The Atom

The atom is a basic unit of matter.  It consists of a nucleus and an electron cloud.   The nucleus is made of protons and neutrons.  The electron cloud is made of orbiting electrons. 

atom

Neutrons have a neutral charge, protons have a positive charge, and electrons have a negative charge.  In a stable element, the charges must balance out.  The number of protons must match the number of electrons.  In hydrogen, you have 1 proton and 1 electron, which makes hydrogen electrically neutral and stable. In oxygen, you have 6 protons and 6 electrons...again, electrically neutral.  If the number of protons do not match the number of electrons, you have an electrically charged atom called an ion.  Ionization is the process of creating ions.  Ionization is what makes x-rays potentially dangerous as it can cause biological damage to the body.

Because protons and electrons are electrically charged, the atom is happiest when the number of protons matches the number of electrons, which results in a neutral charge.  Protons are positively charged.  Electrons are negatively charged.  So what is a neutron?  A neutron helps keep the protons together in the nucleus.  Since protons are positively charged, they would repel each other and fly out of the nucleus.  Neutrons act as a "glue" to keep the nucleus together.  Even though they are neutral in charge, they do impact the property of the atom.  The number of neutrons do not necessarily equal the number of protons.  For instance, Lead Pb) 206 is the common form of Lead that we use as shielding agaist radiation.  It has 82 protons, 82 electrons,  and 124 neutrons.  If you add 4 more neutrons to Lead to make it Lead 210, it actually becomes radioactive itself.  An element with the same number of protons but different number of neutrons are called isotopes.  Lead 206 is the natural and stable form of lead.  Lead 210 is an isotope.

Electron cloud- electrons orbit the nucleus in layers, or shells.  Starting from the innermost shell and going outwards, the names of the shells are K, L, and M.  They continue out with N, O, P, etc.  Each shell requires a certain number of electrons to be stable.  The K shell needs 2, the L shell needs 8, etc.  Each shell requires a certain amount of energy to maintain the electron within that shell. 

Just a side note - In describing an atom's components, it's worth mentioning that an atom is made up of mostly empty space.  Just to give you an idea of scale, let's use the simplest element of all, a hydrogen atom.  a hydrogen atom consists of one proton and one electron.  If that proton were the sun, the electron would be orbiting 1,300 times farther out than the earth.