AP Chem Test 2 (10/05/2020)
Explain why it is harder to break some bonds.
Bond enthalpy is the heat required to break one mole of a covalent bond to produce individual atoms. A super short bond is weak because of repulsion but a super long bond is weak because of distance.
What two properties of a bond are illustrated in a graph of potential energy versus bond distance? How are they indicated?
Bond length and bond energy are indicated at the minimum of the potential energy-bond distance graph.
What does bond order indicate?
Bond order is the number of chemical bonds between a pair of atoms and indicates the stability of a bond.
BF3 is nonpolar while NF3 is polar. Explain why.
Both BF and NF bonds are polar. However, NF3 is tetrahedral and has a lone pair which makes the electron distribution asymmetrical. BF3, however, is trigonal planar and the electron distribution is symmetrically arranged making BF3 nonpolar.
Rank bonds based on polarity or dipole moment
C-O vc C-Cl, C-O because more electronegativity. C-N and C-F, C-F. Use electronegative trend.
Explain why the carbon-oxygen bond length in CO32 - is greater than the carbon-oxygen bond length in CO2.
CO32- has sp2 hybridization while CO2 has sp hybridization. sp has 50% s character while sp2 has 33.3% s character. Since the s orbital sits closer to the nucleus, the greater the s character, the smaller the bond length.
How can Coulomb's law be used to explain increasing bond strength of an ionic compound in terms of the nuclear distance between each ion?
Coulomb's Law indicates that the force of attraction between oppositely charged particles is inversely proportional to the square of the distance between them. Larger ions cannot get as close to each other as ions with smaller atomic radii, thus, the larger the radii, the smaller the Coulombic force between them.
How can Coulomb's law be used to explain increasing bond strength of an ionic compound in terms of the charge of each ion?
Coulomb's Law indicates that the greater the charge, the greater the force of attraction between oppositely charged particles. The greater the charge of each ion, the greater the force of attraction between them.
The bond angle of CH4, NH3, and H2O decreases. Explain why.
Each molecule is tetrahedral. Lone pairs are larger than bonds and cause atoms on the central to move closer together in a molecule. NH3 has one lone pair and H2O has two lone pairs.
How can Coulomb's law be used to predict the electronegativity of an element?
The Coulombic attraction is inversely proportional to the size of the charged particle and directly proportional to the charge of the element. Atoms with larger atomic radii will have weaker Coulombic attractions and thus will have smaller electronegativities.
How can the electron configuration of an element be used to predict the electronegativity of an element?
The Coulombic attraction is inversely proportional to the size of the charged particle. The greater the number of shells, as seen in the electron configuration, the smaller an element's Coulombic attraction to another particle will be.
Use Coulumbs law to determine the strength of ionic attractions (melting points)
The larger the charge, the greater the attraction which equals a higher melting point (- vs 2-) 2-
In a polar bond, which atom is the electron more attracted to, the least electronegative atom or the more electronegative atom? Justify your answer in terms of electronegativity.
The more electronegative atom attracts the electron most. Electronegativity is the ability of an atom to pull electron density in a covalent bond towards itself. Thus the more electronegative the atom, the more it can draw the electron towards itself.
What influences bond length?
The size of the atoms that make up the covalent bond and the number of electron pairs that are shared. The larger the atomic radii, the longer the bond must be. The more electron pairs that are shared, the shorter the bond will be.
Rank molecules based on polarity or dipole moment
Use shapes
Definition of lattice energy
a measure of the energy released when ions are combined to make a compound, the more columbic attraction, the more energy released.
Define dipole
a molecule is a separation of charge within a molecule caused by asymmetric distribution of electron density. It results in one end of a molecule having more electron density around it and is thus a partially negative end. The other end is somewhat electron deficient and is thus a partially positive end.
Ionic solids
brittle, high mp, conducts electricity when dissolved because IONS can move
Metallic solids
ductile, high mp, conducts electricity cause ELECTRONS can move
Covalent network solids
hard, highEST mp, poor conductors
Use electronegativity to determine ionic or covalent character of a bond
less polar is less ionic (more covalent) more polar is more ionic (less covalent)
sp
linear 180
What relative size of metallic atoms would makea substitutional alloy?
made of atoms that have similar atomic radii.
Describe bond lengths in a resonance structure (CO2^3-)
more charges or more multiple bonds equals a stronger bond. A triple bond is going to be closer to the left whereas a single bond will be closer to the right.
Define dipole moment
occurs when there is a separation of charge. In a molecule this arises asymmetric distribution of electrons around an atom that results from differences in electronegativity and/or lone pairs. The dipole moment is a measure of the polarity of the molecule. Dipole moments arise from differences in electronegativity.
sp3d2
octahedral 90 square pyramidal 89 square planer 90
Number of sigma bonds and pi bonds
single - one sigma double - one sigma one pi triple- one sigma two pi
Determine strongest covalent bond based on number of orbital overlaps
single bond, double bond, triple bond
Covalent molecules
soft, low mp, poor conductors
sp3
tetrahedral 109.5 trigonal pyramidal 107.5 bent 105.5
Define electronegativity
the ability of an atom to pull electron density in a covalent bond towards itself.
VSEPR theory
theory that determines molecular shape by orientating electron domains as far away from each other as possible in order to minimise repulsion.
sp3d
trigonal bipyramidal 90, 120 -1 = seesaw 89, 119 -2 = t shape 88, 118
sp2
trigonal planer 120 bent 118
Formal Charge
valance electrons - dots - lines When the formal charge of two molecules is the same, the molecule that assigns the negative formal chrtge to the more electronegative element is correct
Determine strongest covalent bond based on bond length
(down) the shorter the bond, the stronger (across) smaller the atom
Ionic Bond
1 nonmetal and 1 metal
Metallic
2 metals
Covalent bond
2 nonmetals
Does it take more energy, less energy, or the same amount of energy to break apart two ions with a large internuclear distance compared to small internuclear distance. Explain your reasoning.
A smaller internuclear distance would require more energy to break apart ions of opposite charge. A smaller internuclear distance contributes to a higher Coulombic attraction since the force of attraction between oppositely charged particles is inversely proportional to the square of the distance between them.
Describe the features of a molecule that is polar
Asymmetrical distribution of electron density. Has a permanent dipole meaning one end of the molecule has greater electron density around it and is partially negative as a result. The other end is slightly electron deficient and is partially positive as a result.
A nonpolar covalent bond is made of elements with similar electronegativities. Explain why the bond is nonpolar in this instance.
Atoms with similar electronegativities have similar abilities to draw electron density towards themselves. There would be equal or near equal sharing of the electron density and thus no dipole will be established. The bond is therefore nonpolar.
What relative size of metallic atoms would make an interstitial alloy?
Made of atoms with a much smaller radii than the other atoms' radii.
Describe the features of a molecule that is nonpolar
Symmetrical distribution of electron density. Molecule does not have a permanent dipole.
In terms of molecular geometry, account for the fact that the CF4 molecule is nonpolar, whereas the SF4 molecule is polar.
The CF4 molecule is tetrahedral. The molecule has a symmetrical distribution of electron density and as a result is nonpolar. SF4, however, is see-saw geometry, which has an asymmetrical distribution of electron density and is thus polar.
