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Chapter 11: Chemical Elements
Homework: All questions on the “Multiple-Choice” and the odd-numbered questions on“Exercises” sections at the end of the chapter.
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Chemistry
• Chemistry – a division of PhysicalScience
• Chemistry – deals with the compositionand structure of matter and thereactions by which substances arechanged into other substances
• Egyptian, Chinese, and Mesopotamians– wine making, worked metals, dyes,glass, pottery, embalming fluids (asearly as 3500 BC
Intro
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Alchemy & Modern Chemistry
• Flourished from 500 – 1600 AD
• Main objectives (never reached):
– Change common metals to gold
– Find an “elixir of life”
• Modern Chemistry -- began in 1774,with the Frenchman Antoine Lavosier –quantitative methods and avoidedmysticism, superstition, and secrecy
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Major Divisions of Chemistry
• Physical Chemistry – applies thetheories of physics
• Analytical Chemistry – identifies whatand how much is present
• Organic Chemistry – carboncompounds
• Inorganic Chemistry – non-carboncompounds
• Biochemistry – chemical reactions thatoccur in living organisms
Intro
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88 Naturally Occurring Elements
• Either singly or in chemical combination– the 88 naturally occurring elementscomprise virtually all matter.
• Their chemical and physical propertiesaffect us continually
• This chapter (#11) –– Classification of matter
– Discuss elements
– Discuss the Periodic Chart
– Discuss the Naming of Compounds
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Classification of Matter
• In Chapter 5 we saw that matter can beclassified by its physical phase or state –solid, liquid, and gas
• Matter – anything that has mass
• Chemists use this classification, but alsodivide matter into several other classifications
• Pure Substance – element or compound
• Mixture – homogeneous or heterogeneous
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Pure Substance
• Pure Substance – type of matter in which allsamples have fixed composition and identicalproperties
– Element – all atoms have same # of protons (gold,sulfur, oxygen)
– Compound – two or more elements chemicallycombined in a definite, fixed ratio by mass (puresalt, topaz crystal, distilled water)
• A compound can be broken into its separatecomponents only by chemical processes(electrical current)
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Natural minerals -good examples of Compoundsof Pure Substances
Faceted TopazAl2SiO4(OH,F)2
Halite NaCl “rock salt”
Rhodochrosite MnCO3
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Section 11.1
“Lone Star Cut”
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Compound vs. Component ElementsCompound - usually different from the
components
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Mixture
• Mixture – type of matter composed of varyingproportions of two or more substances thatare only physically mixed and not chemicallycombined
– Homogeneous (a solution)– uniform throughout(coffee, alloy) technically, it should bemixed/uniform on the atomic level
– Heterogeneous – non-uniform (pizza, oil/water), atleast two components can be observed
• Formed and broken down by physicalprocesses (dissolving, evaporation)
Section 11.1
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Chemical Classification of Matter
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Liquid Solutions
• Solvent – the liquid or the substance in the larger quantity
• Solute – the substance dissolved in the solvent
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Aqueous Solutions
• Aqueous Solution (aq)– a solution inwhich water is the solvent– When dissolved & stirred the distribution of
the solute is the same throughout(homogeneous)
• Unsaturated Solution – more solute canbe dissolved in the solution at the sametemp.
