Chapter 1: Structure and Bonding

atomic number (Z)

# of protons in nucleus

mass number (A)

protons + nucleus

isotopes

atoms w/same atomic # but dif. mass number

orbitals

• within electron shells there are atomic orbitals

• each can have 2e-

• s-orbitals are spheres centered at the nucleus

• p-orbitals are dumbbell shaped w/nucleus in middle 

electron configuration rules

1. aufbau principle: lowest energy orbitals fill up first

2. pauli exclusion: only 2 electrons of opposite spin can occupy an orbital

3. hund’s rule: if 2+ empty orbitals of equal energy are available, one electron occupies each w/parallel spin until all orbitals are half-full

ionic bonds

an atom donates a valence shell electron to an atom that accepts it

covalent bonds

valence shell electrons are shared between atoms 

formal charge

number of valence electrons according to periodic table - number of valence electrons actually associated w/atom

nonpolar covalent

bonded atoms share electrons evenly

polar covalent

one of the atoms attracts electrons more than the other 

electronegativity

how strongly an atom attracts shared electrons

• determines polarity

• electrons tend to shift away from lower to higher electronegativity atoms

valence bond theory/approach

due to overlapping of atomic orbitals (AO) of atoms forming a bond, electrons are localized in the bond region

• covalent bond forms when 2 atoms approach each other closely in a singly occupied orbital

• one atom overlaps a singly occupied orbital in the other atom = forms sigma bond (head-on overlap of 2 atomic orbitals)

sigma bond

strongest type of covalent bonds

• electrons are referred to as sigma electrons

hybridization

hybrid orbitals are mathematical combinations of atomic orbitals

sp3 hybridization

• carbon has 4 attached groups 

• 25% s and 75% p character 

• tetrahedral and 109.5 bond angle 

• involved in a “s” bond

sp2 hybridization

blend/hybridize s and 2p orbitals to get 3 sets of sp2 orbitals

• each sp2 hybrid and p orbital contains a single unpaired electron

• carbon has 3 attached groups 

• 33% s and 67% p character 

• tetrahedral and 109.5 bond angle 

• each sp2 hybrid is involved in a “s” bond

• p orbital forms “p” bond

• double bond = s + p bond

sp hybridization

blend/hyrbidize s and p orbital —> 2 sets of sp orbitals

• other 2 p orbitals are unaffected

• sp hybrids and 2p orbitals contain a single unpaired electron

• carbon has 2 attached groups

• 50% s and 50% p character

• 180 degrees (sp hybrids point in opposite directions)

• sp hybrid is involved in an “s” bond, p orbitals form the 2p bonds 

• triple bond = s + 2p bonds

molecular orbital theory

molecular orbital (MO): linear combination of atomic orbitals to form molecular orbitals that cover the whole molecule, multiple nuclei

• has bonding orbitals and anti-bonding orbitals

bonding orbital

electrons have a higher probability of being between nuclei than elsewhere

• tend to hold nuclei together

anti-bonding orbital

electrons are present in molecular orbital + spend more time elsewhere than between nuclei

• wearing bond 

sp3 geometric molecules

• tetrahedral

• trigonal pyramidal (one lone pair)

• bent (2 lone pairs)

sp2 geometric molecules

• bent (one lone pair)

• trigonal planar

sp geometric molecules

• linear