BIOL 211 - Chapter 2

An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ...

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

The innermost electron shell of an atom can hold up to _____ electrons.

2

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ...

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.

An atom's atomic number is 7. Its valence is most likely ...

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).

4

The mass number of an atom is 15, and its atomic number is 7. The atom probably has...

8 neutrons in the nucleus.

Which statement is true of the molecule shown here?

It's both a negative ion and a positive ion. 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?

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)?

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.

O-H O and H are at opposite ends of the electronegativity scale, so the polarity is very large.

Which of these figures correctly illustrates the nature of the bonding of H2O?

Oxygen is more electronegative than hydrogen. (Oxygen is negative and hydrogen is positive)

Which model most accurately represents the current view of the structure of the atom?

Probability model

What are the charges and symbols of protons, neutrons, and electrons?

Proton: p +1 charge Neutron: n 0 charge Electron: e -1 charge

Which answer helps to explain why carbon atoms tend to make 4 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.

Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say ...

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.

Atoms with the same number of protons but with different electrical charges _____.

are different ions

Compared to covalent bonds, ionic bonds ...

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.

Without making or breaking bonds, the pictured molecule can change its shape because ...

rotation can occur around single bonds. 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?

single (nonpolar) covalent

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

10

What is the mass number of an ion with 108 electrons, 157 neutrons, and a +1 charge?

(108+1)=109+157= 266

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

In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively.

4, 1, 2, 3

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

5

What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?

6

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

6 electrons.

The ammonia molecule in the diagram has the observed bond orientation because ... N has 7 protons in its nucleus. electrons repel one another. N has four pairs of electrons in the valence shell. All of the above. None of the above.

All of the above.

Which statement is true of the atom shown in the diagram? The atom is in the excited state. The atom has more than one valence electron. An electron will move from the outer to the inner shell. All of the above. 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?

All the atoms lie in a plane.

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.

Which statement is true of atoms?

Electrons determine the atom's size.

If you want a molecule that is highly polar, look for one that contains:

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.

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?

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.

Which atom in the pictured molecule will have the strongest partial positive charge?

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 of these relationships is true of an uncharged atom?

The number of protons is equal to the number of electrons.

Sort the subatomic particles according to their masses.

The proton and neutron both have masses of about 1 amu, whereas the electron mass is only about 5.5×10−4amu.

Which statement is true of the energy levels of electrons in shells?

The valence shell has higher energy than other occupied shells.

Which of these refers to atoms with the same atomic number but different atomic masses?

These atoms are isotopes.

True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule.

True

True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule.

True 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? To view the animation, click here. Then click on the image to start the animation.

a positively charged sodium ion and a negatively charged chlorine ion

Radioactive decay is likely to occur when ...

an atom has too many neutrons.

An ionic bond involves _____.

an attraction between ions of opposite charge

Partial charges occur when ...

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.

The atoms shown here will become ions if they meet because ...

atoms tend to avoid having a partly filled valence shell. 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?

covalent

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).

A(n) _____ bond joins these two oxygen atoms.

double covalent

A phrase that applies to covalent bonding and not other kinds of bonds is ...

electron-sharing. Only in covalent bonds do atoms share electrons.

In a double covalent bond, a carbon atom shares ...

electrons in two orbitals.

The brackets are indicating a(n) _____ bond.

hydrogen

What name is given to the bond between water molecules?

hydrogen

In salt, what is the nature of the bond between sodium and chlorine?

ionic

A(n) _____ refers to two or more atoms held together by covalent bonds.

molecule

When chemists and biologists want to show how atoms are bonded in a molecule, they usually use a ...

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.

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

What determines the types of chemical reactions that an atom participates in?

the number of electrons in the outermost electron shell

Two atoms always represent the same element if they have ...

the same number of protons.