chemicals of life. chemical basis of life principles of chemistry help to understand biology...
TRANSCRIPT
Chemicals of Life
Chemical Basis of Life• principles of
chemistry help to understand biology
• organisms are bags of chemicals
• function of organisms & parts of organisms are determined by– way chemicals are
arranged• compounds &
molecules formed by chemicals
• structure determines function
• Structure Function
long handle to hold easiermade of wood to be strongblunt metal end to hit nailscurved, claws to pull out nails
Chemistry• chemicals give cells properties
• these properties are called life
• Hierarchy
• Chemicalsorganellescellstissuesorgansorganisms
Matter• all living things are made of
matter
–anything that occupies space & has mass
• matter is composed of elements
Elements• substances which cannot be decomposed
into simpler substances by chemical means
• 92 naturally occurring elements
• 25 elements are found in living things
• 96%-H, O, C & N• 4%-Ca, P, K & S• Trace elements-Fe, Mg, Mn (manganese) & I
– essential– cannot live without them
Periodic Table
Atoms• elements are composed of atoms
• only one kind of atom for each element
– smallest units of matter that retainproperties of an element
Sub-atomic Particles• Protons• Electrons• Neutrons
–different elements have different numbers of sub-atomic particles
–put together differently in different atoms
–chemical & physical differences of elements are due to these differences
Sub-Atomic Particles• Protons
– one positive charge
– found in nucleus of atom
• Neutrons– no charge
– found in nucleus of atom
• Electrons– one negative charge
– orbit nucleus
Periodic Table• atom’s structure
determines how element it comprises forms compounds & molecules
• key to this can be found by knowing number of sub-atomic particles an element possess
• found in Periodic Table of the Elements
atomic number-number in upper left corneratomic number-number in upper left corneratomic weight or mass number-number atomic weight or mass number-number located on bottomlocated on bottom
Atomic Number• gives number of
protons in atom
• Helium
• Atomic Number = 2
–has 2 protons
Mass Number• number of neutrons +
number of protons• He = 4• variant forms of elements
can exist• some atoms of an
element may have different mass numbers
• these are isotopes– same number of
protons & electrons; different number of neutrons
Number of Electrons• net charge of atom = zero• each proton has one
positive charge• each electron has one
negative charge• neutrons have no charge• to be neural atom must
have same number of electrons as protons
atom of helium with 2 protons has 2 electrons
ChallengeQuestion• How many protons does Sulfur
have?
• How many electrons?
• Why?
Chemical Properties• arrangement of electrons
determines chemical properties of atom
• electrons orbit around nucleus• found at different energy levels-
shells• each shell accommodates a
specific number of electrons
Electron Shells• innermost shell-2 • 2nd & 3rd-8• number of electrons in
outermost shell determines chemical properties of atom
• those with shells that are not full will interact with other atoms & participate in chemical reactions
• those with full shells do not interact-inert
Electron Shells• H-one electron in outer most shell
– very reactive• C, N, & O
– highly reactive since outer shells are incomplete
• He– inert or nonreactive-outer shell is full
Challenge Question
• Is Chlorine reactive or not reactive?
• How can you tell?
Atom Interactions-Chemical Bonds• when atom with incomplete outer shell
reacts with another atom with incomplete outer shell they can interact or form a bond
• Share
• Donate
• Receive electrons
• in this way both atoms can have a complete outer shell
Types of Chemical Bonds• Covalent Bonds
–share electrons
• Ionic–give or receive
electrons
Sodium & Chloride
Ionic Bonding
Covalent Bonds• 2 atoms with incomplete shells
• share electrons
• so at any one time one atom has a completed outer shell
• molecules are formed
In Class Exercise• Pretend you are an atom
• Take the number of your birth month as your atomic number
• Determine the configuration of electrons in your valence shell
• Find another atom that you might interact with to form ions or new molecules
• Demonstrate-draw on board
Chemical Reactions• elements combine to make molecules &
compounds• 2 H2 + O2 2H2O• 2 molecules of H react with one
molecule of O (reactants) to form 2 molecules of water (product)
• arrow indicates direction of reaction• two sides of equation on either side of
arrow must balance
Water• single most important
constituent of body
• life on Earth depends on unusual structure & nature of water
Importance of Water• Organisms consist mostly of water
– 2/3rds total body weight of humans
• Biochemistry is a wet chemistry– biological molecules do not
react chemically unless in solution
• Water is an important reactant– nearly all chemical reactions in
body occur in water• Foods are digested to building
blocks by decomposition reactions called hydrolysis– involves addition of water
• When large molecules form from smaller ones, water is removed in dehydration synthesis or condensation reactions
Water Structure• 2 H atoms attached
covalently to one O2 molecule• sharing of electrons is not
equal• oxygen pulls more on
electrons than hydrogen • electrons spend more time
near oxygen than hydrogen• unequal sharing produces-
polar bond• bond in which two atoms
involved have an equal pull on electrons-nonpolar
Water Structure• O2 attracts electrons more strongly than H-
giving water an asymmetrical distribution of charge
• result-V-shape
• H end has positive charge
• Oxygen end has negative charge
• water has 2 poles-polar
• polarity results in weak electrical attractions between neighboring water molecules
Polarity of Water• Polarity results in weak
electrical attraction between neighboring water molecules
• slightly positive Hs in one water molecule attract slightly negatively charged O2 in another water molecule
• opposite electrical charges attract
• water molecules attract each othermaking water kind of sticky
• these weak attractions-hydrogen bonds– weaker than covalent or
ionic bonds
Polarity, H Bonding & Water’s Properties
• cohesive nature
• ability to moderate temperature
• ice floating
• universal solvent properties
Dissociation• compounds formed by ionic
bonds will ionize or dissociate in water
• dissociation produces cations (+) & anions (-)
• aqueous solution containing anions & cations will conduct electrical currents
• cations move to negative side have + change
• anions move to positive side having – charge
• soluble inorganic molecules whose ions will conduct an electrical current in solution are electrolytes– NaCl
• NaCl + H2ONa+ + Cl-
Acids & Bases• H+ & OH- are in solution at all times• H2O <-------> H+ + OH- -reversible
reaction• some compounds add more hydrogen ions• others remove them• compounds that donate hydrogen ions-
acid• HClH+ + Cl-
• acidic solution is one that has more H+ than OH-
Acids & Bases• compound that accepts or
removes hydrogen ion is a base
• NaOHNa+ +OH-
• basic solution-one that has more OH- than H+
pH scale• pH = potential hydrogen• scale developed-1909
by Dane Soren Sorensen– beer brewer looking
for way to check acidity of beer
• describes how acidic or basic a solution is
• scale ranges from 0-14• 0 = most acidic• 14 = most basic• 7=neutral
pH• at neutral pH• H+ = OH-
• pH < 7 is acidic• pH > 7 is basic or alkaline
Buffers• pH of blood ranges
between 7.35-7.45• value must be maintained
in narrow range• even small change can
lead to severe metabolic consequences
• biological fluids contain buffers– substances that resist
changes in pH by accepting H+ when in excess & donating H+
when depleted