Unit 3: Molecular Structure Flashcards
how do ionic bonds form
- metal transfers electrons to a nonmetal
- there is no sharing of electrons
- the cation and anion each have noble gas configuration
what keeps ionic compounds together
electrostatic forces
what is the equation for lattice energy of ionic compounds
lattice energy = k(charge of cation * charge of anion/distance between ions)
what causes ionic compounds to have a higher or lower lattice energy
- higher: larger charges, smaller distance
- lower: smaller charges, larger distance
how do covalent bonds form
- orbitals on one non-metal atom overlap orbitals on another non-metal atoms
- sharing of valence electrons
is a covalent bond with higher or lower energy more stable
lower energy is more stable
do atoms in covalent compounds share electrons equally
not always
define electronegativity
- ability of covalently bonded atom to attract electrons to itself
- higher electronegativity = electrons pulled towards that atom
what is the most electronegative atom in the periodic table
fluroine
describe the periodic trend of increasing electronegativity
- increasing moving up
- increasing moving right
define non-polar covalent bonds in terms of electronegativity
- atoms have similar electronegativities
- electrons shared equally
- difference in EN is less than 0.4
define polar covalent bonds in terms of electronegativity
- atoms have different electronegativities
- electrons shared unequally
- difference in EN is between 0.4 and 1.9
define ionic bonds in terms of electronegativity
- atoms have highly different electronegativities
- electrons are transferred to the ion with a higher electronegativity
- difference in EN is greater than 1.9
describe metallic bonding
- metal atoms donate electrons to an electron sea
- electrons are delocalized across all of the metal atoms
- causes electrical conductivity of metals
what do lewis structures represent/show
- valence electrons
- bonding electrons
- nonbonding electrons
do lewis structures resemble to actual shape of a molecule
no
describe how to draw a lewis structure
- determine the total number of electrons needed
- draw the central atom and outer atoms connected by single bonds
- add nonbonding electrons to outer atoms
- change some nonbonding electrons to bonding electrons to use the exact number of total electrons and make sure all atoms have full valence shells
generally, which atom is the central atom in a lewis structure
- the least electronegative one
- never hydrogen
define resonance structures
- lewis structures that are different but both work
- often with double bonds in different places
if there are two resonance structures, does that mean that half of the molecules are built like one and the other half are built like the other
- no
- resonance structures combine to create 1.5 strength bonds instead of a single and double strength bond
explain how we know that resonance structures combine using O3 as an example
- in O3, we know that the bond lengths are the same between each oxygen
- we would expect that a shorter length would be observed if there is a double bond
- we would expect there to be different lengths due to different bonds but that is not what we see
- bonds are the same length, so we know that there aren’t 1 single and 2 double bonds, there are 2 1.5 strength bonds
what are the 3 elements that form an incomplete octet when bonded
- Be
- B
- Al
how many bonds does Be like to form
2
how many bonds does B like to form
3
how many bonds does Al like to form
3
define expanded octet
occurs when elements have more than 8 valence electrons surrounding them when bonded
does fluorine like to make a double bond
no
what is the equation for formal charge
- valence electrons - (lone electrons + 1/2 bonding electrons)
- difference between how many valence electrons an atom started with and how many it ended with
explain how formal charge is related to ions
- the sum of the formal charges of all atoms in a molecule in the charge on that molecule
- neutral molecules have a sum of formal charges equal to 0
are electronegative elements assigned more positive or negative charges in terms of formal charge
negative
what is the best structure related to formal charge
- one that minimizes the formal charges
- one with the greatest number of elements having a formal charge of 0
describe the valence shell electron pair repulsion theory
electron pairs will repel one another so they are placed as far apart in space as possible to minimize the repulsion
define electron domain
- any side of an atom where there are electron: either pairs or bonds
- lone pairs = 1 electron domain
- single bonds = 1 electron domain
- double bonds = 1 electron domain
- triple bonds = 1 electron domain
what is the molecular geometry name for a molecule with 2 electron domains
linear
what is the molecular geometry name for a molecule with 3 electron domains
trigonal planar
what is the molecular geometry name for a molecule with 4 electron domains
tetrahedral
what is the molecular geometry name for a molecule with 5 electron domains
trigonal bipyramidal
