chemistry of life

Question 1

what charge does a nucleus have and why is this ?

Answer 1

the nucleus is positively charged and this is because it only contains protons and neutrons.
porotns are positively charged, whereas neutrons have a neutral/no charge

Question 2

what is the mass of one proton/neutron ?

Answer 2

1 Da

Question 3

what is an element ?

Answer 3

a pure substance that contains only one kind of atom

Question 4

98% of organic tissues are made of only 6 elements. what are these elements ?

Answer 4

carbon, hydrogen, nitrogen, oxygen, phosphorous and sulphur

Question 5

what is atomic number of an element ?

Answer 5

the number of protons in an antom of that element

Question 6

what is the atomic weight of an element ?

Answer 6

is the average mass of a representative sample of atoms of that element, with all the isotopes in their normally occuring proportions

Question 7

what are isotopes of an element ?

Answer 7

atoms with the same number of protons and eletrons but a different number of neutrons

Question 8

why do isotopes of the same element behave in the same way in chemical reactions ?

Answer 8

because their electronic configuration has remained the same

Question 9

what is a radioisotope ?

Answer 9

this is an unstable isotope and these spontaneously give off energy in the form of radiation. this comes from the atomic nucleus.

Question 10

what is the spontaneous release of energy called in radioisotopes ?

Answer 10

radioactive decay - this release of energy transforms the original atom

Question 11

what can radioisotopes be used as ?

Answer 11

tracers - living cells cannot distinguish between isotopes of the same element

Question 12

what is an orbital ?

Answer 12

this is the volume of space within the atom where the electron is likely to be. This is because the location of a given electron in an atom is impossible to determine

Question 13

the energy level of an electron is higher when in a shell …

Answer 13

farther from the nucleus

Question 14

what is the octet rule ?

Answer 14

an atom will always tend to become stable by filling the outermost shell with 8 electrons

Question 15

how are molecules formed ?

Answer 15

when two atoms with incomplete outer shells react, each atoms will share, donate, or receive electrons so that both atoms end up with complete outer shells. these atoms will then remain close forming a molecule

Question 16

what is a compound ?

Answer 16

this is a pure substance made up of two or more different elements bonded together in a fixed ratio

Question 17

what are the two main types of chemical bond ?

Answer 17

covalent bonds and ionic attractions

Question 18

briefly explain what a covalent bond is ?

Answer 18

the sharing of electrons

Question 19

briefly explain what ionic attractions are ?

Answer 19

is when an atoms gains or loses on or more electrons to achieve stability

Question 20

when do chemical reactions occur ?

Answer 20

when moving atoms collide with sufficient energy to combine or to change their bonding partners

Question 21

when do covalent bonds form ?

Answer 21

when two atoms attain stable elctron numbers in their outermost shells by sharing one or more pairs of electrons

Question 22

what are the features of covalent bonds ?

Answer 22

they are very strong so require a lot of energy to break
at temperatures where life exists, the covalent bonds of biological molecules are quite stable
one bonds means 2 electrons are shared

Question 23

is the sharing of electrons in a covalent bond equal ?

Answer 23

not always

Question 24

why is the sharing of electrons in covalent bonds not always equal ?

Answer 24

this is because atoms in a covalently bonded molecule continually compete for shared electrons. the attraction for shared electrons is called electronegativity and the more electronegative atoms pull harder .

Question 25

what are ions ?

Answer 25

are electrically charged particles that form when atoms gain or lose one or more electrons

Question 26

ions can form bonds that result in stable solid compounds. these are called

Answer 26

salts

Question 27

ions can interact with polar molecules. this is because ...

Answer 27

both are charged

Question 28

explain how salts dissolve in water using NaCl as an example .

Answer 28

water molecules surround the individual ions, separating them. the negatively charged chloride ions will attract the positive poles of the water molecules the positively charged sodium ions will attract the negative poles of water molecules the polarity of water is one reason it is such a good biological solvent

Question 29

how do hydrogen bonds form ?

Answer 29

in water, the negatively charged oxygen atom of a water molecule is attracted to the positively charged hydrogen atoms of another water molecule.

Question 30

are hydrogen bonds weak or strong ?

Answer 30

thry are weak but high numbers create a strong bond

Question 31

why does water have a tetrahedral shape ?

Answer 31

the four pairs of electrons in the outer shell of the oxygen atom repel one another. this gives water molecules a tetrahedral shape

Question 32

what are the properties of water ?

Answer 32

the ability of iceto float the melting and freezing temperatures of water the ability of heat to store and transfer heat (heat capacity) waters ability to dissolve many substances, and its inability to dissolve many others

Question 33

why does ice float ?

Answer 33

in ice individual water molecules are held in place by hydrogen bonds. these are farther apart from one another in ice than they are in water. so ice is less dense than water and this is why it floats

Question 34

what is the biological importance of ice floating ?

Answer 34

if ice sunk then a pond would freeze from the bottom up (becoming a solid block of ice in the winter) and it would kill most of the organisms living there. however because ice floats is forms this insulating layer on the top of the pond. this reduces heat flow to the cold air above and so fish, plants and other organisms are not subjected to temperatures lower that 0

Question 35

what is meant by the specific heat capacity ?

Answer 35

the amount of heat energy required to raise the temperature of 1 gram of a substance by 1 degrees

Question 36

why does water have a relatively high specific heat capacity ?

Answer 36

this is because there are many hydrogen bonds connecting the water molecules in ice, and these most be broken to change water from a solid to a liquid

Question 37

specific heat capacity indicates the ability of a substance to ...

Answer 37

store heat e.g. water has a higher heat capacity compared to sand, and this is why sand cools much more quickly compared to water

Question 38

water also has a high heat of vaporization. this means ...

Answer 38

a lot of energy is required to change water from its liquid to its gaseous state - a lot of the energy is used to break the many hydrogen bonds between the water molecules the heat must be absorbed from the environment in contact with the water

Question 39

how does sweating cool the human body ?

Answer 39

sweat evaporates from the skin, and so it uses up some of the adjacent body heat

Question 40

what is cohesion ?

Answer 40

cohesion is defined as the capacity of water molecules to resist coming aart from one another when placed under tension

Question 41

explain the benefits of cohesion in trees ?

Answer 41

water's cohesive strength allows narrow columns of liquid water to move from the roots to the leaves of tall trees, so when water evaporates from the leaves, the entire column moves upwards in response to the pull of molecules at the top .

Question 42

what is adhesion ?

Answer 42

this is the attraction of water molecules to other molecules of a different type

Question 43

adhesion helps water repel ...

Answer 43

the force of gravity e.g. water will "cling" to vertical surfaces

Question 44

why is the surface of water exposed to air difficult to puncture ?

Answer 44

because the water molecules at the surface hydrogen-bonded to other water molecules below them

Question 45

a solution is produced when ...

Answer 45

a substance (the solute) is dissolved in a liquid (the solvent) -if the solvent is water then the solution is called an aqueous solution

Question 46

what is pH ?

Answer 46

it is the concentration of hydrogen ions

Question 47

why do we need to maintain a relatively stable pH in cells ?

Answer 47

chemical processes are very sensitive to concentration of hydrogen and hydroxide ions

Question 48

how do buffers work ?

Answer 48

thry accept hydrogen ions from the solution when they are in excess -with buffers, biological fluids resist changes to their own pH

Question 49

What huffer contributes to the ph stability in blood ?

Answer 49

carbonic acid