Ch. 12 Notes---Covalent BondsCovalent 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

Sharing is Caring!!

Caring is Covalent!!!

Sharing

Ways to Represent Covalent Bonds in Compounds

(1) Quantum Mechanical or Bohr Model of the Atom.

Ways to Represent Covalent Bonds in Compounds

(1) Quantum Mechanical or Bohr Model of the Atom.

Ways to Represent Covalent Bonds in Compounds

(2) “Dots” for bonds.

a) H2 H · + · H H:H

b) F2 :F· + ·F: :F:F:

c) N2 :N · + ·N: :N :: N: (triple bond)

d) NH3 H:N:H

..

......

.. ..

.. ..

·

·

·

·

· ·

..

..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:

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

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

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

• The last shape 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

Figure 12.4 The three possible

types of bonds.nonpolar

polar

ionic

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

This last type of bond will be discussed in detail in Chapter 15.

How To Determine the Bond Type

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

(See p.402 for electronegativity values.)

electronegativity

equal

unequal

transfer

difference

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) CO2

Dipole of NH3

symmetrical tetrahedral

asymmetrical pyramidal

asymmetrical bent

asymmetrical linear

symmetrical linear

nonpolar nonpolarpolar polar polar

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

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-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

Naming Molecular Compounds

• You do not use the ion sheet for molecules because no __________ are needed. They ______________ electrons instead of transferring them.

• Use ________________ to indicate the # and kind of atom in the compound.

mono=1 di=2 tri=3 tetra=4 penta=5 hexa=6 hepta=7 octa=8 non=9 deca=10

• Use the general format shown below…

prefix-(except mono)-name the 1st element prefix-name the 2nd element ending with -ide

Practice Problems: Name the following molecules.

N2O5 CO Cl4F7 SO3

chargesshare

prefixes

dinitrogen pentoxide

carbon monoxide

tetrachlorine heptafluoride

sulfur trioxide

Writing Molecular Formulas

• The prefixes in the name tell you the # of atoms of each element there are. (Those become the _________________ in the formula!)

Practice Problems: Write the formula for each molecule.

nitrogen monoxide carbon tetrachloride diphosphorous pentoxide

subscripts

NO CCl4 P2O5