CHAPTER 6: Energy and Matter
 

(a). Characteristics of Energy and Matter
 

Introduction

Energy is defined simply by scientists as the capacity for doing work. Matter is the material (atoms and molecules) that constructs things on the Earth and in the Universe. Albert Einstein suggested early in this century that energy and matter are related to each other at the atomic level. Einstein theorized that it should be possible to convert matter into energy. From Einstein's theories, scientists were able to harness the energy of matter beginning in the 1940s through nuclear fission. The most spectacular example of this process is a nuclear explosion from an atomic bomb. A more peaceful example of our use of this fact of nature is the production of electricity from controlled fission reactions in nuclear reactors. Einstein also suggested that it should be possible to transform energy into matter.

Energy and matter are also associated to each other at much larger scales of nature. Later on in this chapter, we will examine how solar radiation provides the energy to create the matter that makes up organisms. Organisms then use some of this matter to power their metabolism.

 

Types of Energy

Energy comes in a variety of forms. The simplest definition of the types of energy suggests that two forms exist: kinetic energy and potential energy. Kinetic energy is the energy due to motion. A rock falling from a cliff, a bee in flight, wind blowing leaves of trees, and water following over a waterfall are all examples of kinetic energy. Potential energy is the energy stored by an object that can be potentially transformed into another form of energy. Water stored behind a dam, the chemical energy of the food we consume, and the gasoline that we putting in our cars are all examples of potential energy. Conversion of this energy occurs when the energy in food is used by an organism to energize its metabolism, when the water in the dam flows through turbines to produce electricity from motion, and when the gasoline is used in a engine to produce motion from combustion.

Some other forms of energy include heat, electricity, sound, energy of chemical reactions, magnetic attraction, energy of atomic reactions, and light. Definitions for a few of these types of energy are as follows:

Radiation - is the emission of energy from a material object in the form of electromagnetic waves and photons.
Chemical Energy - is the energy produced or consumed in chemical reactions.
Atomic Energy - is the energy released from an atomic nucleus because of a change in its subatomic mass.
Electrical Energy - is the energy produced from the force between two objects having the physical property of electrical charge.
Heat Energy - is a form of energy created by the combined internal motion of atoms in a substance.

On Earth, there are fundamentally only three ways in which energy can be transferred from one place to another: conduction, convection, and radiation. Conduction involves the adjacent transfer of heat energy from one atom to another through the mass of a gas, liquid, or solid. Condution results in the continuous flow of heat energy along a temperature gradient from areas of higher to lower temperature. Convection involves the transfer of heat energy by way of mass movements of a substance in gas or liquid form in a vertical direction (horizontal transfer is called advection). Convection is often seen as rising masses of gas or liquid called convection currents. It is important to note that energy transfer by way of conduction and convection depends on the presence of matter. These forms of energy transfer do not operate in the vacuum of space. Radiation is the only means of energy transfer that can occur across outer space. The transfer of radiation produced at the Sun's surface through space supplies the Earth with most of its energy.

 

Matter: Elements and Compounds

Matter is the material that makes up things in the Universe. All matter on the Earth is constructed of elements (see WebElements for the periodic table of elements). Chemists have described approximately 115 different elements. Each of these elements have distinct chemical characteristics. Table 6a-1 lists some of the chemical characteristics for 48 common elements found in the Earth's continental crust.

The smallest particle that exhibits the unique chemical characteristics of an element is known as an atom. Atoms are composed of yet smaller particles known as protons, neutrons, and electrons. A proton is a subatomic particle that has significant mass and contributes a single positive electrical charge to an atom. Neutrons also have significant mass but no electrical charge. Electrons are extremely light subatomic particles having a mass that is 1/1840 of a proton. Each electron also has a negative electrical charge.

Protons and neutrons make up the nucleus of an atom. As a result, most of an atom's mass is concentrated in the nucleus. Because protons are positively charged the nucleus has a positive charge equal to the number of these subatomic particles. Electrons are found orbiting outside the nucleus at various distances based on their energy level. The area occupied by the electrons has a negative charge equal to the number of these subatomic particles. If an atom has an equal number of electrons and protons its net electrical charge is zero. If there are more electrons than protons the charge of the atom is negative. Likewise, if there are less electrons than protons the charge of the atom is positive. In both cases, the exact charge is determined by subtracting protons from electrons. As a result, 4 protons minus 6 electrons give an atomic charge of -2.

The number of protons found in the nuclei of the different types of elements is unique and is referred to as the atomic number (Table 6a-1). All atoms of a specific element have the same number of protons in their nuclei. Atomic mass number is an atom's total number of neutrons and protons. Many elements have unequal numbers of neutrons and protons in their nucleus. An element's atomic weight refers to the total weight of neutrons, protons, and electrons. For example, the atomic weight of aluminum is 26.98 (Table 6a-1). Atomic number describes the number of protons found in an atom. For example, silver has an atomic number of 47 or 47 protons in its atom (Table 6a-1). Some elements can have variants containing different numbers of neutrons but similar numbers of protons. We call these variants isotopes. Carbon has two isotopes. Its most common form is carbon-12 which has 6 protons plus 6 neutrons. About 99% of the carbon on our planet is of this type. The isotope carbon-13 has 6 protons plus 7 neutrons. Carbon-14 is the rarest isotope of carbon containing 8 neutrons. Some isotopes are unstable and their nucleus tends to lose subatomic particles forming an element with a lower atomic mass. This process is known as radioactive decay.

