Transcript Electrons
Chemicals of Life Chemical Basis of Life • principles of • Structure chemistry help to understand biology long handle • organisms are bags made of wood of chemicals blunt metal end • function of organisms curved, claws & parts of organisms are determined by – way chemicals are arranged • compounds & molecules formed by chemicals • structure determines function Function to hold easier to be strong to hit nails to pull out nails Chemistry • • • • chemicals give cells properties these properties are called life Hierarchy Chemicalsorganellescellstissues organsorganisms 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 corner atomic weight or mass number-number located 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 levelsshells • 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 producespolar bond • bond in which two atoms involved have an equal pull on electrons-nonpolar Water Structure • O2 attracts electrons more strongly than Hgiving 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 attractionshydrogen 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 ionsacid • 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 • = • pH < 7 is acidic • pH > 7 is basic or alkaline + H OH 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