Chemistry Midterm Chapters 2 & 3 Flashcards
What is EFFECTIVE NUCLEAR CHARGE? (Z*)
The net positive charge experienced by a valence electron in an atom by the nucleus.
How can you calculated the effective nuclear charge?
= number of protons (positive)- number of core electrons (shield)
How much charge does the valence electron encounter?
Not full charge of nucleus (protons) because they are shielded by the core electrons, so some charge is taken
How does effective nuclear charge change as you move LEFT to RIGHT? Why?
same number of core electrons but increased number of protons = more + charge in the nucleus = HIGHER Z*
What is the effect of more nuclear charge?
Increased attractive force between valence electrons and nucleus
What is ATOMIC RADII?
1/2 the length of a bond formed by 2 atoms of the same element
How is IONIC RADII measured?
estimated from crystal lattice because two ions normally don’t form a bond
What is the periodic trend of ATOMIC RADII in rows? Why?
Decreases from LEFT to RIGHT;
more protons = more + charge = more attraction between nucleus and electrons = pulling of electrons closer to electrons
How are ATOMIC RADII and Z* related?
inversely proportional
What is the periodic trend of ATOMIC RADII in groups? Why?
Increases from UP to DOWN;
More electrons occupy higher orbitals
How are the shielding properties of d and f block core electrons? How does this change atomic radii?
poor shielding properties; some elements (ex. Ga) are smaller because there is more attraction between nucleus and valence electrons
How are atomic radii and BOND LENGTH trends related?
directly proportional
How do single, double, and triple bonds compare? Why?
more bonds = shorter bond length
–> more electrons pulling nuclei together
How do cations compare with their neutral parent atom? Why?
electrons removed = more attraction between nucleus and fewer elections = SMALLER than parent atom
How do anions compare with their neutral parent atom? Why?
electrons added = electrons take higher orbital clouds = less attraction between nucleus and electrons = LARGER than parent atom
What are dications? How do they compare in ionic size with monocations?
Dications: 2+ charge
Monocations: 1+ charge
dications<monocations
–>more attraction btwn nucleus and e-
What are dianions? How do they compare in ionic size with monoanions?
Dianions: 2- charge
Monoanions: 1- charge
dianions>monoanions
–> higher orbitals = more space
How does ionic size compare for ISOELECTRONIC SPECIES?
largest is most negative (orbital cloud space)
smallest is most positive (attraction)
What is IONIZATION ENERGY?
minimum amount of energy required to remove a valence electron from the gas phase of an atom (always positive!)
What is FIRST IONIZATION?
first electron removed - most weakly bound
How does IONIZATION ENERGY change in successive removal of e-?
increases - more energy because subsequent electrons are more tightly attracted to nucleus
What is the periodic trend of IONIZATION ENERGY? Why?
INCREASES left -> right
–> higher Z* = more attraction
INCREASES bottom –> top
–> valence electrons are farther away = easy to overcome less attraction
Why is it easier to ionize oxygen than nitrogen?
oxygen has two half filled and one completely filled p orbital – fully filled orbital has more repulsion = easy to remove that electron (occurs for some other gap 16 elements too)
Why is it easier to ionize boron (5) than beryllium (4)?
boron has a p orbital – higher orbital is farther away (occurs for some other grp 13 elements too)
What is ELECTRON AFFINITY?
change in energy (enthalpy) when adding electrons
A(g) + e- –> A-(g)
What is delta H? When is it favourable? When is it not favourable?
Enthalpy - heat added or lost in a system
delta H>0 –> unfavourable - endothermic - heat absorbed
delta H,0 –> favourable - exothermic - heat released
What are the periodic trends of ELECTRON AFFINITY?
INCREASING: bottom –> top
INCREASING: left –> right
**more exothermic, H«0
What is ELECTRONEGATIVITY?
ability for an atom in a chemical bond to draw electron density to itself
How does ELECTRONEGATIVITY compare with ATOMIC RADII?
SMALLER atom = MORE ELECTRONEGATIVE
How does ELECTRONEGATIVITY compare with IONIZATION ENERGY?
directly related!
