Chapter 2 - The Chemical Context of Life Flashcards
What 4 elements make up 96% of living matter?
Oxygen, Carbon, Hydrogen, and Nitrogen
What elements make up about 4% of living matter?
Calcium, Phosphorus, potassium, sulfur, sodium, chlorine, and magnesium
Element definition
Substance that cannot be broken down into other substances by chemical reactions - all 1 type of atom
Compound definition
2+ emements combined (chemically bonded, not mechanically mixed) in a fixed ratio
Emergent properties
A compound has chemical and physical characteristics different from those of its constituent elements
What percentage of natural elements are essential elements?
20-25%
What is an essential element?
An element an organism needs to live a healthy life and reproduce
How many essential elements do humans need?
25
How many essential elements do plants need?
17
What are trace elements?
Elements required by an organism in only minute quantities (still essential)
Atom def
smallest unit of matter that still retains the properties of an element
True or false: Elements and atoms are symbolized with the same abbreviation
True
What is an electron shell? Why don’t electrons fly away?
Rapidly moving electrons forming a cloud of negative charge around the nucleus, which holds them in
Atomic number
Number of protons (and electrons unless it’s an ion)
Mass number
Number of protons + neutrons
True or false: Most Hydrogen atoms (not counting the few isotopes) have an atomic number of 1 and a mass number of 2.
False - they usually don’t have a neutron
Isotope
atom with more or fewer neutrons, same reactivity and chemical properties
Radioactive isotope
nucleus decays spontaneously, giving off particles and energy
Why doesn’t mass number always equal atomic mass? (they are usually very close and sometimes the same)
mass number is protons+neutrons, atomic mass averages the isotopes
How can radioactive isotopes be used in biology?
Fossil dating & tracers to follow attoms through metabolism (cells can use them like any other atom of the same element, trackers when incorporated into biologically active molecules. Good as tracers (eg ingected into blood and followed or paired with PET scanners to monitor cancer))
Why are radioactive isotopes used in medicine if they’re harmful to cellular molecules?
The dose is relatively safe (at least it will hurt you less than the disease that’s making you need it)
Are atoms more or less compact than images in diagrams show?
(e.g o( O )o where o is electrons and O is the nucleus)
Do the nuclei interact with each other in a chemical reaction?
Much less compact - atoms are mostly empty space
No - only e&e, n&e, or e&n (not n&n bc too spread out)
Energy def (biology)
the capacity to cause change (like by doing work)
Potential energy def (biology)
the energy that matter possesses bc of location and structure
T or F: Electrons farther from the nucleus have greater potential energy
True - it takes work to move an electron further away from the nucleus, and it wants to come closer (attraction theory from Sarah so take with grain of salt). More work it took to get there = greater pot energy (climbing 3 feet up a hill gives you less pot energy than climbing Mt Everest)
T or F: Electrons can exist between shells/energy levels
False (at least for long periods of time. I can jump but not fly)
The first electron shell has ____ potential energy than the third electron shell
less
Under what condition can electrons move from one shell to the other?
If they absorb or lose an amount of energy equal to the difference in pot energy btween old shell and new shell. Absorbing -> moves further, losing -> comes closer
T or F: an electron that has gained/lost a lot of energy can move 2 shells
True
Light energy can excite an electron to a higher energy level. How is this used by living organisms?
1st step in photosynthesis
Where does an electron’s lost energy go when it loses energy?
expelled as visible light or uv radiation
Alt name for row of periodic table
Also, what does it correspond with?
period
electron shell
alt name for column of periodic table
Also, what does it correspond with?
group
valence electrons
T or F: The reactivity of an atom arises from the presence of one or more paired electrons in its valence shell, and paired electrons are involved in reactions
False - unpaired electrons do the reacting
Halogens are _____ (synonym of unreactive)
Inert
Examples of chemical bonds
Covalent bonds, metallic bonds, ionic bonds, IM forces, etc
Strongest chemical bonds
Covalent and dry ionic (aq is weak for ionic bonds)
Covalent bond def (bio)
sharing of a pair of valence electrons by 2 atoms - makes a molecule (which is still an element)
T or F: Single bond means 2 electrons in the covalent bond and is represented by a single line
True
Molecular formula and structural formula examples
H₂, H-H
Bonding capacity
number of covalent bonds an atom can form (aka valence)
Why does covalent bonding work?
