Science 8: Bonding, Chemical Reactions and pH AcidBase

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Science 8 Bonding, Chemical Reactions and pH
(Acid-Base)

• Adapted from Chemistry of Matter Prentice Hall
• Adapted by Jim Barnaby 2004

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General Theme

• General theme
• How the periodic table can be used to gain
  insight into the nature of chemical bonding
• Electron Affinity
• The ability of an atom to attract additional
  electrons

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Bonding and periodic table

• How many electrons an atom attracts is a function
  of its position on the periodic table
•  
• Periodic table elements in the upper right
  corner have the greatest electron affinity, while
  those elements in the lower left corner have the
  smallest electron affinity.

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Ion review

• Atoms are electrically neutral
• How can an atom become an ion? ( or charge)
• An atom becomes an ion by gaining or losing
  electrons
• The number of protons must stay the same or
  create a new element
• Electrons of all atoms are identicalEach has the
  same quantity of negative charge and the same
  mass

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Cation review

• Ion
• A charged atom
•  
• Cation
• Positive ion ()
• Loses electrons
• Gives away electrons
• Metals (left side of periodic table)

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Anion Review

• Anion
• Negative ion (-)
• Gains electrons
• Takes electrons
• Non-metals (right side of periodic table)

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Chemical Bonding

• Chemical Bonding
• The combining of atoms of elements to form new
  substances
•  
• Atoms that have complete (filled) outermost
  electron energy levels are stable and therefore,
  usually do not form chemical bonds (ex. Noble
  Gases)

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Bonding rocks

• The electron arrangement of the outermost energy
  level of an atom determines whether or not the
  atom will form chemical bonds.
•  
• In general, an atom will bond with another atom
  if the bonding gives both atoms complete
  outermost energy levels.

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Octet Rule (Crazy 8s)

• Octet Rule
• In forming compounds, atoms tend to achieve the
  electron configuration of a noble gas. All noble
  gases, except He, have 8 valence electrons
•  
• When bonding, atoms want 8 valence electrons (in
  their outer shell)

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Ionic Bonding

• Ionic Bond
• Bonding that involves a transfer of electrons
  (one atom gains electrons, while the other atom
  loses electrons)
• Metal atoms lose electrons to become cations ()
• Non-metal atoms gain electrons to become anions
  (-)

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Ionic Bonds

• Ionic Bond
• Electrons are transferred
• Cations and anions are pulled together by an
  electrical force
• General rule is that opposites attract
• Ionic bonding occurs between metals (cations) and
  non-metals (anions)
• Draw Na and Cl on board

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Ionic Compounds

• Ionic Compound
• A chemical compound made up of ions (ionically
  bonded ions)
• NaCl, CaF2, KI, LiCl, MgCl2, Al2O3
•  
• Ionic compounds typically consist of elements
  found on opposite sides of the periodic table
  (metal ion and non-metal ion)

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Ions

• Na, Li, K each lost 1 electron
• Mg2, Ca2, Ba2 each lost 2 electrons
• O2-, S2- each gained 2 electrons
• F-, Cl-, Br- each gained 1 electron

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Oxidation Number

• Oxidation number
• Na, Ca2, Al3, F-, O2-, N3- number of
  electrons an atom loses, gains or shares to form
  chemical bonds (superscript number with charge)
•  
• The sum of oxidation numbers of atoms in a
  compound must be zero (neutral)

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Ionic Formulas

• For all ionic compounds, positive and negative
  charges must balance (ionic compounds are
  neutral)
•  
• Ca2 F-
• Therefore, 2 F- ions are needed to balance Ca2
  the formula is CaF2

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Ionic Formulas

• Aluminum Oxide
• Al3 O2-
• Need Al2 O3
• Charge 6 6- charges must balance (net charge
  is zero)

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Covalent Bond

• Covalent bond- bonding where electrons are shared
• Co- means sharing valent- refers to valence e-
  being shared
• In covalent bonding, the positively charged
  nucleus of each atom simultaneously (at the same
  time) attracts the negative (-) electrons that
  are being shared. This attraction between the
  nucleus and the shared electrons hold the atoms
  together.

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Covalent Bonds

• Covalent bonds occur between non-metals. (H is
  considered a non-metal) Elements on upper right
  side of periodic table.
•  
• Noble gases are exception,- their outer electron
  shells are full, therefore, they have no
  electron affinity and do not form covalent bonds

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Diatomic molecules

• Covalent bonding often takes between atoms of the
  same element. These elements are called diatomic
  elements. Two diatomic elements bonded together
  forms a diatomic molecule.

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Electron Dot Structures

• Valence electrons are usually the only electrons
  used in chemical bonds, therefore only valence
  electrons are shown in electron dot structures.
• Following are electron dot structures for some
  elements and compounds.
• Draw on board
• Use word document to show double, triple covalent
  bonds

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Molecule

• Molecule
• A group of atoms held tightly together by
  covalent bonds
• Ex H2, O2, N2, CO2, H2O, CO2, H2S

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Metallic Bond

• Metallic Bond
• Formed between metals
• The positive nuclei of atoms of metals are
  surrounded by free-moving, or mobile, electrons
  that are all attracted by the nuclei at the same
  time. All the metal atoms share this sea of
  electrons.

