Week 2 Recall Questions

Question 1

A) Properties of atoms
* ~25 elements make up all living matter. What elements are the most common in living matter?

• The distance of an e– from the nucleus is related to its energy level. Based on the figure and the reading, answer the following questions.

Answer 1

• carbon, hydrogen, oxygen, and nitrogen—accounting for more than 96% of the mass of an organism.
• Seven other elements—calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium—contribute most of the remaining 4%.

Question 2

A) Which is higher in energy, an electron in the first shell or the third shell?

Answer 2

an electron in the third shell.

Question 3

A) Which is closer to the nucleus, an electron in the first shell or the third shell?

Answer 3

1st shell

Question 4

A) What happens as an electron moves from the third shell to the first shell? From the first shell to the third shell?

Answer 4

• The first shell has the lowest amount of energy. If an electron in a higher shell (3), moves to 1st, the atom has lost energy.
• The higher the shell, the higher the energy. So if an electron moved from the 1st shell that has a lower amount of energy, to the 3rd shell, the atom as gained energy.

Question 5

A) The difference between a shell and an orbital is …

Answer 5

• A shell is made up of electrons with the same principal quantum number
• Orbitals are made up of electrons with different spins that are all in the same energy level.

Question 6

A) Based on the figure above, how many valence electrons does nitrogen have?

How many more electrons does nitrogen need to fill its valence shell?

Answer 6

• 5 electrons in total. 3 available to bond
• 3 more electrons

Question 7

A) What is unique about Helium, Neon, and Argon?

Answer 7

Atoms that naturally have enough protons to support electrons that completely fill the valence shell are inert—the “noble gasses” helium, neon, and argon

Question 8

A) How many valence electrons does Oxygen have?

Answer 8

6 in total but only 2 available to bond with.

Question 9

A) How many electrons are needed to fill Oxygen’s valence shell?

Answer 9

2 electrons

Question 10

B) Chemical Bonds

B) Which of the three different bond types is a weak bond and which are strong bonds?

Answer 10

• Covalent bonds are strong.
• ionic bonds are weak
• Hydrogen bonds are weak alone, but strong together.

Question 11

B) Explain the difference between a polar and non-polar covalent bond.

Answer 11

• Polar covalent bonds result when electrons are unequally shared between atoms,
• Nonpolar covalent bonds result when electrons are more equally shared between atoms.

Question 12

B) Why is an O-H bond considered polar whereas an O-O or C-H bond considered non-polar?

Answer 12

• Oxygen’s EN is greater than Hydrogen’s, so it pulls electrons towards it. it is unbalanced
• 2 Oxygens have the same EN and it cancels each other out.
• Carbon and Hydrogen have similar EN’s that cancel each other out.

Question 13

B) How many covalent bonds are found in methanol (CH3OH)? Are they polar or non-polar? (χ H= 2.1, C=2.5, O=3.5)

Answer 13

• 4 covalent bonds.
• they are all polar

Question 14

B) What kind of bond forms between Na and Cl? What happens to the electron?

Answer 14

ionic bond.

• the electron is transfer from Na to Cl. because Cl has a higher EN, therefore pulling the electron more strongly towards it.
• 3.16 - 0.93 = 2.23
• Na has 1 electron in shell, would need 3 more to fill it
• Cl has 7 electrons in shell, would need 1 more to fill it

Question 15

B) What are the rules of hydrogen bonding?

Answer 15

1. Each atom in the hydrogen bond is also covalently bonded to something else via polar covalent bonds
2. always involves a partially-positive hydrogen atom.
3. the second atom is always partially-negative (usually O or N)
4. electrons are not shared. it is an attraction between opposite partial chargers.
5. each hydrogen atom can only form 1 hydrogen bond.
   – molecule can be h-bonded to more than 1 thing, but each partial charge can only be involved in a single h-bond.

Question 16

B) What are the characteristics of a hydrogen bond? Which atoms are always and which of frequently involved?

Answer 16

• Weak in biological settings, but very important.
• weak alone but strong together
• always hydrogen
• in biology, frequently nitrogen and oxygen

Question 17

B) What function do hydrogen bonds have in large molecules like DNA?

Answer 17

They allow the 2 strands in DNA to attach to one another, making it very stable.

• the bases of DNA form h-bonds. which allows the structure to be very strong, b/c there are a lot of h-bonds. and many h-bonds together are strong.

Question 18

B) Is water a polar or non-polar molecule? Explain.

Answer 18

polar. because the oxygen has a greater EN than Hydrogen, therefore Oxygen pulls electrons towards it.

• has 2 strong polar covalent bonds between O-H.

Question 19

B) What is the basis for the ability of water to from hydrogen bonds?

Answer 19

• the fact that the hydrogens have a partial positive charges and oxygen has a partial negative charge, means water can h-bond with anything that has partial charges.
• that is the basis for how water interacts with out molecules

Question 20

B) What are important characteristics of hydrophilic molecules?

Answer 20

• have polar covalent bonds resulting in partial charges
• form h-bonds with water
• dissolve in water
• being able to interact with water and form h-bonds, is what allows molecules to dissolve
• if can h-bond with water = hydrophilic
• Ex: Glucose

Question 21

B) What are important characteristics of hydrophobic molecules?

Answer 21

• have nonpolar covalent bonds
• little affinity for water – cant form h-bonds
• interact with other non polar molecules and excludes water

Question 22

C) Carbon based molecules

C) Explain why Carbon can form 4 covalent bonds.

