Mastering Biology: The Chemical Basis of Life

Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have? 10 9 19 81 28

10 Atomic mass is equal to the number of protons plus the number of neutrons (19-9 = 10).

A(n) _____ refers to two or more atoms held together by covalent bonds. molecule ion isotope shell community

molecule A molecule is defined as two or more atoms held together by covalent bonds.

The mass number of an atom is 15, and its atomic number is 7. The atom probably has... 7 electrons in the nucleus. 7 units of negative charge in the nucleus. about as much mass in electrons as in protons. 8 neutrons in the nucleus. at least 15 electrons.

8 neutrons in the nucleus. Good choice! The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons.

Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true? All the atoms lie in a line. The bonds orient like tripods or pyramids. The groups rotate around the C=C bond. All the atoms lie in a plane. The bonds orient in a tetrahedral fashion.

All the atoms lie in a plane. Right! The double bond limits all the atoms to a plane.

Covalent bonds hold atoms together because they ... (a) fill shells without giving atoms much charge. (b) bring electrons closer to protons. (c) use forces between nuclei as well as forces between electrons. do all of the above. do both (a) and (b).

do both (a) and (b). Right! Electron-sharing brings electrons closer to nuclei and it fills shells without giving the atoms much charge. Both factors stabilize the bond.

Which of the following substances is a compound? sodium liquid nitrogen hydrogen gas sugar

sugar A compound consists of two or more elements in a fixed ratio. Sugar contains carbon, hydrogen, and oxygen in a fixed ratio.

The innermost electron shell of an atom can hold up to _____ electrons. 18 8 2 1 32

2 This is the maximum number of electrons that can occupy the innermost electron shell.

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 ... the second shell should have 8 electrons. the first shell must fill before the second shell can have electrons. no shell can hold more than 2 electrons. the second shell can't have 4 electrons. the first shell shouldn't have 3 electrons.

the first shell shouldn't have 3 electrons. Right! The first shell can only have 0, 1, or 2 electrons.

Two atoms always represent the same element if they have ... the same number of electrons. the same number of particles in the nucleus. the same number of shells. the same mass number. the same number of protons.

the same number of protons. You got it! The number of protons defines a chemical element. The number of neutrons and electrons can differ among atoms of the same element.

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? 1 2 5 3 4

1 Good. A knowledge of bonding capacities makes it easier to understand the structure of molecules.

An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ... 7 electrons. mass number 16, atomic number 7. 9 protons. 10 neutrons. All of the above.

10 neutrons. Bingo! Isotopes have the same number of protons; different numbers of neutrons.

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ... 3 electrons. 1 electron. 8 electrons. 2 electrons. Can't tell without knowing which element it is.

2 electrons. Correct! 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.

An atom's atomic number is 7. Its valence is most likely ... 1 3 7 5 2

3 Good choice! 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.

Radioactive decay is likely to occur when ... an atom has too many neutrons. an atom has too many electrons. atoms collide with one another. protons break into neutrons and electrons. an electron hits the nucleus.

an atom has too many neutrons. Correct! The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity.

What type of bond is joining the two hydrogen atoms? There are 2 hydrogen atoms with a pair of electrons shared between these 2 atoms. hydrogen hydrophobic hydrophilic ionic covalent

covalent A covalent bond is one in which electron pairs are shared.

Which of the following subatomic particles contributes toward the atomic mass of hydrogen? element electron neutron proton

proton Hydrogen has 1 proton and 1 electron. It is the protons that are included in the calculation of an atom's mass number.

This atom can form up to _____ single covalent bond(s). There is an atom with 2 electron shells. The inner electron shell contains a pair of electrons. The outer electron shell contains 4 electrons. 4 1 3 2 0

4 There are four electrons in the outermost electron shell.

Chemical reactions do not create or destroy matter but simply rearrange it. Which example is the correct completed equation for this reaction? 4 NH3 + _____ O2 → _____ NO + _____ H2O 4 NH3 + 5 O2 → 2 NO + 1 H2O 4 NH3 + 5 O2 → 4 NO + 6 H2O 4 NH3 + 6 O2 → 4 NO + 5 H2O 4 NH3 + 1 O2 → 2 NO + 5 H2O

4 NH3 + 5 O2 → 4 NO + 6 H2O Both the reactants and the products contain equal amounts of nitrogen, hydrogen, and oxygen.

In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively. 4, 1, 2, 3 3, 2, 1, 4 3, 2, 4, 2 4, 1, 3, 2 2, 1, 3, 4

4, 1, 2, 3 Correct! By knowing this, you'll make your study of chemistry much easier. Congratulations!

