biology ch 2
Mass Number
number of protons and electrons in an element
Which statement is true of the relation between life and chemical equilibrium? a. (a) Living cells spend energy to stay as close to chemical equilibrium as possible b. (b) Living cells avoid chemical equilibrium by taking in energy and materials c. (c) Life persists only if cells can stay near chemical equilibrium d. Both (a) and (c) e. None of the above
(b) Living cells avoid chemical equilibrium by taking in energy and materials The only way to avoid equilibrium is to exchange materials and energy with the environment.
What is the mass number of an ion with 109 electrons, 159 neutrons, and a +1 charge?
269
A cation with two units of charge has 10 neutrons and 8 protons. The ion also has ... a. 10 electrons b. 6 electrons c. 12 electrons d. 16 electrons e. 8 electrons
6 electrons The part with the two units of + charge is a cation; the part with the unit of - charge is an anion.
Cation
a positively charged ion
Anion
a negatively charged ion
Electronegativity
attractions for shared electrons
Covalent Bond
bond formed by the sharing of electrons between atoms
Energy
capacity to cause change
What type of bond joins the carbon atom to each of the hydrogen atoms? a. single (nonpolar) covalent b. hydrogen c. ionic d. polar covalent e. double (nonpolar) covalent
single (nonpolar) covalent Each carbon-hydrogen bond involves a single pair of equally shared electrons.
Atom
smallest particle of an element
Under standard conditions the reversible reaction A + B C + D has a G = -25 kJ/mol. What is G when: T = 475 K, [A] = 0.5M, [B] = 0.2 M, [C] = 0.2 M, and [D] = 0.3 M? a. -27 kJ/mol b. -25 kJ/mol c. -23 kJ/mol d. -28 kJ/mol e. None of the above
-27 kJ/mol The nonstandard concentrations have lowered ΔG by 2 kJ.mol.
An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________. a. N; it has 6 electrons b. N; it has 6 protons c. O; its mass number is 12 d. C; it has 6 electrons e. C; it has 6 protons
C; it has 6 protons Atoms represent the element carbon (C) if they have six protons.
Chemical Reaction
changes in the chemical composition of matter
Electron
charge and location: negative charge subatomic particle in the nucleus
Neutron
charge and location: neutral charge subatomic particle in the nucleus
Proton
charge and location: positive charge subatomic particle in the nucleus
When chemists and biologists want to show how atoms are bonded in a molecule, they usually use a ... a. ball-and-stick model b. molecular formula c. structural formula d. space-filling model
structural formula This kind of model is designed to show which atoms are bound to one another, but it doesn't accurately picture the sizes of atoms.
Chemical equilibrium is reached when _____. a. the reverse reaction begins to occur b. matter is conserved c. all of the reactants are converted to products d. the rate at which matter is destroyed and the rate at which it is created offset each other e. the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products remain the same
the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products remain the same Chemical equilibrium occurs when the forward and reverse reactions offset each other. This is a dynamic equilibrium because the reactions continue to occur, but the concentrations do not change.
Chemical Equilibrium
the point at which the chemical reactions offset one another exactly
Molecule
two or more atoms held together by covalent bonds, smallest unit of most compounds
Hydrogen Bond
weak attraction between a hydrogen atom and another atom
Which of the following is true of activation energy? a. (a) Molecules usually get it from thermal energy b. (b) Molecules usually get it by breaking bonds c. (c) It's the energy difference between reactants and products d. Both (a) and (c) e. (a), (b), and (c)
(a) Molecules usually get it from thermal energy In a collision, thermal energy is converted to potential energy.
For the reaction ATP + H2O ADP + Pi, the change in standard free energy (G) is -30.5 kJ/mol. From this information we can conclude that ... a. (a) the forward reaction will be spontaneous under standard conditions b. (b) the reverse reaction will be spontaneous under standard conditions c. (c) the reaction will run rapidly d. Both (a) and (c) e. Both (b) and (c)
(a) the forward reaction will be spontaneous under standard conditions
An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule? a. 3 b. 4 c. 5 d. 2 e. 1
1 A knowledge of bonding capacities makes it easier to understand the structure of molecules.
How many grams of water (H2O) are needed to react with 5.0 grams of ferric trichloride (FeCl3)? FeCl3 + 3 H2O Fe(OH)3 + 3 HCl a. 0.55 g H2O b. 0.18 g H2O c. 1.7 g H2O d. 0.99 g H2O e. None of the above
1.7 g H2O It would take 1.7 g of H2O to react with 5.0 grams of FeCl3
Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have? a. 19 b. 10 c. 81 d. 28 e. 9
10 Atomic mass is equal to the number of protons plus the number of neutrons (19-9 = 10).
An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ... a. 7 electrons b. 10 neutrons c. 9 protons d. mass number 16, atomic number 7 e. All of the above
10 neutrons Isotopes have the same number of protons; different numbers of neutrons.
