AP Chem Unit 2 Study Guide

Chemical bond types

Metallic, ionic, and covalent

Lattice energy

The energy released when ions come together to form a lattice structure

Is lattice formation endothermic or exothermic?

Exothermic, meaning the sign would be negative

What impacts lattice energy in an ionic solid?

Ion size

• Larger ions will have a smaller lattice energy

• Smaller ions will have a larger lattice energy

Charge amount

• Higher charges have a higher lattice energy

Why do ionic solids form crystal lattice structures?

Like-like charge repulsion and opposite charge attraction (minimizes repulsion and maximizes attraction)

What is a chemical bond?

Explains the stabliity of molecules and behavior as a single unit (atoms are not free)

• Keep in mind that this is a HUMAN INVENTION used to explain what’s above

What characterizes the strength of a bond?

bond energy

What is the definition of bond evergy?

Energy needed to break one mole released when a mole of a specific chemical bond in gaseous state or energy released when a mole of bond is formed

In a single bond ____ electrons are shared

2

In a double bond ____ electrons are shared

4

In a triple bond ____ electrons are shared

6

Rank bond lengths of the three different types of bonds (single, double, triple)

single > double > triple

Single bonds have fewest shared electrons, meaning they would be more distant. 

As you upward in bonds I(double and triple), there are more shared electrons making them closer

Rank single, double, and triple bonds from greatest to smallest bond strength

triple > double > single

There are more electrons being shared with triple bonds, thus making the molecule much more difficult to break. Single bonds, however, are sharing less electrons, meaning they are much easier to overcome.

What is the difference in both strength between H and the halogens? Why does this happen?

The strength of the bond decreases as you go down the the periodic table (of halogens), as the size of the halogens increase from larger numbers of electron shells.

What do you notice about the strength of carbon-carbon single, double, and triple bonds? What could explain this?

The strength increases, since more energy is needed to break multiple bonds between the same atoms.

What do you notice about the strength of the bonds between two halogen atoms? What could explain this pattern?

They are low, since they are the same type of atom and have a similar electronegativity (similar grasp on electrons). Atoms are also increasing in size as well.

What do you notice about the strength of the carbon-oxygen single, double, and triple bonds?

They are very strong, since carbon has a lower electronegativity in comparison to oxygen

How do you calculate total bond energy?

Add all possible bonds between two different atoms together to find the total! (make sure to draw the lewis structure, makes it easier!)

How is the electronegativity for metals?

Very low

What are the differences between a metal with a + charge and one with a 2+ charge in a metallic bond?

The metal that forms a +2 charge will have a higher conductivity due to higher charge (and higher number of electrons in electron sea)

What are some of the properties of metals that can be explained by the electron sea model?

Conducting electricity

The electron sea model does NOT explain elements past ____ (semi-conductors or other properties of higher elements)

What does the band/molecular orbital model depict?

Depicts the energy levels of atomic orbitals as bands

Why do metals have high density?

metals are organized in a lattice structure, meaning they are packed uniformly and close together to minimize space

Why are metals malleable and ductile (stretched)?

Sheets of atomic cores are moved/rolled when stress acts upon it, allowing the layers will fall back into place once the stress is released in a new formation

What is an alloy?

A mixture of elements tat has metallic properties (steel, bronze brass)

Describe each of the teo types of alloy and give an example of each

Interstitial - has particles in-between gaps of the structure of the atomic cores/lattice structure (Nicromium)

Substitutional - Atoms of a similar size replace another element IN the lattice structure (bronze)

Why are alloys less ductile and more sturdy than pure metals?

They contain different elements, causing the metallic properties of multiple elements

What is the basis of the localized electron (LE) model?

Composed of atoms that share electrons for each molecule (valence electron arrangement for a molecule)

How are electrons classified in an LE model?

Bonding pair (shares electrons) or lone pair (non-shared electrons)

The most important requirement for the formation of a stable molecule is…

an octet (noble gas configuration)

Therefore when drawing Lewis diagrams (structure) we always focus on the…

the number of valence e-

Which elements ALWAYS follow the octet rule?

C, N, O, F (2p)

Some elements form molecules that are exceptions to the octet rule

B, Be (less than 8) 

S, P, Xe, Cl (more than 8) (they have access d orbitals)

Formal charge is the difference between the number of __________ an atom has, and the number of electrons assigned to that atom in the Lewis diagram. 

valence e- 

How do you calculate formal charge?

FC = number of valence electrons - numbers of bonds - numbers of bonded electrons divided by 2

If there is not a Lewis diagram that has a formal charge of 0 for every atom, the most realistic diagram is the one with formal charges closest to 0 and with negative formal charges on the more ________ atoms

electronegative

What does VSEPR stand for?

Valence shell electron pair repulsion

How do you apply the VSEPR model?

