Presentation on theme: "Lewis Dot Structures on Board Ionic uses charges (NaCl) Covalent 1: Find total # Valence e- 2: Each H gets 2, all others get 8 3: Line indicates shared."— Presentation transcript:
1 Lewis Dot Structures on Board Ionic uses charges (NaCl) Covalent 1: Find total # Valence e- 2: Each H gets 2, all others get 8 3: Line indicates shared pair of e- H2O – single bond CO2 – double bond N2 – triple bond
2 Single Bonds ___________ Double Bond ___________ Triple bond
5 Molecular Geometry molecules are really 3-D! CH4 in 2-D on a sheet of paperCH4 looks like this in 3-D
6 How do we know the shape of molecules? X-Ray Crystallography
7 Valence Electrons determine Molecular “VSEPR” Shape VSEPR = “Valence-Shell Electron Pair Repulsion”Electron pairs (bonding or lone pairs) in a molecule repel each other and will try and get as far away from each other as possible… this determines the shape.Lone pair electronsbonding pair electronsNH3 VSEPR shape in 3-DNH3 in 2-D
8 4 Shapes to KnowTetrahedralTrigonal PyramidalBentLinear
9 How Lone Pairs Affect Molecular Shape “paddles” are lone pairs of electrons.Remove the paddles and you can see the shapes.
14 Why Shape matters (drugs) Your body acclimates to drugs and it takes more and more to get the same feeling.
15 Molecular Polarity & Smell Besides shape, polarity also plays a role in your ability to smell.Polar molecules = smellNon-polar = don’t smellYour smell receptors are polar and surrounded by mucous (a watery substance)Ex: Methane gas is odorless-They add this polar stinky chemical to it so that you can smell it:
16 Determining Molecular Polarity Draw correct VSEPR ShapeDetermine if molecule is symmetrical.If the molecule is symmetrical = non-polar- no partial charges are needed!If the molecule is NOT symmetrical = polar- you must show partial charges.
29 Water Hydrogen Bonding due to polarity Positive Hydrogen end attracted to Negative Oxygen end
30 Water Hydrogen Bonding due to polarity Positive Hydrogen end attracted to Negative Oxygen end
31 Water - Hydrogen Bonding Ice density - Water is most dense at 4oC
32 Water Hydrogen Bonding due to polarity Cohesion – Surface Tension
33 Properties of Water due to Hydrogen Bonding & Polarity Cohesion – water molecules are attracted to one anotherCauses water to be “Sticky”This is why water forms dropletsAdhesion – water is attracted to other substancesWater will “stick” to containers & objectsSurface tension – strong forces between molecules cause the surface of a liquid to contractCapillary action- water is attracted to other water molecules and will “rise”“USGS Water Science for Schools: All about water!” US Geological Survey. 9 December
34 More properties…Capillary Action – the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension.Universal Solvent things dissolve in water- polarity“USGS Water Science for Schools: All about water!” US Geological Survey. 9 December
39 Effect on melting & boiling point Effect on melting & boiling point. If the intermolecular forces are strong, you need more energy--and thus a higher melting point--to overcome them. Explanation: Meaning of melting point: The temperature at which a substance changes state from solid to liquid. So what is the purpose of intermolecular forces of attraction ? Holding two molecules together, which helps to keep the substance in a given state. If the intermolecular forces are strong, you need more energy to overcome them. In the case of melting points, the particles in a solid are held by intermolecular forces. To convert the solid into a liquid, you must overcome the intermolecular forces.
40 MeltingSome attractive forces holding the particles together are broken and particles move freely around each other but are still close together. The stronger these forces are, the more energy is needed to overcome them and the higher the melting temperature.BoilingThe remaining attractive forces are broken so the particles can move freely and far apart. The stronger the attractive forces are, the more energy is needed to overcome them and the higher the boiling temperature.