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ATOMS
• SMALLEST PARTICLES OF ELEMENTS
• PROTONS– UNCHARGED PARTICLES
• ELECTRONS– NEGATIVELY CHARGED PARTICLES
• NEUTRONS– POSITIVELY CHARGED PARTICLES
• Protons and neutrons are in the nucleus.
• Electrons move around the nucleus.
The Study of Atoms
Figure 2.1
• ISOTOPES OF AN ELEMENT ARE ATOMS WITH DIFFERENT NUMBERS OF NEUTRONS. ISOTOPES OF OXYGEN ARE:EACH CHEMICAL ELEMENT HAS A DIFFERENT NUMBER OF PROTONS.
ISOTOPES
OCTET RULE
• ATOMS ARE MOST STABLE WHEN THEIR OUTERMOST SHELLS ARE FILLED WITH 2 ELECTRONS THE FIRST FEW ELEMENTS & 8 ELECTRONS FOR THE LARGER ATOMS
ATOMS FORM MOLECULES
• ATOMS COMBINE TO COMPLETE THE OUTERMOST SHELL
• THE NUMBER OF MISSING OR EXTRA ELECTRONS IN THIS SHELL IS THE VALENCE
• COMBINE IN FIXED RATIOS
• A compound contains different kinds of atoms.
• The forces holding atoms in a compound are chemical bonds.
How Atoms Form Molecules: Chemical Bonds
• The number of protons and electrons is equal in an atom.
• Ions are atoms that have gained or lost electrons and are charged.
How Atoms Form Molecules: Chemical Bonds
Figure 2.2a
• Covalent bonds form when two atoms share one or more pairs of electrons.
Covalent Bonds
Figure 2.3a
• Hydrogen bonds form when a hydrogen atom covalently bonded to an O or N atom in another molecule.
Hydrogen Bonds
Figure 2.4
• Ionic bonds are attractions between ions of opposite charge. One atom loses electrons and another gains electrons.
Ionic Bonds
Figure 2.2b
• CHEMICAL REACTIONS INVOLVE THE MAKING OR BREAKING OF BONDS BETWEEN ATOMS.
• A CHANGE IN CHEMICAL ENERGY OCCURS DURING A CHEMICAL REACTION.
• ENDERGONIC REACTIONS ABSORB ENERGY.
• EXERGONIC REACTIONS RELEASE ENERGY.
CHEMICAL REACTIONS
METABOLIC CHEMICAL REACTIONS ARE REVERSIBLE
• USUALLY LITTLE FREE DIFFERENCE BETWEEN REACTANTS AND PRODUCTS
• THIS MEANS AS LONG AS EXTERNAL ENERGY IS AVAILABLE MOST REACTINS IN LIVING CELLS ARE THEORETICALLY REVERSIBLE– ALLOWS CELLS TO CONTROL RELEASE OF
FREE ENERGY– ALLOWS CELLS TO RESYNTHESIZE
BIOLOGICAL MOLECULES
• THE DIRECTION OF A REVERSIBLE REACTION WILL DEPEND ON:– THE CONCENTRATIONS OF THE
CHEMICALS– THEIR ENERGY RELATIONSHIPS – THEIR SOLUBILITY
TYPES OF CHEMICAL REACTIONS
• SYNTHESIS REACTIONS
• DECOMPOSITION REACTIONS
• EXCHANGE REACTIONS
• REVERSIBLE REACTIONS
• Occur when atoms, ions, or molecules combine to form new, larger molecules
• Anabolism is the synthesis of molecules in a cell.
Synthesis Reactions
• Occur when a molecule is split into smaller molecules, ions, or atoms.
• Catabolism is the decomposition reactions in a cell.
Decomposition Reactions
• Can readily go in either direction.
• Each direction may need special conditions.
Reversible Reactions
REDOX REACTIONS
REDOX REACTIONS: PAIRED OXIDATION AND REDUCTION REACTIONS
• OXIDATION: LOSS OF ELECTRONS• REDUCTION: GAIN IN ELECTRONS• ORGANIC MOLECULES LOSE
HYDROGEN ATOMS RATHER THAN JUST ELECTRONS
PROPERTIES OF WATER
• POLAR MOLECULE
• EXCELLENT SOLVENT
• COHESIVE
• ADHESIVE
• TENDS TO MAINTAIN A STABLE TEMPERATURE
• HIGH SPECIFIC HEAT
• Hydrogen bonding between water molecules makes water a temperature buffer.
WATER AS A TEMPERATURE BUFFER
Figure 2.4b
HEAT OF VAPORIZATION
• IT TAKE 540 CALORIES TO CHANGE ONE GRAM OF LIQUID WATER INTO ONE GRAM OF WATER VAPOR
WATER BECOMES LESS DENSE AS IT FREEZES
• REACHES MAXIMUM DENSITY AT 4 DEGREES C
• EXPANDS AGAIN AS TEMPERATURE EXPANDS
• THIS IS WHY LAKES AND POOLS FREEZE FROM SURFACE DOWN & ICE FLOATS
• ALL CHEMICAL REACTIONS IN THE CELLS AND EXTRACELLULAR FLUIDS TAKE PLACE IN SOLUTION
• H+ AND OH PARTICIPATE IN CHEMICAL REACTIONS
Water
• A salt is a substance that dissociates into cations and anions, neither of which is H+
or OH.
NaCl Na+ + Cl
SALTS
Figure 2.6c
IMPORTANCE OF SALTS
• SOURCE OF MINERAL IONS• ESSENTIAL FOR:
– FLUID BALANCE– ACID-BASE BALANCE– NERVE AND MUSCLE FUNCTION– BLOOD CLOTTING– BONE FORMATION– ETC
• The amount of H+ in a solution is expressed as pH.
• pH = log[H+]
• Increasing [H+], increases acidity.
• Increasing [OH] increases alkalinity.
• Most organisms grow best between pH 6.5 and 8.5.
Acid-Base Balance
BUFFERS
• OPERATE TO MAINTAIN APPROPRIATE pH levels
• WEAK ACID, WEAK BASE AND THE SALT OF THE ACID AND BASE