Valence Electrons and Chemical Bonding Review valence electrons Principles of “Bonds Away” Ionic...

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)




• Ionic Bonds

• Metallic Bonds

• Covalent Bonds



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




• Ionic Bonds

• Metallic Bonds

• Covalent Bonds



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




• Ionic Bonds

• Metallic Bonds

• Covalent Bonds



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




• Ionic Bonds

• Metallic Bonds

• Covalent Bonds



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–




• Ionic Bonds

• Metallic Bonds

• Covalent Bonds



Valence Electrons and Chemical Bonding Review valence electrons Principles of “Bonds Away” Ionic...

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