Bonding

Valence Electrons Highest energy electrons (outer shell) Only s and p block elements contain valence electrons, so how many valence electrons can there be????? Noble gas=most stable How many electrons? 8 Octet Rule: 8 valence electron’s are most stable. Elements will find the easiest route to get 8 electrons (either gain or lose electrons)

Lewis Dot structures Lewis Dot Structures/ Structural Formulas Write the atomic symbol; place the appropriate number of dots around the element to show the valence electrons. C, K, Cl, Kr Ionic Compounds Write the elements that are bonding, place appropriate number of valence dots, use an arrow to show where the electrons get traded, end equation with ions, one complete, one empty element Example: NaCl, CaBr2

Lewis dot structures/covalent cmpd Covalent Compounds Lewis Dot: same concept as ionic, but electrons do not transfer Structural Formulas: place a line in between bonded elements, these lines represent paired electrons, left over dots are unpaired electrons. Number of bonds: Single bond: one line, one pair of electrons Double bond: two lines, two pairs of electrons Triple Bond: three lines, three pairs of electrons

Lewis dot structures/covalent cmpd Rules of writing Covalent Compounds: Count valence electrons (add for negative charges, subtract for positive charges) write skeleton with single bonds already in place Place remaining valence electrons around elements make stable octet, increase bond number if needed E.G.: CO2, N2, CH4 Exceptions: H, Li satisfied with 2 electrons Boron family satisfied with 6 electrons (metals) P, S more than 8 electrons is OK When one element is satisfied, but partner is not, the satisfied element with donate a pair of electrons to make another bond = Coordinate Covalent Bonds

Solids, liquids, and gases States of matter

Kinetic-Molecular Theory Particles are hard spheres with insignificant volume, mostly empty space, no attractive or repulsive forces Particles in constant, rapid motion All collisions are perfectly elastic

Solids Particles vibrate about fixed points Highly organized, dense, and incompressible Do NOT take shape of container

Liquids Particles are in motion and are free to slide past one another Vibrate and spin as they move Particles are attracted to each other through intermolecular forces Holds shape of container Less dense than a solid Not enough energy to escape as a gas

gases Particles are in constant motion Take shape of container Less dense than solids or liquids Forces of attraction are weaker

Phase diagram Pressure Temperature

Triple Point Video http://www.youtube.com/watch?v=BLRqpJN9zeA

Graph of phase change Molecules separating into gas formation Molecules separating into liquid formation Boiling Point Gas Melting Point Temperature Liquid Solid Time

Bond Polarity

Bond polarity Covalent bonds differ in how bonded atoms share electrons Electrons are being pulled by both nuclei Non-polar covalent bond: Bonds are pulled equally (usually between two like atoms) H2 Polar Covalent Bonds: Two different atoms bond and electrons are shared unequally More electronegative atoms will have the stronger electron attraction, will acquire a slightly negative charge (Example) Less electronegative atom will acquire a slightly positive charge(Example) Charges are represented by lower case delta  (the atoms charges are less than +1 and -1) (Example)

Determining Polar Molecules A molecule is polar when the atoms do not share electrons equally This creates a slightly positive charge on one end and slightly negative charge on the other Look for: Unshared electrons on the central atom (called lone pairs) Different atoms surrounding the central atom Examples: NH3 What about H2O? CH2Cl2

Ionic, metallic, and network Other types of bonds

Types of bonds Transfer of electrons Compound Description of Bond Functional Unit (drawing) Elements Combined Do They Follow the Octet Rule? Ionic Transfer of electrons Attraction between (+) and (-) Charges Metals lose electrons Non metals gain electrons Crystalline structure Positive attracts to negative (metal to nonmetals) Draw Metals (cations) Non-metals (anions) Yes, non-metals accepts e- to complete outer shell, metals donate e- to revert back to complete outer shell Covalent Sharing of e- No set structure, molecules near one another Two or more non-metals bound together All but Hydrogen Metal Metal ions that are surrounded by free-flowing e- Positive nucleus surrounded by electrons Two or more metals No octet, no full energy level

Properties of bonds Bond Strength of bond Covalent Properties Melting/Boiling Solubility Conductor of electricity? Ionic Strongest Very stable Brittle solid High melting point Usually high solubility Good conductors in solution Weak strong Easiest to break Solid, liquid, and gas states Low melting and boiling point Low to high solubility Poor to non-conductors Metal Not as strong as ionic, stronger than covalent Varied stability Ductile and malleable Solid, except mercury Medium melting point Not soluble Good conductors of electricity (electrons flow freely)

FOrces

Forces between Molecules Intermolecular forces Attraction between molecules Weaker than atom bonding Used to determine physical properties of the molecule (such as state of the molecule solid, liquid, or gas) Strongest  Weak Ionic bond  Hydrogen Bonds  dipole Interaction  Van der Waals

Van der Waals/London Dispersion Types of Forces Van der Waals/London Dispersion Dipole-dipole Hydrogen bonds Strength Increase strength of forces as electron number increases Mimic ionic compounds (attracted by charges, but weaker) Strongest (includes all 3 forces) Types of Molecules Any covalent compound with electrons (non-polar) A force between 2 polar molecules Force between 2 very polar, hydrogen containing molecules Description of force More electrons=stronger the force Positive atom on one molecule attracts the negative atom of another molecule Created with O, F, & N ONLY Examples Diatomic elements: Br I N Cl H O F CH3COCH3 H2O where H of one water is attracted to the O of another water

Forces and properties Physical properties depend on type of bond (ionic or covalent) The variety in covalent compounds are due to intermolecular forces Properties Melting point: only the weak attractions need to be broken. Boiling Point: break apart molecules of liquid Solubility: stronger the intermolecular force the harder it is to be soluble.

Questions Define the following: Boiling point Melting point Evaporation How do each of the above relate to the type of bond in a molecule? What role does intermolecular forces play in the strength of bonds? Draw Isopropyl Alcohol ((CH3)2CHOH), methanol (CH3OH), acetone (CH3COCH3), and water. What type of forces are present in each?