• Saturated Solution – maximum amountof solute is dissolved in the solvent
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Saturated Solution
• A dynamicequilibriumexistsbetween thesolutedissolving andthe solutecrystallizing
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Solubility
• Solubility – the amount of solute that willdissolve in a specified volume or massof solvent (at a given temperature) toproduce a saturated solution
• If the temperature is raised thesolubilities for most solids increase
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The Effect of Temperature on Solubilities ofSalts in Water
• Usually hotter waterwill dissolve moresolute
Section 11.1
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Supersaturated Solutions
• When unsaturated solutions areprepared at high temperatures and thencooled, the saturation point may bereached as the solution cools
• However, is no crystals are present,crystallization may not take place
• Result Supersaturated Solution –contains more than the normalmaximum amount of dissolved solute atthe given temperature
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Seed Crystal added to a SupersaturatedSolution
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Solubility of Gases
• The solubility of gases increases withincreasing pressure– Example: manufacture of soft drinks, CO2 is forced
into the beverage at high pressure
• Once the soft drink is opened, the pressureinside the container is reduced to normalatmospheric pressure and the CO2 startsescaping
• The solubility of gases decreases withincreasing temperature (hot soft drinks quicklylose their CO2)
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Robert Boyle
• In 1661 Robert Boyle proposed that thedesignation element be applied only tosubstances that could not be separated intocomponents by any method
• In addition Boyle initiated the practice ofcarefully and completely describingexperiments so that anyone might repeat andconfirm them
– Due to this procedure (carefully documentingexperiments) scientists have been able to build onprevious knowledge
Section 11.2
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Discovery of the Elements
• The earliest civilizations isolated 12 elements;gold, silver, lead, copper, tin, iron, carbon,sulfur, antimony, arsenic, bismuth, andmercury – later all 12 proved to be elements
• Phosphorus was isolated (from urine) in 1669
– P is the first element whose date of discovery isknown
• By 1746, platinum, cobalt, and zinc had allbeen discovered
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Discovery of the Elements
• Around 1808 Davy, an English Chemist, usedelectricity from the recently invented battery tobreak down compounds, thereby isolating sixadditional elements (Na, K, Mg, Ca, Ba, Sr)
• By 1895 a total of 73 element were known
• During the next three years the noble gasesHe, Ne, Kr, and Xe were discovered
• In addition to the naturally occurring elements,26 synthetic elements have now been created
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Discovery of the ElementsShowing how many elements were known at points in
history
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Occurrence of the Elements
• Human Body = 65% oxygen & 18% carbon
• Analyses of electromagnetic radiation fromspace indicates that the universe consists of:
– Hydrogen – 75% (simplest element)
– Helium – 24% (second most simple element)
– Others – 1%
• Earth’s Atmosphere = 78% nitrogen, 21%oxygen, and about 1% argon
• Earth’s Core = 85% iron & 15% nickel
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Relative Abundance (by Mass) of Elementsin Earth’s Crust
Note that 74% ofthe mass of theEarth’s crust iscomposed of onlytwo elements –oxygen & silicon
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Atoms
a) The individual units (atoms) packed in arepeating pattern
b) Noble gases that occur as single atoms
c) Diatomic atoms (hydrogen)
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Molecules
• Molecule – an electrically neutral particlecomposed of two or more atomschemically combined
• If the atoms are that same element, thenthe molecule is of an element
– Element examples: H2 or N2
• If the atoms are different elements, thanethe molecule is of a compound
– Compound examples: H2O or NH3
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Representations of Molecules
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Seven common elements that exist asdiatomic molecules
• These atoms are tooreactive to exist asindependent atoms.
