CHAPTER 3

A World of Particles

SUMMARY

KEY TERMS

atom

atomic theory

model

nucleus

proton

neutron

electron

atomic number

isotope

mass number

average atomic mass

radioactive isotope

nuclear reaction

radioactive decay

alpha decay

alpha particle

beta decay

beta particle

half-life

radiation

gamma ray

fission

fusion

nuclear equation

parent isotope

daughter isotope

nuclear chain reaction

Can a copper atom be transformed into a gold atom through nuclear processes?

Elements are collections of similar atoms. The number of protons in the nucleus determines the identity of an atom. For instance, all atoms of gold have 79 protons. However, atoms of an element may have different numbers of neutrons. The number of neutrons is related to the stability of the atom. Stable gold atoms have 118 neutrons.

Nuclear fission, nuclear fusion, and radioactive decay can result in new elements. But nuclear fusion and nuclear fission are difficult processes to control and often involve large amounts of energy. Nuclear reactions do take place in the stars where atoms are created. So far it is not yet possible or practical to create gold atoms through nuclear reactions here on Earth.