38.0 - Introduction
“Turn off the lights when you leave the room.” “Don’t
buy that gas guzzler.” “Turn the thermostat down a
few degrees in winter.” These phrases are all about
saving energy, a worthwhile topic, but this chapter is
about where that energy comes from.
The energy powering your computer and lights is
electrical, but that electricity was likely generated from
the burning of oil or coal. In turn, these fossil fuels
came from the remains of ancient animals and plants,
which derived their energy from sunlight. If your
power was generated from hydroelectric sources í
letting water stored behind a dam spin a turbine as it
falls to a lower height í it was sunlight that
evaporated the water, which later turned into rainwater which was stored behind the dam.
Ultimately, the source of our energy here on Earth is the Sun, and nuclear fusion is what powers the Sun. The fusion process takes lighter
chemical elements such as hydrogen, and forms helium and heavier elements, in the process releasing energy.
In that respect, we owe our very existence to nuclear energy. However, to some, the term “nuclear physics” brings darker images to mind. For
better or worse, the world learned what nuclear fission was in 1945 at Hiroshima, although the exact same physics principles behind atomic
bombs are used peacefully every day.In this chapter, you will learn about the nature of atoms, which is a field of study called nuclear physics. You will become more familiar with
protons, neutrons and alpha particles. You will learn what occurs when atoms are split apart (fission), or when they are forced to merge
(fusion).
You will also learn about many peaceful applications in the field of atomic physics such as radioactive dating (no, this does not mean that two
radioactives go out for dinner and a movie) and energy production in nuclear reactors.Nuclear power plants convert the energy stored
in atoms into energy humans can use.38.1 - The atom and the electron
Nobel Laureate Richard Feynman posed a hypothetical situation in which our entire
base of scientific knowledge was destroyed, and we could pass on just one sentence to
our descendants. What would we choose to tell them, in order to convey the most
information in the fewest words?
In the famous “Feynman Lectures”, his choice was to tell the post-apocalyptic
population that all matter is composed of atoms, which are tiny particles that continually
move around, attracting each other when they are fairly close together, but strongly
repelling when they are pressed even closer together.
How did scientists arrive at this modern picture of the atom? In fact, what is an atom?
Humans have spent many millennia asking the question “What is the world made of?”
We have come a long way from the ancient Greeks, who believed that the cosmos was
composed of four elements: water, earth, air, and fire. Now, we know of over 100
chemical elements, which are the fundamental building blocks of matter. You have
heard of many of the elements: hydrogen, oxygen, carbon, gold, lead, and so on.
The modern definition of an element is a substance that cannot be divided or changed
into another substance using ordinary chemical methods. Each element has different
physical and chemical properties such as density, specific heat, and the way in which it bonds with other elements. You can see an example of
a common element, carbon, in Concept 1.
An atom is the smallest piece of an element that still has its chemical and physical properties. Atoms consist of electrons circling a nucleus
composed of protons and neutrons. This is illustrated in Concept 2. The next few sections will discuss the inner structure of the atom.
The modern theory of the atom began with the discovery of the first subatomic particle, the electron, in experiments performed over the course
of about 40 years in the late 1800s. Physicists found that when they applied a high voltage across a low-pressure gas, an electric discharge
was produced. They used a device called a cathode ray tube to achieve this effect. Today, you can witness a similar discharge in a neon sign
or a fluorescent light bulb.
The physicists determined that the gas in the tube was conducting electric charge. The tube’s negative electrode, also called acathode,
emitted a type of “invisible ray” that could cause a glow in the treated glass wall of the tube. Later experiments showed that the rays could be
deflected by electric and magnetic fields. This suggested that the rays were charged particles, and not a form of electromagnetic radiation.
Today, scientists would say that an electric current is flowing through the gas, and the current consists of electrons. The discovery of the
electron is credited to J.J. Thomson in 1897. He showed that these rays were small, negatively charged particles. Thomson also made the first
measurement of the ratio of their charge to their mass.Elements
Fundamental building blocks of matter
Atoms are smallest distinct component
of elements(^698) Copyright 2007 Kinetic Books Co. Chapter 38