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Unformatted text preview: Chapter 02 Basic Chemistry Basic Chemistry 2 Outline Chemical Elements Atoms Isotopes Molecules and Compounds Chemical Bonding Ionic and Covalent Hydrogen Properties of Water Acids and Bases Basic Chemistry 3 Chemical Elements Matter: Refers to anything that has mass and Refers occupies space occupies Only 92 naturally occurring fundamental types Only of matter – 92 Elements Elements Organisms composed primarily (98%) of only Organisms six elements six Carbon, Hydrogen, Nitrogen, Oxygen, Carbon, Phosphorus, Sulfur Phosphorus, CHNOPS Composition of Earth’s Crust versus Organisms 4 Basic Chemistry 5 Atomic Structure Atoms - Smallest particles of elements Atoms composed of three types of subatomic Atoms particles particles Protons ­ Positive charge ­ In nucleus ­ Neutral charge ­ Also found in nucleus ­ Negatively charge ­ Orbit nucleus Neutrons Electrons Basic Chemistry 6 Atomic Symbols Each element represented by unique atomic Each symbol symbol Mass One or two letters First letter capitalized ­ Represents mass number Number Atomic Number 12 6 C Superscripted number before: Carbon Atomic Symbol ­ Count of protons plus count of neutrons Subscripted number before ­ Represents to atomic number ­ Number of protons in nucleus Basic Chemistry 7 Periodic Table Elements grouped in periodic table based on Elements characteristics characteristics Vertical columns = groups; chemically similar Horizontal rows = periods; larger and larger I 1H Periods 1 1.008 3 II 4 2 Groups He III IV V VI VII 4.003 5 6 7 8 9 10 VIII 2 Li Be B C N P O S F Ne 3 Na Mg Al Si 6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18 Cl Ar 4 K Ca Ga Ge As Se Br Kr 22.99 24.31 26.98 28.09 30.97 32.07 35.45 39.95 19 20 21 22 23 24 25 26 39.10 40.08 69.72 72.59 74.92 78.96 79.90 83.60 Basic Chemistry 8 Isotopes Isotopes: Atoms of the same element with a differing Atoms numbers of neutrons numbers Carbon 12 12 6 C Carbon 13 13 6 C Carbon 14 14 6 C Some isotopes spontaneously decay ­ Radioactive ­ Give off energy in the form of rays and Give subatomic particles subatomic ­ Can be used as tracers ­ Mutagenic – Can cause cancer Some Medical Uses for Low Level Radiation 9 Some Medical Uses for High Level Radiation 10 Electron Shells, Orbitals and Energy Levels Basic Chemistry 11 Atoms normally have as many electrons as Atoms protons protons Opposite charges balance leaving atom Opposite neutral neutral Electrons are attracted to the positive nucleus Revolve around nucleus in orbitals Can be pushed into higher orbitals with Can energy energy Release that energy when they fall back to Release lower orbital lower Different energy levels referred to as electron Different shells shells The Octet Rule for The Octet Distribution of Electrons Basic Chemistry 12 Bohr models show electron shells as electron concentric circles around nucleus concentric Each shell has two or more electron orbitals Each electron ­ Innermost shell has two orbitals ­ Others have 8 or multiples thereof Atoms with fewer than 8 electrons in Atoms outermost shell are chemically reactive outermost If 3 or less – Tendency to donate electrons If donate If 5 or more – Tendency to receive electrons If receive Bohr Models of Atoms 13 Periodic Table (Revisited) Vertical columns indicate number of electrons in outermost shell I 1 14 VIII 2 Horizontal periods indicate total number of electron shells 1 2 3 4 H 1.008 3 II 4 III 5 IV 6 V 7 VI 8 VII 9 He 4.003 10 Li Be B C Si 22 N P 23 O S 24 F Ne 6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18 Na Mg Al 19 20 21 Cl Ar 25 26 22.99 24.31 26.98 28.09 30.97 32.07 35.45 39.95 K Ca Ga Ge As Se Br Kr 39.10 40.08 69.72 72.59 74.92 78.96 79.90 83.60 Basic Chemistry 15 Elements and Compounds Molecule - Two or more atoms bonded Molecule together together If all atoms in molecule are of the same If element element ­ Material is still an element ­ O2, H2, N2, etc. If at least one atom is from a different element ­ Material formed is a compound ­ CO2, H2O, C6H12O6, etc. ­ Characteristics dramatically different from Characteristics constituent elements constituent Basic Chemistry 16 Chemical Bonding Bonds between atoms are caused by Bonds electrons in outermost shells electrons The process of bond formation is called a The reaction reaction The intensity of simple reactions can be The