Answer 22

This is because carbon has four unpaired outer electrons that it readily shares to complete its outermost energy level.
- With different combinations of single, double, and even triple bonds, an almost limitless array of molecules is possible

Question 23

C) Explain the difference between a single covalent bond and a double covalent bond.

Answer 23

• A single bond is formed when two atoms share one pair of electrons
• whereas a double bond is formed when two atoms share two pairs (four electrons).

Question 24

C) If a Carbon atom is involved in a double covalent bond, how many additional single
covalent bonds can it form? Explain why.

Answer 24

2 additional single bonds, as there are only valence electrons available to bond.

• Because each carbon atom can form a maximum of four bonds, the number of hydrogen atoms in a molecule decreases as the number of bonds between any two carbon atoms increases

Question 25

C) Some carbon-based molecules are composed only of carbon and hydrogen. These molecules, like the octane molecular (C8H18), are called hydrocarbons.

Would a hydrocarbon be a hydrophobic or a hydrophilic molecule? Explain why

Answer 25

As the hydrocarbon chain becomes longer, the hydrophobic character of the molecule increases, and the solubility of the alcohol in water gradually decreases until it becomes essentially insoluble in water.

• Carbon & Hydrogen form a nonpolar covalent bond. What happens is there is a tendency for water molecules to stabilize around the non-polar molecules. –> pocket of hydrophobic m’s –> surround hydration shell –> H2O H m’s bond –> together –> in most stable way.

Question 26

C) Carbon can form chains, which act as the skeleton of organic molecules.

List four ways that you could take a simple carbon chain and rearrange it to create a variety of different molecules.
(Hint: See page F-22 in textbook)

Answer 26

1. Vary their length.
   - Hexane
   - ethane
2. Add double bonds and put them in different positions
   - Hexene
   - ethene
3. Branching
   - 3- methylpentane
   - 2- methylpentane
4. Presence of rings. Can also contain double bonds
   - cyclohexane
   - benzene

Question 27

C) What are some polar carbon-based molecules, what are some non-polar carbon-based molecules?

Answer 27

• Polar: Carbon & Oxygen (C-O), Carbon & Sulfur (C-S), Carbon & Nitrogen (C-N),
• Nonpolar: Carbon & Hydrogen (C-H),

Question 28

C) What is a functional group? Why are functional groups important?

Answer 28

• functional groups are The atoms in reactive groups.
• important b/c: their covalent bonds are more readily broken or rearranged than the bonds in other parts of the molecules.

–> Carbohydrates, lipids, proteins, and nucleic acids are synthesized and degraded in living organisms through interactions between functional groups attached to the organic molecules.

–> Bonds between atoms can happen only when complexity is increased from single atoms to interactions between atoms. These new properties drive the chemistry of life. therefore give way to macromolecules

Question 29

Functional Groups “Table”

Answer 29

Functional group: Hydroxyl (OH)
Class of compounds: Alcohols
Is it polar or non-polar?: Polar
Is it hydrophobic or hydrophilic?: Hydrophilic
Is it charged or neutral?: Charged, neg on O, pos on H

Functional group: Carbonyl (CHO or CO)
Class of compounds: Aldehydes or Ketones
Is it polar or non-polar?: Polar
Is it hydrophobic or hydrophilic?: Hydrophilic
Is it charged or neutral?: Charged, neg on O, pos on C

Functional group: Carboxyl (COOH)
Class of compounds: Carboxylic acids
Is it polar or non-polar?: Polar
Is it hydrophobic or hydrophilic?: Hydrophilic
Is it charged or neutral?: Charged, carry neg charge

Functional group: Amino (NH2)
Class of compounds: amines
Is it polar or non-polar?: Some polar, some nonpolar
Is it hydrophobic or hydrophilic?: either
Is it charged or neutral?: Some are, some aren’t

Functional group: Sulfhydryl (SH)
Class of compounds: thiols
Is it polar or non-polar?: Polar
Is it hydrophobic or hydrophilic?: Hydrophilic
Is it charged or neutral?: Charged, carry neg charge

Functional group: Phosphate (OPO₃^2-)
Class of compounds: organic phosphates, Nucleotides, nucleic acids,
Is it polar or non-polar?: Non-polar
Is it hydrophobic or hydrophilic?: Hydrophilic
Is it charged or neutral?: charged, neg

Functional group: Methyl (CH₃)
Class of compounds: mythyl group
Is it polar or non-polar?: non-polar
Is it hydrophobic or hydrophilic?: Hydrophobic
Is it charged or neutral?: Neutral

Question 30

Chemical bond characteristics “Table”

Answer 30

Ionic:
e^-: transferred
forces: Electrostatic force of attraction between a metal ion and a non-metal ion
Polarity/Charge: polar
Example: weak interactions best for temporary associations

Polar Covalent:
e^-: shared unequally
forces: Dipole-dipole attraction between dipoles created by partially charged ions
Polarity/Charge: polar
Example: bonds with water?

Nonpolar Covalent:
e^-: shared equally
forces: London dispersion forces
Polarity/Charge: nonpolar
Example: three-dimensional form imparted by these bonds is critical to many molecules, like proteins, functions.

Hydrogen:
e^-: unequal sharing of e.
forces: intermolecular force = dipole-dipole attraction
Polarity/Charge: polar
Example: weak separately but together strong, that’s why in DNA

Vd Waals interactions:
e^-: Not involved
forces: Attraction between transient charge
Polarity/Charge: unpolar
Example: Extremely weak, between molecules