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 6 Li Cl = 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) 1 1 H and 9 19 F 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 (C 5 H 12 ) Alcohols: C, H and OH (hydroxyl group) –Ethanol (C 2 H 5 OH) –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