what is the molecular geometry name for a molecule with 6 electron domains
octahedral
what are the bond angles in a linear geometry molecule
180 degrees
what are the bond angles in a trigonal planar geometry molecule
120 degrees
what are the bond angles in a tetrahedral geometry molecule
109.5 degrees
what are the bond angles in a trigonal bipyramidal geometry molecule
120 degrees and 90 degrees
what are the bond angles in an octahedral geometry molecule
90 degrees
does molecular geometry take into account atoms, nonbonding pairs, or both
- only atoms
- doesn’t take into account nonbonding pairs
is the electron-domain geometry always the shape of the molecule
- no
- doesn’t consider nonbonding pairs which can change the shape of the molecule
what is the molecular geometry of a trigonal planar electron-domain shape with 2 atoms and 1 nonbonding pair
bent
why would the two atoms on a bent shaped molecule (trigonal planar with 2 atoms and 1 nonbonding pair) be closer together than the expected 120 degrees
- nonbonding pairs are physically larger than bonding pairs
- the added nonbonding pair will push the two atoms slightly closer together
what is the molecular geometry of a tetrahedral electron-domain shape with 3 atoms and 1 nonbonding pair
trigonal pyramidal
what is the molecular geometry of a tetrahedral electron-domain shape with 2 atoms and 2 nonbonding pair
bent
what are the top and bottom atoms called in the trigonal bipyramidal electronic geometry
axial bonds
what are the middle atoms called in the trigonal bipyramidal electronic geometry
equatorial bonds
will lone pairs in the trigonal bipyramidal electronic geometry be in the equatorial or axial position and why
- equatorial
- gives electrons the most space
what is the molecular geometry of a trigonal bipyramidal electron-domain shape with 4 atoms and 1 nonbonding pair
seesaw
what is the molecular geometry of a trigonal bipyramidal electron-domain shape with 3 atoms and 2 nonbonding pair
t-shaped
what is the molecular geometry of a trigonal bipyramidal electron-domain shape with 2 atoms and 3 nonbonding pair
linear
what is the molecular geometry of a octahedral electron-domain shape with 5 atoms and 1 nonbonding pair
square pyramidal
what is the molecular geometry of a octahedral electron-domain shape with 4 atoms and 2 nonbonding pair
square planar
what is special about the linear molecular geometry originating from the trigonal bipyramidal electronic geometry and the square planar molecular geometry originating from the octahedral electronic geometry and why
- both have the same ideal bond angles as the electronic geometry (180 for linear and 90 for square planar
- because the lone pairs are all opposite of each other and create equal repulsion
how should you go about determining the geometry of a larger molecule
determine the geometry around each particular atom
what is the overall dipole moment of a nonpolar molecule
0
what is the overall dipole moment of a polar molecule
not 0
explain how to determine if a molecule is polar
- look at individual bonds and identify bond polarity
- draw arrow toward the more electronegative atom in a polar bond and add a + to the positive end
- determine molecular polarity by looking at arrows and seeing if they cancel out (cancel out=nonpolar)
define hybrid orbital
proposed that s and p orbitals mix together to form molecular geometries
describe how to determine the hybridization of an atom
- determine the number of electron domains around the atom
- add orbitals starting from s1 until you have the same number of orbitals as electron domains
- there is 1 s orbital and 3 p orbitals
- hybridization examples are: s, sp, sp2, sp3
what must the orbitals of atoms do when covalent bonds are formed
overlap
what are the 2 types of internuclear bonds
- sigma
- pi
describe the sigma internuclear bond
- occurs when orbitals overlap along the bonding axis, one point of overlap
- the first covalent bond is always sigma
describe the pi internuclear bond
- occurs when orbitals overlap parallel to the bonding axis, two points of overlap
- the second and third covalent bonds are always pi bonds (one bond in a double bond, two bonds in a triple bond)
what is the relationship between bond type (single, double, triple) and bond length
- more bonds (more electrons shared) = shorter bond lengths
- more elections have stronger pull between atoms to make them closer together
what is the relationship between bond type (single, double, triple) and bond energy
- more bonds (more electrons shared) = higher bond energy
- more electrons makes the bond stronger which means it requires more energy to break
what is the relationship between the atoms bonded and bond length
- as you move to the right of the periodic table, the bond lengths get smaller
- C-C is longer than C-O
define constructive inference
- bonding interaction
- two things combine to create something bigger
- stable, low energy
- denoted as sigma
define destructive inference
- antibonding interaction
- two things combine and cancel out
- unstable, high energy
- denoted as sigma *