predicted by the periodic table predicted If two elements are horizontally close in the If table, they usually react mildly table, If they are horizontally far apart, they usually If react vigorously react Types of Bonds: Ionic Bonding Basic Chemistry 17 Ionic Bonds If Octet rule: ­ Atoms “want” 8 electrons in outer shell Consider two elements from opposite ends Consider of periodic table of ­ Element from right side: Has have < 4 outers, desire to donate them If have > 4 outers, desire to receive more ­ Element from left side: Has 7 electrons in outer shell “Desperately wants” one more (7+1=8) only 1 electron in outer shell “Desperately wants” to donate it (1-1=0=8) Types of Bonds: Ionic Bond Example Sodium: From left end Has 1 outer electron Basic Chemistry 18 Chlorine: From right end of table Has 7 outer electrons In reaction, Na completely gives up its outer In electron to Cl electron Na now a positive ion and Cl a negative ion Dissimilar charges now bind ions together Forms sodium chloride ­ An ionic compound ­ NaCl table salt) Formation of Sodium Chloride 19 Types of Bonds: Covalent Bonds Basic Chemistry 20 When atoms are horizontally closer together in the When periodic table periodic The electrons are not permanently transferred from The one atom to the other like in NaCl one A pair of electrons from the outer shell will “time pair share” with one atom and then the other share” This also causes the atoms to remain together Known as covalent bonding Sometimes two par of electrons are shared between Sometimes atoms – a double covalent bond atoms Covalently Bonded Molecules 21 Basic Chemistry 22 Nonpolar Covalent Bonds Consider two elements that are equidistant Consider from the edges of the periodic table from Atoms will have about equal affinity for Atoms electrons electrons ­ One will “want” (with a specific intensity) to One donate electron(s) donate ­ The other will “want,” with the same intensity, The to receive electron(s) to When bonded covalently: ­ The bond electrons will spend about equal time The with both atoms with ­ Such covalent bonds are said to be nonpolar Basic Chemistry 23 Polar Covalent Bonds Consider two elements with one much closer to Consider the edge of the table than the other the Atoms will have unequal affinity for electrons ­ One will “want” (with a specific intensity) to donate One or receive electron(s) or ­ The other will “want” (with a different intensity) to The different donate or receive electron(s) donate When bonded covalently: The bond electrons will spend more time with one The atom than the other atom ­ The atom that gets the most time with the electrons The will be slightly negative will ­ The other will be slightly positive Such covalent bonds are said to be polar Types of Bonds: Hydrogen Bonds Basic Chemistry 24 Water (H2O or H–O–H) is a polar molecule Electrons spend more time with O than H’s H’s become slightly +, O slightly – H’s slightly When polar molecules are dissolved in water The H’s of water molecules are attracted to the The negative parts of the solute molecules negative Results in a weak bond – the hydrogen bond Results the Easily broken, but many together can be quite Easily strong strong Water Molecule 25 Hydrogen Bonding 26 The Chemistry of Water: Heat Capacity Water has a high heat capacity Basic Chemistry 27 Temperature = rate of vibration of molecules Apply heat to liquid ­ Molecules bounce faster ­ Increases temperature But, when heat applied to water ­ Hydrogen bonds restrain bouncing ­ Temperature rises more slowly per unit heat ­ Water at a given temp. has more heat than most liquids Thermal inertia – resistance to temperature change More heat required to raise water one degree than most More other liquids (1 calorie per gram) other Also, more heat is extracted/released when lowering Also, water one degree than most other liquids water Properties of Water: Heat of Vaporization High heat of vaporization Basic Chemistry 28 To raise water from 98 to 99 ºC; ~1 calorie To raise water from 99 to 100 ºC; ~1 calorie However, large numbers of hydrogen bonds must be However, broken to evaporate water broken To raise water from 100 to 101 ºC; ~540 calories! This is why sweating (and panting) cools Evaporative cooling is best when humidity is low Evaporative because evaporation occurs rapidly because Evaporative cooling works poorest when humidity is Evaporative