What are the periodic trends of ELECTRONEGATIVITY?
INCREASES: left to right (more attraction)
INCREASES: bottom to top (less attraction, larger atom)
How does electronegativity relate to reactivity?
If one atom is much more electronegative, there is a highly polarized bond and a greater bond strength
When does an IONIC BOND occur? What does this mean for the bonding valence electrons?
large difference of electronegativity between bonding atoms (~1.9). There is a COMPLETE transfer of e- from the lower to higher electronegative e-, creating an anion and a cation
What is the crystal lattice?
structure formed by Coulombic forces between anions (with multiple cations) and cations (with multiple anions) in the ionic bond in a SOLID STATE
What is the comparative melting point of crystal lattice ionic bond structures?
HIGH melting point because of very strong bond between anion and cation
What is Coulomb’s law? What is it used for?
Force = k(Q1*Q2)/r^2
used to measure attractive force between anions and cations
r is distance between anion and cation
Q1 and Q2 are the ion’s charges
What is the relationship between attractive force and ionic size?
smaller ionic size = shorter distance (r) = more attraction = more force required to break bonds = higher melting point
What are COVALENT bonds?
equal or unequal sharing of electrons
What is a POLAR BOND?
- type of covalent bond
- electronegativity different of 0.5-1.9
- slight positive charge on the less electronegative atom and slight negative charge on more electronegative atom (DIPOLE MOMENT)
What is a DIPOLE MOMENT?
- occurs for polar bond
- pull of electrons from + to - side
- expressed by arrow (vector)
- magnitude increases when electronegativity difference is greater
What is a NONPOLAR BOND?
- type of covalent bond
- less than 0.5 electronegative difference
- no permanent dipole moment
What do the + and - in a Lewis structure indicate?
Formal charge to show # of valence electrons - # of electrons owned in a bond
How does the FORMAL CHARGE compare to the OVERALL CHARGE of a species?
formal charge sum = overall charge
What is the OCTET RULE? When does it apply?
elements “owning” a maximum of 8 electrons; C, N, O, F, and Ne because they have the orbitals 2s and 2p
What is the EXPANDED OCTET?
When an element can “own” more than 8 electrons; occurs for elements with higher orbitals (3s+)
How can you determine the best Lewis Structure for an atom?
- smallest formal charge
- formal charge is on the most electronegative species
- least electronegative is the central atom
What are RESONANCE structure?
structures that are correct and different only in electron position and bonds
What is a RESONANCE HYBRID? Where is the charge and bonds?
- the actual structure of molecules; combination of possible resonance structures
- charge is delocalized and bonds are identical (shown by solid and dashed lines)
What is BOND ORDER? How is it calculated for resonance hybrids?
single bond - 1
double bond - 2
triple bond - 3
average bond order: sum of bond orders/number of bond orders
–> single bond + double bond/2 = 1.5
What are LINE DIAGRAMS? What do they represent?
used for complex organic molecules
- each corner or end is a carbon atom with hydrogen atoms
What are the assumptions of VSEPR theory?
- pairs of bonding or nonbonding electrons occupy the valence shell of the CENTRAL atom
- Electron pairs (regions of electron DENSITY) REPEL each other and position themselves to have the maximum amount of separation with other pairs
- Lone pairs have MORE REPULSION than bonding pairs
- Multiple bonds are treated as SINGLE regions of electron density
What is AXE notation?
A=central atom
Xm –> m = number of atoms bonded to central atom
En –> n = number of lone PAIRS on central atom
m+n = total number of regions of electron density around central atom
What is the difference between ELECTRONIC ARRANGEMENT and MOLECULAR SHAPE?
electronic arrangement depends on lone pairs and bonding pairs
–> where the electrons are around the central atom
molecular shape depends on BONDING PAIRS only
What is the electronic arrangement of 2 regions of electron density?
LINEAR
What is the electronic arrangement of 3 regions of electron density?
TRIGONAL PLANAR
What is the electronic arrangement of 4 regions of electron density?
