Coulomb's law states that ________ charges attract each other with a force ______ _______ to the square of the distance between the enters of the charges
- inversely proportional
Coulomb's attractive forces cause energy to be released as the neutral atoms are brought together. The resulting energy _______ is called _____ ______
When atoms attracted to each other reach a certain closeness, no more _____ is released. The distance between the two ______ is called the _____ _____.
- bond length
Bringing atoms closer together than their stated bond length causes a sharp increase in energy. Why?
As opposites attract, like charges repel, if atoms are too close, the electron-electron and nuclear-nuclear repulsions become stronger than the attractive forces
- covalent bond: formed by the sharing of electrons, so each atom attains a noble gas config.
- ionic bond: based on the electrostatic attraction of two ions with opposite charges
The energy necessary to remove an electron from an atom. Sodium has an _______ ______ of 119 kcal/mol. and chlorine has an ______ ______ of -83 kcal/mol. What is the net energy input to remove an electron from Na?
- ionization potential (IP)
- ionization energy
- electron affinity
- 119-83=36 kcal/mol
Very few bonds are actually purely ionic or purely covalent, most bonds are _____ ______. So some covalent bonds will share ____ characteristics and some ionic bonds will share _____ characteristics
- polar covalent
Atoms of the left of the periodic table are often called _______, electron donating/pushing while on the right they are called _______, electron accepting/pulling.
Most covalent bonds are between atoms of differing electronegativity resulting in their ________. This is caused by a shift of the center of _______ ______ in the bond toward the more electronegative atom
- electron density
The larger the difference in electronegativity, the ______ the charge separation. Bonds that are within the charge separation of .3-2.0 units are said to _____ ______. Above that are said to _____ _____ and below are ______ ______
- polar covalent
- pure ionic
- pure covalent
Dipoles are the separation of ______ charges and they are symbolized by ______ with a crossed tail pointing from ______ to ______.
- opposite charge
- positive (δ+) to negative (δ-)
VSEPR gives us the accurate _____ and _____ size of molecules and is an abbrv for?
- size & shape
- valence-shell electron-pair repulsion
4 rules to drawing Lewis structures pg13
- Draw the molecular skeleton. For example consider methane has 4 hydroges bonded to one central carbon atom
- Count the number of available valence electron. Add up all the valence electrons of the component atoms. Special care has to be taken with charged structures (anions/cations), in which case, the approp number of electrons has to be added or subtracted to account for extra charges
- The octet rule: Depict all covalent by two shared electrons, giving as many atoms as possible a surrounding electron octet, except for H, which requires a duet. Make sure the number of electrons used is exactly the number counted according to rule 2. Elements at the right of the periodic table may contain pairs of valence electrons not used for bonding, called lone pairs
- Assign formal charges to atoms in the molecule= [number of valence electrons - number of lone pair electrons - (1/2*number of bonding electron)]
3 Exceptions to the lewis structure rules
- Correct Lewis structures contain an even number of electrons; all are distributed as bonding or lone pairs. This distribution is not possible in species having an odd number of electrons like NO, and neutral methyl
- Some compounds of the early second row elements, such as BeH2 and BH3 have a deficiency of valence electrons. Because compounds falling under exceptions 1 & 2 do not have octet configurations, they are unusually reactive and transform readily in reactions that lead to octet structures.
- Beyond the second row, the simple Lewis model is not strictly applied, and elements may be surrounded by more than eight electrons, a feature referred to as valence shell expansion. For example phosphorus (trivalent) and sulfur (divalent)
3 guidelines to determining the major resonance contributor/hybrid
- Structures with a maximum of octets are most important
- Charges should be preferentially located on atoms with compatible electronegativity
- Structures with less separation of opposite charges are more important resonance contributors than those with more charge separation. A simple consequence of coulomb's law: separating opposite charges requires energy; so neutral structures are better than dipolar ones
In theory, the movement of an electron around a nucleus is expressed in the form of equations that are very similar to those characteristic of ______. The solutions to ______ _______, allow us to describe the probability of finding the electron in a certain region in space. The shapes of the regions depend on the ______ of the electron
- electron orbitals
Pauli exclusion principle state no orbital may be occupied by more than _____ ______. Hund's rule states that though orbital have electron pairs when filled, they are first filled in ____ at a time