Chemistry 1110-Section 3 Lewis Diagrams

What two types of covalent bonds are there?

Non-polar covalent: electrons are shared equally btw atoms, no separation of charge

Polar covalent: electrons are not shared equally btw atoms, separation of charge denoted by dipole arrow (partial charges)

What is electronegativity and its trend?

Electronegativity describes the atoms ability to compete for electrons with another atom it is bonded to

It increases up a group and from left to right, with Fluorine being the most electronegative atom

How are the types of bonds recognized using electronegativity difference?

Ionic: large difference ( approx. > 2.0)

Polar covalent: intermediate difference (approx 0.4-2.0)

Non-polar covalent: small difference ( approx. <0.4)

Why do we draw resonance structures?

To indicate some electrons are not localized between two atoms

What does spreading electrons over a greater space do?

Delocalizes them, lowering the energy of the molecule (called resonance stabilization)

What are exceptions to the octet rule?

Free radicals: odd number of e- results in an unpaired electron (highly reactive compounds)

Incomplete octet: limited to B,Al, Be, satisfied without a complete octet 

Expanded valence shell: elements in third row and below can have more than an octet when central atom is bigger.