WATER

Physical Science

¾ of the Earth is covered with it

Exists on Earth as a solid, liquid AND gas

POLAR!!!

Do you remember the 3 types of bonds?2

1. Metallic2. Ionic3. Covalent- actually there are two types…

1. Polar Covalent2. Nonpolar Covalent

How do you know which type will form???

So actually- there are four types of bonds you must know:

3

1. Metallic- 1. metal with a metal

2. Ionic1. Metal with a nonmetal

The four types of bonds you must know:4

3. Nonpolar Covalent:-Nonmetal with a nonmetal

-If two of the same element

The four types of bonds you must know:5

4. Polar Covalent:-Nonmetal with a nonmetal-If Nitrogen, Oxygen or Fluorine are one of the elements, they are VERY electronegative and

will hog the electrons…and create POLAR COVALENT

BONDS!

6

Water background rewind

What elements are in a water molecule?

What type of bond will form between them?

How do you know it will be a polar covalent bond? _______________ with a ____________

Polarity of Water

A water molecule is a polar molecule with opposite ends of the molecule having opposite charges. oxygen is more electronegative so it pulls on the

electrons more So… the OXYGEN end has a slight negative charge. The HYDROGEN end has a slight positive charge.

8

This leads to a new type of “bond”…

Called a…

10Hydrogen bond

Hydrogen Bonds

Occur between molecules (not within) Bonds within water molecules are POLAR COVALENT!!!

HYDROGEN BONDS

As far as BOND go, they are weak, about 1/20th as strong as covalent bonds.

They form, break, and reform with great frequency

12

Each water molecule can form hydrogen bonds with up to four neighbors.

** Label the polar covalent bonds and hydrogen bonds in your notes right now…

14Hydrogen bonds affect the properties of water

Special Arrangement:

Water molecules arrange themselves in a very specific way…

WHY???

15

OPPOSITES ATTRACT

BUT Like charges repel each other…

17

H and H repel each other, as do O and O

18

What two ends of the molecule attract each other?

Hydrogen and Oxygen What will be repelled by each other?

O + O and H + H

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.1

The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.

Properties of H bonds…

Cohesion – water molecules sticking to each other (by H bonds) plays a key role in the

transport of water against gravity in plants

Adhesion- water molecules stick to other things Like the meniscus!

19

20Surface tension

Meniscus- adhesion

Surface Tension- cohesion

Hydrophilic vs Hydrophobic

Hydrophilic Any substance that likes water (WATER-

LOVING)Ionic or polar substancesMost hydrophilic substances dissolve

in water (ex salt) Hydrophobic: any substance that

doesn’t like water (WATER –FEARING)

Usually nonpolar/non-ionic substance (ex-oil)

“Like Dissolves Like”22

Polar Solutions (like water) are able to dissolve other polar molecules as well as ionic compounds. Why?

Likewise, nonpolar solutions (like oil) will not dissolve polar and ionic compounds and will instead dissolve NONPOLAR molecules.

Hydrophilic dissolves Hydrophilic

WILL DISSOLVE: • Ionic Compounds,• Polar Molecules• (anything with a charge)

Water

Hydrophobic dissolves Hydrophobic

WILL DISSOLVE: • only nonpolar,

hydrophobic things

(things with NO CHARGE)

Oil