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Chemical Bonding. Unit 3 – Lecture 1 No one wants to be alone…. Why atoms bond. Most atoms are not found alone in quantity in the universe, they are bonded to other atoms All atoms except the ones in Group 18 (the Noble Gases) have an unstable electron configuration

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chemical bonding

Chemical Bonding

Unit 3 – Lecture 1

No one wants to be alone…

why atoms bond
Why atoms bond
  • Most atoms are not found alone in quantity in the universe, they are bonded to other atoms
  • All atoms except the ones in Group 18 (the Noble Gases) have an unstable electron configuration
  • Atoms will gain, lose, or share valence electrons until they become stable
reviewing the octet rule
Reviewing the “Octet Rule”
  • Elements will gain, lose, or share electrons to fill their valence shells with 8 e-s
    • major groups (1,2,13-17) gain, lose or share until 8 or zero valence e-s
    • zero valence electrons means that layer is stripped and the full inner layer is exposed, making them stable
counting outer shell electrons
Counting outer shell electrons
  • An Electron-Dot Diagram allows us to draw atoms and show their valence electron configuration
    • Write the element’s symbol
    • Begin placing dots around the symbol equal to the number of outer-shell electrons
      • 1 to a side, then double up
reviewing lewis diagrams
Reviewing Lewis Diagrams
  • …show valence e- configuration
    • element symbol in center
    • surround with # of dots equal to valence e- number
    • e-s pair if have more than 4
reviewing oxidation s
Reviewing Oxidation #s
  • Oxidation number:
    • charge on the atom after an atom gains, loses, or shares electrons to become stable
    • the + or – number tells you how many e-s the atom gained or lost
      • positive = surplus loses e-s
      • negative = deficit  gains e-s
slide7

Oxidation/Charge Numbers

+1 +2 ----------------------------------------- +3 +/-4 -3 -2 -1 0

practice
Practice
  • Mg
    • valence electrons?
    • oxidation number?
    • how many e-s gained, lost or shared?
practice cont d
Practice – cont’d
  • Ge
    • valence electrons?
    • oxidation number?
    • how many e-s gained, lost or shared?
practice10
Practice
  • Cl
    • valence electrons?
    • oxidation number?
    • how many e-s gained, lost or shared?
reviewing ions
Reviewing Ions
  • Ion – a charged particle
    • positively charged particle = cation
    • negatively charged particle = anion
ionic bonds
Ionic Bonds
  • Ionic bond – typically formed btw metal & non-metal
    • one atom loses 1 or more e-s
      • Metal
    • one atom gains 1 or more e-s
      • Non-metal
    • attraction between the + and – charge ions cause them to bond with a lot of electromagnetic force
ionic bonds cont d14
Ionic Bonds – cont’d
  • Compounds with Ionic Bonds
    • are created from elements on opposite sidesof the Periodic Table
      • large difference in electronegativity
      • example: NaCl
    • form repeating units
ionic bonds cont d15
Ionic Bonds – cont’d
  • Compounds with Ionic Bonds
    • dissolve into aqueous solutions easily
      • soluble [solid dissolves in liquid]
      • miscible [liquid dissolves in liquid]
      • dissociation – particles are pulled apart by water
ionic bonds cont d16
Ionic Bonds – cont’d
  • Compounds with Ionic Bonds
    • can have very strong bonds which cause them tohave unusually high melting and boiling points
      • exist usually as solids at room temperature
covalent bonds
Covalent Bonds
  • Covalent Bond – formed between atoms which share valence e-s to complete their octet
    • once bond is formed, atoms are stuck until they bond to something else [do not dissociate].
covalent bonds contd
Covalent Bonds – contd
  • Compounds with Covalent Bonds
    • are created from elements somewhat close to each other on the Periodic Table
    • can be liquids or solids at room temp
    • do not dissolve easily into aqueous solutions
      • immiscible
    • form distinct molecules
metallic bonds
Metallic Bonds
  • Metallic Bond – formed between metals
    • positive nuclei arrange into crystal latticeelectrons flow freely from atom to atom
      • sometimes called a “sea of electrons”
    • this accounts for physical properties of metals, such as strength, malleability, ductility, thermal and electrical conductivity, opacity, and luster.
metallic bonds cont d
Metallic Bonds – cont’d
  • Compounds with Metallic Bonds
    • have strength, malleability, ductility, thermal and electrical conductivity, opacity, and luster because of flow of electrons
    • are solid at room temp
metallic bonds cont d22
Metallic Bonds – cont’d
  • Compounds with Metallic Bonds
    • may lose e-s to substances outside of the bond
      • causes corrosion or oxidation [rusting]
      • usually happens with oxygen
reviewing electronegativity
Reviewing Electronegativity

