Chemical Reactions (copy)

Chemical Behavior of an atom

  • Determined by the number and arrangment of valence electrons

  • Elements in the same column of the periodic table have similar chemical properties

Compounds and Molecues

  • A chemical compound consists of atoms of 2+ elements

  • Atoms combine in a fixed ratio

  • Atoms mau join to form a molecule

    • 2+ atoms joing together very stronlgy as a stable particle

    • Not all compounds are molecules-depends on the type of bonding that occurs

Chemical Formula

  • A ehemical formula describes the chemical compostion of a substance - 3 types

    • Simplest

    • Molecular

    • Structural

Simplest

  • H2O

  • CH2O

  • C4H5N2O

Molecular

  • H20 — Stays the same

Structural Formula

  • Types, #, arrangement of atoms in the molecule

  • Molecules ,may have the same molceular formula, but have a different structural formula (i.e., organic molecules)

Molecular Mass

  • E Atomica masses of atoms ina molecue

  • N2H4

  • N: 2 × 14.0 = 32.0

  • H: 4 × 1.0 = 4.0

Chemical Reactions in an organism

  • Described by chemical reactions

  • Reactantys are on left

  • Productes are on right

  • Reactions may proceed in both directions

    • Dynamic Equilibrium= forward and revsre rates are equal

  • Coefficents proceed the symbol/for,ula and indicate # of atoms/molecules

Redox Reactions

  • Many energy conversions in a cell invlove in an electron trasnfer from one substance to another

  • Known as oxidation-reduction or redox reaction

  • Reduction: gain of 1+ electrons by an atoms, ion or molecule

  • Oxidation: Loss of 1+ electrons

  • Energy relaese or gained v e-

  • Example: Rusting

Why do redox reactions occur simultaneously

  • Electroms are not easily removed from covalent compuns

  • In cells, redox reactions often invlove atom removal/addition

Hydrogen Bonds

  • Tend to form between

    • An atom with partial negative charge and a hyrogen atom covalenlty bonded to oxygen or nitrogen

  • Readily formed and broken

  • while indivulally weak, hydrogen bons are strong when present in large numbers

  • Interaction of wateer molecules

Water

  • Most of an organis mass= water

    • How much?

  • Water is important as an internal constituent and enviroemental factor

Water is polar

  • H-Bonding

  • Excellent solvent

  • Water facilities chemical reactions

    • Hydrophilic substanctes - interact readilu with water

      • NaCl

    • Hydrophobic substances - dissolved by water

      • fats and other non polar substances

Cohesion and Adhesion

  • Cohesion

    • Like Molecules sticking together

    • Sufrace tesnsion- cohesive forces acting at the surface; water molecules crowd togehter to make a strong layer

  • Adhesion

    • Different molcecules sticking together

    • Why water makes clothes wet

Kinetic energy

  • Energy of motion

  • Increases as temperutre increases —- some molecules to move fatser (must breal some H-Bonds)

Specfic Heat

  • Amount of energy needed to increase water temperture

  • Water hs high specfic heat

    • 1 cal for 1g H2O to 1 degree celsius

  • Why is this important biologically and/or ecologically

Heat of vaporization

  • Amount of energy needed to change 1g of a substance from liquid — vapor

  • H-Bonds give water a high heat of vaporization

  • Evaporative cooling

    • Evaporation of fast moving (heated) water molcules causing cooling

    • sweating

Water Properties

  • Water exists as gas, liquid, or soild

  • Hydrogen bonds are formed or broken as water changes state

  • Why does water expand as it freezees?

  • Water (solid) has 10% lower densisty than in a luqid form

Acid and Bases

  • Acids

    • Substances that dissociates in solution to yield hydrogen ions and an onion

    • Proton donor (H)

  • Base

    • Substance taht dissociates to yield a hydroxide ion and cation when dissolved in water

    • Proton acceptor

pH

  • Defintion of pH

    • The negaive logarithm of hydrogen ion concentrartion

      • -Log[H]

  • The degree of a soultions acidity is expressed in pH

  • Neutral Solution

    • pH=7

  • Acidic Solution

    • pH<7

  • Base Solution

    • pH>7