exam 3: chapters 8 & 9 Flashcards by Abby Kreisler

Ionic bond

metal + nonmetal
(cation + anion)
- EN > 1.7

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Covalent

nonmetal + nonmetal
- sharing of e- b/w 2 atoms

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Nonpolar

covalent b/w same element
- equal pull

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ionic bonding

metal loses e-, nonmetal gains e-

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Born-Haber Cycle (energetics of ionic bonding):

Break into separate elements
Add energy (heat) to transform Na (s)(g)
Add energy (heat) to transform ½Cl2 (g)  (g)
Electron is transfers/added to Cl (g)
Opposites attract; Na and Cl attract

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Lattice energy

energy to separate 1 mol of (s) –> 2 ions (g)
- ↑ w/ ↑ charge of ions
- ↑ w/ ↓ size of ions

charge > energy

consumes energy

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Lewis’ Rule

Column/group # = # of valence e-
- ex: group 3A = 3 v. e-

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Octet rule

atoms tend to gain, lose, or share electrons until they’re surrounded by 8 valence e-
- (full s and p subshells)

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↑ # bonds = __ distance

= ↓ distance
- additional bonding e- attract nuclei more

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Bond polarity

measures how equal/unequal e- shared in covalent bond

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nonpolar covalent bond

e- shared equally
- EN < 0.4

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polar covalent bond

1 atom exerts greater attraction for the bonding e-
- partially (+) or partially (-)
- 0.4 < EN < 1.7

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Electronegativity (EN)

ability/strength of atom to attract e-
- increase left–>right, bottom–>top

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Polar molecule

separation of (+) and (-) charges in molecule
- unequal pull

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dipole

2 electrical charges of = magnitude but opposite sign separated by distance

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dipole moment (μ)

2 equal & opposite charges (Q+/Q-) separated by distance (r)
- μ = Qr
- Unit (μ) = D

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Formal charge =

= (# v.e. atom brings) – (# e- surrounding on LS)

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Resonance structures

1 LS can’t accurately depict molecule
- Need multiple LS
- ex: Ozone (O3)

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Bond angles

angles made by lines joining nuclei of atoms

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Valence-Shell Electron-Pair Repulsion Model:

Electron pairs repel each other
- best arrangement = minimizes repulsions

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region e- most likely to be found

bonding pair

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Hypervalent

more than octet of e-
- break octet rule

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Bond dipole

dipole moment w/ 2 atoms
- Bond dipole and dipole moments = vector quantities
- must consider 3D shape

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nonpolar bond dipole

equal/opposite bond dipoles = symmetric
- Linear

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polar bond dipole

bent in nature = asymmetric - Overall dipole moment = up/towards O (partial -) away H (partial +)

Valence-bond theory

“overlap” of orbitals - Sharing of space b/w 2 e- of opposite spin = covalent bond - share space b/w nuclei

Hybrid orbitals

“mixing” of 2+ atomic orbitals on the same atom

degenerate orbitals

"new orbitals" after hybridization - 2 orbitals mix --> create 2 orbitals - 6 e- start --> 6 e- end

Orbital Shape

orbitals in bonded molecules (molecular orbitals) have diff shape an unbonded atom (atomic orbitals)

Orbital Energy Level

energy level changes from atomic  molecular

Sigma (σ) bond

to-head overlap (direct collision @ end points) ; forms covalent bond - cylindrical symmetry of e- density about nuclear axis

Pi (∏) bond

sideways overlap of p orbitals - e- density above and below nuclear axis - ALWAYS involves p orbitals

localized electrons

σ, ∏, lone pair: - Bonding e- shared only b/w 2 atoms

delocalized electrons

∏, lone pair: - Bonding e- shared by 3+ atoms - Due to Resonance!

largest lattice energy magnitude

large charge + small ion

ionic size increases...

from top to bottom (right to left)

polarity is based on

electronegativity

acid in Lewis Structure

O-H

average bond order =

(# of bonds)/(# of bonding domains)

hybridization =

ED # - 1 (ex: N = 4 ED = sp3)

zero dipole moment

nonpolar - equal pull

nonzero dipole moment

polar - unequal pull

When to subtract from bond angles?

1 lone pair = -2 degrees

an atom with low first ionization energy and low electron affinity is more likely to form a ___.

more like to form a cation (than an anion)

T/F: the most common ion for an atom of a representative element generally adopts a noble-gas electron configuration

true

the stability of KBr is due to the _______ between the potassium ions and the bromide ions

electrostatic attraction

the attraction b/w cations and anions increases as the ___ increase.

charges on the ions

the attraction b/w cations and anions decreases as the ___ increase.

radii of the ions

what happens to electron density as you increase the distance between nuclei in a covalent bond?

- repulsions in nuclei decrease - attraction b/w nuclei and e- decrease - repulsions b/w e- = unaffected

cations

(+), metal, smaller radius

anions

(-), nonmetal, larger radius

strength of a bond increases, as # of __ increase

e- - ex: H2 > H2+

electron affinity vs electronegativity

electron affinity- energy released when 1 atom gains an e- to form a (1-) ion electronegativity- ability of atom to attract e- - no units

electron affinity vs electronegativity

- electron affinity- energy released when 1 atom gains an e- to form a (1-) ion - electronegativity- ability of atom to attract e- - no units

elements w/ high EN, usually also have high ____

first ionization energy and electron affinity

Benzene:

{circles inside of hexagon} - circle = 3 double bonded C (w/ resonance- 1 single) - vertices on hexagon = 1 carbon atom - H atoms = omitted - notation = blend of 2 = resonance structures

reaction enthalpy can be estimated by:

- energy added to break bonds + energy released forming bonds

avg bond enthalpies

- Energy to break bonds - More bonds = more energy to break - # of bonds ↑, bond length ↓, bond enthalpy ↑

dipole energy/direction of arrow is based on ___

Electronegativity

in valence bond theory, bonds are formed by the overlap of ___

atomic orbitals in different atoms

as two atoms are pulled apart, the overlap between their atomic orbitals ___

decreases

bond order =

1/2 (# bonding electrons - # nonbonding electrons)

(*) =

antibonding molecular orbital

paramagnetism

more unpaired e- = stronger attractive force

diamagnetism

no unpaired e- = weakly repelled by magnetic field

SO3 is polar or nonpolar?

polar

IF5 is polar or nonpolar?

polar

PCl3 is polar or nonpolar?

polar

XeF4 is polar or nonpolar?

nonpolar - octahedral ; square planar

partial charge for diatomic molecules

partial = (Formal Charge on atoms of interest) / (# of atoms of interest) - ex: NO3

partial charge for diatomic molecules

partial = (Formal Charge on atoms of interest) - (# of atoms of interest) - ex: NO3 - (-1 + -1 + 0) / (3)

sulfuric acid

H2SO4

acetic acid

CH3COOH

perchloric acid

HClO4