ICPE Chemical Bonding Chapter 17

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ICPE Chemical BondingChapter 17

• Adapted from Conceptual Physical Science Hewitt
• Adapted by Jim Barnaby

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Chemical Bonding

• General theme
• How the periodic table can be used to gain
  insight into the nature of chemical bonding

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Electron Affinity

• Electron Affinity
• The ability of an atom to attract additional
  electrons
•  
• How many electrons an atom attracts is a function
  of its position on the periodic table
• See figure 16.29 page 399

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Electron Affinity continued

• 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.
• Know figure 17.1 page 405
• Atoms are electrically neutral

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Eye ons

• 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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ION

• Ion
• A charged atom
• Atoms are electrically neutral
• If an atom becomes charged it becomes an ion

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Cation

• Cation
• Positive ion ()
• Loses electrons
• Gives away electrons
• Metals

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Anion

• Anion
• Negative ion (-)
• Gains electrons
• Takes electrons
• Non-metals

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Cations and anions

• Cation
• Any atom or group of atoms that has a positive
  charge
•  Anion
• Any atom or group of atoms that has a negative
  charge
•  
• When bonding, atoms want 8 valence electrons (in
  their outer shell)

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Bonding and the periodic table

• Draw periodic table box for a metal atom on the
  board, draw a Bohrs model as well
• Now do an alkaline earth metal and/or a non-metal
• Everyone needs to understand this concept

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Metals

• Metals
• Valence (outer) electrons of most metals are
  weakly held to the atomic nucleus, therefore,
  electrons are easily lost (taken), leaving
  positively charged metal ions.
• Metals tend to be cations () lose electrons

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Metallic Bond

• Show metallic bond streaming video
• Metallic Bond
• A chemical bond in which metal atoms are held
  together by their attraction to a common pool of
  electrons
•  Metal ions are held together by freely flowing
  electrons. This electron mobility accounts for a
  metals high heat and electrical conductivity,
  opaque and shiny (metallic) luster, ductile and
  malleable properties

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Alloy

• Alloy
• A mixture of 2 or more metallic elements
• Ex white gold Au and Pd
• Sterling silver 92.5 Ag 7.5 Cu
• Steel 97 Fe 2 Mn 1 C
• Stainless steel (does not rust)
• 71 Fe 18 Cr 10 Ni 1 C
•  Aluminum cans are alloys of Al, Zn and Mn

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Ionic bond

• Show ionic bond streaming video
• Ionic Bond
• Metal atoms lose electrons to become cations ()
• Non-metal atoms gain electrons to become anions
  (-)
•  Cations and anions are pulled together by an
  electrical force

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Ionic Bond continued

• Ionic Bond
• An electrical force of attraction between two
  oppositely charged ions
•  
• Remember atoms want 8 electrons (in general) in
  outer shell
• Draw Na and Cl on board (Lewis dot diagram
  videos??)

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Ionic Compounds

• Ionic Compound
• A chemical compound made up of ions (ionically
  bonded ions)
• NaCl, CaF2, KI, LiCl, MgCl2
• Ionic compounds typically consist of elements
  found on opposite sides of the periodic table Fig
  17.1 (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
•  
• Numeral 1 is optional in super script notation

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Ionic compounds

• For all ionic compounds, positive and negative
  charges must balance
•  Ca2 F-
• Therefore, 2 F- ions are needed to balance Ca2
  the formula is CaF2
•  Aluminum Oxide
• Al3 O2-
• Need Al2 O3
• Charge 6 6- charges must balance (net charge
  is zero)

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3-d bonding

• Q One Cl- ion may be attracted to a Na ion,
  but can two?
• A Yes, provided the second Cl- approaches from
  another angle
• Electric fields are 3 dimensional Cl- ions may
  approach from outside the plane of the board
•   Fig 17.10 page 409

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Ionic Crystals

• Oppositely charged ions packed together in such
  an orderly 3-dimensional fashion form an ionic
  crystal.
• Easter egg demo

