Atoms and the Periodic Table

• Learn patterns of the periodic table that can be used to create models of atoms.

• Learn how elements combine, depending upon their properties, to form molecules and compounds.

• atomic number = the number of protons (also equal to number of electrons)

• atomic mass = the number of protons plus neutrons

• energy levels - where the electrons are outside the nucleus (the first energy level can hold up to 2 electrons, the second and third energy levels can hold up to 8 electrons)

• valence electrons - the electrons in the outer energy level

• bonding - when electrons are shared or transferred to gain stability

• molecules - have two or more atoms

• compounds - have two or more elements

• Atomic number is a whole number.

• It is equal to the number of protons.

• It is also equal to the number of electrons.

• Mass number is not a whole number.

• It is equal to the number of protons and neutrons.

# of Neutrons =

Mass number - (minus)

Atomic number

for example, for Sodium (Na),

23-11=12

Sodium has 12 neutrons.

• Elements are arranged by increasing atomic number.

• The group (AKA family) number (labeled with a Roman numeral above each column) is equal to the number of electrons found in each valence. 

• Every element in group one has one electron in its outer shell (valence). Every element in group two has two electrons in its valence. etc. 

• Elements with valences that are not full are more reactive, and more likely to share or transfer their electrons

• Only Family (Group) 8 elements have their valences full. They are the noble gases.

• Other groups' elements need to gain or lose electrons to fill their valences. They are reactive.

• The row number corresponds to the number of energy levels for the elements that row.

• For example, the elements in the top row have one energy level. The first energy level can hold up to two electrons.

• The second row elements have two energy levels. The third row elements have three energy levels. The 2nd and 3rd energy levels can hold up to 8 electrons.