Chemical Components of Cells Flashcards
(55 cards)
What is the structure of an atom? What can we infer from the elements atomic number?
Atom consists of a dense positively charged nucleus surrounded by negatively charged particles attracted by electrostatic forces
- Nucleus: protons, neutrons
- Surround: electrons
- There has to be the same amount of protons and electrons
- Atomic number tells us how many protons does an element have e.g. H2 has 1
Why do we need neutrons in the mix?
They stabilize the nucleus -> if there are too many or too little the nucleus might disintegrate by radioactive decay
What are isotopes? Give example.
= elements that can exist in chemically identical forms with structural/physical differences
- having the same number of protons yet different of neutrons
E.g. stable isotope carbon 12 (6 p, 6 n) X unstable isotope carbon 14 (6 p, 8 n) -> we can study how it undergoes radioactive decay
What is meant by atomic weight? How is it in stable and unstable carbon? What units do we use?
Atomic weight = its mass relative to that of hydrogen atom
- Summation of protons and neutrons (electrones are too light to contribute)
- stable: 12, unstable: 14
- Unit: dalton (1 = approximately eaqual to mass of hydrogen)
What is a mole?
Mole = represents the number of molecules available to participate in chemical reactions
- Avogadro’s number = 6 x 10(23)
What can you say about the “behavior” of electrons?
- form the accessible part of atoms that specify bounding rules between atoms creating molecules
- contiously move around in orbits
- Each orbit represents ELECTRON SHELL which have limits on how many electrones they can accomodate:
- First (innermost): 2e
- Second: 8e, Third: 8e
- Fourth: 18e, Fifth: 18e
How is stability of an atom related to electron shells? What is the consequence?
Most tighly bound electrons are those closest to the nucleus -> most stable
- electrons usually fill those first before moving to the next
=> atoms that have filled closer shells are less reactive e.g. Helium
What is the difference between Helium and Hydrogen atoms?
Although both have their electrons in the innermost electron shell, helium fills it up completaly (2) while hydrogen is missing 1e -> incomplete shell makes atoms more likely to react/interact with other atoms to gain or lose elecrones to achieve complete shell
- NOTE: number of electrons atom can lose or gain to fill out the shell determines how many bonds they can form
- NOTE: Atoms in similar situations (e.g.inert gases) will act similarly -> determines the periodic table
What are the 2 types of chemical bonds that bind atoms to one another? Which one does H prefer and to what elements does it bound?
- Ionic bond = electrons are donated by one atom to another
- Covalent bond = two atoms sharing a pair of electrons
- Generally H shares atom with C, N, O, P, or S
- E.g. 2 H share their 2e
What are the most prevalent elements in livng organisms? And how would you define a molecule?
- Hydrogen, oxygen, nitrid, carbon
- Molecule = a cluster of atoms held together by covalent bonds
NOTE: depending on number of possible bounds the final molecule creates a specific geometrical shape
What do we mean by bond length?
= a specific distance between nuclei in which the repulsive and attractive forces are at balance
- shared e create a dense negative charge which attracts otherwise repeling nuclei
What are the 2 types of covalent bonds and how are they different?
- Single bonds = sharing 1 pair of e
- allows for rotation of one atom relative to the other around the bond axis
- Double bonds = sharing 4 pairs of e
- shorter and stronger
- prevents rotation, more rigit
NOTE: some molecules can create “intermediate” bonds e.g. benzen molecule forms a ring of 6 evenly distributed carbon atoms
What do we mean by polar and nonpolar covalent bond?
Polar bond = e are shared in an unequal manner
- often between different elements
- positive charge is concentrated towards one end (positive pole) while negative charge towards the other (negative pole) e.g. O-H
While nonpolar bonds are sharing equally e.g. C-H
What is the last characteristic of covalent bonds that needs to be discussed?
