Chemistry 8.4

Bell Work: Draw and name the structure of Sulfur Dioxide.

8.4 Bond Polarity The bonding pairs of electrons in covalent bonds are pulled by the nuclei. The nuclei of atoms pull on the shared electrons, much as the knot in the rope is pulled toward opposing sides in a tug-of-war.

8.4 Bond Polarity Chlorine is more electronegative than Hydrogen so it attracts the electron cloud more than the hydrogen atom does. This electron-cloud picture of hydrogen chloride shows that the chlorine atom attracts the electron cloud more than the hydrogen atom does. Inferring Which atom is more electronegative, a chlorine atom or a hydrogen atom?

A molecule that has two poles is called a dipolar molecule, or dipole. 8.4 Polar Molecules In a polar molecule, electrons are not shared equally. One end of the molecule (the more electronegative) has a stronger pull and is slightly negative and the other end is slightly positive A molecule that has two poles is called a dipolar molecule, or dipole.

Polar or Non-Polar? a) O2 b) HCl c) H2O d) CO2

Polar bond vs Polar molecule Sometimes a bond is polar but the molecule is non polar!!

8.4 Bond Polarity Bottom Line: The higher the electronegativity difference, the more polar the molecule!!

Warm Up Draw the structure for BH3 and determine its polarity.

Attractions Between Molecules 8.4 Attractions Between Molecules (2 types of intermolecular attractions = very weak) Van der Waals Forces Dipole Interactions: when polar molecules are attracted to one another. Dispersion Forces: Caused by the motion of electrons. Creates temporary Dipoles.

Attractions Between Molecules 8.4 Attractions Between Molecules Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons. The strength of dispersion forces generally increases as the number of electrons in a molecule increases.

Attractions Between Molecules 8.4 Attractions Between Molecules 2) Hydrogen Bonds Hydrogen bonds are attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.

Attractions Between Molecules 8.4 Attractions Between Molecules Hydrogen Bonding in Water The strong hydrogen bonding between water molecules accounts for many properties of water, such as the fact that water is a liquid rather than a gas at room temperature.

Attractions Between Molecules 8.4 Attractions Between Molecules The relatively strong attractive forces between water molecules cause the water to form small drops on a waxy surface. The strong attractions between water molecules cause the water to pull together into small drops rather than spread over the surface of the flower.

8.4 Section Quiz. 8.4.

8.4 Section Quiz. 1. In a molecule, the atom with the largest electronegativity value repels electrons more strongly and aquires a slightly negative charge. repels electrons more strongly and aquires a slightly positive charge. attracts electrons more strongly and aquires a slightly positive charge. attracts electrons more strongly and aquires a slightly negative charge.

molecules stick to the positive plates. 8.4 Section Quiz. 2. When polar molecules are placed between oppositely charged plates, the negative molecules stick to the positive plates. molecules stick to the negative plates. ends of the molecules turn toward the positive plates. ends of the molecules turn toward the negative plates.

8.4 Section Quiz. ionic bond Van der Waals force covalent bond 3. Which of the following bond types is the weakest? ionic bond Van der Waals force covalent bond hydrogen bond

Chem ASAP Concept Map 8 Solve the Concept Map with the help of an interactive guided tutorial.

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