Unit 6 Molecular Geometry and Polarity Overview of bond types: ionic covalent metallic

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 tabPT 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 separation Pull of val e- is =

Polar Unequal pull H Cl Cl EN is greater than H so Cl pulls more strongly H 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 to 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 CaF 2

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 tetrachloride Methane Carbon ion Ammonium 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 tetrachloride Methane Carbon ion Ammonium ion

exception NH 4 + nonmetals form this cation Only polar atomic ion formed by two nonmetals

EXCEPTIONS TO OCTET RULE?