Lewis stuctures and Lewis acids and bases

Lewis stuctures

90 degree angle

8 valence electron except H - Oxtate rule for early p block element

Double bond = 4 electrons

Single bond = 2 electrons

Molecule → lewis structure

Remember the one atom with lowest EN in the middle except H - can’t make more than 1 bond)

If lacking the octett rule → forms double bonds

Example NF3

Problem

C - lowest EN in centere

Cl,F, H - NOT IN CENTER - ONLY 1 BOND

Solution b

Remember!! Add - or + - adding or taking away an e

Dosen’t matter were you put the extra electron

Methanol, n2, c02

N---N - Octett rule

Resonance structures

Both structures are correct

There are multiple ways to draw them

Equal strength in both bonds

However - if it would be 1 double bond and one single bond the double bond would be much shorter + stronger than the single bond. But the molecule is equal in reality - thats why it has 2 resonance structures - BOTH correct, unclear were the bond is

Exceptions to the octet rule

B and Be

Free radicals - very reactive- more than 8 e - expanded shell

NONmetalls - period 3 and higher - due to 3d orbital exists - expanded

(s+3p - 8)

Expanded valence shells

Examples of expanded valence shells

Bonding looses energy - the goal

Problem and plan

2 extra lone pairs

F is very EN- many protons- dragging the electron away from the Xe

Lower energy

The Lewis Acid-Base Definition

Lewis base/acid not the same as Bronstedt

H+ - Acid - anything accepts an electron pair

Lewis base - donates an electron pair

H20 is a base- dative bond

Lewis Acids and Bases

Remember lone pairs!!

Vacant orbital- EMPTY

Electron-Deficient Molecules as Lewis Acids

Dative bond - weaker than a covalent bond, easily broken

Metal Cations as Lewis Acids

Metals- lewis acids- forms dative bond- hemoglobin, chlorophyll

EMPTY ORBITALS

Chlorophyll

Mg2+= lewis acid

EMPTY ORBITALS

Lewis base have LONE PAIRS

Problem

Coordination Compounds

Ligands- lewis bases, around metals

Counter ions- outside the klammrar/box

Complex ion- metal cation bonded to ligands

Coordination Number

Specific for each element

Number of ligands bonded directly to the metal ion

Ligands and examples

NH3- ions or molecules, lewis bases

Mg2+- lewis aid in chlorophyll

Acids are often metals, compounds or H+- THEY HAVE EMPTY ORBITALS

Chelates

Form rings

Bi- two bonds

Poly- more than 2

Mono- 1 bond

Grabbing a metal ion to neautralize

Severeal lon pairs - more bonds