The Periodic Table 98 % of living organisms are made up of C, H, N, O, S, P
Isotopes Some isotopes are unstable: Radioisotopes give off energy in the form of alpha, beta, and gamma radiation from the nucleus.
ElectronsThe number of electrons determines how atoms will interact.Chemical reactions involve changes in the distribution of electrons between atoms.
Orbital TheoryLocations of electrons inan atom are described byorbitals.Orbital: region whereelectron is found at least90% of the time.Orbitals havecharacteristic shapesand orientations, and canbe occupied by twoelectrons.Orbitals are filled in aspecific sequence.
Orbital TheoryOrbitals occur in a series called electron shells orenergy levels.First shell: one s orbital (holds 2 electrons)Second shell: 1 s and 3 p orbitals (holds 8electrons)Additional shells: 4 orbitals (8 electrons)Octet Rule!
So how does Orbital Theory work?Fill electrons from the inside out.The outermost energy shell is called theValence Shell
How Do Atoms Bond to Form Molecules?Chemical bond: attractive force thatlinks atoms together to formmolecules.Valence shells of each atom interact
Covalent Bonds Atoms share one or more pairs of electrons, so that the outer shells are filled.Strongest Bonds(takes a lot of energy to break)
Compound: amolecule made upof two or moreelements bondedtogether in a fixedratio.The molecularweight of acompound is thesum of the atomicweights of allatoms in themolecule.
Element Usual # of Covalent Bonds Hydrogen (H) 1 Oxygen (O) 2 Sulfur (S) 2 Nitrogen (N) 3 Carbon (C) 4Phosphorus (P) 5
Types of Covalent BondsCovalent bonds can be• Single—sharing 1 pair of electrons• Double—sharing 2 pairs of electrons• Triple—sharing 3 pairs of electrons
ElectronegativitySharing of electrons in a covalent bond is not always equal.Electronegativity: the attractive force that an atomic nucleus exerts on electrons.
Polar / Non-polar Covalent Bonds• A polar covalent bond results when electrons are drawn to one nucleus more than to the other, because one atom has more electronegativity What type of polar molecule Is this?• What about a non-polar covalent bond?
Ionic BondsWhen one atom is much more electronegative than the other, a complete transfer of electrons may occur.This results in two ions with fully paired electrons in their outer shells. (Not an ionic bond!)
Ionic Bonds• The charged ions the interact to form an ionic bond• Opposites attract…
IonsIons: electrically charged particles— when atoms lose or gain electrons Cations—positive Anions—negativeIonic bonds are formed by the electrical attraction of positive and negative ions.Salts are ionically bonded compounds.
Water is a polar compoundwhich can dissolve a salt
Hydrogen BondsHydrogen bonds:attraction betweenthe δ– end of onemolecule and the δ+hydrogen end ofanother molecule.Water/DNA/Proteins
Hydrophobic InteractionsPolar molecules that formhydrogen bonds with waterare hydrophylic (“water-loving”).Nonpolar molecules suchas hydrocarbons thatinteract with each other,but not with water, arehydrophobic(“water-hating”).
van der Waals forcesvan der Waals forces: attractions betweennonpolar molecules that are closetogether.Individual interactions are brief and weak,but summed over a large molecule, can besubstantial.
Chemical ReactionsOccur when atoms collide with enoughenergy to combine or change theirbonding partners.
Water has a unique structure whichallows it to have “Special Properties” - Polar molecule - Forms hydrogen bonds - Tetrahedral shape
Phase Shift of Water• Latent Heat – heat given off or absorbed during phase change www.piercecollege.com/offices/weather/water.html
Special Properties of Water: Ice Floats– Less Dense– Most Stable (lower energy state)EnvironmentalSignificant? • Oceans • Horticulture
Special Properties of Water: Heat CapacityHeat StorageWater has high specificheat: the amount of heat energy required to raise the temperature of 1 gram of water by 1°C. http://sci.gallaudet.edu/strait.gif Environmental Significance?
Special Properties of Water: Evaporational CoolingHeat of Vaporization (Latent) • Uses Energy to break H-bonds • Energy is absorbed during the transition from liquid to water vaporEnvironmental Significance?
Special Properties of Water: CohesionIn liquid 3.4 H- bonds at all timesEnvironmental Significance – Surface Tension – Transpiration
Aqueous SolutionsA solution is a substance (solute)dissolved in a liquid (solvent).Acids/BasesBuffers
Acids and Bases + − HCl → H + Cl Acids: dissolve in water Strong Acid and release hydrogen ions: H+ (protons). − COOH → −COOH − + H + Weak Acid NaOH → Na + + OH − Bases: accept H+ ions. Strong Base − + OH + H → H 2O − HCO3 + H + → H 2CO3 Weak Base Reduces H +
Is water an acid or a base? + − H 2O → H + OH• Water acts as both a weak acid and a weak base.• Water has a slight tendency to ionize.
pHpH = negative log of themolar concentration of H+ions. pH = − log H [ ] +H+ concentration ofpurewater is 10–7 MpH = 7.10–7 [H+] + 10–7 [OH-] = 10–14Lower pH numbers meanhigher H+ concentration, orgreater acidity.
pH Questions• If the pH of a • If a solution has a solution was 2. [ H+]=10-5 – [ H+]=? – pH=? – [OH-]=? – [OH-]=?
BuffersLiving organisms + HCO3 + H ⇔ H 2CO3maintain constantinternal conditions(homeostasis).Buffers help maintainconstant pH.A buffer is a weak acidand its correspondingbase.