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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
• Sketch on board

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Octet Rule

• 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
•  
• An octet is a set of 8

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Covalent Bonds

• See covalent bond streaming video
• Covalent bond- a chemical bond where atoms are
  held together by their mutual attraction for the
  2 electrons they share
•  
• Co- means sharing valent- refers to valence
  e- being shared

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Covalent Compounds

• In a covalent bondthere are no ions involved but
  the force holding the two atoms together is still
  electrical.
• Covalent compound- any group of atoms held
  together by one or more covalent bonds
• Ex H2, O2, N2, CO2, H2O

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Covalent Compounds cont.

• Fig 17.1 again
• Covalent bonds primarily involve elements toward
  upper right hand side of periodic table (these
  are elements with high electron affinities)
• 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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Covalent fun facts

• Oxygen has affinity for 2 extra e-
• Oxygen finds 2 extra e- when it bonds with 2H
  atoms to form water.
• Each H atom gets access to an additional e- by
  bonding to O.
• Win Win situation for O and H 

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Covalent fun facts II

• The number of covalent bonds an atom is able to
  form is equal to the number of additional
  electrons it can attract.
• Draw molecules on board
• There may be more than 1 covalent bond between 2
  atoms

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Double? Triple? Covalent bonds

• O2 two O atoms connected by 2 covalent bonds
  called a double covalent bond (4 electrons are
  shared, 2 from each atom)
•   O O
•  
• N2 triple covalent bond, 6 electrons are shared,
  3 from each atom
• N N

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Single covalent bond dots

• Single covalent bond
• Sketch on board
• Pairs of electrons not shared between atoms are
  called unshared pairs
• Sketch on board
• Read p. 414 in Addison Wesley chemistry book (do
  not get bogged down in the details)

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Double, triple covalent bond dots

• Double covalent bonds
• Sketch on board
• Triple covalent bonds
• Sketch on board

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Molecules

• Molecule
• A group of atoms held tightly together by
  covalent bonds
•  
• A diamond is a single large molecule made of many
  carbon atoms connected by numerous covalent bonds

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Compare and Contrast

• Compare ionic, covalent and metallic bonds
•  
• Metallic bond network of positively charged
  metal ions are held together within a fluid of
  freely moving electrons

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Compare and Contrast 2

• Ionic bond each ion is attracted to all the
  oppositely charged ions surrounding it
•  
• Covalent bond involves only the two atoms
  sharing electrons (like a marriage)

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Do not write this down

• Different atoms have different pulling powers.
  This pulling power, also known as electro
  negativity, is a function of how strongly the
  atomic nucleus is able to pull on the valence
  electrons. The greater the pulling power, the
  greater its ability to pull bonding electrons
  closer to itself. An atom that pulls electrons
  closer to itself will be slightly negative in
  charge because of the greater amount of time the
  electron spends on that side of the bond.

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Dipole

• Dipole
• Segregation of charge
•  
• Slightly () H F Slightly (-)
•  
• H F as Fgreater electro negativity

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To Polar or not to polar?

• A Covalent bond is either polar or non-polar
• When the 2 atoms have the same electro
  negativity, no dipole is formed and the bond is
  non-polar (ex H2, N2)

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Polar

• When the electro negativities of the 2 atoms
  differ, a dipole is formed and the bond is polar
  (ex H-F, H2O)
•  
• The greater the electro negativity, the greater
  the polarity
•  
• See figure 17.23 page 414

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Review

• Does everyone know how to use their periodic
  table to get charges of ions in order to write
  chemical formulas?

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Predict the 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
• Use word document for this activity

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Write the chemical formula

• Use your periodic table and the following
  information to predict the chemical formulas for
  the following ionic compounds.
• Hydroxide ion OH-
• Sulfate ion SO42-
• Ammonium ion NH4
• Carbonate ion CO32-
• Use word document for this activity

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Prepare for bonding quiz

• Students create review activities for other
  groups???????