Ch. 12---Chemical BondingCovalent Bonds

• ____________ electrons between two atoms in order to fill the outer energy level (or shell)

• Each bond involves the sharing of _____ _________ of electrons.

Single Bonds= __ e-’s Double Bonds= __ e-’s Triple Bonds=__ e-’s

Sharing

one pair

2 4 6

Ways to Represent Covalent Bonds in Compounds

(1) “Circled Arrows” for bonds.

a) H2 H ___ 1s

H ___

1s

b) F2 F …___ ___ ___ ___ 2s 2p

F …___ ___ ___ ___ 2s 2p

↑

↑

↓↑ ↓↑ ↓↑ ↑

↓↑ ↓↑ ↓↑ ↑

c) NH3 N …___ ___ ___ ___

2s 2p

d) H2O O …___ ___ ___ ___

2s 2p

H ___ 1s

H ___ 1s

H ___ 1s

↓↑ ↑ ↑ ↑

↑↑↑

↓↑ ↑ ↑ ↑↓

H ___ 1s

↑H ___ 1s

↑

Ways to Represent Covalent Bonds in Compounds

(2) “Dots” for bonds. (Lewis Structures)

a) H2 H · + · H

b) F2 :F· + ·F:

c) N2 :N · + ·N: (triple bond)

d) NH3

..

......

·

·

·

·

..

..H

H:H

.. ..

.. ..:F:F:

··:N::N:

H:N:H

Ways to Represent Covalent Bonds in Compounds

(3) “Lines” for bonds.

a) H2

b) F2

c) N2

d) NH3

e) H2O

.. ..

.. ..

׀H

׀H

..

H–H

:F–F:

:N≡N:

H–N–H

H–O:

↓↑ ↑

Coordinate Covalent Bonds• Both of the electrons that make the bond come from the ________ _______________ .

–Example: CO (carbon monoxide)

sameelement

C …___ ___ ___ ___ 2s 2p

↑

O …___ ___ ___ ___ 2s 2p

↓↑ ↑ ↑↓ ↑

:C O:......

Two of the bonds are “normal”, and the third bond is a coordinate covalent bond.

:C O:←––

Carbon’s Hybrid Orbital

C …___ ___ ___ ___ (Before)

2s 2p

↓↑ ↑ ↑

C …___ ___ ___ ___ (After: 4 covalent bonds available)↑ ↑ ↑↓

Practice Problem: Draw CH4 using arrows, dots, and lines for bonds.

2sp3

↑ ↑ ↑ ↑

2sp3

C …___ ___ ___ ___

H ___ 1s

H ___ 1s

H ___ 1s

H ___ 1s

↑ ↑ ↑ ↑

↑

The 7 Diatomic Elements

• Some elements will covalently bond to themselves to form a molecule composed of ____ atoms.

• These elements are never found in nature as single atoms. Instead, they will be bonded as a ________ when they are in the “_________________” state.

• The 7 diatomic elements are the gases H, O, N, and all of the _________________, (Group 7A).

H2, O2, N2, Cl2, Br2, I2, F2

“HONClBrIF”

two

elementalpair

halogens

Air contains N2 and O2 molecules.

The decomposition of two water molecules

Octet Rule

• Atoms want ___ e-’s in their outer shell when forming compounds.

• This will mean ___ dots around them all together. This is the stable e- configuration of a __________ _______!

• Important exception: Hydrogen = only needs __ to be full (like He).

• Other Exceptions:

PCl5 (___ e-) SF6 (___ e-) BF3(___e-)

8

8 noble gas

2

10 12 6

Resonance

• Resonance is the ability to draw 2 or more different e- dot notations that obey the octet rule.

Examples: O3 (ozone) and SO2

Practice Problem: Draw the resonance structures for CO3-2.

VSEPR Theory: Molecular Shapes

• Most shapes are based on a __________________.

Examples: CH4 CCl4

• Removing the top of the tetrahedral makes the ________________ shape.

Examples: NH3 PCl3

tetrahedral

pyramidal

VSEPR Theory: Molecular Shapes

• Removing one side of the pyramid makes the _____________ shape.

Examples: H2O H2S

• If there are only two atoms bonded, it is ______________.

Examples: O2 HCl CO2 (linear because of its double bonds.)

bent

linear

VSEPR Theory: Molecular Shapes

•Another we will need to know is called “trigonal planar”. “Trigonal” means that the central atom is bonded to ___ other atoms. “Planar” means that the 3 atoms all lie in the same ______________.

Example: BF3

• (Notice that Boron will only have ___ e-’s around it. The missing pair of electrons will make it planar instead of ________________.)

3plane

6pyramidal

VSEPR Theory: Molecular Shapes

• Finally, the last 2 shapes occur when there are 5 or 6 regions of electrons are around the central atom. (These molecules are also exceptions to the octet rule!)

-___________________ (5 electron domains)

-__________________ (6 electron domains)

Examples: PCl5 and SF6

Trigonal bipyramid

Octahedral

Polar and Nonpolar Bonds

• Even though the electrons in a covalent bond are shared, sometimes the attraction for the bonded pair, (the _____________________), is uneven. This gives rise to 3 bond types.

