be a greenhouse gas. d. True. Because oxygen is not a greenhouse gas, it is unlikely to combine with anything at a higher level of organization to form a greenhouse gas. e. False. Compounds can have emergent properties that are very different from those of the elements that form them.

e Emergent properties of compounds are more than simply the sum of their parts.

When one or more pairs of valence electrons are shared by two neutral atoms, what type of bond is formed? a. a hydrogen bond b. a neutral bond c. an electronegative bond d. an ionic bond e. a covalent bond

e. Covalent bonds are formed between atoms that share one or more pairs of valence electrons.

An atom that normally has __________ in its outer shell would NOT tend to form chemical bonds with other atoms. a. one electron b. three electrons c. four electrons d. six electrons e. eight electrons

e. Eight electrons will leave no unpaired electrons in the valence shell. In this configuration, atoms are chemically unreactive or inert.

Ionic bonds form as a result of __________. a. the asymmetric distribution of electrons in constant motion b. unequal sharing of electrons between atoms c. sharing of electron pairs between atoms d. attraction between a hydrogen and other atoms that share electrons unequally e. attraction between ions that have opposite charges

e. Oppositely charged ions attract each other electrically, forming an ionic bond.