 

Table 6a-1: Characteristics of some of the common chemical elements found in the Earth's continental crust.
Element

Chemical

Symbol

Atomic

Number

Common

Atomic

Mass

Number

Atomic

Weight

Percent in

Continental

Crust

Required

for all

Life

Required

for

Some

Lifeforms

 

Element

Type

Moderately

Toxic

Extremely

Toxic
Aluminum
Al
13
27
26.98
8.2300
-
X
Metalloid
-
-
Antimony
Sb
51
122
121.75
0.00002
-
-
Metalloid
-
-
Arsenic
As
33
75
74.92
0.00018
-
-
Metalloid
-
X
Barium
Ba
56
137
137.34
0.0425
-
-
Metal
-
-
Beryllium
Be
4
10
9.01
0.00028
-
-
Metal
-
X
Bismuth
Bi
83
209
208.98
0.000017
-
-
Metal
-
-
Boron
B
5
11
10.81
0.0010
-
-
Metalloid
-
-
Bromine
Br
35
80
79.91
0.00025
-
-
Nonmetal
-
-
Cadmium
Cd
48
112
112.40
0.00002
-
-
Metal
-
X
Calcium
Ca
20
40
40.08
4.1000
X
-
Metal
-
-
Carbon
C
6
12
12.01
0.0200
X
-
Nonmetal
-
-
Chlorine
Cl
17
35.5
35.45
0.0130
-
X
Nonmetal
X
-
Chromium
Cr
24
52
52.00
0.0100
-
-
Metal
X
-
Cobalt
Co
27
59
58.93
0.0025
-
X
Metal
-
-
Copper
Cu
29
63.5
63.54
0.0055
X
-
Metal
X
-
Fluorine
F
9
19
19.00
0.0625
-
X
Nonmetal
X
-
Gallium
Ga
31
70
69.72
0.0015
-
-
Metal
-
-
Germanium
Ge
32
73
72.59
0.00015
-
-
Metalloid
-
-
Gold
Au
79
197
196.97
0.0000004
-
-
Metal
-
-
Hydrogen
H
1
1
1.008
1.4000
X
-
Nonmetal
-
-
Iodine
I
53
127
126.90
0.00005
-
X
Nonmetal
-
-
Iron
Fe
26
56
55.85
5.6000
X
-
Metal
-
-
Lead
Pb
82
207
207.19
0.00125
-
-
Metal
-
X
Lithium
Li
3
6
6.94
0.0020
-
-
Metal
-
-
Magnesium
Mg
12
24
24.31
2.3000
X
-
Metal
-
-
Manganese
Mn
25
55
54.94
0.0950
X
-
Metal
-
-
Mercury
Hg
80
201
200.59
0.000008
-
-
Metal
-
X
Molybdenum
Mo
42
96
95.94
0.00015
X
-
Metal
-
-
Nickel
Ni
28
59
58.71
0.0075
-
-
Metal
-
X
Nitrogen
N
7
14
14.01
0.0020
X
-
Nonmetal
-
-
Oxygen
O
8
16
16.00
46.4000
X
-
Nonmetal
-
-
Palladium
Pd
46
106
106.40
0.000001
-
-
Metal
X
-
Phosphorus
P
15
31
30.97
0.1050
X
-
Nonmetal
-
-
Platinum
Pt
78
195
195.09
0.0000005
-
-
Metal
-
-
Potassium
K
19
39
39.10
2.1000
X
-
Metal
-
-
Rubidium
Rb
37
85.5
85.47
0.0090
-
-
Metal
-
-
Selenium
Se
34
79
78.96
0.000005
-
X
Nonmetal
X
-
Silicon
Si
14
28
28.09
28.2000
-
-
Metalloid
-
-
Silver
Ag
47
108
107.87
0.000007
-
-
Metal
-
X
Sodium
Na
11
23
22.99
2.4000
-
X
Metal
-
-
Sulfur
S
16
32
32.06
0.0260
X
-
Nonmetal
-
-
Thorium
Th
90
232
232.04
0.00096
-
-
-
-
-
Tin
Sn
50
119
118.69
0.00020
-
-
Metal
X
-
Titanium
Ti
22
48
47.90
0.5700
-
-
Metal
-
-
Tungsten
W
74
184
183.85
0.00015
-
-
Metal
-
-
Uranium
U
92
238
238.03
0.00027
-
-
-
-
-
Vanadium
V
23
51
50.94
0.0135
-
X
Metal
X
-
Zinc
Zn
30
65
65.37
0.0070
X
-
Metal
-
-

 

Elements can be classified as being either metals, nonmetals, or metalloids (Table 6a-1). Metals are elements that usually conduct heat and electricity and are shiny. Nonmetals do not conduct electricity that well and are normally not shiny. Metalloids have characteristics that are in between metals and nonmetals.

Elements with a net positive or negative charge are called ions. Chemists indicate the number of positive or negative charges on an ion using a superscript after the element's symbol. For example, calcium has two positive charges and is written as Ca2+. Some common negatively charged ions include nitrate (NO3-), sulfate (SO42-), and phosphate (PO43-).

Positive and negative ions are electrically attracted to each other. This mutual attraction allows for the bonding of atoms to occur forming structures of matter that are larger than just one atom. When similar atoms bond together they construct molecules. Atoms of different elements joined together form compounds (Figure 6a-1). Sodium chloride (or table salt), is an ionic compound consisting of sodium (Na+) and chloride (Cl-). In nature, it forms as a three-dimensional array of oppositely charged ions (Figure 6a-2). Many of the Earth's substances have a molecular structure similar to sodium chloride.

Figure 6a-1: Some common molecules and compounds. The molecules in the top row bond with each other by sharing electrons. The compounds in the bottom row also share electrons. However, these joins are called ionic bonds.

 

Figure 6a-2: Atomic representation of sodium chloride or table salt. This compound forms in nature as a highly ordered, three-dimensional network of oppositely charged