TETRAHEDRAL
What is the electronic arrangement of 5 regions of electron density?
TRIGONAL BIPYRAMIDAL
What is the electronic arrangement of 6 regions of electron density?
OCTAHEDRAL
What is the angle between atoms in a LINEAR molecular shape? What is the AXE notation?
180; AX2E0
When is the electronic arrangement the same as the molecular shape?
NO LONE PAIRS around the central atoms
What is the angle between a TRIGONAL PLANAR molecular shape? What is the AXE notation?
120; AX3E0
What is the molecular shape when there is 2 BONDING pairs and 1 LONE pair?
BENT; AX2E1
How many regions of electron density does a BENT molecular shape have?
3
What is the angle between atoms in a BENT shape? Why?
slightly less than 120 because the lone pair repels the bonding pairs, pushing the bonding pairs closer together
What is the angle between TETRAHEDRAL molecular shape? AXE?
109.5; AX4E - 4 bonding and 0 lone pairs
What is the molecular shape with 3 BONDING pairs and 1 LONE pair?
TRIGONAL PYRAMIDAL - AX3E1
What is the angle between atoms in TRIGONAL PYRAMIDAL? Why?
less than 109.5; lone pair repulsion
What is the molecular shape with 2 BONDING pairs and 2 LONE pairs? AXE? ANGLE?
BENT; AX2E2; 105 - more lone pair repulsion
What is an example of AX2E2?
Water!
What does the TRIGONAL BIPYRAMIDAL molecular shape look like?
linear + trigonal planar: triangular plane bonds have 120 degrees between - EQUATORIAL - and the perpendicular bonds make 90 degrees - AXIAL
5 regions of electron density
What is the molecular shape of 4 BONDING pairs and 1 LONE pair? Which position is the lone pair in? Why? Angle?
SEESAW - lone pair is an equatorial electron density - most space - <90 and <120
What is the molecular shape of 3 BONDING pairs and 2 LONE pairs? Which position are the lone pairs in? What does the remaining atoms look like?
T-SHAPE - lone pairs are in equatorial plane - the remaining atoms are in one plane
–> <90
What is the molecular shape of 2 BONDING pairs and 3 LONE pairs? Which position are the lone pairs in?
LINEAR - equatorial plane consists of all lone pairs - three remaining atoms are in 1 plane - 180
What does the OCTAHEDRAL molecular shape look like?
4 equatorial bonds (square plane) 2 axial bonds (perpendicular)
–> ALL 90 degrees
What is the molecular shape of 5 BONDING pairs and 1 LONE pair? Which position is the lone pair in?
SQUARE PYRAMIDAL - lone pair removed from anywhere
–> <90
What is the molecular shape of 4 BONDING pairs and 2 LONE pairs? Which position are the lone pairs in?
SQUARE PLANAR - axial lone pairs removed to maximize space
What are the representations of symbols in line-wedge notation?
line - in the plane of the page
wedge - towards you out of the page
dashed - into the page
What are polar and non polar MOLECULES?
polar - nonzero net dipole movement
non polar - zero net dipole movement
How can you determine if a molecule is polar or non polar?
see if the dipole movements on each bond cancels out
–> symmetrical = non polar
What are INTERMOLECULAR FORCES?
NON-COVALENT interactions between two or more molecules
What are van de Waals forces?
dipole-dipole interactions and dispersion
What are DISPERSION forces?
WEAK interactions between molecules caused by MOMENTARY changes in electron density
–> ~ 0.05-10 kJ/mol
How do DISPERSION forces occur?
one molecule temporarily has one atom having more of the electron density –> temporary dipole – another molecule does the same –> these 2 molecules have dispersion forces
Which compound exhibits DISPERSION forces?
ALL!
What kind of intermolecular forces do NONPOLAR molecules exhibit?
DISPERSION - non polar = equal electron sharing = weak interactions with other non polar molecules
How are SURFACE AREA and DISPERSION FORCES related?
more surface area = more attractive force between 2 molecules = stronger intermolecular force
What are DIPOLE-DIPOLE INTERACTIONS?
