Dressen-lewis structures

Electron Dot Structures : 

Electron Dot Structures

Lewis Structures : 

Lewis Structures - Diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. - Introduced by Gilbert Lewis in 1916.

Slide 3: 

Lewis Structures (Electron-dot formulas) for Ionic Compounds. Remember, in an ionic compound, the metal loses e-’s and the non-metal gains. There is no sharing. Here is the e-dot formula for sodium chloride (NaCl) Na+

Slide 4: 

Here is the e-dot formula (Lewis Structure) for the ionic compound MgF2 : Mg2+ Notice, there is no sharing. The F atoms took both valence e-’s from Mg, forming ions which do not share electrons. The + and – charges on the ions cause them to attract each other.

Slide 5: 

Drawing Lewis Structures for Covalent Compounds Let’s try SiH4 (silane) 1) First count all the valence electrons 2) Decide which atom will be your central atom -Carbon is always in the center -Hydrogen is never in the center -If no carbon, least electronegative element is placed in center 3) Decide which atom will be your central atom and then connect the atoms by electron-pair bonds 4) Make sure all H’s have two electrons and all other nonmetals satisfy the “Octet Rule” 5) Make sure your final structure has same number of electrons as you had in step 1

Slide 6: 

Electron-dot formula for Methane (CH4) C H H H H Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

Slide 7: 

Electron-dot formula for Methane (CH4) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet. Each H atom “feels” like a stable “He” atom with 2e-s

Slide 8: 

Electron-dot formula for Ammonia (NH3) N H H H Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

Slide 9: 

Electron-dot formula for Ammonia (NH3) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e- like Helium.

Slide 10: 

Write the electron-dot formula for CF4 Because “F” is a halogen, it has 7 valence e-s, so you must show all 7 red dots around each “F” atom!

Slide 11: 

Write the Electron-Dot Formula for SeF2 Because “F” is in Group 17, they have 7 valence e-s, so they must have 7 red dots around them.

Formaldehyde CH2O : 

Formaldehyde CH2O Some elements, especially C, N, and O can share more than one pair of electrons!! Two pairs of electrons shared = double bond Three pairs of electrons shared = triple bond

Resonance StructuresOzone, O3 : 

Resonance StructuresOzone, O3 Resonance - Bonding in molecules cannot be correctly represented by a single Lewis structure Actual structure of ozone is an average of these two structures

Benzene: Classic Case of Resonance : 

Benzene: Classic Case of Resonance kekule's dream

Yes, we can see molecules! : 

Yes, we can see molecules!

Bond Energy vs Bond Length : 

Bond Energy vs Bond Length

Bond Energy vs Bond Length : 

Bond Energy vs Bond Length

Bond Energy vs Bond Length : 

Bond Energy vs Bond Length

Ionic Structure : 

Ionic Structure Calcium Sulfide