Unit 1 Atomic Structure

Objectives After studying this unit, you should be able to: –List the three principal parts of an atom –State the law of charges –Discuss centripetal force –Discuss the differences between conductors and insulators

Preview Electricity –Driving force that provides most of the power for the industrialized world Electric sources –Direct current (DC): unidirectional –Alternating current (AC): bidirectional

Early History of Electricity 2500 years ago: Greeks –First to discover electricity Amber could be charged Called amber elektron Early 1600s: William Gilbert –Discovered other materials could be charged Electriks: could be charged Nonelektriks: could not be charged

Early History of Electricity (cont’d.) 300 years ago: Charles DuFay –Charged glass would repel some charged objects and attract others Repulsion Attraction

FIGURE 1-1 List of charged materials.

FIGURE 1-2 Unlike charges attract and like charges repel.

Atoms Basic building blocks of the universe –Matter: combination of atoms –Element: substance that cannot be chemically divided into simpler substances Principal parts of an atom –Proton: positive charge –Electron: negative charge –Neutron: no charge

FIGURE 1-3 Water can exist in three states, depending on temperature and pressure.

Atoms (cont’d.) Table of elements –Lists natural and artificial elements Refer to Figure 1-4 Nucleus of an atom –Formed by neutrons and protons combining Atomic number of an element –Same as the number of protons in the nucleus

FIGURE 1–6 Helium contains two protons, two neutrons, and two electrons.

FIGURE 1–7 The lines of force extend outward. FIGURE1–9 The lines of force come inward.

The Law of Charges Figure 1–10 Unlike charges attract and like charges repel.

FIGURE 1–11 Unlike charges attract each other.

FIGURE 1–12 Like charges repel each other.

Structure of the Atom Bohr’s model of the atom –Electrons exist in specific orbits around the nucleus FIGURE 1–13 Bohr’s model of the atom proposed that electrons orbit the nucleus in much the same way that planets orbit the Sun.

Electron Orbits Electron orbit of an atom –Contains a set number of electrons Form a shell around the nucleus FIGURE 1–14 Electron orbits.

FIGURE 1–15 Electrons orbit the nucleus in a circular fashion.

Valence Electrons Located in the outer shell of an atom –Valence shell: outer shell of an atom FIGURE 1–16 The electrons located in the outer orbit of an atom are valence electrons.

FIGURE 1-17 A copper atom contains 29 electrons and has one valence electron.

Electron Flow Electrical current: the flow of electrons –Bump theory Current flow occurs when an electron from one atom knocks electrons of another atom out of orbit Striking electron may settle into orbit Electron that was struck moves off to strike another

FIGURE 1–18 An electron of one atom knocks an electron of another atom out of orbit.

FIGURE 1–19 The energy of the cue ball is given to the ball being struck.

FIGURE 1-20 The energy of the striking electron is divided.

FIGURE 1-21 The energy of the cue ball is divided between the two other balls.

Insulators Materials containing seven or eight valence electrons –Resist the flow of electricity Examples: rubber, plastic, glass, and wood FIGURE 1-24 The energy of the striking electron is divided among the eight electrons.

Semiconductors Materials that are neither good conductors nor good insulators –Contain four valence electrons –When heated, their resistance decreases –Common materials: silicon and germanium

FIGURE 1-25 Semiconductors contain four valence electrons.

Molecules Smallest part of a compound –Compound example: water FIGURE 1–26 A water molecule.

Methods of Producing Electricity Six basic methods: –Magnetism –Chemical action –Pressure –Heat –Friction –Light Involves the use of photons (massless particles of pure energy)

Electrical Effects Five basic effects: –Magnetism –Chemical reactions –Pressure –Heat –Light

Summary Atom: smallest part of an element –Principal parts Protons: positive charge Electrons: negative charge Neutrons: no charge Valence electrons –Located in the outer orbit of an atom

Summary (cont’d.) Conductors –Materials provide an easy path for electron flow Contain one to three valence electrons Insulators –Materials do not provide an easy path for electron flow Contain seven or eight valence electrons

Summary (cont’d.) Semiconductors –Contain four valence electrons Used in construction of all solid-state devices Molecule –Smallest part of a compound Six basic methods for producing electricity –Magnetism, chemical action, light, heat, pressure, and friction

Summary (cont’d.) Five basic effects that can be caused by electricity –Magnetism, chemical reactions, light, heat, and pressure Photon: massless particle of pure energy –Can be produced when electrons move from one energy level to another