CHEM 119 Unit 6

Octet rule

atoms want to have 8 valence electrons in valence shell

exceptions to octet rule

Hydrogen, Lithium (2 electrons) and noble gases (stable)

metals valence electrons, forming _

lose, cations

non-metals valence electrons, forming _

gain, anion

strong electrostatic force exist between [] in an [] due to its _ structure

ions, ionic compound, lattice structure

lattice energy increases when

ion size and charge increases/smaller size

lattice energy

indicator of strength of the electrostatic interactions between ions in an ionic compound

electronegativity

ability of a covalently bonded atom to attract electrons to itself (unequal sharing = polar)

electronegativity increases on periodic table 

left to right, down to up (fluorine being most)

pure covalent bond electronegativity difference

less than 0.5

polar covalent

0.5-1.9

ionic

greater than 1.9

lewis dot structure

1 dot = 1 valence electron

lone pairs

nonbonding valence electrons (dots) in lewis structure

how to draw lewis structure of covalent

1. select central atom (least electronegative other than Hydrogen)

2. Find valence electrons of each atom

3. draw single bonds

4. check if all have a complete octet

how to draw lewis structure for polyatomic ions

1. select central atom (least electronegative)

2. find valence electrons of each atom

3. subtract/add electrons base on charge

4. draw single bonds

5. check if all have a complete octet

6. add [ ]^#±

lewis dot exceptions to the octet rule

• BF₃ (incomplete octet) <8 electrons

• PCl₅(expanded octet) >8 electrons

• ICl₄^-(expanded octet)

resonance structures

molecule/compound that can have multiple valid lewis structures without changing the arrangement of atoms (change electrons, or bonds)

resonance hybrid

blend of combining two resonance structures

formal charge

valence e- - [lone pair e- + ½ bonding e-], helps us decide which lewis structure is more stable

• the best one is the one that minimizes formal charges

• sum = charge on molecule

• more electronegative elements are assigned more negative changes

There is no _ relationship between the formula of a compound and the shape of its molecules

direct

VSEPR theory

repulsion between pairs of valence electrons on all atoms, and atoms will tend to arrange themselves in a manner in which the repulsion is minimized

electron domain

for a central atom = # of lone pairs + other atoms central atom is bonded

2 electron domains

linear, 180 degrees

3 e- domains

trigonal planar 120 degrees

4 e- domains

tetrahedral, 109.5 degrees

5 e- domains

trigonal bipyramidal 120 degrees and 90 degrees

6 e- domains

octahedral 90 degrees (2)

molecular geometry is only defined by

positions of only atoms in the molecules, not the nonbonding pairs

nonbonding pairs are __ than bonding pairs. therefore,

larger, their repulsions are greater which decreases bond angles in a molecule

double and triple bonds

greater electron density on one side of a central atom so they also affect bond angles

2 bonding domains and 1 (or 2) non bonding domain(s)

bent shape (less than 120 degree angle)

3 bonding domains and 1 nonbonding domain

trigonal pyramidal

4 bonding domains and 1 nonbonding domain

seesaw

3 bonding domains and 2 nonbonding domains

t-shaped

2 bonding domains and 3 nonbonding domains

linear

5 bonding domains and 1 nonbonding domain

square pyramidal

4 bonding domains and 2 nonbonding domains

square planar

determining molecular polarity

determine elements’ electronegativities, draw arrows towards the most electronegative element, determine symmetry (symmetric- nonpolar, asymmetric- polar)

molecules that contain one type of element are

nonpolar

hydrocarbon polarity

nonpolar

nonpolar molecule rules

1. molecular shape around central atom has no lone pairs or it is square planar or linear

   1. all atoms around central atom are the same

hybridization

atomic orbitals fuse to form newly hybridized orbitals which influence molecular geometry and bonding properties ex: s + p + p + p = sp³

4,3,2 (atoms + lone pairs) hybridization

sp³

sp²

sp

sigma bond

electrons shared between two atoms in a covalent bond, the orbitals overlap, head to head

1- single bond

1 + pi bond - double bond

1 + 2 pi bonds- triple

pi bond

p orbitals on adjacent atoms overlap parallel to internuclear axis

1 + sigma bond - double bond

2 + 1 sigma bond- triple

more electrons shared between two atoms…

stronger, more energy, and shorter the bond

the more bonds

the shorter the bonds (therefore stronger and more energized)