Unit 6 Molecular Geometry and Polarity

Overview of bond types:ionic

covalentmetallic

Water Why bent shape? Why important?

Why does NaCl dissolve in water?Why polar?

Electrostatic attraction + -

• Between nuclei and e- clouds• e- that satisfy octet rule stick around b/c of +-• Chemical bond result of e.a. between nuclei

and e-• Bond contains energy- E needed to break• Forces- attractive between atoms• Repulsion- between e- in bonding atoms and

charged nucleus

Bond formation

• Valence e- only• At highest energy level• Use PT to determine valence• Bonds- result in octet rule satisfaction• All atoms want to be NOBLE• Which periods of atoms want to be which

NOBLES?

• RESULT:• Lowest potential energy• Process of bonding- exothermic• Energy released• IF E released is large then = strong bond• Small E release= weak bond

For valence e- only

• Ionic - transfer of e-• Covalent- sharing of e-• Metallic- free e-

Valence e-

Transfer, shared and free

All to get to octet.. All atoms want to be NOBLE

Lewis Structures and Symbols

• Chemical symbol represents nucleus and core electrons

• Dots are valence e- Si

Your Turn PT Table orbital tab

• Do • Nitrogen• Phosphorus• Arsenic • Antimony

• Notice anything?

Try me…

P

As

Sb

Bi

Lewis Dot Structures in bonding

• Lewis structures show presence of all valence electrons in a compound.

• If ionic, metallic or covalently bonded compounds may all be represented.

• This unit concentrates on covalently bonded molecular compounds but ionic compound representation is required.

• Metallic Bonds also crystal lattice • Ions fixed • Valence e- free

• Ionic bonds

Na + Cl

Covalent bonds

• Do Lewis dot structures for HCl

H + Cl

Non polar

F F diagram.. No charge separationPull of val e- is =

Polar

• Unequal pull

H Cl

Cl EN is greater than H so Cl pulls more stronglyH b/comes more + as e- pulled more towards Cl

Unequal sharing use lower case delta ᵟ

Can do EN calculation

ᵟ+ H Cl ᵟ-

The greater difference in EN, the more likely loss of e- and ionic

0-.3 .3to 1.00 1.00 to 1.7 more than 1.7

• Ionic transfer of v e-

• Metallic free v e-

Another ionic compound

One e- from Ca atom may be given to each fluorine atom to satisfy octet rule

Lewis Structure for CaF2

Your Turn

• Sodium Chloride • Iron II flouride• Potassium Bromide

• Covalent compounds and polyatomic ions can be described by

• Molecular formula: kind/types numbers of atoms but give no information of bonds connectivity

• Structural formula: depicts arrangement of atoms in space

But gives no information regarding arrangement of valence electrons

Lewis Structures Does …

• Shows valence e- arrangement

• Lewis structures written for molecules that obey Octet Rule!

• (exceptions: deficiency, extended and odd#)

Lewis Dot Diagram Rule 1:• Count valence e- of each atom • Add totals for all atoms• Make adjustment for charge if any• (-1 charge add e- +2 charge 2 less e-)

Rule 2:

• Arrange atoms in the diagram as follows:• Choose least EN atom as central atom- usually

atom closest to left side of PT or largest• Arrange other atoms around central atom (CA)• Hydrogen can only form one bond- never CA• Carbon has 4 single bonds except in CO and

CN (Has 3 bonds and unshared v e- pair)

Rule 2 continued…

Arrange other atoms around central atom (CA)

Hydrogen can only have one bond, why?Carbon has 4 single bonds except CO and CN-1

Your Turn…

Calculate val e- and organize CA and outside atoms in the following:Carbon dioxide Ammonia Carbon tetrachlorideMethaneCarbon ionAmmonium ion

Rule 3

• Place vale e- around CA as follow:• Connect outer atoms to CA with single

covalent bond- each bond takes 2 e-• Calculate # of remaining val e-• Fill octets of outer atoms• Place any remaining e- on CA

Rule 4

• Check CA if Octet Rule satisfied• IF NOT- make multiple bonds double or triple• (this done by moving unshared e- pair on

outer atom to CA• ONLY FEW ELEMENTS CAPABLE OF FORMING

MULTIPLE BONDS: C N O P S • AND RARE-CHLORINE

Your Turn..

Return to these diagrams Add val e- Make Lewis Structures for each Carbon dioxide Ammonia Carbon tetrachlorideMethaneCarbon ionAmmonium ion

exception

NH4+

nonmetals form this cation

Only polar atomic ion formed by two nonmetals

EXCEPTIONS TO OCTET RULE?