• nonpolar covalent bonds: ____________ sharing of the e- pair

• polar covalent bonds: ________________ sharing of the e- pair

• ionic bonds: a ___________ of e-’s from the metal to the nonmetal

How To Determine the Bond Type

• Bond type is based on the electronegativity _____________ between the two bonded atoms.

(See p.403 for electronegativity values.)

electronegativity

equal

unequal

transfer

difference

Figure 12.4 The three possible

types of bonds.nonpolar

polar

ionic

How To Determine the Bond Type

0 to 0.4 = ______________ covalent bond

0.5 to 2.0 = _____________ covalent bond

Above 2.0 = _______________ bond

•Practice Problems: Determine the type of bond that forms between the atoms in the following compounds.

a) CO2 b) NaCl c) CH4

nonpolar

polar

ionic

2.5 3.5 0.9 3.0 2.5 2.1

1.0 = polar covalent 2.1 = ionic 0.4 = nonpolar covalent

Polarity of Molecules

• One side is slightly (__) and the other side is slightly (__).

• Polar molecules are also known as _______________.

• Polarity depends on the __________ and symmetry of the molecule.

• symmetrical molecules (looks the same on all sides)= ___________

• asymmetrical molecules = ___________

• Polar molecules are moved by ____________ charges. (DEMO!)

+ –

dipole

shape

nonpolar

polar

static

Molecular Polarity

Practice Problems: Determine if the following molecules are polar or nonpolar based on their shape.

a) CH4 b) NH3 c) H2O d) HCl e) BF3

symmetrical tetrahedral

asymmetrical pyramid

asymmetrical bent

asymmetrical linear

symmetrical trigonal planar

nonpolar nonpolarpolar polar polar

Dipole of NH3

Dipole of H2O

Bond Dissociation Energy

• This is the energy needed to ___________ the bond.

• Generally, the longer the bond, the _____ energy it takes to break it.

• Single bonds take ________ energy to break than double bonds and triple bonds require the _________ energy to break.

• When bonds form, energy is _____________.

(Breaking bonds requires the addition of energy.)

released

less

lessmost

break

Bond Dissociation Energy

Intermolecular Attractions

• The __________ attractions between one molecule and another are called _______ ______ ________ forces.

• They cause gas particles to stick together and _______________ at low temperatures.

weak Van der Waals

condense

Dispersion Forces

There are two types of intermolecular forces:

(1) ____________________ forces: (the weaker type)

– caused by random _______________ motion

– generally _____________ with ________ electrons in the molecule

Dispersion

electronstronger more

− exist between all types of molecules

− This force causes Br2 to be a liquid and I2 to be a solid at room temperature.

Dipole Interaction Forces

(2) ____________ interactions: (the stronger force)

– caused by the attraction of the (__) side of one polar molecule and the (__) side of a different polar molecule

Dipole

+–

Hydrogen Bonds

• “________________ Bonds” are a special type of dipole interaction.

• They occur between the hydrogen of one polar molecule and the ____, ___ or ___ of another polar molecule.

Hydrogen Bonding in Water

Hydrogen

N O F

Hydrogen Bonds

• The ladder rungs in a DNA molecule are hydrogen bonds between the base pairs, (AT and GC).

Hydrogen Bonds in

DNA

Ionic Bonding & Ionic CompoundsIonic Bonds

• Form when ___________ transfer their _____________ electrons to a _______________.

• The forces of attraction between the ____________ (+) and the _____________ (-) bind the compound together.

How to Represent an Ionic Bond

(1) Electron Configuration:

Na 1s2 2s2 2p6 3s1

Cl 1s2 2s2 2p6 3s2 3p5

metals valencenonmetal

cationanion

Na… ___ 3s

↑

Cl… ___ ___ ___ ___ 3s 3p

↓↑ ↑ ↑↓ ↓ ↓

How to Represent an Ionic Bond

2) Electron Dot Notations:

Na + Cl [ ] [ ]

Practice Problems: (1) Draw the electron dot notation for the formation of an ionic compound between sodium and oxygen.

(2) Draw the electron configuration notation for the formation of an ionic compound between magnesium and fluorine.

Na+1 Cl -1

Practice Problems:

3) a) Draw the electron dot notation for a potassium atom.

b) Draw the electron dot notation for a potassium ion.

(4) a) Draw the electron dot notation for a sulfur atom.

b) Draw the electron dot notation for a sulfur ion.

K

[K+1]

S

[ S -2]

Properties of Ionic Compounds and Covalent Molecules

Ionic:

•_______________ of electricity when dissolved water or melted.

•formed between __________ and _________________

•have _________ melting points

•usually ________ soluble in water

• form ___________________ solids

Conductors

metals nonmetals

high

very

ionic crystalline

(dissolved salt)

Figure 15.1-- Polar water molecules interacting with positive and negative ions of a salt.

Crystalline Patterns

Properties of Ionic Compounds and Covalent Molecules

Molecular:

• ________________ of electricity

• formed between two _______________

• usually have ________ melting points

• solubility in water _______: (polar =dissolve; nonpolar = insoluble)

For a compound to to conduct electricity it must have:

(1) Charged Particles (________)

(2) Particles Free to Move (___________ or __________ phase)

Insulators

nonmetals

low

varies

ions

liquid aqueous

Demonstration

good conductor

poor conductor

nonconductor

PureH2O

great conductor