Chemical Bonding

Outline for Chemical Bonding General bonding information Ionic compounds and their properties. 1.naming ionic compounds. Covalent compounds Lewis dots Shapes of molecules Polar and nonpolar molecules Summary of covalent compounds. Metals and metallic bonding

General information All bonds are the result of a (+) and (-) attraction. Only valence e- are directly involved in bonding A pair of valence e- makes one bond. Transitional metals may have their valence e- come from the last two E.L.

Properties of ionic compounds An atom which loses electrons combines with an element that gains electrons. A cation and an anion are formed in ionic bonds. Ionic charges are used to determine the empirical formula. Ex CaCl2, K2S Ionic compounds form crystals have a distinct geometric arrangement are brittle and so shatter when hit. http://www.youtube.com/watch?v=hiyTfhjeF_U

Properties of Ionic crystals continued high melting points. When dissolved in water - form free moving ions which conduct electricity. molten state - semi conductors, ions can only slide over each other very slowly. not conductive as solids- no movement in the ions.

Model of an NaCl crystal

Photos of ionic crystals

Photos ionic crystals

Properties of most covalent compounds Rarely break apart to form ions in water. Usually they do not conduct electricity under any circumstance.

Molecular geometry The shape of a molecule depends on: The number of outer atoms. The central atom’s number of valence e-. Specifically, are there any unbonded valence e?

Some examples of shapes

Pyramidal shape molecule

Covalent compounds can be divided into 2 categories Polar covalent Molecules have a (+) and (-) end (dipole) to them. A dipole is created when there is a difference of 0.5 or greater in electronegativity A dipole is created when F,O,N, or Cl is in the molecule and they are not bonded to an identical element. HI MRS.TURNER Nonpolar covalent Molecules have no charge on them Either there are no dipoles, or the dipoles cancel out. dumb

Determining whether a covalent compound is polar or nonpolar. First: determine if there are any bonds with dipoles in the molecule. Second: determine the shape of the molecule. Third: determine if the dipoles cancel on the molecule. If they cancel, the molecule is nonpolar. If they add up to create a (+) or (-) end, then the molecule is polar.

First step: determining dipoles A dipole is a bond with a (+) end and a (-) end. Dipoles are created when F,O,N, and Cl, are bonded to any other element other than itself. Exception: N bonded to Cl does not make a dipole.

Dipoles continued Determine which bonds have dipoles; N-F, C-S, N-Br, O=O, N-Cl, H-S, N-H, H-O The bonds with dipoles are: N-F, N-Br, N-H, H-O The element which is more electronegative will have a partial (-) charge, the other element will have a partial (+) charge.

Second step. Determine the shape Use your chart on molecular geometry to determine the shape of the molecule. Note the number of outer atoms and if the central atom has an unbonded pair of valence electrons. Example: BH3 and NH3 BH3 is planar, but NH3 is pyramidal because the “N” has an unbonded pair of e-

Third and final step. Determining whether a molecule is polar or nonpolar. Applying the rules: Example: NF3 Time to use the whiteboard!!!!! Leave space in your notes to write several examples .

Differences between the physical properties of polar and nonpolar molecules Not soluble in water, makes a separate layer from water. Volatile- easily evaporate Low melting and boiling points. Not very dense At room temp.: small molecules are gases, larger ones are liquids or soft solids. https://www.youtube.com/watch?v=o8TssbmY-GM Polar molecules Soluble in water Low volatility- do not evaporate easily Relatively high melting and boiling points for their molar mass. More dense than non polar At room temp. very few are gases, most are liquids and solids. Solids have crystal lattices https://www.youtube.com/watch?v=9ZEdApyi9Vw

Examples of polar and nonpolar substances Water Vinegar Blood Alcohols HCl Acetone Sugars hair Nonpolar substances Oils Waxes Most fuels, ex. Gasoline, methane paint thinner Sulfur. Oil base paints

Summary of the Two types of bonds Ionic Bonds Occur between metals and nonmetals Occur between an element with a low IE and one with a high IE Metal loses e- to the nonmetal Attraction is between an anion and a cation, (so ions are present). Covalent bonds Occurs between nonmetals only Both elements have high IE Valence e- are shared No ions are formed but dipoles may form.

Summary of the compounds Ionic compounds Form crystals Compounds found in rocks, minerals, bones Conduct only when molten or aqueous Many compounds dissolve in water. Covalent compounds Only polar ones make distinct crystals Found in living things Rarely conductive electricity. Only polar molecules dissolve in water

Van der Waals Dipole-dipole interaction Hydrogen bonding