Flashcards in Bonding Deck (34):
What determines the physical properties of molecules-intermolecular forces or intramolecular forces?
Why is the formation of covalent bonds energetically unfavorable compared to that of ionic bonds?
Atoms of the covalent bonds have similar electronegativities, requiring more input of energy to form the bonds than the energy release upon their formation
What is the strength of the intermolecular forces of ionic bonded molecules and covalently bonded molecules? What effect does this have on their physical properties?
Ionic bonds have strong intermolecular forces due to electrostatic attraction between the ions. This confers a high melting and boiling point. In contrast, covalently bonded molecules have weak intermolecular forces resulting in low melting and boiling points
Can both ionic bonded and covalently bonded molecules conduct electricity?
Only ionic bonded molecules can conduct electricity. This can be done ONLY in the liquid and aqueous states.
Why do atoms form covalent bonds?
To complete their valence shell with 8 electrons
What differentiates between polar-covalent (partially ionic) and covalent?
Electronegativity differences between the two atoms. If the the difference is less than 1.5, its covalent. If its between 1.5 and 2.0 (greater than 2.0 is ionic) then it is polar covalent.
What are the two types of covalent bonds? Where is their electron density located?
Sigma bond's electron density is located in the internuclear region. Pi bond electron density are located above and below the internuclear region
What effect do bonding orbitals have on bond length?
Each atom undergoes hybridization of their valence electron orbitals to form a bond with another atom. The more s character that orbital has, the shorter the bonding orbital. The amount of s character is determined by now many bonding orbitals is required of the atom. The more atoms to which that atom is attached to, the less s-character it has since it must utilize the p-orbitals, extending the bond orbital due to the p-orbital dumbbell shape. Therefore, bond length is dependent on the orbital hybridization of the two atoms.
What must be true of the spin of electrons in order for electron densities to overlap during bonding?
The spins of the electrons must be the same
How does sharing of electrons confer bond length and strength?
The more electrons that are shared between atoms, the stronger the bond, and the closer the atoms are pulled together, resulting in decreased bond length. The rule is ENTIRELY depending on electron density.
How does subtstitution of one atom change bond strength between two atoms?
A substituted atom will create bond of lesser strength because of inductive effects, decreasing the electron density between the two atoms. Because bond strength is directly proportional to electron density, the less electron density confers a weaker bond
When drawing a lewis structure, what is characteristic about the central atom? What are the remaining steps to drawing a lewis structure
1. The central atom is the least electronegative atom
2. Count the number of valence electrons of all the atoms, for all of these will be involved in creating the overall molecular structure
3. Draw the single (sigma) bonds between the atoms. Sigma bonds are always the first bonds created (provides the molecular foundation)
4. Calculate the remaining valence electrons. Add the remaining electrons to the outer atoms - the outer atoms are more electronegative (see #1)
5. If the central atom does not meet octet rule, create double or triple bonds
What is the formal charge and how is it calculated?
Formal charge is the notation given to an atom that has more or less than the number of valence electrons it has during its isolated state.
Formal charge is calculated by subtracting the number of bonding and nonbonding electrons from the # valence electrons in its isolated state.
What is bond dissociation energy and what role does it play in determining bond stability and strength?
Bond dissociation energy is the energy required to to cleave a bond in a homolytic fashion. As bonds break and reform, energy is released. If the energy released upon the formation of new bonds is greater than the energy required to break the bonds, it is said that the molecule is more stable and stronger. A more stable and stronger bond will require more energy input to break in (greater bond dissociation energy).
What are the four main intramolecular features that determine the distribution of electron density in a molecule?
Resonance, inductive effects, steric hinderance, aromaticity. Because electron density determines the strengths of bonds, anything that changes the electron density between bonds affects the stability and strength of the bond.
What are the rules to forming the major resonance contributor?
1. All atoms obey octet rule
2. Minimize formal charge
3. Negative charge on most electronegative atom, positive charge on least electronegative atom
What is the primary difference between resonance and inductive effects in regards to electron density distribution?
Resonance delocalizes electron density through p-orbitals (pi bonds) whereas inductive effects does so through sigma bonds via electronegative atoms.
How does the inductive effect affect nucleophilicity/electrophilicity? Acidity/Basicity?
For a given atom, because its electron density is decreased, this decreases its nucleophilicity and increases its electrophilicity. A loss of electron density also increases its acidity since the proton is not being held as tightly due to electrostatics. This decreases basicitiy because the atom will be less likely to donate a pair of electrons since it has lost its density already
What is the acronym for electronegative atoms?
What two factors must be taken into consideration when analyzing the inductive effect?
Proximity and electronegativity
Steric hinderance follows what bonding repulsion principle?
Valence shell electron pair repulsion
What is Huckel's rule for aromaticity? What are the conditions which confer aromaticity
In order for a molecule to exhibit aromaticity stability, it must have 4n+2 **pi** electrons in a continuous overlapping ring of p-orbitals.
What are three types of covalent bonding?
Polar covalent, nonpolar covalent, and coordinate covalent
What is the valence shell electron pair repulsion theory?
Theory that explains the three-dimensional spatial arrangement of bonded atoms and lone pairs about a central atom based on the fact that nonbonding and bonding valence electrons orient themselves in such as way as to minimize their repulsion to the greatest extent
What is the primary factor that determines bond angles?
Electron pair repulsion
What are the four types of solids?
Ionic solids, network solids, metallic solids, molecular solids
How are each of the solids held together?
Ionic solids - lattice of electrostatic interaction (strongest)
Network solids - lattice of covalent bonds
Metallic solids - sea of electrons (conduction electrons)
Molecular solids - intermolecular forces (hydrogen bonding, dipole-dipole, London Dispersion)
What two solids have the same intramolecular and intermolecular forces
Ionic - electrostatic
Network - covalent
How do the melting and boiling points between solids differ?
Molecular solids have the lowest MP and BP since the forces that hold the molecules together are weaker. Molecular solids are usually liquids or gases at room temperature
How do ionic solids differ in melting and boiling point?
MP and BP for ionic solids are dependent primarily on the magnitude of the charges, and to lesser extent on the size
What determines the magnitude of the london dispersion force?
The amount of electrons it has
What is an intermolecular force?
weak electrostatic interactions between NEUTRAL molecules