1

Chemistry Review

Chapter 2

2

Outline

• Structure of Atoms• Isotopes

– Radioactive Isotopes• Electrons and Chemical Behavior• Chemical Bonds

– Ionic versus Covalent• Water Chemistry

– Hydrogen Bonding• pH• Functional groups

3

Atoms

• All matter is composed of atoms.– Protons (+) and neutrons (neutral) are

found on the atom’s nucleus, while electrons (-) circle the nucleus.

Atomic number - number of protonsAtoms with the same atomic number

belong to the same element, and thus have the same inherent properties.

4

Atoms

5

Atoms

• Mass refers to the amount of a substance.• Weight refers to the force exerted on a

substance by gravity.• Atomic mass of an atom refers to the sum of

the masses of protons and neutrons.– measured in Daltons

• What is atomic weight? Can it be determined for a single atom? How is it determined?

6

Isotopes

• Isotopes - Atoms of an element that possess a different number of neutrons.

– Radioactive isotopes - Spontaneously decay into elements of lower atomic number.

emit energy and/or subatomic particlesHalf-life refers to the amount of time

necessary to decay half the atoms of a given sample.

Carbon-126 Protons6 Neutrons6 Electrons

Carbon-136 Protons7 Neutrons6 Electrons

Carbon-146 Protons8 Neutrons6 Electrons

Isotopes

8

Electrons

• Atoms with the same number of protons as electrons are electrically neutral.

– Ions - Atoms in which the number of protons and electrons differ.

Cation - Contains more protons than electrons, and carries a positive charge.

Anion - Contains fewer protons than electrons, and carries a negative charge.

9

Electrons and Atomic Behavior

• Orbital refers to the area around a nucleus where an electron is most likely found.

– Chemical behavior of an atom is determined by the number and arrangement of its orbitals.

Electrons are attracted to the positively charged nucleus, thus it takes energy to hold electrons in place.

potential energy of position

10

Atomic Energy Levels

11

Electrons and Atomic Behavior

• During some chemical reactions, electrons are transferred between atoms, while still retaining their energy of position.

– Oxidation - loss of an electron– Reduction - gain of an electron

12

Kinds of Atoms

• Ninety-two naturally occurring elements– Periodic table arranged by grouping atoms

based on valence electrons (electrons in the outer energy levels).

Octet rule Inert atoms have outer level filled.Reactive atoms do not have outer

level filled.

13

Periodic Table of the Elements

14

Chemical Bonds

• A molecule refers to a group of atoms held together by energy in a stable association.

– Compound is composed of two or more different types of atoms.

Atoms in a molecule are joined by chemical bonds.

15

Chemical Bonds

• Ionic bonds are formed because ions of opposite charge attract one another.

– table salt• Covalent bonds are formed when two or more

atoms share pairs of valence electrons.– Strength depends on number of shared

electrons.

16

Chemical Reactions

• A chemical reaction occurs during the formation or breaking of chemical bonds.

– Reactants refer to original molecules.– Products refer to resultant molecules.

• Chemical reactions can be influenced by:– temperature– concentration of reactants and products– catalysts

17

Water Chemistry

• Water consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds.

– stable atom with no electrical charge most outstanding property is its ability to

form weak chemical associations

18

Hydrogen Bonding

• In a water molecule, both the oxygen and hydrogen atoms attract the shared electrons in the covalent bond (electronegativity).

– Oxygen atom is more electronegative than the hydrogen atoms.

distinct ends with partial charge (polar)hydrogen bonds

19

Water Chemistry

• Water clings to polar molecules.– Cohesion refers to attraction to other

water molecules. responsible for surface tension

– Adhesion refers to attraction to other substances.

Water is adhesive to any substance with which it can form hydrogen bonds.

20

Water Chemistry

• Water stores heat.– High specific heat

Amount of heat that must be absorbed or expended to change the temperature of 1g of a substance 1o C.

– High heat of vaporization Amount of energy required to change 1g

of liquid water into a gas (586 calories). large number of hydrogen bonds

21

Water as a Solvent

• Water is an effective solvent as it can form hydrogen bonds.

– Water clings to polar molecules causing them to be soluble in water.

Hydrophilic - attracted to water– Water tends to exclude nonpolar

molecules. Hydrophobic - repelled by water

22

pH

• pH scale expresses hydrogen ion (H+) concentration in a solution.

– logarithmic scale ranging from 0-14 neutral = 7

• Acids dissociate in water to increase the concentration of H+.

– pH values lower than 7• Bases combine with H+ ions when dissolved in

water, thus decreasing H+ concentration.– pH values above 7

• Buffers act as a reservoir for hydrogen ions, donating or removing them from solution as necessary.

23

pH

24

The pH scale

• The pH scale is the concentration of hydrogen ions in a given substance.

HpH log

25

Definitions of Acids and Bases

• An acid is a substance that breaks into ions in an aqueous solution.

• A Base (alkaline) is a substance that breaks into ions in an aqueous solution.

• Note: aqueous solution is any solution where is the solvent.

H

OH

OH 2

26

Characteristics Of Acids

Acids can be characterized by:

1. A sour taste.

2. It turns blue litmus paper red

3. It tastes sour. Try drinking lemon juice (citric acid)

27

Characteristics of Bases

A Base is characterized by:

1. A bitter taste. (Milk of Magnesia)

2. It feels slippery. (Soapy Water)

3. It turns Red Litmus Blue.

28

Test Your Knowledge

• What is the range of an ACID on the pH scale?

Ans: 0-7

• What is the range of a BASE and what is another name for a BASE?

Ans: 7-14, Alkaline

29

Hydroxyl

Carbonyl

Carboxyl

Amino

Sulfhydryl

Phosphate

Methyl

Acetic acid

Functional Group

StructuralFormula

Example

Acetaldehyde

Alanine

-mercaptoethanol

Glycerol phosphate

Pyruvate

HS

P

O–

O

O

HC

H

H

OH

O

OHC

H

HN

CO

Ethanol

C

H

H

CH

H

H

OH

CH

H

HC

O

OH

H

CH3

OH

CCHO NH

CH

H

HHC

O

CHOH

H HS HC

H

CH

OH

HC

OH

H HOC

H

P

O

C

O

C

O

HHC

H

O–

O–

O–

O–

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• Functional Groups tend to act as units during chemical reactions and confer specific chemical properties on the molecules that posses them.

– Ex. amino groups make a molecule more basic while carboxyl groups make a molecule more acidic.

• Functional groups have definite chemical properties that they retain no matter where they occur.

– The hydroxyl group is polar because oxygen draws electrons toward itself

• A bunch more on this later!!• Eventually you will have to

memorize this (and more!)