Chapter 2

Types of chemical bonds:

Ionic bonds Covalent bonds Hydrogen bonds

The valence number determines

the number and type of bonds an atom can form

Valence Number

the number of unpaired electrons in the valence shell

3rd shell can hold

up to 18 electrons

An electron in which shell will have the highest potential energy?

3rd shell

Which of the following is the most polar molecule? a. HF b. CO2 c. F2 d. NO2

a. HF

Electrons in the outer shell are involved in

chemical bonds

Certain chemical reactions cause atoms to gain or lose electrons. The result is an:

ion

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

ionic *Sodium and chlorine ions are attracted to each other.

A covalent bond is likely to be polar if __________.

one of the atoms sharing electrons is much more electronegative

A double bond is the sharing of

two pairs of electrons

What is the mass number of an atom?

Protons + neutrons

An ionic bond is formed when

an atom donates one (or more) electron to another atom. After the electron transfer, both atoms are ions.

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

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 _____. - are different isotopes - are different ions - have different numbers of neutrons - have different atomic masses - have different atomic numbers

are different ions *Different isotopes of an atom have different numbers of neutrons. Ions are charged atoms.

Valence electrons

are those in the valence shell

In a covalent bond, the shared electrons count as part of each

atom's valence shell

Isotopes of an element will always differ in __________.

atomic mass

Ionic bonds form as a result of __________.

attraction between ions that have opposite charges

A phrase that applies to covalent bonding and not other kinds of bonds is ... - paired electrons. - great strength. - charge attraction. - electron-sharing. - All of the above.

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

An atom with more protons is more ______________ than an atom with fewer protons

electronegative

An element is made up of

only one type of atom

What happens if an atom gains or loses a proton?

It is a different atom.

2nd shell can hold

8 electrons

Energy is

the capacity to cause change

Rules for filling electron shells:

1. The first 2 electrons go into the first shell. 2. The next 4 electrons go into second shell, unpaired. 3. The next 4 electrons pair up with the first 4 in the second shell, making pairs.

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

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 ... - 10 neutrons. - 9 protons. - 7 electrons.mass number 16, atomic number 7. - All of the above.

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

1 st shell can hold

2 electrons

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ... - 8 electrons. - 3 electrons. - 1 electron. - 2 electrons. - 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.

This atom can form up to _____ single covalent bond(s). - 2 - 0 - 3 - 4 - 1

4 *There are four electrons in the outermost electron shell.

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

How many electrons will you find in the 3rd shell of an Aluminum (Al) atom (atomic # = 13)

3 Explanation: 2 in 1st shell, 8 in 2nd shell which meants 2 + 8 =10. 13 - 10 = 3

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

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 - 16 - 0 - 6 - 11

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

Draw the electron shell diagram for Phosphorous (atomic # = 15), Identify the number of valence electrons, the valence number, and the number of bonds it will form.

5 valence electrons, valence number = 3, will form 3 bonds. Shell 1 will be full with 2 electrons, shell 2 will be full with 8 electrons, and the third shell will have 5 electrons, three of those are unpaired.

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

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

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

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.

anion

An atom that has gained an electron is negatively charged

cation

An atom that has lost an electron is positively charged

Lithium has a valence number of 1 and often donates that electron to another atom. The atom that received the electron would now be a(n):

Anion

Ionic Bonds

Atoms sometimes donate/receive electrons to/from their bonding partners

Nonpolar covalent bond:

Both atoms involved in the bond have equal or almost equal electronegativity

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

C; it has 6 protons. *Elements are defined by the number of protons in the nucleus. Atoms represent the element carbon (C) if they have six protons.

In the example above, after it donates an electron, Lithium is a(n):

Cation

ion

Change the number of electrons

isotope

Change the number of neutrons

What happens when the number of protons changes?

Change the protons, you change the element.

If you want a molecule that is highly polar, look for one that contains: - C-S - C-H - S-H - O-N - H-N

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 brackets are indicating a(n) _____ bond.

Hydrogen *A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.

What name is given to the bond between water molecules? - single (nonpolar) covalent - polar covalent - hydrophobic - hydrogen - ionic

Hydrogen *A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.

HONC = 1234

Hydrogen = 1 Oxygen = 2 Nitrogen = 3 Carbon = 4

What are the four essential elements of Life?

Hydrogen, Oxygen, Carbon, & Nitrogen

What are the four most abundant elements found in living systems?

Hydrogen, oxygen, nitrogen, and carbon

Explain the difference between ionic bonds and covalent bonds

In ionic bonds atoms gain or lose electrons whereas in covalent bonds, atoms share electrons

The number of ________ differs in isotopes

Neutrons

What does it mean for an atom to have a full valence shell? How will it interact with other atoms?

No bonds will form

Which statement is most useful in explaining why chemists assign atoms to chemical elements by counting protons? - The nucleus doesn't change in stable isotopes. - Protons at the atom's surface determine the atom's behavior. - 99% of the atom's mass consists of protons. - The proton's negative charge holds electrons in the atom. - 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)? - O, N, H, C - N, O, C, H - O, N, C, H - C, H, O, N - N, O, H, C

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. - N-H - O-N - O-C - O-H - C-H

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

What characteristics below are those of a hydrogen bond?

