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The electron cloud is divided into layers, called energy levels.
Electrons in the outermost energy level are called valence electrons.
Protons and Neutrons to scale
The mass of a proton is about 1.7 x 10-24 g.
A neutron is just a little bigger than a proton, but it is also equal to one a.m.u.
Most of the mass in an atom is in the nucleus.
Protons and electrons to scale
Electrons are very small in mass. They are so small, that they are almost zero.
If an atom does not have an equal number of protons and neutrons, then it is called an ion.
Isotopes
All atoms of the same element have the same number of protons.
Not all atoms of an element have the same number of neutrons.
An isotope is an atom that has the same number of protons but a different number of neutrons as other atoms of the same element.
Reading the Periodic Table
All elements on the periodic table are grouped by physical properties.
Group 1 - Alkali metals (Reactive metals)
Soft enough to be cut with a knife, most reactive metal, react violently with water.
Group 2 - Alkaline-earth metals (Reactive metals)
Very reactive, but not as much as alkali metals, silver colored.
Group 3-12 - Transition metals
Less reactive than Alkaline-earth metals, shiny, good conductors of electricity.
Groups 13-16--Groups with Metalloids
Group 13 - Boron Group
Group 14 - Carbon Group
Group 15 - Nitrogen Group
Group 16 - Oxygen Group
Group 17 - Halogens
Very reactive non-metals, poor conductors of electric currents.
Group 18 - Noble Gases
Unreactive non-metals, passing an electric current through noble gases makes them glow (neon lights), safer to use than other elements.
Hydrogen
So different it's in a group of it's own, reactive, most abundant element in the universe, used to fuel space rockets.
The atomic mass is the average of all the naturally occurring isotopes of an element.
Look here for a good website on atoms
Look here for a good website about the Periodic Table
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