What is the molecular mass of caffeine (C8H10N4O2)? a. 43.0 b. 138.2 c. 178.2 d. 194.2 e. None of the above
194.2 This is the correct molecular mass of caffeine.
The innermost electron shell of an atom can hold up to _____ electrons. a. 2 b. 8 c. 32 d. 18 e. 1
2 This is the maximum number of electrons that can occupy the innermost electron shell.
Choose the correct balanced equation for the following reaction. C8H18 + O2 CO2 + H2O a. 4 C8H18 + 50 O2 → 32 CO2 + 36 H2O b. C8H18 + 12.5 O2 → 8 CO2 + 9 H2O c. 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O d. C8H18 + 17 O2 → 8 CO2 + 18 H2O e. None of the above
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O This equation has every element balanced and has the smallest possible whole number coefficients.
An atom's atomic number is 7. Its valence is most likely ... a. 1 b. 5 c. 3 d. 7 e. 2
3 The neutral atom has 7 electrons. Two electrons fill the first shell, and 5 go into the second (valence) shell. The atom needs 3 more electrons to fill the valence shell.
This atom can form up to _____ single covalent bond(s). a. 3 b. 2 c. 0 d. 4 e. 1
4 There are four electrons in the outermost electron shell.
In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively. a. 4, 1, 3, 2 b. 3, 2, 1, 4 c. 2, 1, 3, 4 d. 3, 2, 4, 2 e. 4, 1, 2, 3
4, 1, 2, 3 By knowing this, you'll make your study of chemistry much easier.
We can represent atoms by listing the number of protons, neutrons, and electrons-for example, 2p +, 2n 0, 2e - for helium. Which of the following represents the isotope of oxygen? a. 9p +, 9n 0, 9e - b. 7p +, 2n 0, 9e - c. 10p +, 8n 0, 9e - d. 6p +, 8n 0, 6e - e. 8p +, 10n 0, 8e -
8p +, 10n 0, 8e -
How many grams of glucose would you need to make 1 liter of an aqueous 0.5M glucose solution? (Atomic masses: C = 12.01, H = 1.008, O = 16.00.) a. 180.2 grams of glucose b. 70.36 grams of glucose c. 120.1 grams of glucose d. 60.05 grams of glucose e. 90.08 grams of glucose
90.08 grams of glucose
What happens when two atoms form a chemical bond? a. A chemical bond forms when two atoms transfer or share outer electrons to complete their outer shells. b. A chemical bond forms when two atoms transfer or share protons to achieve a stable nucleus. c. Two atoms fuse together to form a chemical bond.
A chemical bond forms when two atoms transfer or share outer electrons to complete their outer shells. Only the electrons of atoms participate in chemical bonds, which form when atoms transfer or share outer or valence electrons.
The ammonia molecule in the diagram has the observed bond orientation because ... a. N has four pairs of electrons in the valence shell b. electrons repel one another c. N has 7 protons in its nucleus d. All of the above e. None of the above
All of the above Since N has 7 protons, it must fill the second shell, giving it 4 pairs of electrons. The electrons form 3 bonds and 1 lone pair of electrons. Each pair of electrons repels the other pairs, so they are equally far apart.
Which statement is TRUE of the atom shown in the diagram? a. The atom is in the excited state b. An electron will move from the outer to the inner shell c. The atom has more than one valence electron d. All of the above e. None of the above
All of the above The atom has a vacancy in its inner shell; an electron has moved to the outer (valence) shell. The result is an unstable excited state. An electron will move back to the inner shell, restoring the ground state as the atom gives off energy.
Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true? a. The bonds orient like tripods or pyramids b. The bonds orient in a tetrahedral fashion c. All the atoms lie in a plane d. All the atoms lie in a line e. The groups rotate around the C=C bond
All the atoms lie in a plane The double bond limits all the atoms to a plane.
What does the term electron orbital describe? a. An electron orbital describes the exact distance of an electron from the nucleus b. An electron orbital describes the orbit of an electron around the nucleus c. An electron orbital describes a three-dimensional space where an electron can be found 90% of the time
An electron orbital describes a three-dimensional space where an electron can be found 90% of the time We cannot know the exact location of an electron. Instead, we can describe a three-dimensional space in which an electron spends most of its time.
Which statement is true of the transition state? a. (a) It can break apart to yield either reactants or products b. (b) It is extremely unstable and lasts only an instant c. (c) It has less potential energy than the reactants but more than the products d. Both (a) and (b) e. Both (b) and (c)
Both (a) and (b) It's an arrangement that quickly breaks apart, emitting either the original molecules or new product molecules.
Choose the appropriate balanced equation for the following chemical reaction. C6H6 + H2 C6H12 a. C6H6 + 6 H2 → C6H12 b. 2 C6H6 + 6 H2 → 2 C6H12 c. C6H6 + 3 H2 → C6H12 d. C6H6 + 6 H2 → 2 C6H12 e. None of the above
C6H6 + 3 H2 → C6H12 The equation is balanced appropriately by making sure that the same quantity of each element appears on both sides of the arrow.
Which fact is most important in explaining how molecules convert thermal energy to activation energy (EA)? a. Distortion increases a molecule's potential energy b. Thermal energy is a form of potential energy c. Distortion decreases a molecule's potential energy d. Potential energy decreases when molecules make bonds e. Potential energy increases when molecules make bonds
Distortion increases a molecule's potential energy In a collision, kinetic energy becomes the potential energy of distortion, which can weaken bonds enough to permit a reaction.
Which statement is TRUE of atoms? a. Most of an atom's volume is filled with matter b. Protons repel electrons c. Protons attract other protons d. Electrons determine the atom's size e. All of the above
Electrons determine the atom's size With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.
If you want a molecule that is highly polar, look for one that contains: a. C-H b. O-N c. H-N d. S-H e. C-S
H-N N and H differ in electronegativity more than any other bonded pair of atoms in the list, making the N-H bond most polar.
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. a. H2S b. H3S2 c. HS2 d. H4S e. HS
H2S
Which statement is true of the molecule shown here? a. It's both a cation and an anion b. It's a cation because the + charge outweighs the - charge c. It's an anion because the + charge outweighs the - charge d. It's not an ion because its net charge is zero e. It's an anion because the - charge outweighs the + charge
It's both a cation and an anion The part with the full unit of + charge is a cation; the part with the unit of - charge is an anion.
Which of the following is a chemical reaction? a. Making a hydrogen bond between a water molecule and a sugar molecule b. Dissolving a lump of sugar in a cup of coffee c. Changing a carbon atom to a nitrogen atom by radioactive decay d. Melting ice e. None of the above
None of the above A chemical reaction alters the covalent bonding between atoms, making new kinds of molecules. That doesn't happen in any of the events listed here.
Which model most accurately represents the current view of the structure of the atom? a. Probability model b. Planetary model
Probability model We cannot determine the exact motion of electrons. We can only compute the regions where electrons occur most of the time. To emphasize the uncertainty, a diagram showing random motion is more suitable than planetary paths.
Dr. Haxton says he has found a reaction that is truly irreversible. What would a good student say? a. All reactions are irreversible b. Patent it, Doctor. You can use it to make a perpetual motion machine c. This is possible, given a suitable catalyst d. Sorry, Doctor. All reactions are reversible e. What's new? We've always known that some reactions are truly irreversible
Sorry, Doctor. All reactions are reversible Some reactions look irreversible because the reverse reaction is very slow, but the laws of thermodynamics guarantee that all are reversible.
Which atom in the pictured molecule will have the strongest partial positive charge? a. The H that's bound to O b. The N atom c. The O atom that's in C=O d. The C that's bound to N e. The C that's in C=O
The C that's in C=O This C atom is bound to the two most electronegative atoms in the molecule (O), both of which are pulling electrons from C.