• When writing formulas w/these seven elements weus the diatomic form: H2
+Cl2 2HCl
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Allotropes
• Allotrope – two or more forms of thesame element that have differentbonding structures in the same physicalphase
• Example: Diamond and Graphite
• Both pure Diamond and pure Graphiteare each 100% carbon (C), and areboth solid
• But the atomic arrangement of thecarbon atoms is different
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Three Allotropes of CarbonDiamond, Graphite, and Buchminsterfullerene (C60)
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Oxygen also has two AllotropesOxygen gas (O2) and Ozone (O3)
Section 11.3
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The Periodic Table
• The periodic table puts the elements inorder of increasing atomic number, intoseven horizontal rows, called periods
• The elements’ properties show regulartrends going up or down these periods
• In 1869 the Russian Chemist,Mendeleev, published the originalperiodic table
• The fifteen vertical columns in theperiodic table are called groups
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The Periodic TableDivided into 7 Periods and 18 Groups
Section 11.4
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One way to Classify the periodic table
RepresentativeElements (green)
TransitionalElements (blue)
Inner TransitionElements (purple)
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Metals & Nonmetals
• Another way of classifying the elements isinto – metals and nonmetals
• A metal is an element whose atoms tend tolose electrons during chemical reactions (+)
• A nonmetal is an element whose atoms tendto gain (or share) electrons (-)
• The metallic character of the elementsincreases as one goes down a group, anddecreases across (left to right) a period
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Metals/Nonmetals in the Periodic Table
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General Properties of Metals & Nonmetals
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Electron Configuration
• Electrons are located in energy levels orshells that surround the nucleus
– Level 1 – maximum of 2 electrons
– Level 2 – maximum of 8 electrons
– Level 3 – maximum of 18 electrons
• The chemical reactivity of the elementsdepends on the order of electrons inthese energy levels
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We will generally only discuss the“representative elements” – Groups 1A - 8A
Section 11.4
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Valence Electrons
• The outer shell of an atom is known asthe valence shell
• The electrons in the outer shell arecalled the valence electrons
• The valence electrons are the electronsinvolved in forming chemical bonds – sothey are extremely important
• Elements in a given group all have thesame number of valence electrons (and\ similar chemical properties)
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Guidelines: Shell Electron Configurations
• The number of electrons in an atom is thesame as the element’s atomic number (Z)
• The number of shells that contain electronswill be the same as the period number that itis in
• For the A group (representative) elements,the number of valence electrons is the sameas the group number
• Let’s look at Example 11.1 & ConfidenceExercise 11.1 on pages 294-295 in your text
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Electron Shell Distribution for Periods 1,2,3This is an important and very useful figure!
Protons (Z)Electrons
Section 11.4
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The Periodic Nature of Atomic Size
• The atomic size of the elements also variesperiodically (refer to the Periodic Table) – from0.074 nm (H) to 0.47 nm (Cs)
• Atomic size increases down a group
• Atomic size decreases across a period
• The atoms on the far left are the largest due toless charge (fewer protons) in the nucleus and\ the outer electrons are more loosely bound
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Relative Atomic Sizes
Note - the Periodic Table can be used to determine relative atomic size
Section 11.5
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Ionization Energy – also Periodic
• Ionization energy – the amount ofenergy that it takes to remove anelectron from an atom
• Ionization energy increases across aperiod due to additional protons in thenucleus
• Ionization energy decreases down agroup because of the additional shellssituated between the nucleus and theouter electron shell.
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Ionization Energy Trend
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Chemical Formulas
• In order to easily and conveniently discusschemistry we can use their chemical formulas
• Chemical formulas are written by putting theelements’ symbols adjacent to each other –usually w/ the more metallic element first
• A subscript following each symbol designatesthe number of atoms – H2O
• Some compounds have special names
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ElevenCompoundswith Special
Names
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Naming a Binary Compound(Metal + Nonmetal)
• Binary => two-element compound
• First give the name of the metal and thegive the name of the nonmetal,changing its ending to – “ide”
• NaCl sodium chloride
• Al2O3 aluminum oxide
• Ca3N2 calcium nitride