high because evaporation occurs slowly high Evaporative Cooling of Animals 29 Properties of Water: Heat of Fusion Heat of fusion (melting) Basic Chemistry 30 To raise ice from -2 to -1 ºC; ~1 calorie To raise water from -1 to 0 ºC; ~1 calorie To raise water from 0 to 1 ºC; ~80 calories! This is why ice at 0 ºC keeps stuff cold MUCH This longer than water at 1 ºC longer This is why ice is used for cooling NOT because ice is cold But because it absorbs so much heat before it But will warm by one degree will Heat Content of Water at Various Temperatures 31 Properties of Water: Water as a Solvent Solutions consist of: Basic Chemistry 32 Polar compounds readily dissolve; hydrophilic Polar hydrophilic Nonpolar compounds dissolve only slightly; Nonpolar hydrophobic hydrophobic Ionic compounds dissociate in water Na+ Cl­ Attracted to negative (O) end of H2O ­ Each Na+ completely surrounded by H2O ­ Attracted to positive (H2) end of H2O ­ Each Cl- completely surrounded by H O A solvent (the most abundant part) and solvent A solute (less abundant part) that is dissolved in solute the solvent the Properties of Water: Uniqueness of Ice Basic Chemistry 33 Frozen water less dense than liquid water Otherwise, oceans and deep lakes would fill Otherwise, with ice from the bottom up with Ice acts as an insulator on top of a frozen Ice body of water body Melting ice draws heat from the environment Density of Water at Various Temperatures 34 A Pond in Winter 35 Water as a Transport Medium 36 Properties of Water: Cohesion & Adhesion Cohesive and Adhesive Basic Chemistry 37 Cohesion – Hydrogen bonds hold water molecules tightly together tightly Adhesion – Hydrogen bonds for between water and other polar materials other Allow water be drawn many meters up a tree in a Allow tubular vessel tubular High Surface Tension High Surface Water molecules at surface hold more tightly than Water below surface below Amounts to an invisible “skin” on water surface Allows small nonpolar objects (like water strider) to Allows sit on top of water sit pH of Water: Acids Basic Chemistry 38 Acids Dissociate in water and release Dissociate hydrogen ions (H+) hydrogen Sour to taste Hydrochloric acid (stomach acid) is a Hydrochloric gas with symbol HCl gas ­ In water, it dissociates into H+ and Cl­ Dissociation of HCl is almost total, therefore Dissociation it is a strong acid it pH of Water: Bases Basic Chemistry 39 Bases: Either take up hydrogen ions (H+) or or release hydroxide ions (OH-) release Bitter to taste Sodium hydroxide (drain cleaner) is a Sodium solid with symbol NaOH solid ­ In water, it dissociates into Na+ and OH­ Dissociation of NaOH is almost total, Dissociation therefore it is a strong base therefore Basic Chemistry 40 pH Scale pH scale used to indicate acidity and pH alkalinity of a solution. alkalinity Values range from 0-14 ­ 0 to <7 = Acidic ­ 7 = Neutral ­ >7 to 14 = Basic (or alkaline) Logarithmic Scale ­ Each unit change in pH represents a change of Each 10X 10X ­ pH of 4 is 10X as acidic as pH of 5 ­ pH of 10 is 100X more basic than pH of 8 The pH Scale 41 Basic Chemistry 42 Buffers and pH When H+ is added to pure water at pH 7, pH goes down and water becomes acidic goes When OH- is added to pure water at pH 7, pH goes up and water becomes alkaline goes Buffers are solutes in water that resist change Buffers in pH in When H+ is added, buffer may absorb, or counter by adding OHcounter When OH- is added, buffer may absorb, or counter by adding H+ counter Basic Chemistry 43 Buffers in Biology Health of organisms requires maintaining pH Health of body fluids within narrow limits of Human blood normally 7.4 (slightly alkaline) Many foods and metabolic processes add or Many subtract H+ or OH- ions subtract or OH ­ Reducing blood pH to 7.0 results in acidosis ­ Increasing blood pH to 7.8 results in alkalosis ­ Both life threatening situations Bicarbonate ion (-HCO3) in blood buffers pH to in 7.4 7.4 Basic Chemistry 44 Review Chemical Elements Atoms Isotopes Molecules and Compounds Chemical Bonding Ionic and Covalent Hydrogen Properties of Water Acids and Bases Ending Slide Chapter 02 Basic Chemistry ...
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This note was uploaded on 02/22/2011 for the course ECO 101 taught by Professor Na during the Spring '11 term at Central GA Tech.

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