Which statement is TRUE of all atoms that are anions? a. The atom has more neutrons than protons. b. The net charge is 1-. c. The atom has more electrons than protons. d. The atom has fewer protons than does a neutral atom of the same element. e. The atom has more protons than electrons
The atom has more electrons than protons.
Which statement is TRUE of the energy levels of electrons in shells? a. The valence shell has higher energy than other occupied shells b. Electrons must lose energy to move from the first to the second shell c. All the electrons in an atom have similar amounts of energy d. All of the above e. None of the above
The valence shell has higher energy than other occupied shells The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells.
Which of these refers to atoms with the same atomic number but different atomic masses? a. These atoms have different numbers of protons b. These atoms have different numbers of electrons c. These atoms are isomers d. These atoms are isotopes e. These atoms are different elements
These atoms are isotopes Atoms with the same atomic number and different atomic masses are referred to as isotopes.
True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule. a. True b. False
True For example, a hydrogen nucleus (H+) may move between two water molecules, making an H3O+ ion and an OH- ion.
Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say ... a. Yes. O attracts electrons more strongly than C b. Wrong again, Ralph. Both bonds are nonpolar c. Right! O is electronegative, so O2 is polar d. No way. C is more electronegative than O e. No, both bonds are highly polar
Wrong again, Ralph. Both bonds are nonpolar When two atoms of the same kind form a covalent bond, they share electrons equally because their electronegativity is the same.
Valence
a bonding capacity of a given atom; usually equals the number of paired electrons required to complete the atom's outermost (valence) shell
Single Bond
a single covalent bond; the sharing of a pair of valence electrons by two atoms
Compound
a substance formed by chemical union of two or more elements or ingredients in definite proportion by weight
Radioactive decay is likely to occur when ... a. protons break into neutrons and electrons b. an atom has too many electrons c. an atom has too many neutrons d. an electron hits the nucleus e. atoms collide with one another
an atom has too many neutrons The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity.
Atomic Nucleus
an atom's dense central core, containing protons and neutrons
Isotope
are alternate mass forms of an element. It has the same number of protons and electrons but differ in their number of neutrons
Covalent bonds hold atoms together because they ... a. (a) fill shells without giving atoms much charge b. (b) bring electrons closer to protons c. (c) use forces between nuclei as well as forces between electrons d. do all of the above e. do both (a) and (b)
do both (a) and (b) Electron-sharing brings electrons closer to nuclei and it fills shells without giving the atoms much charge. Both factors stabilize the bond.
In a double covalent bond, a carbon atom shares ... a. two electrons b. both valence and nonvalence electrons c. electrons in two of its shells d. electrons in two orbitals e. None of the above
electrons in two orbitals A double bond involves two orbitals, each with a shared pair of electrons.
Essential Element
elements that an organism needs to live a healthy life and reproduce
Nonpolar Covalent Bonds
elements with equally shared electrons
Product
ending materials in a chemical reaction
Radioactive Isotope
have many uses in research and medicine. , an unstable atom in which the nucleus decays (breaks down) releasing particles and energy
The brackets are indicating a(n) _____ bond. a. hydrogen b. ionic c. hydrophobic d. polar covalent e. single (nonpolar) covalent
hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.
In salt, what is the nature of the bond between sodium and chlorine? a. polar covalent b. ionic c. nonpolar covalent d. hydrophobic e. hydrogen
ionic Sodium and chlorine ions are attracted to each other.
Salt
ionic compound w/ metal and nonmetal
Catalysts speed reactions mainly by ... a. providing activation energy b. increasing of activation energy barrier c. lowering EA. d. raising the kinetic energy of the reactants e. None of the above
lowering EA. Catalysts always lower EA, though they may have other effects as well. With a lower EA, a larger fraction of collisions can produce the transition state.
Which of the following is a trace element required by most living organisms? a. oxygen b. nitrogen c. carbon d. hydrogen e. magnesium
magnesium By weight, magnesium accounts for only 0.1% of most living things.
A(n) _____ refers to two or more atoms held together by covalent bonds. a. community b. molecule c. ion d. isotope e. shell
molecule A molecule is defined as two or more atoms held together by covalent bonds.