The electron(s) of each atom is attracted to the proton(s) in each other atom’s nucleus
T or F: Methane is a compound which takes 4 hydrogen atoms which each have a valence of 1 to complete the valence shell of a carbon atom, which has a valence of 4
True
Electronegativity def
The attraction of a particular atom for the electrons of a covalent bond - more electronegative means stronger pulling of shared electrons towards itself
Nonpolar covalent bond
When 2 of the same atoms covalently bond, they have the same electronegativity - no strong negative or positive and electrons are shared equally
Polar covalent bond
When 2 or more atoms with different electronegativity bond, there’s a strong negative and positive (how strong varies) and electrons aren’t shared equally - in water, electrons spend more time near oxygen nucleus than hydrogen nucleus
How are the positive and negative regions on a water molecule notated?
2 regions on the oxygen atom have a partial negative charge and are indicated with a d- (delta not d)
Each hydrogen atom has a partial positive charge and is notated with a d+ (delta not d)
How does the polarity of water bonds compare with the polarity of methane bonds?
Methane bonds are less polar bc electronegativities of carbon and hydrogen are pretty similar
T or F: More electrons = more electronegative
True
T or F: The transfer of an electron in an ionic bond is the formation of a bond
False. It allow a bond to form because it results in two ions of opposite charge
What are compounds formed by ionic bonds called?
Salts or ionic compounds (NOT A MOLECULE)
T or F: The term ion also applies to electrically charged molecules
True (e.g. nitrate or ammonium ions)
T or F: Weak chemical interactions are useless
False - they’re very useful in cells, holding large biological molecules together in their functional form, and temporary connections (come together, affect each other, separate)
Hydrogen bonds
When a hydrogen atom is covalently bonded to an electronegative atom, the h atom has a partially positive charge so it can attract to a different electronegative atom nearby (it cheats on its spouse with another electronegative ion). These are noncovalent attractions, and the partners are usually N or O.
Van der waals interactions
Wiggles.
The electrons wiggle around and aren’t always distributed symmetrically, so they may accumulate by chance in various regions of the molecule. This makes changing positive and negative regions that let all molecules stick to one another. They’re weak and only happen when close together, but lots occur simultaneously and can be powerful.
T or F: Carbon often bonds with 4 other atoms to form a tetrahedron (triangle based pyramid) shape.
True
Why is molecular shape important?
It dictates how they recognize and respond to each other (molecules) with specificity - they bind temporarily to each other, but only if they have a complimentary shape.
Chemical reactions def
The making and breaking of chemical bonds, leading to changes in the composition of matter
T or F: Matter is conserved in a chemical reaction
True - no atoms are created or destroyed
photosynthesis formula
6CO2+6H2O use sunlight——-> C6H12O6 + 6O2
T or F: All chemical reactions are theoretically reversible where products -> reactants
True - 2 headed arrow indicate this
T or F: more reactants (concentration) leads to slower reactions
False - it makes them faster bc more collision opportunities
Chemical equilibrium def
forward and reverse reactions happen at the same rate and relative concentrations stop changing. reactions keep going but ratio of concentrations have stabilized. (not necessarily equal concentrations of stuff)
What percentage of cells are water?
70-95%
How does hydrogen bonding in water work?
partially charged hydrogen of one attracts partially charged negative of another-> weak hydrogen bond. at any given moment most water molecules in a droplet are bonded to each other, even though each bond only lasts about a few trillions of a second
Cohesion def
Many molecules in liquid water are linked by several hydrogen bonds, making water more structured than most other liquids. H bonds collectively hold the substance together.
Adhesion def
clinging of one substance to another eg water to cell walls
surface tension def
how hard it is to stretch or break the surface of a liquid - asymmetry of water gives it high surface tension
specific heat of water
1 calorie per grap per degree celsius - unusually high
What does the high specific heat of water mean?
when given or losing a a given about of energy, it will change its temperature less easily (water needs more energy to get it to do stuff)
temperature def
avg kinetic energy of molecules
