unit 6 molecular geometry and polarity overview of bond types: ionic covalent metallic
TRANSCRIPT
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
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?
• 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.
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
• 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