A carbon atom and a hydrogen atom form what type of bond in a molecule? a. Van der Waals interaction b. ionic bond c. hydrogen bond d. nonpolar covalent bond e. polar covalent bond
nonpolar covalent bond Atoms with similar electronegativities form nonpolar covalent bonds.
Atomic Number
number assigned to an element by the number of protons it contains
Electron Shells
number of electrons for an element to be stable
Which of the following subatomic particles always has a positive charge? a. atom b. proton c. electron d. element e. neutron
proton Each proton has one unit of positive charge.
Changing the number of _____ would change an atom into an atom of a different element. a. bonds formed by an atom b. protons in an atom c. particles in the nucleus of an atom d. neutrons in an atom e. electrons circling the nucleus of an atom
protons in an atom Atoms of each element have a unique number of protons within their nuclei. Changing the number of protons in an atom occurs only in nuclear reactions, not chemical reactions.
Compared to covalent bonds, ionic bonds ... a. are more abundant in biological molecules b. are more stable in water c. rely much less on electron-sharing d. have less bond energy e. are stronger
rely much less on electron-sharing Covalent bonds are entirely based on sharing electrons, whereas ionic bonds are attractions between ions that keep their electrons.
Radiometric Dating
scientists measure the ratio of different isotopes and calculate how many half-lives (in years) have passed since an organism was fossilized or rock was formed
Polar Covalent Bonds
slightly electromagnetic bonds
Reactants
starting materials in a chemical reaction
Octet Rule
states that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons
Ionic Bond
the attractive force between two ions of opposite charge
The reactivity of an atom arises from a. the average distance of the outermost electron shell from the nucleus b. the energy difference between the s and p orbitals c. the potential energy of the valence shell d. the existence of unpaired electrons in the valence shell e. the sum of the potential energies of all the electron shells
the existence of unpaired electrons in the valence shell
The type of bonding and the numbers of covalent bonds an atom can form with other atoms is determined by _____. a. the number of protons b. the nucleus c. the number of unpaired electrons in the valence shell d. the size of the atom; smaller atoms are chemically more reactive the number of neutrons
the number of unpaired electrons in the valence shell The fullness of the valence shell determines the pattern of covalent bonding or ionization. The reactivity of an atom is a function of the presence of unpaired electrons in one or more orbitals of their valence shells.
Valence Shell
the outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom
Hydrogen bonding is most often seen _____. a. in molecules whose three-dimensional shape is tetrahedral b. when hydrogen is covalently bonded to an electronegative atom c. when multiple carbon atoms are present d. when the bonds within the molecule are nonpolar covalent bonds e. if the molecule consists of three or fewer atoms
when hydrogen is covalently bonded to an electronegative atom Highly electronegative atoms attract shared electrons more strongly than hydrogen does, resulting in a slight positive charge on the hydrogen atom. The slightly positive hydrogen atom is then attracted to another electronegative atom, forming a hydrogen bond.
Which statement about weak bonds is correct? a. Weak chemical bonds form only between atoms of similar electronegativity. b. Weak bonds are transient and easily reversible. c. Weak bonds are less important to living things than strong covalent bonds.
Weak bonds are transient and easily reversible. Molecules that form weak bonds can come together, interact, and then separate. The combined effect of many weak and transient hydrogen bonds or Van der Waals interactions can produce important emergent properties.
Double Bond
a double covalent bond; the sharing of two pairs of valence electrons by two atoms
An ionic bond involves _____. a. an attraction between ions of opposite charge b. no atoms other than sodium and chlorine c. the unequal sharing of an electron pair d. the sharing of a single pair of electrons e. water avoidance
an attraction between ions of opposite charge
Chemical Bonds
an attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells
Valence Electron
an electron in the outermost electron shell
Trace Element
an element indispensable for life but required in extremely minute amounts
Potential energy is always ... a. the energy of chemical bonds b. associated with motion c. associated with chemical reactions d. energy that could exist but is not yet present e. associated with position or arrangement
associated with position or arrangement Potential energy occurs in many forms, but it's always associated with the arrangement of objects in space. Often the objects exert forces on each other.
Ionic Compound
compounds formed by ionic bonds
Compared with 31P, the radioactive isotope 32P has a. a different charge b. one more neutron c. one more proton d. a different atomic number e. one more electron
one more neutron
Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that ... a. the first shell shouldn't have 3 electrons b. the second shell can't have 4 electrons c. the first shell must fill before the second shell can have electrons d. no shell can hold more than 2 electrons e. the second shell should have 8 electrons
the first shell shouldn't have 3 electrons The first shell can only have 0, 1, or 2 electrons.
