Chemical Basis Of Life

Question 1

How many protons, electrons, and neutrons does a neutral atom of mercury have, given that its atomic number is 80 and its atomic mass is 201?

Answer 1

80 protons, 80 electrons, 121 neutrons

Question 2

What is an isotope? Give an example

Answer 2

Atoms with the same number of protons but a different number of neutrons, such as carbon-12

Question 3

What is the difference between an atom, element, molecule, and compound?

Answer 3

An atom is a neutral particle that is the smallest representation of an element. An element is a pure substance that cannot be broken down into simpler substances by ordinary chemical means (a sample of only one type of atom). A molecule is a particle consisting of two or more atoms held together by chemical bonds, they may be broken down into constituent atoms. A compound is a sample of identical molecules

Question 4

What three forces govern the formation of molecules from atoms?

Answer 4

The tendency for electrons to order themselves in pairs to fill orbitals, the tendency of atoms to balance positive and negative charges, and the tendency for the valence shells of an atom to be full

Question 5

What is electronegativity?

Answer 5

A measure of attraction that an atom has for the electrons in a bond

Question 6

What types of intramolecular bonds are possible?

Answer 6

Ionic, covalent, and polar covalent

Question 7

Describe ionic bonds

Answer 7

Occurs between atoms of very different electronegativities. They are between metals and non-metals. The metal (lower EN) loses one or more electron to the non-metal (higher EN), resulting in two oppositely charged ions that now have paired electrons and filled valence shells. Attraction between the two oppositely charged ions creates a strong bond

Question 8

Describe covalent bonds

Answer 8

Occurs between atoms of two non-metals with similar electronegativity. The electrons are shared by both atoms

Question 9

Describe polar covalent bonds

Answer 9

Occurs between two non-metals of somewhat different electronegativity values, resulting in an unequal sharing of one or more pairs of electrons between atoms. Due to the different electron affinities, the electron pair will spend more time around the more electronegative nucleus and a polar bond is created. Due to the shape of the molecule, polar covalent bonds may result in a polar molecule with one side having a partial negative (δ-) or partial positive (δ+) charge

Question 10

Is a molecule with polar bonds and an asymmetrical shape a polar or non-polar molecule?

Answer 10

Polar

Question 11

Is a molecule with polar bonds and a symmetrical shape a polar or non-polar molecule?

Answer 11

Non-polar

Question 12

What’s the difference between a polar and non-polar molecule?

Answer 12

A polar bond is a type of covalent bond in which the valence electrons are shared unequally. A non-polar bond occurs when two of the same atoms come together (i.e. diatomic molecules) and share valence electrons equally, because both nuclei attract electrons the same

Question 13

Name all conditions under which a molecule might be polar

Answer 13

Must have polar bonds and an asymmetrical shape (a base bonded to two unique atoms is automatically asymmetrical)

Question 14

Name all conditions under which a molecule might be non-polar

Answer 14

Either contains no polar bonds or contains polar bonds but has a symmetrical shape

Question 15

What is the general trend of electronegativity on the periodic table?

Answer 15

EN increases as you move up and to the right of the table

Question 16

What is the most electronegative and least electronegative element? Also, do metals or non-metals generally have a greater electronegativity?

Answer 16

The most electronegative element is fluorine and the least electronegative is francium. Non-metals generally have a greater EN that metals

Question 17

How do lone electron pairs affect polarity?

Answer 17

Lone electron pairs take up more space than bonded electrons, due to exposure, repelling bonds further away

Question 18

What are intermolecular bonds?

Answer 18

Chemical bonds between separate molecules, weaker than the intramolecular bonds that hold atoms/ions together in molecules

Question 19

What are the three main types of intermolecular forces of attraction?

Answer 19

Van der Waals’ forces, permanent dipole-permanent dipole interactions, and hydrogen bonding

Question 20

What are Van der Waals’ forces?

Answer 20

Forces of attraction that exist between all molecules. They are much weaker than all other types of bonding. They are a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movements of electrons in atoms and molecules

Question 21

When are Van der Waals’ forces significant?

Answer 21

In atoms and molecules that have no other type of intermolecular forces of attraction, such as discrete non-polar molecules and Group 0 elements

Question 22

How is the strength of Van der Waals’ forces measured?

Answer 22

It is relative to the size of atoms and molecules. The bigger the atom or molecule, the bigger the Van der Waals’ force

Question 23

What are permanent dipole-permanent dipole interactions?

Answer 23

Additional electrostatic forces of attraction between permanent polar molecules. They are stronger than Van der Waals’ forces for molecules of equivalent size.

Question 24

What is a permanent dipole?

Answer 24

Due to the difference in electronegativity between atoms in a covalent bond. It is what defines a polar molecule

Question 25

What is hydrogen bonding?

Answer 25

Permanent dipole-permanent dipole interactions, consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen, or nitrogen. It is stronger than other forms of permanent dipole-permanent dipole interactions because its nucleus is bare, but much weaker than a covalent bond

Question 26

What are five properties of water given by hydrogen bonds?

