Textbook Notes #2

Second set of textbook notes for midterm #2

All atoms except very smallest (like hydrogen) tend to lose, gain, or share electrons so that each atom has 8 valence electrons

octet rule

How to Draw a lewis structure

1. Determine total number of ____________

2. Arrange symbols of elements to show how atoms are bonded, connect with _________

3. Complete octets of all atoms (except hydrogen) bonded to _______ by adding lone pairs

4. Compare the number of valenece electrons in the lewis structure with the number from the first part

5. Confirm an _____ on the central atom

valence electrons

bonds

central atom

octet

the number of electron pairs the 2 atoms share

• as this increases between two atoms ______ decreases

the energy needed to break 1 mole of bonds in the gas phase

• generally increases as _____ does

bond order

bond length

bond strength/energy

bond order

the existence of multiple lewis structures; same arrangement of _____ but different arrangement of bonding _____ and _______

Resonance

atoms

atoms

electrons

lone pairs

spreading out of a bonding pairs

• reduces an electrons’ ______ and lower _____ of the molecule

delocalization

potential energy, energy

resonance ______: delocalization reduces electrons’ potential energy and lower energy of the molecules

• spreads electrons out over ______ volume

• redues ______

• allows greater nuclei interaction → increases ______ attraction

stabilization

greater

repulsion

electrostatic

__________: an accounting system for the number of electrons formally assigned to an atom in a structure of a molecule or polyatomic ion

Equation: ______

this calcuation assumes each atom is formally assigned all its lone-pair electrons and ______ the electrons shared in bonding pairs

formal charge

(# of valence electrons)-[(# of electrons in lone pairs) + 1/2(# of shared electrons)]

all; half

How to determine the best structure

• the ______ on each atom is Zero

• most atoms have formal charges equal to zero or as ______ to zero as possible

• Any negative FC’s should be on the most ______ atoms

FC

close

electronegative

• When atoms get larger the bond becomes ______

  • this is because the nuclei are ______ apart

• ______ > ______> ______

  • in terms of bond length

• Things that stay the same in resonance forms

  • ______ present, ______ of atoms, net ______ of molecules/ion, ______ of electrons

• average ______= (# of bond pairs/# of resonance structures)

• ______ : the number of electron pairs tha hold two atoms together

longer, farther

single, double, triple

atoms, arrangement, charge, number

bond order

Energy is always ______ to make bonds

Energy is always ______ to break bonds

released

required

Three cases of electron exceptions

1. when there is an ______ number of valence electrons

2. when there are too ______ valence electrons

3. when there are too ______ valence electrons

odd

few

many

__________: contain an unpaired valence electron

• typically very highly reactive and __________

• generally __________ to form more stable molecules

free radicals

unstable

react

Incomplete octets

• generally only found in molecules with __________, __________, __________

Boron, beryllium, aluminium

Expanded Valence Shells

• more common than incomplete

• involves highly __________ atoms and a __________ central atom in the __________ period or below

• commonly occur with  __________, __________, __________

• Chemists say that additional ionic interactions between __________ negative charges on surrounding atoms and strong positive charges on __________ atoms might be occurring

electronegative, nonmetal, third

Fluorine , chlorine, and oxygen

partial, central

__________: the positions of the atomic nuclei in a molecule

__________: helps to look at the 3D structure of molecules

molecular geometry, VSEPR

Electron Domain Geometry

2 domain: __________

3 domains: __________

4 domains: __________

linear

trigonal planar

tetrahedral

Molecular geometries

2 domains, 0 nonbonding domain: __________

3 domains, 0 nonbonding domain: __________

4 domains, 0 nonbonding domain: __________

3 domains, 1 nonbonding domain: __________

4 domains, 1 nonbonding domain: __________

4 domains, 2 nonbonding domains: __________

linear

trigonal planar

tetrahedral

bent

trigonal pyramidal

bent

Electronegativity

• __________ across the periodic table

• ___________ down the periodic table

increases

decreases

If the electronegativities of bonded atoms are not equal, the bond is _________ to the more electronegative atom

S^-: indicates the ________ electronegative ion

S⁺: indicates the ________ electronegative ion

polarized

more

less

________: are created due to different electronegativities in a covalent bond; separation of electrical charge created

bond dipoles

________ dipole: permanent separation of electrical charge in a molecule

• Many molecules will typically just have ________ dipoles due to fluctuating electric fields

permanent

temporary

________: asymmetrical charge distribution in a polar substance produces this

• indicate the dipole by writing an ________ above the molecule. ________ will show direction of electron flow by pointing toward the ________ electronegative atom. 

dipole moments

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