Orbital
the three-dimensional space where an electron is found 90% of the time
Half-Life
the time it takes for 50% of the parent isotope to decay
Atomic Mass
the weight of the atom
The mass number of an atom is 15, and its atomic number is 7. The atom probably has... a. 7 units of negative charge in the nucleus b. about as much mass in electrons as in protons c. 8 neutrons in the nucleus d. at least 15 electrons e. 7 electrons in the nucleus
8 neutrons in the nucleus The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons.
Dalton
a measure of mass for atoms and subatomic particles, the same as the atomic mass unit ( or amu)
Element
any substance that cannot be broken down into simpler substances
Matter
anything that has mass and takes up space
Atoms with the same number of protons but with different electrical charges _____. a. have different atomic masses b. have different atomic numbers c. are different isotopes d. are different ions e. have different numbers of neutrons
are different ions Ions are charged atoms.
The atoms shown here will become ions if they meet because ... a. atoms tend to have filled valence shells b. a nearly empty shell attracts electrons very strongly c. a nearly full shell has little attraction for electrons d. All of the above e. None of the above
atoms tend to have filled valence shells The valence shell is unfilled in both atoms. By taking an electron from lithium, fluorine can fill its valence shell. When lithium loses the electron, its outer shell is emptied; its full inner shell becomes its valence shell. Both atoms become stable ions.
What type of bond is joining the two hydrogen atoms? a. hydrophobic b. hydrogen c. covalent d. hydrophilic e. ionic
covalent
A phrase that applies to covalent bonding and not other kinds of bonds is ... a. charge attraction b. great strength c. electron-sharing d. paired electrons e. All of the above
electron-sharing Only in covalent bonds do atoms share electrons.
A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) _____. a. element b. molecule c. isotope d. proton e. compound
element
Potential Energy
the energy that matter possess because of its location or structure
What determines the types of chemical reactions that an atom participates in? a. the number of electrons in the outermost electron shell b. the number of protons it contains c. its atomic mass d. its atomic number e. the number of electrons in the innermost electron shell
the number of electrons in the outermost electron shell An atom is least likely to participate in a reaction when its outermost shell is stable.
Ion
when an atom loses or gains electrons
In the equation G = H - TS, the change in the amount of disorder in the system is symbolized by ... a. ΔH b. TΔS c. ΔS d. ΔG e. T
ΔS S is entropy, which is a measure of disorder. ΔS indicates how much the entropy is changed.
Partial charges occur when ... a. (a) a covalent bond links atoms of two kinds b. (b) atoms share electrons unequally c. (c) two ions are close together d. any of the above occur e. both (a) and (b)
(b) atoms share electrons unequally Each kind of atom has a different attraction for electrons. Thus, atoms of different kinds share electrons unequally. That gives one atom a partial negative charge; the other atom a partial positive charge.
Which statement is true of the relationship between life and chemical equilibrium? a. (a) Living cells spend energy to stay as close to chemical equilibrium as possible b. (b) Life depends on enzymes that move reactions away from equilibrium c. (c) Life persists only if cells can stay near chemical equilibrium d. (d) Living cells avoid chemical equilibrium by taking in energy and materials e. Both (a) and (c)
(d) Living cells avoid chemical equilibrium by taking in energy and materials The only way to avoid equilibrium is to exchange materials and energy with the environment.
What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons? a. 6 b. 12 c. 18 d. -1 e. 0
6 This is an atom of carbon, an element with 6 protons. Atomic number is the number of protons in an atom.
Which statement about relative potential energy of electrons is correct? a. An electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell b. An electron in the 2 p orbital of the second electron shell has more potential energy than an electron in the 2 s orbital of the second electron shell c. An electron in the 2 p orbital of the second electron shell has more potential energy than an electron in the 3 p orbital of the third electron shell
An electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell
The reaction shown below is at equilibrium. What could you do to make this reaction produce more methyl benzoate? a. (a) Add more benzoic acid b. (b) Remove some methanol (HOCH3) c. (c) Remove some water d. (d) Add more water e. Both (a) and (c)
Both (a) and (c) By removing water, you slow the reverse reaction; by adding a reactant, you speed the forward reaction. Both changes make the forward reaction faster than the reverse reaction. Therefore, the reaction will produce more methyl benzoate as it returns to equilibrium.
