Chapter 1 Flashcards
define constitutional isomer
constitutional isomers are compounds with the same molecular formula but a different arrangement of internal atoms. they have different physical properties and different names.
How many bonds does H or F,Cl,Br,I tend to form? What is that called?
monovalent - generally forms 1 bond
How many bonds does O tend to form? What is that called?
divalent - generally forms 2 bonds
How many bonds does N tend to form? What is that called?
trivalent - generally forms 3 bonds
How many bonds does C tend to form? What is that called?
tetravalent - generally forms 4 bonds
define covalent bond
two atoms sharing a pair of electrons
define lone pair
a pair of electrons that is not share between two atoms in a molecule. that is, they are only associated with 1 atom.
define octet rule
the octet rule says that second row elements will try to form the necessary number of bonds to fill all 8 “spots” for an electron around each of those atoms (can also go down to 8 in next-to-last shell)
define formal charge. explain how to calculate it.
formal charge is associated with an atom that does not exhibit the appropriate # of valence electrons. a bond contributes 1 electron to an atom. a lone pair contributes 2 electrons to an atom. if the atom does not “have” enough electrons to balance out the nucleus, then it will have a formal charge
define electronegativity
electronegativity is a measure of the ability of an atom to attract electrons
in what directions does electronegativity increase?
what is the electronegativity of Hydrogen?
2.1
what is the electronegativity of Carbon?
2.5
what is the electronegativity of Nitrogen?
3.0
what is the electronegativity of Oxygen?
3.5
what is the electronegativity of Chlorine?
3.0
what are the (roughly) 3 types of intramolecular bonds?
covalent bond
polar covalent bond
ionic bond
describe a covlent bond. what approximate difference in electronegativities results in a covalent bond?
in a covalent bond, electrons are considered to be shared “equally” between the 2 atoms. the difference in electronegativity is 0.5.
describe a polar covlent bond. what approximate difference in electronegativities results in a polar covalent bond?
electrons are not shared equally between the atoms. the difference is electronegativity is between 0.5 and 1.7
describe an ionic bond. what approximate difference in electronegativities results in an ionic bond?
electrons are not shared at all between the atoms. (salt) the difference in electronegativity is greater than 1.7
describe induction
induction is the movement of electrons towards a more electronegative atom, resulting in a partial charge.
define electron density
electron density is the probability of finding an electron in a particular region of space
describe an orbital (quantum mechanically)
define atomic orbital and list 4 types of atomic orbital
an atomic orbital is an orbital with respect to the nucleus of a single atom. examples include the s, p, d, and f orbitals.
what do simple s and p orbitals look like?
what is a node?
what are degenerate orbitals?
degenerate orbitals are orbitals with the same energy level (for example: 2px , 2py , and 2pz )
what three pinciples/rules govern the way that orbitals are filled?
- Afbau Principle - the lowest energy orbital is filled first
- Pauli exclusion principle - each orbital can accommodate a maximum of 2 electrons that have opposite spin
- Hund’s Rule - for degenerate orbitals (like p), one electron is placed in each degenerate orbital first, before the elctrons are paired up
what is the difference between valence bond theory and molecular orbital theory?
valence bond theory is a simple way of describing how atomic orbitals overlap, while molecular orbital theory is a complex way of describing how atomic orbitals overlap.
how are nodes generated (in valence bond theory)?
valence bond theory treats the atomic orbitals as waves. when these waves have equal and opposite magnitude, that creates a node.
what is a sigma bond?
a sigma bond is an intramolecular bond characterized by circular symmetry with respect to the bond axis. all single bonds are sigma bonds.
describe molecular orbital theory
molecular orbital theory uses math to describe the new molecular orbitals formed from overlapping atomic orbitals (more complex)
how many molecular orbitals do you get when combining 2 atomic orbitals? 3 atomic orbitals?
2 and 3, respectively.
of orbitals in = # of orbitals out
describe difference molecular orbitals.
the antibonding MO has the higher energy. it is formed from destructive interference. it has 2 vertical nodes.
the nonbonding MO has the middle energy. it has 1 vertical node.
