Chapter 3: Bonding And Chemical Interactions Flashcards
What is the octet rule?
The octet rule states that an atom tends to bond with other atoms so that it has eight electrons in its outermost shell, thereby forming a stable electron configuration similar to that of the noble gases.
What are the three ways to remember exceptions to the octet rule?
Incomplete octet: elements that are stable with fewer than eight electrons in their valence shell. Include hydrogen (stable with two electrons), helium (2), lithium (2), beryllium (4), boron (6). Elements in group 2 (like beryllium) and group 13 (like boron) are most likely to exhibit incomplete octets.
Expanded octet: any element in period three and greater can hold more than eight electrons. Phosphorus (10), sulfur (12), chlorine (14), and many others.
Odd number of electrons: Any molecule with an odd number of valence electrons cannot distribute those electrons to give eight to each atom. Nitric oxide, for example, has seven valence electrons.
What is an ionic bond?
Iconic bonding is when one or more electrons from an atom with low ionization energy (typically a metal), are transferred to an atom with high electron affinity (typically a non-metal). The resulting electrostatic attraction between opposite charges is what holds the ions together.
what is covalent bonding?
Covalent bonding is when an electron pair is shared between two atoms, typically nonmetals, that have relatively similar values of electronegativity.
What is a nonpolar covalent bond, what is a polar covalent bond, and what is a coordinate covalent bond?
A nonpolar covalent bond happens if the electron pair is shared equally.
A polar covalent bond happens if the parish shared unequally.
A coordinate covalent bond happens if both of the shared electrons are contributed by only one of the two atoms.
Describe the atomic differences between ionic and covalent compounds.
Ionic bonds formed between ions and involve gain or loss of electrons. Covalent bonds occur when electrons are shared between atoms.
Which periodic trend determines whether a covalent bond, polar or nonpolar?
The polarity in a covalent bond is determined by differences and electronegativity between the two atoms involved.
What do atoms that lose electrons become?
Atoms that lose electrons become cations (+).
What are atoms that gain electrons become?
Atoms that gain electrons become anions.
For an electron transfer to occur, what must the difference in electronegativity be on the Pauling scale?
In order for an electron transfer to occur, and thus create an ionic bond, the difference in electronic negativity must be greater than 1.7.
What two classifications of atoms typically form ionic bonds?
The two classifications of atoms that typically form ionic bonds are metals and nonmetals. For example, alkali and alkaline earth metals (groups I and IIA, or groups 1 and 2) readily for ionic bonds with the halogens of group VIIA (group 17).
The atoms of the active metals loosely hold onto their electrons, whereas the halogens are more likely to gain an electron to complete their valence shell.
What are the characteristic physical properties of ionic compounds?
The characteristic physical properties ionic compounds are:
High melting point
High boiling point
Dissolve readily in water and other polar solvents
Good conductors of electricity in molten or aqueous state
In the solid state the ionic constituents of the compound for a crystalline lattice (minimize repulsive forces)
Large electronegativity differences between the ions
Why do ionic bonds tend to form between metals and nonmetals?
Metals lose electrons because they have low ionization energies (high ionization E means it’s takes a lot of E to remove an e-), while nonmetals gain electrons because they have high electron affinities. These processes are complementary, leading to the formation of an ionic bond.
Regarding single, double, and triple covalent bonds, talk about the comparative bond length and bond strength among them.
Single covalent bonds are the longest and weakest.
Double covalent bonds are in the middle of both length and strength.
Triple covalent bonds are the shortest and the strongest of the three.
What is bond length?
Bond length is the average distance between the two nuclei of an atom in a bond. As the number of shared electron pairs increases, the two atoms are pulled closer together, resulting in a decreasing bond length.
What is bond energy?
Bond energy is the energy required to break a bond by separating its components into their isolated, gaseous atomic states. The greater the number of pairs of electron shared between the atomic nuclei, the more energy is required to break the bonds holding the items together.
What is polarity and when does it occur in a molecule?
When atoms come together in covalent bonds, they must negotiate the degree to which the electron pairs will be shared. Polarity occurs when two atoms have a relative difference in electronegativities between 0.5 and 1.7 on the Pauling electronegativity scale.
When does a nonpolar covalent bond occur?
A nonpolar covalent bond occurs when atoms that have identical or nearly identical electronegativities (0.5 or less) share electron pairs.
What are the seven common diatomic molecules?
H2, N2, O2, F2, Cl2, Br2, and I2.
It’s easy to remember there are seven of them, because most of them are in Group VII (F, Cl, Br, and I).
When is the range of electronegativities for nonpolar bonds, polar bonds, and ionic bonds?
The range of electronegativities for:
Nonpolar bonds is zero to 0.5
Polar bonds 0.5 to 1.7
Ionic bonds 1.7 and above
The dipole moment of the polar bond or polar molecule is a vector quantity given by what equation?
p=qd
p is the dipole moment
q is the magnitude of the charge
d is the displacement vector separating the two partial charges
The dipole moment vector is represented by an arrow, pointing from the positive to the negative charge and is measured in Debye units (coulomb-meters)
What is a coordinate covalent bond?
A coordinate covalent bond happens when both of the shared electrons originated on the same atom. Once a coordinate covalent bond forms, it is indistinguishable from any other covalent bond. The distinction is only helpful for keeping track of the valence electrons and formal charges.