Draw the Lewis Structure

Count the electron pairs and arrange as far apart as possible

Determine position of atoms

“________” name of the strucutre

What is the difference between having a bonding pair and a lone pair of electrons? Why does this occur?

The non-bonding pair takes up more space than a bonding pair of electrons. The lone pairs are able to spread out more by only being around one nucleus.

What is the molecular geometry of

What is the difference between molecular geometry and electron geometry?

Molecular geometry disregards lone pairs in its classification, while electron geometry accounts for lone pairs

What is the molecular geometry of a molecule with 2 bonds and has 0 lone pairs on the central atom?  What is the bond angle?

linear, 180 degrees

What is the molecular geometry of a molecule with 3 bonds and has 0 lone pairs on the central atom?  What is the bond angle?

Trigonal Planar, 120 degrees

What is the molecular geometry of a molecule with 2 bonds and has 1 lone pair on the central atom?  What is the bond angle?

Bent, <120 degrees

What is the molecular geometry of a molecule with 4 bonds and has 0 lone pairs on the central atom?  What is the bond angle?

tetrahedral, 109.5 degrees

What is the molecular geometry of a molecule with 3 bonds and has 1 lone pair on the central atom?  What is the bond angle?

Trigonal Pyramidal, <109.5 degrees

What is the molecular geometry of a molecule with 2 bonds and has 2 lone pairs on the central atom?  What is the bond angle?

Bent, <109.5 degrees

What is the molecular geometry of a molecule with 5 bonds and has 0 lone pairs on the central atom?  What is the bond angle?

Trigonal Bipyramidal, 90 and 120 degrees

What is the molecular geometry of a molecule with 4 bonds and has 1 lone pair on the central atom?  What is the bond angle?

Seesaw, <90 and <120

What is the molecular geometry of a molecule with 3 bonds and has 2 lone pairs on the central atom?  What is the bond angle?

T-shaped, <90 and <120 degrees

What is the molecular geometry of a molecule with 2 bonds and has 3 lone pairs on the central atom?  What is the bond angle?

Linear, 180 degrees

What is the molecular geometry of a molecule with 6 bonds and has 0 lone pairs on the central atom?  What is the bond angle?

Octahedral, 90 degrees

What is the molecular geometry of a molecule with 5 bonds and has 1 lone pair on the central atom?  What is the bond angle?

Square Pyramid <90 degrees

What is the molecular geometry of a molecule with 4 bonds and has 2 lone pairs on the central atom?  What is the bond angle?

Square Planar, 90 degrees

To find the total dipole moment of a molecule, we must…

determine shape and number of bond types (polar/non-polar and number of lone pairs (and their arrangement)

Can non-polar molecules have polar bonds?

Yes, they need to be symmetrical

Can non-polar molecules contain lone pairs?

Yes, IF they are symmetrical

Must polar molecules contain polar bonds?

No, because asymmetrical lone pairs can make the molecule polar

If a molecule is non-polar, how must lone pairs or polar bonds be arranged?

Symmetrically!

A molecule will be polar ig it is ______ and will have a _____ dipole if it has a highly electronegative atom on or towards one end.

asymmetric, greater

What do we actually mean by an orbital?

A possible location of where an electron could be

What is a hybrid orbital?

A formation of identical shapes in order to form a specific geometry suited for covalent bonding

What happens when four sp3 hybrid orbitals form an s orbital and three p orbitals?

The 4 equal sp3 hybrid orbitals form a tetrahedral arrangement. 

What happens to energy levels when the atomic orbitals hybridize?

They have a single, intermediate energy level (same number of orbitals, just merged together and make a different shape)

What if the sp3 hybrid orbitals were higher energy than the 2p orbitals in the free atom? How would that impact our model of bonding?

Bonding would not be energetically favorable and would not form correctly as predicted

Would NH3 have hybridized orbitals?

Yees, since thee are 4 bonds needed,since there is a lone pair present

Which atomic orbitals combine to form sp2 hybridized orbitals?

1s and 2p

What are some examples of sp2 hybridization? How do you know?

BH3 BF3 C2H4 (three bonds needed)

Axial overlap (along the axis of the bond leads to…

sigma bonds

the leftover p orbital on each C atom (in C2H4) is used to make…

pi bonds

The 2pm orbital is at a higher energy level than the hybridized sp2 orbitals. What does that mean about the strength of the pi bond compared to the sigma bond?

The strength of the pi bond is weaker than the sigma bond, as the 2nd bond would break first, then the sigma bond would break with more energy

What orbitals are involved in sp hybridization?

1s and 1p

The number of orbitals in atomic orbitals must equal

the number of hybridized orbitals

s + p

2sp (2 orbitals involved, one s orbital involved, one p orbital involved)

s + p + p

3sp2 (3 orbitals involved, one s orbital involved, two p orbital involved)

s + p + p + p

4sp3 (4 orbitals involved, one s orbital involved,  three p orbitals involved)