chemical bonding

Chemical BondingChapter 6

Pages 174-213(no Section 4)

The The breakingbreaking of of bonds and the bonds and the

formingforming of bonds of bonds occur during occur during

chemical reactionschemical reactions..

AspirinWhat is the

formula for a molecule of

aspirin?

What do we call the things that hold a molecule of aspirin together?

• C9H8O4

• covalent compound (made of all nonmetals - no ions)

Is it an ionic or covalent

(molecular) compound?

Aspirin

• C9H8O4


Aspirin (Odyssey Program)

• C9H8O4


The Attachment Between Atoms

atoms combine to form

ionic bonds covalent bonds(M + NM) (NM + NM)

chemical bond – a mutual electrical attraction between the nuclei and valence electrons of two atoms that binds the atoms together

Ionic Bonding• ionic bond – electrical attraction between

cations and anions; when electrons are taken by one atom from another atom

metal and a nonmetal

NaCl

cation and anion

(The charges are “hidden” to make a neutral compound.)

1s

2s

2p

3s

1s

2s

2p

3s

Na 11e- F 9e-

Ionic Bonding: taking of electrons

Na+ 10e- STABLE!!! F- 10e- STABLE!!!

I’m Positive!

A metal ionA metal atom A nonmetal atomA nonmetal ion

I’m Negative

I’m Positive!

A metal ion A nonmetal ion

I’m Negative

When a metal and a nonmetal atom are around each other there is the opportunity for….

…the transfer of electrons producing ions that would like to cling to each other.

Ionic bonding!!!

The simplest ratio of the packed ions is called:

The Formula Unit Ex: NaCl

“cubic”shape

Ions

• Metals form cations.

(metals lose e-)

• Nonmetals form anions.

(nonmetals gain e-)

Ions

• cations (+)• anions (-)

• monatomic ions – ions • formed from one atom Examples:

Na+ or O-2

• polyatomic ions - ions formed from two or more atoms bonded together

Examples: NH4+ or SO4

-2

Naming Ions• monatomic ions

• cations – named like the atom, only add ion to it

» Example: Na+

is the sodium ion

• anions – remove the ending to the atom name and add –ide and ion to it

» Example: Cl-

is the chlorine

+ide ion

or the chloride ion

• polyatomic ions • You do not determine their names, you memorize them

Ionic Compounds

• solid at room temperature (forming crystals)• high melting points (thus are usually solid at RT)• formula unit represents the lowest ratio of ions

that combine to form a neutral compound• when dissolved in water, the ionic compounds

will break up into ions (dissociate)• the solutions of ionic compounds will conduct

electricity (electrolytes)

Dissociation

2H O(l) + -NaCl(s) Na (aq) + Cl (aq)

solid placed in water hydrated ions

(surrounded by water)

dissociation – when an ionic compound dissolves to break apart into hydrated ions

Dissociation

Electrolytes and Nonelectrolytes

When an ionic compound dissolves to produce ions, it is called an electrolyte because it conducts electricity in water.

When an compound does not dissolve to produce ions, it is called a nonelectrolyte because it does not conduct electricity in water.

Electrolytes or salt?

Check for Understanding

1. What kinds of atoms form ionic bonds?

2. What is a polyatomic ion?

3. Name 5 things you learned about ionic compounds.

You Try It.

Do the Dissociation Equations worksheet.

Covalent Bondingcovalent bond – when electrons are shared

between two atoms– the electronegativity difference between the

two atoms is less than 1.7– usually two nonmetals – NO ions formed! (no electrons are taken…just

shared)

When a nonmetal and another nonmetal atom are around each other there is the opportunity for….

…the sharing of electrons producing molecules in which the atoms like to cling to each other.

Covalent bonding!!!

The formation of a bond between two nonmetal atoms.

Atoms sufficiently far apart to have no interaction

Figure 5 Page 179

Covalent Compounds

• Also called molecular compounds• solid, liquid, or gas at room temperature• low melting points • molecular formula represents the actual ratio of

atoms that combine to form a neutral compound• when dissolved in water, the molecular

compounds DO NOT break up into ions

(NO dissociation)• the solutions of molecular compounds DO NOT

conduct electricity (nonelectrolytes)

Pure Covalent

Ionic

The two fundamental

types of bonds.

Pure Covalent

Ionic

There is another type of bond, not

purely covalent and not

purely ionic.

Polar Covalent

Nonpolar Covalent

Sharing of Electrons

• How would you know if an electron is going to be taken by one atom from another?

• Is there ever a time in which the electron is not taken but shared?

• Is the electron always shared equally?

Electronegativity

• electronegativity – a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound

The difference in electronegativity values for two atoms will indicate whether the two atoms form an ionic bond (e- taken) or a polar or nonpolar covalent bond (e- shared).

Electronegativity Differences• 0.0 to 0.4 nonpolar covalent

• 0.5 to 1.6 polar covalent

• 1.7 and up ionic

These ranges are flexible, although the general rule is a metal and nonmetal will

form an ionic bond and two nonmetals will form a covalent bond.(Learn these values!)

PS: They are different than your book!

Ionic, Polar Covalent, or Nonpolar Covalent?

What kind of bond would each pair form?

1. N and S

2. S and C

3. Mg and Cl

4. C and F

5. Ba and O

Which one of these bonds has the least ionic character?

Valence Electrons

• valence electrons – the electrons in the highest energy level

Na: 1s22s22p63s1 - 1 valence e-

O: ? Ne: ? Al: ? He: ?

Octet Rule• octet rule – most atoms will gain or lose

electrons to have 8 valence electrons (e- in the highest energy level)– Exceptions: H, He, Li, Be, B, and some atoms

P and higher on the periodic table

Why is an atom like Ca more stable once it becomes an ion?

How many valence electrons would calcium have to lose to have 8?

VSEPR Theory

Valence

Shell

Electron

Pair

Repulsion Theory

Repulsion between the sets of valence-level electrons

surrounding an atom causes these sets to be oriented as far

apart as possible.

Regions of Electron Density

What is a Region of electron density?

• Single bond (2e- connecting 2 atoms)

• Double bond (4e- connecting 2 atoms)

• Triple bond (6e- connecting 2 atoms)

• Lone pair (unbonded pair) (2e- alone on an atom)

LINEAR180o

2 Regions of Electron Density2 Bonds

bonded pair of electrons

bonded pair of electrons

TRIGONAL PLANAR120o


3 bonded pairs of electrons

BENT119o

3 Regions of Electron Density2 Bonds & 1 Lone Pair

2 bonded pairs of electrons 1 lone pair

of electrons

You don’t have to know this!

TETRAHEDRAL109.5o



TRIGONAL PYRAMIDAL107o



1 lone pair of electrons

BENT105o

4 Regions of Electron Density2 Bonds & 2 Lone Pairs

All of these have 4 regions of electron density

(although the number of bonded pairs is different)

TRIGONAL BIPYRAMIDAL120o & 90o


SEE-SAW120o & 90o



T-SHAPED120o & 90o



LINEAR180o



OCTAHEDRAL90o


SF6

SQUARE PYRAMIDALapproximately 90o



BrF5

ICl4-

SQUARE PLANAR90o


chemical bonding

Documents

polyatomic ions ions

packed ions

ionic compound dissolves

eionic bonding

lowest ratio of ions

chloride ionpolyatomic

covalent molecular compound

enonmetals form anions