(the one that doesn’t form for 2 in –> 2 out)
the bonding MO has the lower energy. it is formed from constructive interference. it has no vertical nodes.
what does HOMO stand for?
highest occupied molecular orbital
what does LUMO stand for?
lowest unoccupied molecular orbital
how are the sp, sp2, and sp3 hybrid orbitals formed? what is different about this than filling atomic orbitals?
the difference is that all of the orbitals are filled with only one electron (before one with opposite spin is added), even the s orbital
what geometry (both electron and atom) do the hybridized orbitals result in?
what is a pi bond?
a pi bond is formed from the overlap of p-orbitals (spare orbitals after hybridization).
a double bond has 1 pi bond; a triple bond has 2 pi bonds.
what is the relationship between # of bonds, bond strength, and bond length?
as # of bonds increases (double and triple bonds),
bond length decreases,
and bond strength increases
define steric number
steric number is the total number of (sigma) bonds and lone pairs around one atom
(VSEPR theory)
which repels more strongly, lone pairs or bonds?
lone pairs repel more strongly
what angle corresponds to a tetrahedral arrangement of atoms? (VSEPR theory)
approx. 109.5 degrees
what angle corresponds to a trigonal pyramidal arrangement of atoms? (VSEPR theory)
approximately 109.5 degrees (or slightly less)
what angle corresponds to a trigonal planar arrangement of atoms? (VSEPR theory)
approximately 120 degrees
what angle corresponds to a linear arrangement of atoms? (VSEPR theory)
approximately 180 degrees
what angle corresponds to an sp3 bent arrangement of atoms? (VSEPR theory)
approximately 109.5 degrees
describe dipole moment and give formula
the dipole moment is an indicator of polarity, based on the amount of partial charge on either end of the dipole & the distance of separation.
both bonds and lone pairs can have associated dipole moments.
what are typical magnitudes of:
dipole moment
partial charge
distance
for the dipole moment calculation?
dipole moment – 10-18 esu cm
partial charge – 10-10 esu
distance – 10-8 cm
what is a debye?
1 debye (D) = 10-18 esu cm
define percent ionic character
% ionic character =
observed dipole moment
calculated dipole moment (as if it were 100% ionic)
what is a molecular dipole moment?
a molecular dipole moment (net dipole moment) is the vector sum of all dipole moments in a molecule
define intermolecular forces
intermolecular forces are the attractive forces between molecules.
they determine the physical properties of the compound.
describe dipole-dipole interactions
compounds with net dipole moments can either repel or attract
in solid phase, molecules line up to attract each other.
in liquid phase, moleculaes are free to tumble but tend to move so that they attract more often than they repel.
what is the relationship between net dipole moment and melting/boiling point?
as the net dipole moment increases,
the melting & boiling points increase
describe hydrogen bonding
hydrogen bonding is not a bond, but a specific (strong) type of dipole-dipole interaction
occurs when a hydrogen atom is connected to a (strongly) electronegative atom
the hydrogen atom will bear a partial positive charge because of induction. this partial + can then interact with a lone pair (partial -) in a neighboring molecule.
strong bond b/c hydrogen is a very small atom & thus can get very close to the other molecule
what is a protic compound?
a protic compound is any compound with a proton (H) connected to an electronegative atom
describe London Dispersion Forces (van der Waals Forces)
London/van der Waals forces are a fleeting, weak attraction between 2 molecules
due to a fleeting dipole-dipole moment in one molecule inducing a fleeting dipole-dipole moment in a nearby molecule
how do fleeting dipole moments form in molecules?
large hydrocarbons (or other molecules with no strongly electronegative atoms) have an average dipole moment of zero.
however, as the electrons move around the molecule, it can momentarily have a dipole moment.
which experiences stronger London dispersion forces–
a larger hydrocarbon or a smaller hydrocarbon?
larger hydrocarbons –> more surface area –> experiences stronger London dispersion forces
which experiences stronger London dispersion forces–
a heavier hydrocarbon or a lighter hydrocarbon?
heavier hydrocarbons –> more surface area –> experiences stronger London dispersion forces
which experiences stronger London dispersion forces–
a branched hydrocarbon or a “straight” hydrocarbon?
“straight”
a branched hydrocarbon experiences fewer London dispersion forces:
branched hydrocarbons –> decreased surface area –> fewer London dispersion forces
describe solubility
for compounds, solubility is a measure of how well they dissolve in a solvent.
like dissolves like:
polar compounds are more soluble in polar solvents
nonpolar compounds are more soluble in nonpolar solvents
what makes soap special?
soap has both polar and nonpolar ends.
the nonpolar ends surround the oil, forming a sphere of soap molecules with the polar tails facing the water
