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Atoms

TOMS make up all matter. Matter is

everything around you, the chair you sit in,

the car you drive, the food you eat, and your

body. By understanding the atom, we can

classify elements into conductors (metals),

nonconductors (insulators), and semiconductors.

The movement of electrons has made it possible

for us to generate energy, launch space crafts,

build computers, and design a global

communications network. Understanding the

different properties of these elements has

allowed us to change our world.

Objectives:

þ 1. Explain atom basics.

2. Describe the differences between conductors, semiconductors, and insula-

tors.

Key Terms:

Understanding Atom Basics

The three subatomic parts of an atom are protons, neutrons, and electrons. These particles

make up a standard atomic model of an atom. An atom is the smallest particle of an element

that retains its identity. Matter composed of the same type of atoms is an element (has only

one atom type). Elements may be classified as solids, liquids, or gases. We will focus on the fol

lowing solids: conductors (metals), nonconductors (insulators), and semiconductors (neither

metals nor insulators). If two or more different atoms are combined, they create a new sub

stance called a compound.

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atom

conductor

electron

element

insulator

neutron

periodic table

proton

semiconductor

valence shell

HISTORY OF ATOMS

Atoms were first conceptualized in Ancient Greece. Physicist G.J. Stoney proposed that

electricity was made of negative particles (“electrons”) around 1891. The word “electron”

refers to anything with an electric charge. Around 1904, J.J. Thomas proposed that the electron

is part of an atom. This was the first of the subatomic parts to be discovered. It took from 1897

until 1932 to discover that the atom is composed of three subatomic particles: protons,

neutrons, and electrons.

PARTS OF AN ATOM

The three parts of an atom are called protons, neutrons, and electrons.

Proton

A proton is a positively charged particle and is inside the nucleus. It is about the same

weight as a neutron. All the subatomic particles have an extremely small mass, but a proton

weighs about 1.6726231*10

–27

kg.

Neutron

A neutron is a particle without a charge located inside the nucleus. It weighs about the

same as amount as a proton, but it is slightly larger at 1.6749286*10

–27

kg per unit.

Electron

An electron is a negatively charged

particle that orbits around the nucleus. It

is the smallest particle of an atom and

weighs about 9.1093897*10

–31

kg. The

weight of protons, neutrons, and elec

trons stated in kilograms with such small

numbers is hard to understand. The unit

is so small that it is hard to comprehend

the size. For comparison, you may think

of an electron as weighing about the

same as a dime and a proton as weighing

about 8 pounds (the same weight as a

gallon of water). Approximately 1,836

electrons would equal one gallon of

water.

Electrons are the only particles in an

atom that can easily move. They form

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FIGURE 1. This is the structure of an atom.

shells that surround the nucleus. The valence shell is the outer shell of an atom. Examine

the number of electrons in the valence shell to determine what kind of element is present. The

maximum number of electrons in the valence shell is eight. Elements have different physical

properties depending on the number of electrons in the outer shell or valence shell. The

movement of electrons is necessary to generate electricity.

PERIODIC TABLE

The periodic table is an illustration of the chemical elements on earth. Understanding

the different properties of these elements has allowed scientists to create new substances,

thereby forming chemical reactions. When different elements come together, they form com-

pounds. For example, when iron and sulfur combine, they form a compound called iron sul-

fide. Compounds formed from conductors (metals) and nonconductors (nonmetals) contain

ions. Ions are created when electrons are gained and lost. Metals lose electrons, leaving them

positively charged ions. Nonmetals gain electrons, creating negative ions.

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FIGURE 2. This is the periodic table of the chemical elements.

Conductors, Semiconductors, and Insulators

The stability of electrons in the valence shell determines whether a material is a conductor,

semiconductor, or insulator.

CONDUCTOR

A conductor is an element whose elec

trons can easily move from one atom to

another. A conductor does not have a full

electron outer ring or valence shell; elec

trons can move easily from one atom to

another. The valence shell of a conductor

has one or two electrons. Most metals

make good conductors. Examples are sil

ver, gold, and copper. The movement of

electrons through a conductor causes cur

rent flow. Current flow is the same as elec-

trical current. Current flow is measured by

the number of electrons flowing by a cer-

tain point in one second.

INSULATOR

An insulator is an element whose

outer electron ring or valence shell is full.

Insulator electrons cannot move easily.

Examples of insulators are plastic, glass,

wood, rubber, neon, and argon. Insulators

(e.g., rubbers and plastics) are used in elec

tronics and electrical wiring to protect con

sumers from electrical shock.

SEMICONDUCTOR

A semiconductor is an element

whose outer electron ring or valence shell

is not full or empty. The valence shell will

contain three or four electrons. A semicon

ductor is the work horse of electronics; it

amplifies, rectifies, and directs signals.

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FIGURE 3. This is an illustration of the element gold.

FIGURE 4. This is an illustration of the element argon.

Examples are carbon and silicon, which are

used to make electrical components (e.g.,

diodes, transistors, and integrated circuits).

Understanding the properties of ele-

ments and creating new materials joining

them together to make compounds and

ions has changed our world. Scientists and

chemists use these properties to manufac-

ture many things (e.g., batteries, steel

alloys, titanium alloys, copper alloys, and

rubber compounds). Modern manufactur-

ing processes have revolutionized our

world. In the past hundred years, we have

launched space crafts, built computers, and

designed a global communications

network.

Summary:

Knowledge has revolutionized our world, resulting in stronger, lighter, denser,

shinier, less expensive, and more pliable materials. The stability of electrons in the

valence shell determines whether a material is a conductor, semiconductor, or insu

lator. The three parts of an atom are called protons, neutrons, and electrons. A pro

ton is a positively charged particle and is inside the nucleus. It is about the same

weight as a neutron. A neutron is a particle without a charge located inside the

nucleus. An electron is a negatively charged particle that orbits around the nucleus.

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FIGURE 5. This is an illustration of the element carbon.

EXPLORING OUR WORLD…

SCIENCE CONNECTION: Manufacturing Alloys

Alloys are made by combining two different metals. They are heated until they are in a molten

state and are then mixed together. While still in the molten state, they are poured into molds.

Alloys are used because they have unique properties. Some are harder, lighter, denser, shinier,

less expensive, and more pliable. Some go back to their original shape after they are heated.

Aluminum alloys are aluminum mixed with copper, zinc, silicon, or magnesium. They are lighter

and do not corrode as easily as plain carbon steel. A silver necklace, the car you ride in, the

plane you fly in, and the silverware you eat off of are all made of alloys. Nitinol tubes are alloys

of nickel and titanium. These tubes are used by doctors as stents to keep the cardio vascular

system working. Duralumin is used to make airplanes. It is made of manganese, magnesium,

and copper combined with aluminum to increase its strength.

Checking Your Knowledge:

´ 1. Who were the first people to conceptualize the atom?

2. What are the three parts of an atom and their charges?

3. List three examples of conductors.

4. How many electrons are in the valence shell of conductors, semiconductors,

and insulators?

5. Who proposed that the electron is part of an atom?

Expanding Your Knowledge:

Contact a manufacturing facility that makes alloys. Ask if you can tour the facility

(alone or with classmates). You may want to inquire about interviewing an

employee as well regarding the process as well as improvements that have been

made.

Web Links:

: Career Opportunities in Safety Engineering

https://www.asme.org/engineering-topics/articles/uncertainty-analysis/diverse-

career-opportunities-in-safety-engineering

Occupational Outlook Handbook

http://www.bls.gov/ooh/architecture-and-engineering/health-and-safety-

engineers.htm

Business Safety

https://www.osha.gov/

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