ATTRACTIVE forces between PERMANENT dipoles of two POLAR MOLECULES
–> 5-25 kJ/mol
How do dipole-dipole interactions occur?
partial negative dipole of one molecule aligns with partial positive dipole of the other molecule
How do dipole-dipole interactions compare with dispersion forces?
dipole-dipole interactions are MUCH STRONGER (permanent vs. temporary dipoles in molecules)
What is HYDROGEN BONDING?
a HYDROGEN covalently bonded to a highly electronegative atom (F, O, N) is attracted to a LONE electron pair on ANOTHER electronegative atom of a DIFFERENT molecule
–> 10-40 kJ/mol
Can a hydrogen bonded to a carbon participate in hydrogen bonding?
No! C-H bond is not sufficiently polar – hydrogen is not positive enough to be attracted to a different electron
How do the strengths of hydrogen bonds compare with dipole-dipole?
Hydrogen bonds are much STRONGER!
How does the strength of hydrogen bonds relate to boiling point?
High boiling points are the result of strong hydrogen bonds. It requires a lot of heat to break these bonds and create gaseous state
How many hydrogen bonds can a single water molecule have?
4 - 2 with hydrogens attracted to other water molecules and 2 with other water molecules attracted to the oxygen
What are IONIC INTERACTIONS?
electrostatic forces between PERMANENTLY charged IONS
–> >400kJ/mol
How does the strength of IONIC interactions compare with intermolecular forces?
MUCH STRONGER than all types of intermolecular forces
Dispersion < dipole-dipole < hydrogen bonding < ionic bonds
What is BOILING POINT?
TEMPERATURE of a substance when VAPOUR PRESSURE = ATMOSPHERIC PRESSURE
How does intermolecular force affect boiling point?
stronger intermolecular force = higher boiling point = more energy needed to break the bonds
How does molecular mass impact boiling point? Why?
more molecular mass = more SA = higher boiling point
–> more intermolecular forces to break
How does surface area impact boiling point?
more SA = less branching = higher boiling point
How does MELTING POINT compare to BOILING POINT?
similar trend! SYMMETRY/PACKABILITY is more important than SA
–> molar mass changes melting point
–> packing ability of multiple molecules
How does symmetry affect MELTING POINT?
more symmetrical = more compact = lower melting point
What is the difference between CIS and TRANS on the structure?
trans - carbons are on opposite sides of the double bond
–> not naturally found
cis - carbons are along the same axis on the double bond
–> naturally found
What are monounsaturated fatty acids?
What are polyunsaturated fatty acids?
1 double bond (cis or trans)
multiple double bonds (cis or trans)
What is a saturated fat?
No carbon-carbon double bond = higher melting point than unsaturated
What is HYDROGENATION?
takes a cis bond (alkine) and adds two hydrogen –> alkane (saturated bond)
–> some of the cis turns into trans through isomerization
How can you make trans fatty acid if they are not naturally occurring?
–>Hydrogenation
–>Heating cis to a high temperature which breaks the double bond, rotates it, and reforms the bond
What are the VALENCE BOND THEORY principles?
- covalent bonds between 2 nuclei are formed when EACH atom contributes 1 valence electron to a COMMON ORBITAL.
–> the common orbital is an OVERLAP of atomic orbitals that has 2 electrons of OPPOSITE SPIN - The overlap causes electrons to be LOCALIZED (limited) to the area between 2 nuclei
- Element of the second on higher numbered rows can form bonds using HYBRID atomic orbitals
What is a SIGMA BOND?
single bond formed by HEAD-ON overlap of orbitals in a space region
What is a head on overlap? What shape does this produce?
sigma bond orbital formed where the electrons and nuclei lie on the same axis.
–> sigma bonds are cylindrically similar about the internuclear axis
What is HYBRIDIZATION?
mixing of pure atomic orbitals to produce a “hybrid orbital” that is consistent with the geometry of experimentally observed bonds
What is sp3 hybridization?
