Subatomic Particles

There are three kinds of particles found in a typical atom: protons and neutrons, which together
make up the nucleus, and electrons, which are found in specific regions of space (known as orbitals)
around the nucleus.

PROTONS

Protons carry a single positive charge and have a mass of approximately one atomic mass unit or
amu (see Table 3.1). The atomic number (Z) of an element is equal to the number of protons found
in an atom of that element. All atoms of a given element have the same atomic number; in other
words, the number of protons an atom has defines what kind of element it is.

Table 3.1 Properties    of  Subatomic   Particles

Subatomic   Particle Symbol Relative    Mass Charge Location

Proton 11 H 1 +1 Nucleus

Neutron 10 n 1 0 Nucleus

Electron e− 0 −1 Electron   Orbitals

The atomic number of an element can be found in the periodic table (see chapter 4 ) as an integer
above the symbol for the element.

NEUTRONS

Neutrons carry no charge and have a mass only slightly larger than that of protons. The total
number of neutrons and protons in an atom, known as the mass number, determines its mass.

The convention is used to show both the atomic number and mass number of an X atom, where
Z is the atomic number and A is the mass number.