1. Take out water lab – we will refer to it today Do Now 11.14 OBJECTIVES: Identify and describe 4 special properties of water 2. Define polar molecule and Hydrogen bond. 3. Explain how electrical charges on the molecular level give water its special properties TASK: 1. Take out water lab – we will refer to it today 2. Make a big chart on a sheet of notebook paper: “Special Properties of Water,” with 2 columns (Property and Description) and 4 rows.

Water is a Compound Composed of Molecules An atomic bond is a force which joins atoms together to form a molecule H O Atomic bond Water H

O-H Polar Covalent Bonds in Water In a polar covalent bond, electrons are shared unevenly. Since electrons are negative, the atom that attracts electrons the most becomes a little negative, and the atom losing the electrons becomes a little positive.

Water is Special Property #1: Water resists changes in temperature & phase Demonstration High “Specific Heat Capacity” Related Property: high melting & boiling points

Related: High Melting & Boiling Points

Property 2: High Surface Tension, etc.

Property 2: High Surface Tension, etc. Adhesion: Water sticking to other surfaces “Capillarity” Cohesion: Water sticking to Water

Property #3: Excellent Solvent Water is very good at dissolving substances, particularly polar or ionic ones. “Universal Solvent”

Property #4: Density Anomaly Ice floats on water! Water is one of only a few substances known where the solid form is less dense

WHY WATER HAS SPECIAL PROPERTIES: HYDROGEN BONDS A Hydrogen bond is a weak bond between 2 different polar molecules

New Bond - Hydrogen Bond: Pathetically WEAK! A Hydrogen bond is a weak bond between 2 different polar molecules

Water is a polar molecule. The O-H bonds are polar covalent Molecules with positive and negative parts are called polar molecules. Polar molecules form hydrogen bonds

How H-bonds Give Water it’s Special Properties Property How H-Bonds Make it Happen Temperature & Phase Stability Energy is required to break H-bonds, reducing the amount of energy for T increase or phase change Surface Tension, etc. Can form H-bonds with itself or other substances, making it “sticky” Solvent Areas of charge arrange around charged parts of molecules Density Anomaly H-bond length increases as temperature drops from 4oC to 0oC

HOMEWORK Complete Lab Report No Section F