1 s orbital and 3 p orbitals used to form 4 equal energy orbitals in the tetrahedral electron arrangement with 109.5 degrees between the orbitals
–> for ALL tetrahedral ELECTRON ARRANGEMENT
Where do lone pairs go in hybridized orbitals?
Lone pairs can be contained in a hybrid orbital
What is sp2 hybridization?
1 s and 2 p orbitals used to form 3 equal energy orbitals in TRIGONAL PLANAR arrangement with 120 degrees between the orbital
Where is the remaining p orbital in sp2 hybridization?
remains open for pi bond perpendicular to trigonal plane
What is sp hybridization?
1s and 1 p orbital used to form 2 equal energy orbitals in LINEAR arrangement with 180 degrees between orbitals
–> remaining 2 p orbitals are perpendicular to each other and remain open for double or triple bonds
What is sp3d hybridization?
1 s, 3 p, and 1 d orbital form 5 equal energy orbitals in the TRIGONAL BIPYRAMIDAL electron arrangement
–> four remaining d orbitals
What is sp3d2 hybridization?
1 s 3 p, and 2 d orbitals form 6 equal energy orbitals in OCTAHEDRAL ELECTRON ARRANGEMENT
–> 3 remaining d orbitals
How does the number of hybrid orbitals compare to the number of bonding and nonbonding electron pairs on the central atom?
of hybrid orbitals = # of bond e- + # lone pairs
How do multiple bonds get represented in hybridization?
double bonds, triple bonds, single bonds, and lone pairs are each ONE REGION of electron density
In sp2 hybridization, how does a double bond form?
pi bonds form with the REMAINING P ORBITALS from two atoms in SIDE-ON overlap 90 degrees to the plane
What does SIDE ON overlap limit for an atom?
the atom cannot rotate
In sp hybridization, how does a triple bond form?
1 sigma + 2 pi bond from the 2 REMAINING P ORBITAL from two atoms in SIDE ON overlap 90 degrees to the plane of both orbitals
What are the deficiencies of VB Theory?
- electrons are localized, but resonance lewis structures shows that electrons are delocalized and bonds sometimes have partial charges
- Relative energies of electrons are unknown
- Fails to explain paramagnetic and diamagnetic molecules
What are PARAMAGNETIC and DIAMAGNETIC MOLECULES?
Paramagnetic - molecule that contains at least one unpaired electron and are attracted to a magnetic field - must have a net spin
Diamagnetic - molecule that contains no unpaired electrons and are not attracted to a magnetic field - zero net spin
What is the MOLECULAR ORBITAL theory?
focuses on wave behaviour of electrons and the molecule as a whole rather than localizing electrons with specific bonds and atoms
According to MO theory, how are two 1s orbitals (H + H) combined if there are constructive (in phase) waves?
- a new wave function is formed containing the 2 1s orbitals (H2)
- increases electron density between 2 nuclei
- when you look down an atom, it is spherical - orbital spans the whole molecule
- σ1s bonding MO (subscript 1s shows the atomic orbitals used to form the bonding MO)
According to MO theory, how are two 1s orbitals (H + H) combined if there are destructive (out of phase) waves?
- a new wavefunction is formed containing the 2 is orbitals
- decreases electron density between 2 nuclei
- creates a new NODE
- σ*1s anti bonding MO
What is the relative energy of σ1s orbital compared to the 1s atomic orbital? Is the orbital occupied?
STABILIZED –> lower in energy
–> orbital is occupied by both electrons
What is the relative energy of σ*1s orbital compared to the 1s atomic orbital? Is the orbital occupied
DESTABILIZED –> higher in energy
–> orbital is empty
What are the principles of MO Theory?
- # of MOs formed = total # of atomic orbitals combined
- Bonding MOs are lower in energy than the atomic orbitals from which they are formed. Antibonding MOs are higher in energy (has a node) than the atomic orbitals from which they are formed
- MOs follow the Aufbau principle (σ1s filled first, then σ*1s), Pauli exclusion principle, and Hund’s rule
- MOs are formed most effectively when the originating atomic orbitals are close in energy (same element)
What are Highest Occupied Molecular Orbitals?