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“ide” Nomenclature
Section 11.5
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Compounds of Two Nonmetals
• The more metallic or less nonmetallicelement (farther left or farther downperiodic chart) is usually written first inthe formula and named first
• The second element is named using the“ide” ending
• Greek prefixes are used to designatethe number of atoms in the molecule
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Examples:
• HCl hydrogen chloride
• CS2 carbon disulfide
• PBr3 phosphorus tribromide
• IF7 iodine heptafluoride
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Polyatomic Ions
• Ion – an atom or chemical combination ofatoms having a net electric charge
• Monatomic ion – an ion formed from a singleatom (Cl-)
• Polyatomic ion – an electrically chargedcombination of atoms (CO3
2-)
• Name the metal and then the polyatomic ion
– ZnSO4 zinc sulfate
– NaC2H3O2 sodium acetate
– Mg(NO3)2 magnesium nitrate
– K3PO4 potassium phosphate
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CommonPolyatomic Ions
Section 11.5
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Acids -- when hydrogen (H) is combinedwith polyatomic ions
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Naming Compounds - Example
• H2SO4 sulfuric acid (special name)
• ZnCO3 zinc carbonate (metal + polyatomicion)
• Na2S sodium sulfide (binary compound ofmetal + nonmetal)
• NH3 ammonia (special name)
• NH4NO3 ammonium nitrate (ammoniumion + polyatomic ion)
Section 11.5
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Flowchart: Naming Compounds
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Groups of Elements
• Recall that in the Periodic Table eachindividual column is called a group
• All the elements in a group have thesame number of valence electrons
• If one element in a group reacts with asubstance – the other elements in thegroup usually react similarly
• The formulas of the compounds createdare also similar
• We will discuss four of these groups …
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Alkali Metals Noble Gases
Alkaline Earth Metals Halogens
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Alkaline Earth Metals Halogens
Alkali Metals Noble Gases
1 2 7 8
Section 11.6
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Noble (Inert) Gases – Group 8A
• The exist as single atoms (monatomic)
• Almost never react and form compounds
• Noble gases have 8 electrons in their outershells (except He that has a full shell with 2)– Eight electrons in the outer shell must be VERY
stable
• “Neon” signs contain minute amounts ofvarious noble gases – electric current glow!
• Argon gas is used inside light bulbs becauseeven at high temps. it will not react with thetungsten filament (W)
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Alkaline Earth Metals Halogens
Alkali Metals Noble Gases
1 2 7 8
Section 11.6
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Alkali Metals – Group 1A (not H)
• Each alkali metal atom has only one valenceelectron
• \ tends to lose this electron ( +) and readilyreact with other elements – active metals
• Na & K are abundant (Li, Rb, Cs are rare)
• So reactive w/ oxygen and water that they mustbe stored in oil
• NaCl, K2CO3 (potash), Na2CO3 (washing soda).NaOH (lye), NaHCO3 (baking soda)
• Predict formulas KCl, LiCO3
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Alkaline Earth Metals Halogens
Alkali Metals Noble Gases
1 2 7 8
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Halogens – Group 7A
• Each halogen atom has seven valence electrons
• \ tends to gain an electron and readily reactwith other elements active nonmetals
• Only occur in nature as a compound, but whenpurified occur as a diatomic molecule (F2, Cl2) –generally poisonous
• F is the most reactive – will corrode Pt andcause wood, rubber, water catch fire on contact
• Iodine is necessary for proper thyroid function
• AlCl3 (aluminum chloride), NH4F (ammoniumfluoride), CaBr2 (calcium bromide)
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Iodine Deficiency Goiter
• A lack ofiodine in thediet can leadto anenlargedthyroid gland
Section 11.6
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Alkaline Earth Metals Halogens
Alkali Metals Noble Gases
1 2 7 8
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Alkaline Earth Metals – Group 2A
• This group contains two valence electrons, andtend to lose two electrons ( +2)
• Not as chemically active as alkali metals (1A),and are generally harder and stronger
• Be2Al2(SiO3)6 – (beryl) , Mg(OH)2 (milk ofmagnesia), CaCO3 (calcite), Ca3(PO4)2 (bones& teeth), BaSO4 (barite); Sr (red) & Ba (green)give color in fireworks
• Ra is radioactive – RaCl2 used on watch dials(glowed in dark) until a number of Swiss dial-painters came down with stomach cancer!!
Section 11.6
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Hydrogen – Group 1A usuallysometimes Group 7A
• Although a nonmetal, H usually reacts likea alkali metal (HCl, H2S)
• Sometimes reacts like a halogen – NaH,CaH2
• At room temp. – colorless, odorless,diatomic
• Lightest element – was used in earlydirigibles
• Will burn in air to form water
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Hindenburg, Lakehurst, NJ; 5/6/37
• UsedflammableH forbuoyancy.Airshipstoday useHe.
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