Valence Electrons and Chemical Bonding
• 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– 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 + 1735.5Cl = 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 chlorideLi + 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)• 1
1H 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–
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