Which statement about the following reaction is TRUE? 4 Fe + 3 O2 2 Fe2O3 a. Four atoms of Fe react with 3 molecules of O2 to form 2 molecules of Fe2O3 b. The reaction is not balanced. c. Fe2O3 is the reactant in this reaction. d. Four grams of Fe reacts with 3 grams of O2 to form 2 grams of Fe2O3. e. None of the above.
Four atoms of Fe react with 3 molecules of O2 to form 2 molecules of Fe2O3 The reactants Fe and O and the product as Fe2O3. You also knew that the coefficients in the equation correspond to the number of atoms or molecules that take part in the reaction.
An orbital is dumbbell-shaped. Which statement is most likely TRUE? a. It's in the first electron shell b. Each lobe can hold one electron c. Each lobe can hold two electrons d. Its electrons move along a figure-8 path e. None of the above
None of the above Only the second and higher shells have dumbbell-shaped orbitals. Each orbital can hold just two electrons, and the electrons move in unknown paths such that both electrons can be in one lobe at one moment, and in opposite lobes at the next moment.
Which statement is most useful in explaining why chemists assign atoms to chemical elements by counting protons? a. Protons at the atom's surface determine the atom's behavior b. The nucleus doesn't change in stable isotopes c. The proton's negative charge holds electrons in the atom d. 99% of the atom's mass consists of protons e. None of these. Elements are defined by the number of protons
None of these. Elements are defined by the number of protons Protons give an enduring basis for atomic behavior because they are permanently anchored in the nucleus, where their attraction determines how many electrons the atom can hold. By contrast, electrons come and go, and the numbers vary.
Which answer correctly ranks the atoms in terms of decreasing electronegativity (the highest electronegativity first)? a. N, O, H, C b. O, N, C, H c. O, N, H, C d. N, O, C, H e. C, H, O, N
O, N, C, H Remember this, and you'll be able to predict polarity when molecules have O or N linked to C or H.
Use your knowledge of electronegativity to pick out the most polar bond in the list below. a. C-H b. O-N c. O-H d. N-H e. O-C
O-H O and H are at opposite ends of the electronegativity scale, so the polarity is very large.
By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero? a. The atom has 8 electrons b. The valence shell has 6 electrons c. Shared electrons aren't always near oxygen d. The atom lost electrons from other shells e. The charge isn't near zero; it's -2
Shared electrons aren't always near oxygen Oxygen keeps 6 electrons to itself. The 4 shared electrons migrate between O and the other atoms, thus contributing 4 half-charges to oxygen. This gives oxygen about 8 units of negative charge, balancing the atom's 8 protons.
Given what you know about the human body, what do you think accounts for the high percentage of oxygen (65.0%)? a. The human body is made up mainly of water, and there are two oxygen atoms in every water molecule. b. The human body breathes in oxygen constantly, and oxygen in the blood and tissues makes up a large percentage of body mass. c. The human body breathes in oxygen constantly, and because oxygen is a heavy element, it makes up a large percentage of body mass. d. The human body is made up mainly of water, and there is one oxygen atom in every water molecule.
The human body is made up mainly of water, and there is one oxygen atom in every water molecule. The human body is mostly made up of water (H2O), and there is one oxygen atom in each molecule of water. Note that, although each water molecule also contains two hydrogen atoms, the atomic mass of hydrogen (about 1) is much smaller than the atomic mass of oxygen (about 16). Because of this, hydrogen contributes less to human body mass than oxygen.
Which of these relationships is true of an uncharged atom? a. The number of electrons is equal to the number of neutrons b. The number of neutrons is equal to the number of protons c. The atomic mass is equal to the atomic number d. The atomic mass is equal to the number of electrons e. The number of protons is equal to the number of electrons
The number of protons is equal to the number of electrons In this situation the number of positive charges is equal to the number of negative charges.
Which of the following bonds can form between atoms of equal electronegativity? a. Ionic bonds can form between atoms of equal electronegativity. b. Hydrogen bonds can form between atoms of equal electronegativity. c. Van der Waals interactions can form between atoms of equal electronegativity.