Occurs between water molecules and other polar molecules Extremely important to the specific properties of water A bond of molecular force

What does it mean for a molecule to be polar?

One atom has more electronegativity than other so the electrons spend more time around it than they do around the less electronegative atom. This results in one side of the molecule having a partial positive charge and the other side having a partial negative charge.

Polar covalent bond:

One atom is more electronegative than the other. Unequal sharing of electrons causes a partial positive area and a partial negative area across the molecule

Which atom in the pictured molecule will have the strongest partial positive charge? - The C that's in C=O. - The O atom that's in C=O. - The H that's bound to O. - The N atom. - The C that's bound to N.

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

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

Which statement is true of the energy levels of electrons in 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. - The valence shell has higher energy than other occupied shells. - All of the above.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 answer helps to explain why carbon atoms tend to make 4 covalent bonds? - There are four unpaired electrons in the valence shell. - The first electron shell has 4 orbitals. - The carbon nucleus has 4 protons. - All of the above. - None of the above; carbon makes 3 covalent bonds.

There are four unpaired electrons in the valence shell. *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.

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

These atoms are isotopes. *Atoms with the same atomic number and different atomic masses are referred to as isotopes.

Which of the following statements is true about chemical reactions?

They involve the making and breaking of chemical bonds.

What is the result of an ionic bond between Na & Cl?

Two molecules that are attracted to each other due to resulting charges Transferring of electrons

Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say ... - Yes. O attracts electrons more strongly than C. - No way. C is more electronegative than O. - No, both bonds are highly polar. - Right! O is electronegative, so O2 is polar. - Wrong again, Ralph. Both bonds are nonpolar.

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.

Electronegativity is the

ability of an atom to attract electrons Depends on number of protons Depends on molecular structure

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). *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.

Elements with full valence shell are

chemically inert (noble gases such as Helium, Neon, Argon)

What type of bond is joining the two hydrogen atoms? - hydrogen - hydrophilic - covalent - hydrophobic - ionic

covalent *A hydrogen bond forms between a covalently bonded hydrogen atom and another atom. A covalent bond is one in which electron pairs are shared.

A hydrogen bond forms when a hydrogen atom that is ____________ bonded to an electronegative atom is _________ to another electronegative atom. This is an bond of molecular force; there is no sharing or stealing of electrons

covalently; attracted

A(n) _____ bond joins these two oxygen atoms. - double covalent - ionic - single covalent - quadruple covalent - hydrogen

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

Magnesium has an atomic number of 25 and a mass number of 55. Which of the following is true? a. Magnesium has 25 electrons b. Magnesium has 25 protons c. Magnesium has 30 neutrons d. None of the above are true e. All of the above are true

e. All of the above are true

Nonpolar covalent bonds are always formed from atoms that are __________.

equal in their electronegativity

The number of protons in an uncharged atom __________.

equals the number of electrons

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

figure 3 *Oxygen is more electronegative than hydrogen.

Chemical bonds help atoms

fill their valence shell

___ shell (lowest energy level)

first/1st

Weak chemical bonds such as hydrogen bonds __________.

form when a hydrogen atom that is covalently bonded to an electronegative atom like oxygen or nitrogen is attracted to another electronegative atom

The Shell Model describes

how many electrons reside in each energy shell

When the proton number and electron number are unequal, the atom or molecule __________.

is an ion

Potential energy

is the energy that matter has because of its location or structure

A covalent bond __________.

is the sharing of a pair of valence electrons by two atoms

The molecular shape of a biological molecule is important because __________.

it determines how biological molecules recognize and respond to one another

The fact that oxygen is an atom that is strongly electronegative means that __________.

it more strongly pulls shared electrons toward itself when forming a covalent bond with a less electronegative atom

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

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

A single bond is the sharing of

one pair electrons

Hydrogen bonds occur when __________.

partial opposite charges on molecules come close enough to attract each other

An atom is made up of

protons, neutrons (both in the nucleus), and electrons

___ shell (next highest energy level)

second/2nd

What type of bond joins the carbon atom to each of the hydrogen atoms?

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

The more electronegative an atom, the more _________ it pulls covalently shared electrons toward itself

strongly

The reactivity of an atom arises from __________.

the existence of unpaired electrons in the valence 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. - the second shell can't have 4 electrons. - the first shell shouldn't have 3 electrons. - no shell can hold more than 2 electrons.

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 protons it contains - its atomic number - the number of electrons in the outermost electron shell - its atomic mass - 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.

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

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.

A covalent bond is

the sharing of a pair of valence electrons by two atoms. Very strong, stable bonds

In ionic interactions, __________.

the transfer of valence electrons results in a completed valence shell for each ion

Individual electrons in an atom differ in

their amounts of potential energy

Atoms are most stable when

their valence shell is full

___ shell (highest energy level in this model)

third/3rd

Outermost shell is the

valence shell

Ionic Bonds: Sodium and Chlorine

• Chlorine (Cl) strips an electron from Sodium (Na). This completes atom's valence shell •After this transfer, Sodium has a positive charge (cation) and Chlorine has a negative charge (anion) •The opposite charges create an attraction that holds the elements together