Answer 26

High surface tension (cohesion), adhesion, high specific heat capacity, moderate temperature due to high specific heat capacity, and that solid water is less dense than liquid water (ice floats)

Question 27

Describe cohesion. Give an example

Answer 27

Water molecules cling to one another causing surface tension. E.g. insects can walk on water

Question 28

Describe adhesion. Give an example

Answer 28

Capillary action causes water to creep up sides of narrow columns. E.g. water climbing the xylem vessels in plants

Question 29

Describe the specific heat capacity of water

Answer 29

Water absorbs a lot of heat before becoming a gas, therefore it has a high SHC and a relatively high boiling point

Question 30

Describe the affect hydrogen bonding has on temperature

Answer 30

Water absorbs a large amount of heat before temperature rises and it must lose a lot of heat before temperature decreases. This is due to the high specific heat capacity of water

Question 31

What are hydrogen bonds between other polar molecules responsible for?

Answer 31

That water is the universal solvent, dissolving many substances (mostly polar), they hold the two backbone strands of DNA together, they provide secondary and tertiary structures of proteins

Question 32

Describe water ionization

Answer 32

In any given sample of water, the molecules move about due to kinetic energy. As some of them collide, a small fraction of them will become ionized. Therefore in a container of water there will be three types of particles present, H2O, OH-, and H3O+

Question 33

With respect to water ionization, how can water be pure?

Answer 33

When the amount of hydronium ions (H3O+) is equal to the amount of hydroxide ions (OH-)

Question 34

What is a base?

Answer 34

Any substance that, when dissolved in water, increases the OH- or decreases the H3O+. This can be achieved either by the substance ionizing when dissolved in water to produce OH- ions (e.g. NaOH —> Na+ + OH-) or by the substance combining directly with H+ ions when dissolved (e.g. NH3 + H2O —> NH4 + OH-)

Question 35

What is an acid?

Answer 35

Any substance that increases the H3O+ to a level higher than pure water

Question 36

When a solution contains more hydronium ions than hydroxide ions, is it an acid or a base?

Answer 36

Acid

Question 37

When a solution contains more hydroxide ions than hydronium ions, is it an acid or a base?

Answer 37

Base

Question 38

What is the hydronium and hydroxide count of pure water?

Answer 38

1x10^-7 mol/L

Question 39

What is the formula for determining the pH of a solution?

Answer 39

-log[H3O+]

Question 40

Describe the pH scale

Answer 40

Pure water has a pH of 7. Acids have a pH lower than 7 and bases have a pH greater than 7. It is logarithmic, meaning a solution with a pH of 5 is 100 times more acidic than pure water, or has 100 times more hydronium ions than pure water

Question 41

What kind of reaction occurs when an acid is mixed with a base?

Answer 41

Neutralization

Question 42

Describe a neutralization reaction

Answer 42

An acid and a base will combine to form water and a salt

Question 43

What are buffers?

Answer 43

Biochemical systems and reactions that are very sensitive to pH. Slight variations in acidity will greatly affect regular life activities

Question 44

What is the average pH of blood?

Answer 44

7.4

Question 45

Describe the effect a change in pH has on blood

Answer 45

A change in pH from 7.4 to 6.8 will result in acidosis, and from 7.4 to 8.0 will result in alkalosis, both of which can cause the proteins to break apart and the enzymes to denature, possibly leading to death

Question 46

Describe the buffer system in human blood

Answer 46

CO2 reacts with water molecules in bodily fluids to form carbonic acid. This then ionizes to form bicarbonate ions and hydrogen ions. If you add [H+] ions into the bloodstream (e.g. vinegar), the hydronium ion count increases, which shifts the equilibrium to the left, mopping up excess H+ ions. If base enters the blood (e.g. Tums) and removes H+ ions, carbonic acid ionizes to replace them, shifting the equilibrium to the right to make up for what was lost

Question 47

What is the equilibrium reaction for the blood buffer?

Answer 47

H2O + CO2 <—> H2CO3 <—> HCO3- + H3O+

Question 48

Describe why solid water is less dense than liquid water

Answer 48

As water molecules freeze, they form an ice water lattice. The hydrogen bonds keep them spread apart, reducing the density so that it is less than liquid water

Question 49

At what temperature does water experience its greatest density?

Answer 49

4^0C

Question 50

How does the density pattern of water affect life?

Answer 50

Fish and other aquatic organisms survive in winter because water freezes from the top down. Snow is also a good insulator, proving protection from extreme cold for many organisms

Question 51

Define hydrophilic

Answer 51

Polar or charged molecules that are strongly attracted to water

Question 52

Define hydrophobic

Answer 52

Non-polar molecules that are not strongly attracted to water

Question 53

How can Van der Waals’ forces determine the state of a substance?

Answer 53

The more atoms in a molecule, the more Van der Waals’ forces exist, and thus the more likely it is to be a solid or liquid than a gas