An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have? 5 6 0 16 11

5 The atomic number is equal to the number of protons.

What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons? 12 6 -1 18 0

6 This is an atom of carbon, an element with 6 protons. Atomic number is the number of protons in an atom.

A positive ion with two units of charge has 10 neutrons and 8 protons. The ion also has ... 10 electrons. 16 electrons. 8 electrons. 6 electrons. 12 electrons.

6 electrons.

An element has 8 protons, 9 neutrons, and 8 electrons. Its atomic number and its mass number, respectively, are _____. 8 and 16 8 and 17 9 and 16 9 and 17

8 and 17 The number of protons, 8, gives the atomic number. The mass number is the sum of the number of protons and neutrons, or 8 plus 9, which equals 17.

The ammonia molecule in the diagram has the observed bond orientation because ... There is a ball-and-stick model of ammonia, NH3. Three hydrogen atoms are attached to nitrogen. N has 7 protons in its nucleus. N has four pairs of electrons in the valence shell. All of the above. None of the above.

All of the above. Correct! 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? There is an atomic structure: six negatively charged particles are around the nucleus. One negatively charged particle is in the inner shell, and another five are in the outer shell. The atom has more than one valence electron. An electron will move from the outer to the inner shell. The atom is in the excited state. All of the above. None of the above.

All of the above. Perfect! 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.

An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________. C; it has 6 protons. N; it has 6 protons. O; its mass number is 12. C; it has 6 electrons. N; it has 6 electrons.

C; it has 6 protons. Exactly! Atoms represent the element carbon (C) if they have six protons.

Covalent bonds can occur where atoms share one or more pairs of electrons. Which of the following would form a double covalent bond? NH3 Cl2 NaCl CO2

CO2 Carbon has 4 electrons in its outer shell, and oxygen has 6. When a covalent bond is formed, the carbon atom shares two electron pairs with each oxygen atom.

Which statement is true of atoms? Protons repel electrons. Electrons determine the atom's size. Protons attract other protons. Most of an atom's volume is filled with matter. All of the above.

Electrons determine the atom's size. Correct! With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.

Which statement is true of the molecule shown here? There is a ball-and-stick model for NH3CHRCO2 in which the first oxygen is attached to carbon by double bond and another oxygen is attached by single bond. Nitrogen has a charge of 1 plus. Oxygen, with a single bond, has a charge of 1 minus. It's a negative ion because the + charge outweighs the - charge. It's not an ion because its net charge is zero. It's a positive ion because the + charge outweighs the - charge. It's both a negative ion and a positive ion. It's a negative ion because the - charge outweighs the + charge.

It's both a negative ion and a positive ion. Good choice! The part with the full unit of + charge is a positive ion; the part with the unit of - charge is a negative ion.

Which statement is most useful in explaining why chemists assign atoms to chemical elements by counting protons? The proton's negative charge holds electrons in the atom. Protons at the atom's surface determine the atom's behavior. The nucleus doesn't change in stable isotopes. 99% of the atom's mass consists of protons. None of these. Elements are defined by the number of protons.

None of these. Elements are defined by the number of protons. Right! 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 model most accurately represents the current view of the structure of the atom? There are two different models of atomic structure. In a planetary model negatively charged particles are at specific orbits and move around the nucleus. In a probability model there is not any orbit, and the motion of negatively charged particles has no order. Probability model Planetary model

Probability model Good choice. 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.

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? The charge isn't near zero; it's -2. Shared electrons aren't always near oxygen. The valence shell has 6 electrons. The atom has 8 electrons. The atom lost electrons from other shells.

Shared electrons aren't always near oxygen. Correct! 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.

Which of these relationships is true of an uncharged atom? The number of neutrons is equal to the number of protons. The number of protons is equal to the number of electrons. The number of electrons is equal to the number of neutrons. The atomic mass is equal to the number of electrons. The atomic mass is equal to the atomic number.

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 statement is true of the energy levels of electrons in shells? The valence shell has higher energy than other occupied shells. All the electrons in an atom have similar amounts of energy. Electrons must lose energy to move from the first to the second shell. All of the above. None of the above.

The valence shell has higher energy than other occupied shells. Right! The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells.

Which answer helps to explain why carbon atoms tend to make 4 covalent bonds? The first electron shell has 4 orbitals. The carbon nucleus has 4 protons. The valence shell needs 8 electrons. All of the above. None of the above; carbon makes 3 covalent bonds.

The valence shell needs 8 electrons. Good choice! 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.

An ionic bond involves _____. the unequal sharing of an electron pair no atoms other than sodium and chlorine the sharing of a single pair of electrons water avoidance an attraction between ions of opposite charge

an attraction between ions of opposite charge This is the definition of an ionic bond.

Atoms with the same number of protons but with different electrical charges _____. have different atomic masses are different isotopes have different numbers of neutrons are different ions have different atomic numbers

are different ions Ions are charged atoms.

