UNIT 2 REVIEW QUESTIONS

What is the purpose of a chemical bond?

The purpose of a chemical bond is to allow atoms to reach a more stable, lower energy state through the transfer or sharing of electrons. In general, the most stable state for an atom is having eight electrons in the outermost shell.

What are the common properties of an ionic solid? What factors affect these properties?

Common properties of ionic solids are low conductivity, and high boiling & melting points. The melting point of a ionic solid is affected by the charge of the ions and the size of the ions. THe greater the charge, the greater the force of attraction and therefore the higher the melting point. In the same way, the smaller the atoms the greater the force of attraction and the higher the melting point.

What is the sea of electrons model when talking about metals and alloys?

The positively charged cores, nucleus and core electrons, of metals are stationary while the valence electrons do not belong to any particular atom and are mobile. This allows for high conductivity among metals.

What is the difference between an interstitial alloy and a substitutional alloy?

Interstitial alloys form between atoms that have very different radii while substitutional alloys form between atoms with very similar radii.

Describe the relationship between single, double, and triple bonds as it relates to bond length and energy

The single bond has the largest length and lowest energy; the double bond is intermediate in length and energy; the triple bond is highest in energy and shortest in length

When does the bond length of a covalent bond occur? What factors affect the potential energy of a bond?

The bond length of a covalent bond occurs at the minimum potential energy. The minimum potential energy is affected by size of the atoms and number of bonds (both of which affect bond length). The smiler that the bonded atoms are the smaller their potential energy will be. Further, if the atoms are bonded by a triple or double bond, their potential energy will also decrease since those bonds are higher in energy and shorter.

What is a network solid and what are their properties? Examples?

A network solid is a molecule in which atoms are held together in a lattice of covalent bonds. They are poor conductors of electricity due to the electrons being localized, and have high melting and boiling points. Examples include quartz and diamond.

How well does each kind of bond conduct electricity in the different states: solid, liquid, aqueous, and gas?

Covalent compounds do not conduct electricity in any state because their electrons are localized and they do not dissociate into ions. Ionic compounds conduct electricity in the aqueous and liquid state because they dissociate into ions in the aqueous state and their electrons are free to move around in the liquid state. Metals and alloys conduct electricity in the solid and liquid state because their electrons are free to move between atoms.

What two factors determine the conductivity of an aqueous ionic compound?

The concentration of the compound will affect its conductivity as well as the number of ions it dissociates into. For example, NaCl at a 0.1M concentration will conduct less than NaCl at a 1 M concentration. Further, CaCl2 will conducit better than NaCl because it dissociates into three ions compared to two.

What are resonance forms?

Resonance forms are equivalent ways to draw the lewis diagram in which double bonds or lone pairs could be placed in different positions

How do you calculate the bond order of a molecule with resonance forms? What does the bond order signify?

You add the bond orders of each bond and divide by the number of resonance structures. The bond order represents the length and strength a bond or bonds in a molecules.

Which atoms are considered stable with an incomplete octet? Which atoms are able to have a expanded outer shell of up to 12 electrons?

Helium and Hydrogen are stable with 2 outer electrons and Boron is considered stable with 6 outer electrons. Any atom that has a d'subshell available can have a expanded octet; any atom from n = 3 or greater

How do you determine the more likely of multiple possible lewis structures?

To determine the more likely of multiple possible lewis structures you use the formal charges of the atoms. To calculate the formal charge you subtract the number of assigned electrons from the valence electrons. The less atoms with formal charges in an atom, the more likely it is to occur. Further, if there is a negative formal charge, it should be assigned to the more electronegative atom in the bond.