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Metallic Bonding

• This sea of electrons (electron mobility)
  accounts for metallic properties high heat and
  electrical conductivity, opaque and shiny
  (metallic) luster, ductile and malleable
  properties

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Compare bonds

• Compare ionic, covalent and metallic bonds
• Metallic bond network of positively charged
  metal ions are held together within a fluid of
  freely moving electrons
• Ionic bond transfer of electrons
• Covalent bond sharing electrons (like a
  marriage)
• Review bond types using periodic table (word doc)

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Determine type of bond

• Based on their positions in the periodic table,
  predict whether each pair of elements will form
  an ionic, covalent or metallic bond
• Au Pt
• S Cl
• Ca Cl
• Fe Cr
• C Br

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Determine bond type

• C C
• Rb I
• S Mg
• Ge As
• Cl I
• Ba At
• Al O
• H O

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Chemical Reaction

• Review
• Chemical Change (Chemical Reaction)
• New substances with different properties are
  formed
• A substance changes its chemical identity, atoms
  are re-arranged to produce a new substance with
  different properties

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Chemical Reaction

• Chemical Reaction
• New substance is formed by the re-arrangement of
  atoms

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Evidence of Chemical Rxn

• Evidence of chemical change
• Color change, rust, exothermic (hot-produces
  heat energy), endothermic (cold-absorbs heat
  energy), light, bubbles, burning, explosion
  (releases energy), flammabilityability to burn
• The main difference between a physical and a
  chemical change is that a chemical change
  involves the production of a new substance.
  Physical changes are easily reversed.

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Energy and Reactions

• Chemical Reaction
• Always forms a new substance
• Chemical reaction
• In a chemical reaction, energy is either absorbed
  or released
• Existing bonds are broken, atoms are rearranged,
  new bonds are formed to produce new substances

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Chemical Equations

• Chemical Equation
• Representation of a chemical reaction showing
  numbers of reactants and products
•   Yield
• Reactants Products

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Reactants/Products

• Reactants
• are substances about to react. (left side of
  arrow)
• Products
• new substance formed by the chemical reaction
  (right side of arrow)
• Coefficients
• Numbers in front of chemical formulas (ex 5
  HCl, 4 NaOH)

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Conservation of Mass

• Principle of Conservation of Mass
• Matter is neither created or destroyed in a
  chemical reaction
• No atoms are gained or lost in a chemical
  reaction. Atoms (rearrange) switch partners to
  form new molecules

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Balancing Equations

• Due to law of conservation of mass the equation
  must be balanced (each atom in the equation must
  appear on both sides of the arrow the same number
  of times)
• Write equation on board
• You may change the coefficient but never change
  the subscript

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Balancing Equations

• Use the law of conservation of mass to balance
  the following equations. (write on board and
  balance as a class, volunteers)
• Complete balancing equations worksheet
• Use textbook to complete study guide

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Molecular Mass

• Molecular Mass (Formula Mass)
• Add the atomic masses of all the atoms in a
  molecule (compound)
• H2O
• 2 H atoms 2 ? 1.0 amu 2 amu
•     1   O atom 1 ? 16.0 amu 16 amu
• 18 amu

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Formula Mass

• CaCl2
• 1 Ca atom 1 ? 40.0 amu 40 amu
• 2 Cl atoms 2 ? 35.0 amu 70 amu
• 110 amu
•  H2SO4
• C12H22O11
• NaHCO3

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Energy and Chemical Reactions

• Energy and Chemical Reactions
• It takes energy to break a chemical bond and
  energy is released when a chemical bond is formed

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Energy and Chemical Reactions

• Analogy with magnets energy to pull apart and
  energy is released when the magnets come together
  in the form of KE and heat energy. Holding with
  the principle of conservation of energy, the
  amount of energy required to break a bond is
  equal to the amount of energy released when a
  bond is formed. (This energy is called bond
  energy and is a characteristic property of
  individual bonds)

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Bond Energy

• Energy is always released on the formation of a
  chemical bond.
• Energy is always absorbed on the breaking of a
  chemical bond

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Exothermic reactions

• Exothermic Chemical Reaction
• exo out of thermic heat
• Heat energy is released (hot)

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Endothermic reactions

• Endothermic Chemical Reaction
• endo into thermic heat
•  
• Heat energy is absorbed (cold)
• Need to add heat energy to keep the reaction
  going

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Catalysts

• Catalyst
• Any substance that increases the rate of a
  chemical reaction (speeds up the reaction)
• Examples heat with glow stick, Na increases
  rate of rusting iron, food molecules digest
  quicker in presence of vitamins

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Inhibitors

• Inhibitor
• Slows down a chemical reaction
• Examples preservatives, salt on meat, cold
  temperature (refrigerator), iced glow sticks

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Acids and Bases

• Acids and Bases
• pHmeasure of the hydronium ion concentration
  (H3O) H H2O
• pHmeasure of a substances acidity
• Draw pH scale on board

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Acids and Bases

• Acids Bases
• Sour taste Bitter taste
• Squeaky Slippery
• pH lt 7 pH gt 7
• starts with H ends in OH

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Acids and Bases

• Acids Bases
• H donor H acceptor
• Litmus paper red Litmus paper blue
• HCl, HNO3 NaOH, KOH,
• H2SO4, HF Ca(OH)2, LiOH

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Indicators

• Acid-Base indicator
• Changes color in different pH solutions
• Shows a definite color change when mixed with an
  acid or base
• Demo
• Phenolphthalein, UI, Phenol red, RCJ, BCG, BTB
  indicator solutions on stir plate with acids and
  bases (run through entire range of colors)

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Mix acid and base

• What happens when a strong acid and strong base
  are mixed? What are the products?
•  
• HCl NaOH H2O NaCl
•  
• When acids and bases are mixed, they produce
  water and a salt.

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Whats next

• Complete acid/base/pH indicator/pH paper lab
•  
• Complete Acid rain simulation lab
•  
• Prepare for unit quiz