Unit 2 Flashcards
Electronegativity
A measure of the ability of an atom to attract shared electrons
When does electronegativity increase
Electronegativity increases as you move across a period on the periodic table, from left to right. This is because
the atomic radius is decreasing while the number of protons (and effective nuclear charge) is increasing
Nonpolar covalent bond
- equal sharing of electrons
- electronegativity difference <0.5
- no bond dipole moment
Polar covalent bond
- unequal sharing of electrons
- electronegativity difference 0.5-1.7
- partial bond dipole moment
Ionic bond
- transferred electrons
- electronegativity difference >1.7
- positive and negative bond dipole moment
Ionic bonds are stronger when. . .
Charges are larger and the ions are smaller ( this can be explained by electrostatic force/Coulomb’s law equation
Properties of ionic substances
- Form crystals (lattice of positive and negative ions)
- High melting and boiling points
- Hard
- Brittle
- Conduct electricity when dissolved and when molten (melted)
- Good insulators as a solid
How do metallic bonds attract
Due to multiple metallic cations being attracted to a delocalized sea of valence electrons
When is the IMF stronger for metallic bonds
The IMF is stronger when there are smaller metallic cations and when there are more valence electrons
Properties of metallic substances
- Shiny (Luster)
- Malleable and ductile
- Conduct heat and electricity
- Metallic oxides are basic and ionic
- Lose electrons to form cations
Properties of Nonpolar and Polar Covalent Molecules
x Non-lustrous, various colors
x Brittle, hard or soft
x Poor conductors
x Nonmetallic oxides are acidic and covalent
x Form anions by gaining electrons
Polar covalent bond rules
a) The atom with the higher electronegativity will develop a partial negative charge relative to the other
atom in the bond.
b) In single bonds, greater differences in electronegativity lead to greater bond dipoles.
c) All polar bonds have some ionic character, and the difference between ionic and covalent bonding is
not distinct but rather a continuum.
Bond energy
Bond energy is the energy required when breaking a bond, or the energy released when a bond is formed
How is bond energy different
- Larger atomic radii increase the bond length. Longer bond length decreases the bond energy
- Increasing the bond order increases the bond energy, as there are more electrons involved and therefore greater
coulombic attraction and the bond length has decreased
Lattice energy
Energy to separate ions in ionic compounds
How to calculate lattice energy
Larger charges = more attraction = more energy required to separate the ions.
Smaller radii = more attraction = more energy required to separate the ions.
Why does KBr (672 kJ/mol) have a higher lattice energy than KI (632 kJ/mol)?
Bromide ions (Br-) have a smaller ionic radius than iodide ions (I-). This results in a smaller distance
between the potassium ion and the bromide ion. The smaller distance increases the coulombic attraction
resulting in higher lattice energy.
How are metals composed
Metals are composed of cations that are embedded in delocalized sea of valence electrons. The number of valence electrons determines the amount of electrons in the delocalized sea of electrons.
Alloys
Mixtures of metals. There are two types interstitial and substitution. The difference between them is the size of the atoms that are being added to the metal
Attraction of alloys
When the charge on the cations and the
number of electrons increases the attractions are greater. Additionally, when the ionic radius decreases the attraction increases.
Interstitial
The atoms added to the metal are small and fit in
between the metal atoms in the existing holes
(interstices). (H, B, C and N are commonly added)
Substitutional
The atoms added to the metal have similar radii so
they replace the atoms in the lattice
Formal charge
Formal Charge = (# Valence Electrons) - (# lone electrons +# bonds connected)
The most valid structure
- Formal Charges as close to zero for all atoms. (Most preferable is “no formal charge.”)
- Negative Formal Charges will be placed on the most electronegative atom
How to represent resonance
Draw all the structures of the molecule, keeping the arrangement of the atoms the same
but changing the location of the electrons. Double arrows are drawn between the structures indicating that the
structures are superimposed to make a hybrid.
Resonance structures
when drawing a Lewis Structure you might find that there is more than one arrangement of
bond/electrons that are equally valid; you might find that a double (or triple) bond could be placed in one of two or more places in a molecule or ion. Look at the NO21- ion shown; both images are valid so both must be included when drawing a Lewis structure
VSPER model
The valence shell electron-pair repulsion (VSPER) theory predicts the geometries of molecules and polyatomic
ions
Linear
- 0 lone pairs
- 2 lines
- 180
Trigonal planar
- 0 lone pairs
- 3 lines
- 120
Bent one lone pair
- 2 lines
- 1 lone pair
-<120
Tetrahedral
- 4 lines
- 1 front one back
- 109.5
Trigonal pyramidal
- one lone pair
- 3 lines
- one front one back
- 109.5
Bent 2 lone pairs
- 2 lone pairs one front one back
- 2 lines
- <109.5
Trigonal bipyramidal
- no lone pairs
- 5 lines 1 front 1 back
Seesaw
- 1 lone pair
- 4 lines 1 front 1 back
- <90, <120
T shape
- 2 lone pairs 1 front 1 back
- 3 lines
- <90 between electrons
Linear 3 lone pairs
- 3 lone pairs 1 front 1 back
- 2 lines
- 180
Octahedral
- no lone pairs
- 6 lines 2 front 2 back
- 90
Square pyramidal
- 1 lone pair
- 5 lines 2 front 2 back
- <90
Square planar
- 2 lone pairs
- 4 lines 2 front 2 back
- 90
T shape .2
- 3 lone pairs 1 front 2 back
- 3 lines one front
- <90 between 2 electrons
Linear 4 lone pairs
- 4 lone pairs 2 front 2 back
- 2 lines
- 180
How do lone pairs effect angles
Lone pairs of electrons repel more than bonds and tend to compress the angle between bonding atoms.
How to find hybridization
the sum of the superscripts on the hybrid orbitals equals the number of electron clouds around the central atom
Order of hybridization
s, sp, sp2, sp3, sp3d
Single bond contains. . .
Contains one sigma bond
Double bond contains. . .
One sigma one pi bond
How are double and triple bonds formed
Formed from unhybridized p orbitals and are called pi bonds
Triple bond contains. . .
One sigma two pi
Rank bonds from highest energy
Triple bonds > double bonds > single bonds
Bond order
Number of bonds between 2 atoms
Bond order of resonance bonds
bonds that have resonance are experimentally determined to be the same length (and order of 2 and 1 would be 1.5 for both)
Bond polarity described
When electrons are shared in a covalent bond, the shared electrons spend more time around the more electronegative element in the bond resulting in a polar molecule
Partial charges
Polar covalent bonds gives the more electronegative element a partial negative charge and the less electronegative element a slightly positive charge
Symmetrical shapes
- linear, Trigonal planar, tetrahedral, Trigonal biqyramidal, square planar, and octahedral
