Chemistry

• Atoms 


  Smallest part of an element that can exist. Made of 3 subatomic particles: protons neutrons and electrons.
• Element


  Substance made of only one type of atom.
• Compound 


  Substance made of 2 or more elements chemically combined
• Mixture


  Two or more different substances that are not chemically combined.
• Ion


  Atom, or group of atoms which have an electronic charge. Formed by loss or gain of one or more electrons.
• Mass number


  Number of protons + number of neutrons. Always and integer.
• Period


  Horizontal row of the periodic table. Elements in the same periods have the same number of energy levels. Period number = number of energy levels
• Group


  Elements in the same group have the same number of electrons in their outer energy level. Group number = number of electrons in outer energy level
• Electronic structure


  Arrangement of electrons within an atom. Determines the chemical reactivity