Van der Waals interactions can form between atoms of equal electronegativity. Even nonpolar covalent bonds have temporary regions of partial positive and negative charge, due to the chance movements of electrons. Attractions between such transient positive and negative charges create weak Van der Waals interactions.
A(n) _____ bond joins these two oxygen atoms. a. ionic b. quadruple covalent c. single covalent d. double covalent e. hydrogen
double covalent The oxygen atoms are sharing two pairs of electrons.
The atoms of different phosphorus isotopes _____. a. have different atomic numbers b. have different numbers of electrons c. have different numbers of neutrons d. have different numbers of protons e. react differently with other atoms
have different numbers of neutrons The phosphorus atom is defined by its proton number. Changes in neutron number alter the mass of the atom, but not its chemical behavior or reactivity.
What name is given to the bond between water molecules? a. hydrogen b. single (nonpolar) covalent c. polar covalent d. hydrophobic e. ionic
hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.
An ionic bond is formed when _____. a. both atoms are nonpolar b. both atoms are electrically neutral c. atoms are subjected to radioactive isotopes d. one atom transfers an electron to another atom e. both atoms are equally attractive to electrons
one atom transfers an electron to another atom Transfer of an electron from one atom to another results in a positive ion (cation) and a negative ion (anion), which usually attract each other to form an ionic bond. However, the ions need not have acquired their electrical charge due to an electron transfer with each other.
Without making or breaking bonds, the pictured molecule can change its shape because ... a. rotation can occur around single bonds b. some atoms make longer bonds than others c. proximity of other atoms alters bond angles d. electrons can move from one bond to another e. None of the above
rotation can occur around single bonds Rotation allows groups of atoms to change position while preserving the usual bond angles around each atom.
In the term trace element, the adjective trace means a. the element can be used as a label to trace atoms through an organism's metabolism b. the element passes rapidly through the organism c. the element is required in very small amounts d. the element enhances health but is not essential for the organism's long-term survival
the element is required in very small amounts
Two atoms always represent the same element if they have ... a. the same number of protons b. the same number of electrons c. the same mass number d. the same number of particles in the nucleus e. the same number of shells
the same number of protons The number of protons defines a chemical element. The number of neutrons and electrons can differ among atoms of the same element.
To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ... a. 1 electron b. 2 electrons c. 3 electrons d. 8 electrons e. Can't tell without knowing which element it is
2 electrons The neutral atom has 8 electrons. Two electrons fill the first shell, and 6 go into the second (valence) shell. Two more electrons would fill the valence shell.
What coefficients must be placed in the following blanks so that all atoms are accounted for in the products? C6H12O6 → _____ C2H6O + _____ CO2 a. 3; 1 b. 2; 2 c. 1; 3 d. 1; 2 e. 1; 1
2; 2
An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have? a. 5 b. 11 c. 0 d. 16 e. 6
5 The atomic number is equal to the number of protons.
Which of the following statements correctly describes any chemical reaction that has reached equilibrium? a. The reaction is now irreversible. b. The concentrations of products and reactants are equal. c. Both forward and reverse reactions have halted. d. The rates of the forward and reverse reactions are equal. e. No reactants remain
The rates of the forward and reverse reactions are equal.
A chemist calculates that a certain reaction would result in H = -9 kJ and TS = +1 kJ. What can you conclude? a. The reaction will occur spontaneously, because it decreases H b. The reaction will not occur spontaneously, because it increases G c. The reaction will occur spontaneously, because it decreases G d. The reaction will not occur spontaneously, because ΔS is negative e. None of the above
The reaction will occur spontaneously, because it decreases G ΔG = ΔH - TΔS = -9 -(-1) = -8. Since the free energy decreases, the reaction will run spontaneously.
Which answer helps to explain why carbon atoms tend to make 4 covalent bonds? a. The carbon nucleus has 4 protons b. The valence shell needs 8 electrons c. The first electron shell has 4 orbitals d. All of the above e. None of the above; carbon makes 3 covalent bonds
The valence shell needs 8 electrons Without help, C can only hold 4 electrons in the valence shell. To fill the shell, 4 more electrons must be shared, making 4 covalent bonds.
