Chemistry Basics-Part Two

Covalent Bonds Can Be Nonpolar Or Polar…Covalent Bonds Can Be Nonpolar Or Polar…

• Remember that covalent bonds occur between atoms that share electrons.

• There are two types of covalent bonds:

•Nonpolar

•Polar

What’s the Difference? What’s the Difference?

•While Nonpolar Molecules Share The Electrons Equally, Polar Molecules Do Not…

•This results in one part of the molecule being slightly positive and another part being slightly

negative.

Water Is A Polar Molecule Water Is A Polar Molecule

• The oxygen in water is slightly negative, and the two hydrogen atoms are slightly positive. (–) (–)

(+) (+)

O

HH

Hydrogen bond(+)

(+)

H

H(+)

(+)

(–)

(–)

(–)(–)

O

Hydrogen Bonds are weak bonds that form Hydrogen Bonds are weak bonds that form between slightly + and – molecules…between slightly + and – molecules…

Hydrogen Bonds Hydrogen Bonds Form BETWEEN Form BETWEEN Water Molecules, in Water Molecules, in our DNA, and in our DNA, and in proteins…proteins…

animation

Because of Hydrogen Bonds…Because of Hydrogen Bonds…

• Water is cohesive.

•Cohesion is the tendency of water molecules to stick together.

•Cohesion on the surface of water is called surface tension!

• Water is adhesive.

•Adhesion is the attraction between molecules of different substances.

The surface tension of water allows a water strider to walk on water…

Water is rarely found in its pure form… Water is rarely found in its pure form…

• Water is often found mixed with other molecules and elements.

•There are two types of mixtures:

•Solutions

•Suspensions

A Solution Is A A Solution Is A Homogeneous MixtureHomogeneous Mixture……

• In a solution the atoms or molecules of the different substances are equally distributed.

•Examples: salt water & KoolAid

+–

–

–

–

––

–

–

––+

++

++

Na+

+

Na+

Cl–

Cl–

Solutions Are Composed Of Two Parts… Solutions Are Composed Of Two Parts…

• Solutions are always composed to two parts, a solute and a solvent.

• The solute dissolves in the solvent.

• Water is called the universal solvent because so many things dissolve in it.

Suspensions are Suspensions are heterogeneous mixturesheterogeneous mixtures… …

• In a suspension the atoms or molecules that are mixed together do not spread out equally.

•Examples:

•Pennies in a glass of water

pH Stands For Potential Hydrogen…pH Stands For Potential Hydrogen…

• Mixtures are important to living things – one thing you need to know about mixtures is that they always have a pH (potential Hydrogen).

• pH measures whether it is an ACID or BASE.

In Solution Water Breaks Into Two Halves… In Solution Water Breaks Into Two Halves…

Acids Have A Low pH & Bases Have A High pHAcids Have A Low pH & Bases Have A High pH

• When water mixes with a base a lot of OH- (hydroxide ions) are produced.

• Bases have a pH higher than 7 on the scale.

• When water mixes with an acid a lot of H+ (hydrogen ions) are produced.

• Acids have a pH lower than 7.

The pH scale

Basic solution

Oven cleaner

Acidic solution

Neutral solution

pH scale

0

1

2

3

4

5

6

7

8

9

10

11

12

Lemon juice, gastric juice

Grapefruit juice, soft drink

Tomato juice

Human urine

Pure waterHuman blood

Seawater

Milk of magnesia

Household ammonia

Household bleach

Incr

easi

ngly

AC

IDIC

(Hig

her

conc

entr

atio

n of

H+)

NEUTRAL[H+]=[OH–]

H+ H+

H+ OH– H+

H+ H+

OH– H+ H+

OH–

OH–

H+ H+OH–

OH– OH–

H+ H+H+

OH–

OH–

OH– OH–

OH–OH– H+

Incr

easi

ngly

BA

SIC

(Low

er c

once

ntra

tion

of H

+)

OH–

H+

14

13

Animation

Chemical Reactions Occur In All Living Things…Chemical Reactions Occur In All Living Things…

• Chemical reactions are reactions that change the composition of matter.

• The general form of a chemical reaction is:

Reactants Products.

• The reactants are the starting material, and the products are the result.

Sodium & Chlorine Combine To Make Table Sodium & Chlorine Combine To Make Table SaltSalt

• What are the reactants and products of this reaction?

Sodium Chlorine Sodium Chloride

Hydrogen & Oxygen Combine To Form WaterHydrogen & Oxygen Combine To Form Water

• What are the reactants and products of this reaction?

2 H2O2 2 H2O

Equations Are Always Balanced…Equations Are Always Balanced…

• Notice that the number of atoms on each side of the equation is equal.

• This is a balanced equation!

2 H2O2 2 H2O