

Scientific Method
Includes qualitative and quantitative observations, hypotheses, predictions and controlled investigations.
 Hypothesis
 Proposed answer or explanation to a scientific question using evidence that has to be testable
 Theory
 Well-tested scientific explanation of phenomena supported by evidence that is supported by the scientific community
 Independent Variable
 The one factor you change on purpose.
 Dependent Variable -
 The factor that is the measured response.
 Control
 Factors that you do not change or are held constant.

 Water is a compound that contains two hydrogen atoms (+) and one oxygen atom (-).
 Chemical formula is H
2
O.
 Looks like Mickey Mouse.

Covalent vs. Hydrogen Bonding
Covalent Bond
Hydrogen Bond

Covalent Bond Hydrogen Bond

Water is a Polar covalent Molecule
 Covalent bond = sharing of electrons
 Polar = unequal sharing of electrons
What is the net charge of a water molecule?
 Why polar?
 Oxygen atom pulls on the shared electrons in each hydrogen causing a partial POSITIVE charge on each hydrogen and a partial NEGATIVE charge on the oxygen

 Please get out your interactive notebooks .

Covalent Bonding Overview
Two Types
1. Polar covalent bond – unequal sharing of electrons
Ex: water molecules
2. Nonpolar covalent bonds – equal sharing of electrons
Ex: Methane (CH4)

Hydrogen Bonds
 WEAK bond
 Slightly positive Hydrogen is attracted to a slightly negative charge atom
*Think of magnets*
 H-bonds form and break easily
 H-bonding allows water molecules to bind to other polar molecules

Answer:
Water is a polar molecule, because it contains a positive and negative charge.
Examples:
Polar molecule mix with polar molecule.
(saltwater)
Polar and nonpolar do not mix.
(oil and water)
Nonpolar mix with nonpolar.
(milk and chocolate syrup)

1.
Universal Solvent
2.
Adhesion
3.
Cohesion
4.
Capillary Action
5.
Surface Tension
6.
Density/Buoyancy
7.
High Specific Heat

How is water a universal solvent?
Definition:
Water’s unique property to dissolve most substances (solutes).

Solution, Solute, & Solvent
Solution is made up of two parts…
Solute – Substance that is dissolved
Solvent – Does the dissolving
Example: Ice Tea: water = solvent; Tea and Sugar = solutes
+ =

Water as a Universal Solvent
Real-World Examples:
Salt and water - Instant pancake mix
- Kool-aid - Alka-seltzer
Question
How would our lives be different if water could not dissolve most substances?

Suction cups use water’s property of adhesion
Adhesion = water to sticks to other substances
Real-World Examples:
Suction cup on a window
Rain on a rain jacket
Rain drops on your car windshield

Water’s property of cohesion allows water to bubble on top of the penny
Cohesion = water molecule H-bonds to another water molecule
Water molecules are very attracted to each other

What will happen when the straw is lowered into water?

Capillary Action
*Think water in a straw*
How does water move a straw?
Because of both
Adhesion + Cohesion
When adhesion and cohesion work together = capillary action

How do plant roots get their water from the soil?
Plants roots rely on water’s property of capillary action
Capillary Action = the process that moves water through a narrow porous space.
Real-World Example
How all plants get their water

 Capillary action allows roots to absorb H
2
O from soil
 Transpiration
(evaporation from leaves)
H
2
O
H
2
O

When entering a swimming pool your body is breaking the water’s surface tension
Surface Tension = t he force that acts on the particles in water that allow it to become tight

 Topic:
 What property of water allows ice to float?
 How would our world be different without this property?

How do cruise ships float if they are so big?
Upward force of buoyancy & density .
Density = is the mass to volume ratio
Buoyancy = the ability of a water to exert an upward force on an object that is immersed

High Heat Capacity
Water has a high heat capacity.
“ The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.
”

High Specific Heat
Properties of Water
 High specific heat


H
2
O acts as a heat reservoir and its temperature remains relatively stable
Helps reduce temperature fluctuation in plants and animals
 High heat of vaporization


It takes a lot of heat to evaporate just a little H
2
O
This keeps water in lakes and ponds in the summer
 High heat of fusion
 It takes much longer for lakes and streams to freeze in winter

 Evaporative Cooling
 During evaporation (liquid  gas), surface temperature of water decreases
 Mammals sweat to stay cool in high temps

1.
2.
3.
4.
5.
6.
7.
Universal Solvent
Adhesion
Cohesion
Capillary Action
Surface Tension
Density/Buoyancy
High specific heat