Bond strength = the amount of energy that must be supplied to break the bond
- usually expressed in kilocalories per mole or kilojoules per mole
- NOTE: typically covalent bonds are stronger than average energies (e.g. thermal) so that bonds don’t get broken by them -> yet some things can break it e.g. enzymes
When do we get ionic bonds? What happens in that case? Give example. How do we call these molecules? What happens if they come into contact with water?
Forms between atoms that can complete their outer shell most easily by getting or donating e
- Na needed to get rid of 1e while Cl needed 1e => NaCl
- When e jumps from one ion to the other the ions become charged (because it has one less or more e than p -> thus their net charge becomes positive or negative) e.g. Na+ and Cl-
=> due to their opposite charges they attract each other and are held by their ionic bond
=> Ions held by strictly ionic bond are called SALTS
=> Salts are highly soluable in water -> makes them dissociate and create individual ions
If ionic bonds became so weak in aqueous solutions - what then helps to create associations between molecules?
Noncovalent bonds - individually quite weak but if summed up they may create strong force between molecules
- Ionic force holding Na+ and Cl- in salt crystal is called elctrostatic attraction
- strongest when atoms involved are fully charged
- BUT weaker also exist at polar bonds -> larger molecules can have pattern of positive and negative charges which can be paired (electrostatically attracted) with another molecule complementary in its surface charges
What is a the type of bond without which the life as we know it wouldn’t exist?
Each water molecule (H2O) is made of 2 H linked with O -> bonds between the 2 elements are highly polar, with unequal distribution of electrons
=> O creates the negative pole
=> 2 H will be 2 positive poles
=> In this composition they can attract another H2O that would bind its O to their H = Hydrogen bond
- weak, easy to be broken down (even by thermal forces) => producing network of hydrogen bonds that keep forming and breaking (water = liquid)
Does hydrogen bond form only between water?
No. In general they can form between any H+ within a molecule of polar covalent bond and O or N of another molecule.
- Can also occur at different parts of larger molecules and help them fold in a specific manner
How do we differentiate molecules based on how they react towards hydrogen bonds?
If molecules contain polar bonds that can attach to water and become hydrogen bonds (i.e. they mix well with water) = Hydrophilic
- E.g. alcohol, DNA, RNA, proteins
If molecules are uncharged and don’t form hydrogen bonds = Hydrophobic
- do NOT dissolve in water
What are hydrocarbons? Why are they useful?
Hydrocarbons = molecules in which H atoms are covalently linked to C atoms by nonpolar bonds -> NO net charge -> NO hydrogen bonds => hydrophobic
- Cells use libid molecules (that have hydrocarbon tails) to create membrane barriers and keep one aqueous environmen from the other.
What happens if a strongly polar covalent bond between H and another atom dissolves in water?
The H gave its e almost entirely to the other atom leaving it as only positively charged hydrogen nucleus = proton (H+)
-> gets attracted by partial negative charge of O of water molecules -> proton dissociates from its origin and bonds to the new water molecule = Hydronium ion (H3O+)
- the reverse may also happen
=> protons are constantly attaching to different molecules within aqueous solution
How do we call the substances that release protons when dissolving in water? How do we represent it as a number + the borders of the scale?
Acids -> raising concentration of H3O+ by releasing their H+
- the more H3O+ = the more acidic solution (although we usually just refer to it as H+ concentration)
- The concentration is represented by logarithmic pH scale
- pure water pH = 7 = neutral
- pH < 7 = acidic
- pH > 7 = basic
Reflect on the statement “Acids are characterized as being strong or weak”. Explain why this is useful?
The distinction is made based on how readily do the acids give up their H+
- Strong acids = lose H+ easily e.g.HCl
- Weak acids = hold onto their H+
=> Allows the molecules to “monitor” pH level and regulate it
- If pH is low even weak acids will give up their H+
- If pH is high they tend to accept H+ back
How do we call the substances that accept protons when dissolved water?
Base -> raising concentration of hydroxyl (OH-) by removing proton from the water molecule
- e.g. If NaOH gets dissolved in water -> deparates into Na+ and OH-