“I’m not stealing, I’m sharing unequally…”

  • Electronegativity – the ability of an atom to pull electrons to itself
    • ie, how well an atom holds onto its own electrons or steals from others
    • increases ↑ the PT
    • increases  PT
reviewing reactivity
Reviewing Reactivity
  • Reactivity for Metals
    • increases  and  from the stair step
    • Cesium/Francium = most reactive metals
  • Reactivity for Non-Metals
    • increases  and  from the stair step
    • Fluorine = most reactive non-metal
polarity
Polarity &…
  • Polar-Covalent Bonds – form when atoms in covalent bond do not share e-s equally.
    • one end of compound = slightly negative
    • one end of compound = slightly positive
polarity cont d
Polarity &… – cont’d
  • Polarity & Solubility
    • “Like Dissolves Like”
      • polar & ionic solutes dissolve in polar solvents
      • non-polar solutes dissolve in non-polar solvents
      • remember, “surround & separate”
        • polar cannot dissolve non-polar
        • non-polar cannot dissolve polar
practice27
Practice
  • Most atoms bond because…
    • lonely too many valence e-s too few valence e-s
  • What number of valence e-s is suitable for most atoms?
    • 2 8 0 6
  • What model is used to show valence e-s on an atom?
    • Bohr Lewis Wave Scale
  • Atoms which have more or less e-s than normal are…?
    • ions positrons negatrons
  • How do atoms become stable?
    • gain e-s lose e-s share e-s all of these
practice cont d28
Practice – cont’d
  • Atoms which have gained e-s are called…?
    • anion cation ion
  • Atoms which have lose e-s are called …?
    • anion cation ion
  • Ionic bonds are held together by a … force.
    • strong nuclear strong electromagnetic
    • weak nuclear weak electromagnetic
  • Atoms far apart on the PT will usually bond ….
    • ionically covalently metallically not at all
practice cont d29
Practice – cont’d
  • Covalent bonds are formed when atoms..
    • gain e-s lose e-s share e-s all of these
  • Ionic bonds are formed when atoms …
    • gain e-s lose e-s share e-s all of these
  • Groups 3-12 will use which type of bond?
    • ionic covalent metallic none of these
  • Which part of a metallic bond explains why metals are lustrous and good conductor of electricity?
    • crystal lattice “sea of electrons”
    • nuclear density metals aren’t good conductors…
practice cont d30
Practice – cont’d
  • Atoms with a strong attraction to their electrons are …?
    • positronicgravometricthaleonic electronegative
  • What is the most reactive nonmetal?
    • Cl F O S
  • A covalent bond where the atoms do not share evenly is called a … bond
    • polar equatorial longitudinal latitudinal
  • Most atoms are found … in nature.
    • bonded unbonded free free-range
practice cont d31
Practice – cont’d
  • What is the rule concerning how polar and nonpolar bonds react?
    • “Opposites Attract” “Like Repel” “Like dissolves like” “Surround and Separate”
  • How does oxidation affect a metal?
    • strengthens it weakens it does not affect it
  • Which of these is the most electronegative?
    • O Cl F Ar
  • When all atoms share electrons equally in a covalent bond, it is called
    • polar non-polar ionic metallic
practice cont d32
Practice – cont’d
  • Draw the Lewis diagram for Selenium (Group 16, Period 4, Atomic # 34).
  • Which group of elements loses electrons most easily?
    • group 1 group 3 group 15 group 17
  • How many dots should be drawn around the element Oxygen in its Lewis diagram?