3 Ionic or molecular; polar or nonpolar If a nonmetal atom can pull electrons completely to itself, relatively to a metal atom, the bond will beionic.Na Cl-If two (nonmetal) atoms are identical, the electron inside their bond will be right in the middle and the bond will benonpolar covalentBr---BrMany bonds are somewhere inbetween: sharing electrons, but not symmetric, making the bondpolar covalent+ H---O-
4 Electronegativity: An Attraction for Electrons How each atom fares in a tug-of-war for shared electrons is determined by comparing the electronegativities of the two bonded atoms.Electronegativity is the tendency of one atom to attract the electrons inside a chemical bond
9 Polar covalent bondsare called polar because the unequal electron sharing creates two poles across the bond.ElectronsCloser tohigherENmorenegativeJust as a battery has separate positive and negative poles, so polar covalent bonds have poles.The negative pole is centered on the more electronegative atom in the bond.
11 Exceptions: For example CO2 has two polar bonds Exceptions: For example CO2 has two polar bonds. However, the dipoles point in opposite directions and cancel out. As a molecule CO2 is nonpolar.On the other hand, water is a bent molecule and both dipoles point upward. As a molecule H2O is polar.
18 less dense than cold liquid water Density of waterWater has itshighest density at 4CTherefore…Ice FloatsIce crystalless dense than cold liquid water
19 Demos: dollar + paper cup Water has a high specific heat(lots of energy is absorbed when heating up water or during vaporization)Water is earth’s thermostat (Moderating climate)Cools down your body during perspiration, etc.Demos: dollar + paper cup
20 Water the “Universal Solvent” Dissolves polar covalent and ionic compounds… thus rarely pureSolution: Homogeneous mixture e.g saltwaterSolute: Dissolved particles in a solution saltSolvent: The dissolving medium in a solution waterThe concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solventdilute solutionconcentrated solutionSaturated solution
21 Is a measure of concentration in chemistry MolarityIs a measure of concentration in chemistryMolarity (M) is the number of moles of a solute dissolved per liter of solution, mol/L.Molarity (M) = moles of solute liters of solutionexample2 mol glucose = 0.4 mol/L = 0.4 M5 L solution
22 Water dissolving ionic compounds such as NaCl Polar water molecules surround ions facing each with its oppositely charged dipole
23 Why is sugar highly soluble in water? Polar water molecules form multiple hydrogen bonds with each sucrose moleculesimulation 19
24 Most compounds dissolve better at higher temperatureThink of sugar in hot teaor ice tea(but there are exceptions)
25 Book assignment p1) Describe how water dissolves ionic compounds2) Describe how water dissolves polar covalent compounds3) Explain the expression “like dissolves like”. Which compounds does water dissolve and which compounds are typically not soluble in water?When finished show us your work and you will receive your homework sheet