The atoms shown here will become ions if they meet because ... There are two atomic structures. The first structure has two shells: there are 2 electrons in the inner shell and one electron in the outer shell. The second structure also has two shells: there are 2 electrons in the inner shell and 7 electrons in the outer shell. a nearly empty shell attracts electrons very strongly. atoms tend to avoid having a partly filled valence shell. a nearly full shell has little attraction for electrons. All of the above. None of the above.

atoms tend to avoid having a partly filled valence shell. Correct! 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.

Partial charges occur when ... (a) a covalent bond links atoms of two kinds. (b) atoms share electrons unequally. (c) two ions are close together. any of the above occur. both (a) and (b).

both (a) and (b). Good job! 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.

A(n) _____ bond joins these two oxygen atoms. There are 2 oxygen atoms with 2 shared electron pairs. Also, each of the atoms has a pair of electrons in the inner electron shell. In the outer electron shell, each atom has 2 pairs of electrons in addition to those 2 which are shared. hydrogen ionic quadruple covalent double covalent single covalent

double covalent The oxygen atoms are sharing two pairs of electrons.

In a double covalent bond, a carbon atom shares ... electrons in two of its shells. electrons in two orbitals. both valence and nonvalence electrons. two electrons. None of the above.

electrons in two orbitals. Excellent! A double bond involves two orbitals, each with a shared pair of electrons.

In salt, what is the nature of the bond between sodium and chlorine? ionic polar covalent nonpolar covalent hydrophobic hydrogen

ionic Sodium and chlorine ions are attracted to each other.

Without making or breaking bonds, the pictured molecule can change its shape because ... There is a ball-and-stick model of NH2CH2CH2OH. rotation can occur around single bonds. electrons can move from one bond to another. proximity of other atoms alters bond angles. some atoms make longer bonds than others. None of the above.

rotation can occur around single bonds. Correct! Rotation allows groups of atoms to change position while preserving the usual bond angles around each atom.

What type of bond joins the carbon atom to each of the hydrogen atoms? There is a carbon atom with 4 hydrogen atoms attached to it. Carbon atom shares an electron pair with each of the hydrogen atoms. hydrogen ionic polar covalent double (nonpolar) covalent single (nonpolar) covalent

single (nonpolar) covalent Each carbon-hydrogen bond involves a single pair of equally shared electrons.

What determines the types of chemical reactions that an atom participates in? its atomic mass the number of electrons in the outermost electron shell the number of electrons in the innermost electron shell its atomic number the number of protons it contains

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.

Which of these figures correctly illustrates the nature of the bonding of H2O? There is an oxygen atom with 2 hydrogen atoms attached to it. Oxygen atom is charged negatively. Both hydrogen atoms are charged positively. There is an oxygen atom with 2 hydrogen atoms attached to it. Oxygen and 1 of the hydrogen atoms are charged positively. 1 hydrogen atom is charged negatively. There is an oxygen atom with 2 hydrogen atoms attached to it. Oxygen atom is charged positively. Both of the hydrogen atoms are charged negatively. There is an oxygen atom with 2 hydrogen atoms attached to it. All 3 atoms are charged positively. There is an oxygen atom with 2 hydrogen atoms attached to it. All 3 atoms are charged negatively.

There is an oxygen atom with 2 hydrogen atoms attached to it. Oxygen atom is charged negatively. Both hydrogen atoms are charged positively. Oxygen is more electronegative than hydrogen.

Which of these refers to atoms with the same atomic number but different atomic masses? These atoms are isotopes. These atoms have different numbers of electrons. These atoms have different numbers of protons. These atoms are different elements. These atoms are isomers.

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. False True

True Correct! For example, a hydrogen nucleus (H+) may move between two water molecules, making an H3O+ ion and an OH- ion.

What is the result of the animated process? electron jumped from sodium to chlorine a negatively charged sodium ion and a positively charged chlorine ion a positively charged sodium ion and a negatively charged chlorine ion a positively charged sodium ion and a positively charged chlorine ion a negatively charged sodium ion and a negatively charged chlorine ion covalent bond formation

a positively charged sodium ion and a negatively charged chlorine ion Sodium loses an electron and thus becomes positively charged; chlorine gains an electron and thus becomes negatively charged.

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? an atom with 20 protons, 21 neutrons, and 20 electrons an atom with 18 protons, 20 neutrons, and 18 electrons an atom with 21 protons, 20 neutrons, and 21 electrons an atom with 20 protons, 20 neutrons, and 18 electrons

an atom with 20 protons, 21 neutrons, and 20 electrons Isotopes of an atom have the same number of protons but different numbers of neutrons.