The Periodic Table

Mendeleev organized his periodic table based on the properties of the elements, specifically, reactivity and atomic mass. Elements in each section of the periodic table have similar properties. Reactivity describes whether an element will chemically combine with other common substances and also describes the speed of the reaction. Mendeleev's arrangement of the elements helped predict the existence of undiscovered elements.

Basic Patterns:

• Elements in the same group have similar properties (same number of valence electrons, etc.)
• Elements in the period have the same number of electron shells
• Atomic size increases going down
• Metals are on the left, non-metals on the right, other methal, metalloids, and transition metals are in the middle, halogens and noble gases to the very left, actinide and lanthanide series are listed at the bottom
• The number of protons corresponds to the atomic number
• Electronegativity and Ionization energy increase going up and right
• Reactivity of metals increases going down, reactivity of non-metals increases going up

Group- a vertical column in the periodic table

Period- horizontal rows on the periodic table

Noble Gases- elements in group 8A; are not reactive (noble gases have no reaction)

Element Squares:

• Contain- atomic number, symbol, name, and atomic mass
• About the atom
  • Diameter of the nucleus and electron cloud are measured in femtometers
  • The nucleus is dense- its mass is made up of protons and nuetrons
  • The electron cloud is mostly open space
  • Electrons are identical, but have different energy levels
  • Neutral atoms- # of protons = # of neutrons
  • amu- atomic mass unit
  • # of protons + # of neutrons = mass of atom in amu