What is Lewis acid? What is the Lewis base? Provide a classic example of a Lewis acid base reaction.
A Lewis acid is any compound that will accept a loan pair of electrons, while a base is any compound that will donate a pair of electrons to formal covalent bond.
Individual atoms can be considered Lewis acid and bases.
A classic example of a Lewis acid-base reaction is the interaction between boron trifluoride (BF3) and ammonia (NH3), where ammonia acts as the Lewis base (electron pair donor) and boron trifluoride acts as the Lewis acid (electron pair acceptor), forming a coordinate covalent bond between the boron atom and the nitrogen atom.
Lewis symbols of the elements in the second period of the periodic table. This is not a question, it is an example of atoms demonstrated in a Lewis structure.
What are the five steps for drawing a Lewis structure?
Draw out the backbone of the compound, in general, the least electronegative atom is the central atom.
Count all the valence electrons of the atoms. The number of valence electrons of the molecule is the sum of the valence electrons of all atoms present.
Draw single bonds between the central atom and the atoms surrounding it. Each single bond corresponds to a pair of electrons.
Complete the octet of all the atoms bonded to the central atom, using the remaining valence electrons left to be assigned.
Place any extra electrons on the central atom. If the central atom has less than an octet, try to write double or triple bonds between the central and surrounding atoms using loan pairs on the surrounding atoms.
Example using HCN:
How would you calculate the formal charge of the neutral nitrogen atom of [NH4]+?
Nitrogen is in Group VA, so it has five valence electrons. The nitrogen has four bonds, one to each each hydrogen, meaning it has eight bonding electrons and non-bonding electrons.
V=5, Nbonding=8, Nnonbonding=0
FC=5-0-0.5(8)=+1
Formal charge of the nitrogen is +1.
You can also use logic to determine the formal charge. The nitrogen has four bonds in the NH4+ molecule, meaning that the end has four valence electrons in the molecule. And it’s normal state, and has five valence electrons thus, nitrogen has fewer electrons than its normal state, and a +1 charge.
What are resonance structures?
Resonance structures demonstrate the same arrangement of atoms but differ in the specific placement of electrons.
A good example would be SO2, which has three resonance structures
Example from the book. Write the resonance structures for [NCO]-
When seeing a Lewis structure with a central atom that has more than four bonds, should it be discounted? Why or why not?
When seeing a Lewis structure with a central atom with more than four bonds, do not immediately discount it as elements in period three or beyond can take on more than eight electrons in their valence shells. These electrons can be placed into orbitals of the d subshell, and as a result, atoms of these elements can form more than four bonds.
Summarize the electronic geometry as predicted by VSERP theory with regions of electron density from 2 to 6. (What are the electronic shapes of a molecule around the central atom given different regions of electron density)?
Predict the electrical and molecular geometry of NH3.
The molecular geometry will be pyramidal.
Predict the geometry of CO2.
What is the difference between electronic geometry and molecular geometry?
What is the electronic and molecular geometry of CH4, NH3, and H2O?
Electronic geometry, describes the spatial arrangement of all pairs of electrons around the central atom, including both the bonding and the loan pairs.
Molecular geometry describes the spatial arrangement of only the bonding pairs of electrons.
CH4 electron geometry: tetrahedral, molecular geometry tetrahedral.
NH3 electron geometry is tetrahedral, molecular geometry is pyramidal.
H2O electron geometry is tetrahedral, molecular geometry is bent/angular.
Can polar molecules be nonpolar? Why or why not?
Polar molecules can be nonpolar if their net dipole moment, the sum of all the dipole vectors, is zero. Such as in the case of carbon tetrachloride.
What is the sigma bond, what is a pi bond?
When orbitals overlap head to head, the resulting bond is a sigma bond. Sigma bonds allow for free rotation about their axis because the electron density of the bonding orbital is a single linear accumulation between the atomic nuclei.
When the orbitals overlap in such a way that there are two parallel electron cloud densities, a pi bond is formed. Pi bonds do not allow for free rotation because the electron densities of the orbitals are parallel and cannot be repositioned in such a way that allows continuous overlapping of the clouds of electron densities.
Draw the Lewis dot structure for the carbonate ion (CO3 2-) and its two other resonance structures. What is it electronic and molecular geometry?
What are dipole dipole interactions and how does their strength compared to the other two intermolecular forces?
Dipole dipole interactions are the result of polar molecules tending to orient themselves in such a way that the oppositely charged ends of the respective molecule dipole are closest to each other. These interactions are in the middle strength wise between London, dispersion forces and hydrogen bonds.
Present in the solid and liquid phase, these interactions become negligible in the gas phase because of the significantly increased distance between gas particles. Polar species have higher melting points and boiling points than nonpolar species of comparable molecular weight due to the dipole dipole interactions.
What are hydrogen bonds and how does their strength compared to the other intermolecular forces?
Hydrogen bonds are specific unusually strong form of dipole dipole interactions that may be intra or intermolecular. When hydrogen is bonded to one of three highly electronegative atoms: nitrogen, oxygen, or fluorine, the hydrogen atom carries only a small amount of the electron density in the covalent bond. This causes the bonded hydrogen atom to essentially act as a naked proton.
Substances that display hydrogen bonding tend to have unusually high boiling points compared to compounds of similar molecular weights that do not exhibit hydrogen bonding.