HOMO; highest energy MO with one of more electrons
What are Lowest Unoccupied Molecular Orbitals?
LUMO; lowest energy MO with no electrons
How does attraction between atoms in a molecule differ with bonding and anibonding MOs? What does that mean for the stability/existence of any molecule?
bonding = electrons increases attraction between the atoms in the molecule
anti bonding = electrons decreases attraction between the atoms in the molecule
–> there must be more bonding than anibonding MOs
How is BOND ORDER defined by MO theory?
= [(# of bonding e-) - (# of anti bonding e-)]/2
How is bond order and stability related?
higher bond order = more stability
How can paramagnetism be predicted?
Through ground state electron configuration (see if there are unpaired electrons)
How many MOs are formed in second row electrons with n=2?
8; 2s = 2 + 2p = 6
What happens when creating 2p MO by overlapping?
Only one axis (one lobe from each) can have SIGMA overlapping
–> the other orbitals overlap with π BONDS (side ways) because the lobes are 90 degrees from each other
What happens during constructive interference of two 2p (one from each atom) along the axis?
The same phases overlap creating three regions of alternating phase along the axis and no nodes
–>σ2px - bonding MO
What happen in destructive interference of two 2p (one from each atom) along the axis?
Opposite phases overlap creating four regions of alternating phase along the axis and one node in the middle
–> σ*2px anti bonding MO
What is the shape of sigma bonds?
Symmetrical about the bond axis; look down one atom it is spherical
What happen in constructive interference of two 2p in π bond?
bonding –> two of the same phase add at the top an two in the same phase combine at the bottom
What happens in destructive interference of two 2p in π bond?
anti bonding –> opposite phases overlap sideways
–> creates two opposing phase at the top and two opposing phase at the bottom
–> a new node from cancellation that is 90 degrees from sigma bond
How do the relative energies of second period MOs compare?
different for each molecule
–> π bonds are degenerate, but σ have different energies
Energy: 2sσ < 2s σ* 2pσ < 2pπ < 2p (atomic orbitals) < 2pπ* < 2pσ*
How do pi bonds and sigma bonds compare in energy?
sigma bonds are stronger = lower in energy (takes more energy to break bond)
pi bonds are weaker = higher in energy (doesn’t take much more energy to break bond)
How do pi bonds and sigma bonds compare in energy?
sigma bonds are stronger = lower in energy (takes more energy to break bond)
pi bonds are weaker = higher in energy (doesn’t take much more energy to break bond)
What is a HYDRATE?
crystalline solid compound that has a specific number of water molecules associated with it
What is an ANHYDROUS compound?
no water molecule bonded to compound
How is the mass percent of water determined?
sample heated to a constant mass and does not decompose
What is density? What does density depend on?
m/V (g/mL or g/L)
–> depends of temperature (solid, liquid and gas) and pressure (gas)
How can you find the mass of water removed? mass % of water removed from a hydrated salt?
mass of water removed = initial mass of sample - mass of sample after heated
mass % of water removed = mass of water removed/initial mass of sample x 100%
How does mass reading relate to temperature?
mass reading fluctuates if the substance is too hot because the mass is unstable
What is a coordination complex?
a CENTRAL METAL ION bonded to 2+ other groups
–> cationic, anionic, or neutral
What are LIGANDS?
groups attached to central metal ion in a coordination complex
What is a coordination compound?
NEUTRAL substance that contains a COORDINATION COMPLEX
What is LIMITING REAGENT?
the reagent that is used up first; once consumed, the reaction stops
What does the LIMITING REAGENT determine?
THEORETICAL YIELD – maximum amount of product that could be made
amount of excess reagent that remains
How can you determine the limiting reagent amount?
5B/3A = x mol B/1.23 mol A
–>compare limiting reagent with product (NOT EXCESS REAGENT)
What is the actual yield?
amount actually made in the laboratory; usually less than the theoretical yield
What is the % yield>
actual amount of product obtained/theoretical amount of product x 100
What does photosensitive mean?
substances that decompose in light
When does precipitate form?
Low solubility
