Transcript Atomic Structure and Function

Valence Electrons and Chemical
Bonding
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Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Take Home Message
• When atoms combine to produce molecules and
compounds, expect the chemical properties of the
molecules/compounds to be far different than that of the
constituent atoms (hierarchy theory)
• Atoms bind together by re-arranging and sharing their
electrons
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Ionic bonds
Metallic bonds
Covalent Bonds
Intermolecular forces (e.g., hydrogen bond)
• Chemical interactions make and break bonds between
atoms and in so doing effect a change in energy
(potential and kinetic)
• Weak chemical bonds (e.g., covalent bonds) play a very
important role in the chemistry of life
Chapter Deletions
• Pp 262 (Covalent compounds and
formulas) – 265 (Coordinate covalent
bonds)
• Pp 267 (Ionic compound names) – 270
(Covalent compound names)
• Pp 279 (Percent Composition of
Compounds) – 295 (Quantitative use of
equations)
Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Atoms in Proximity: Bonds Away
• Hypothesis: when two atoms are brought
together, electrons will tend to re-arrange
themselves to the lowest energy state where the
valence electrons are most stable
• Product: electrons are re-arranged into bonds
– Give away electrons
– Accept electrons
– Share electrons
Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Ionic Bonding
• Atoms give away electrons while other
atoms receive electrons
• Example of lithium chloride
3
6Li +
17
35.5Cl
= LiCl
Ionic Bonding
• Lithium (Li)
Li gives up 1 electron and is left with 2 electrons (-) and 3 protons (+); net
positive (+) charge
• Chlorine (Cl)
Cl has 1 unpaired electron in valence shell, so Cl tends to accept an electron
and is left with 18 electrons (-) and 17 protons; net negative (-) charge
Ionic Bonding
• Atoms give away electrons while other atoms receive
electrons
• Example of lithium chloride
Li + Cl = LiCl
• Bonding via electrical attraction between Li+ and Cl– Li+ + Cl - = Li+Cl-
• Consequence: ionic bonds are underpinned by charged
ions and tend to form crystals of very specific and
repeating geometry (very rigid)
• Example: NaCl is based on ionic bonds and is salt
Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Metallic Bonds
• Elements that do not give or take electrons (ionic
bonds) BUT share electrons
• Valence electrons tend to move freely between
both atoms (contrast with ionic bonds)
• Significance of sharing electrons: compounds
tend to show two features
– Malleability (easily worked or pounded)
– Conductive of electricity (good conductors)
• Examples
– Gold jewelry
– Copper wire
Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Covalent Bonds
• Extremes of behavior in bonding
– Accept or give away electrons (ionic bonds)
– No tendency to share (noble gases)
• Intermediate between these two extremes but
– Do not form ionic bonds
– Do not form metallic bonds
– Yet share 1,2, 3 and 4 electrons in unique
arrangement called covalent bonds
• Key: orbits of valence electrons are shared so that electrons
are shared (and move) between valence shells of adjacent
atoms
Covalent Bonds
• Example of hydrogen fluoride (HF)
• 11H and 919F
• Note: Valence shell for both atoms are full
– Single bond shared
– Double bond
Next Week’s Lab:
Evaporation and Chemical Structure
• Vaporization and chemical properties of
molecules
– Liquid to gas state change
– State change has energy cost: endothermic
(temperature decrease)
• Temperature change is a function of
chemical structure of molecule
– Bonding and polarity
Evaporation and Chemical Structure
• Organic compounds
– Carbon based or hydrocarbons bond with other
elements via covalent bonds)
• Alkanes: C and H only
– Pentane (C5H12)
• Alcohols: C, H and OH (hydroxyl group)
– Ethanol (C2H5OH)
– Structural formula
• Hydrogen bonding: H bonded to N, O or F (tight
bond)
• Process: as chemical vaporizes, temperature
change is chemical specific and is a “window”
onto the chemical structure
Evaporation and Chemical Structure
• Hypothesis: temperature changes with
vaporization in a manner that is predictable,
based on the bonding among atoms involving C,
H and OH
• Method
– Measure temperature change electronically
– Record for 5 hydrocarbons
– Analyze data (graphically) based on understanding of
the bonds for each molecule
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Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions
Valence Electrons and Chemical
Bonding
•
•
•
•
•
•
•
Review valence electrons
Principles of “Bonds Away”
Ionic Bonds
Metallic Bonds
Covalent Bonds
Intermolecular Forces
Common Chemical Reactions