These three gasses are highly unreactive and always found in their pure form in nature: _______________________, ____________________, and _____________________.

The mass per unit volume is called ___________________________. 

The third energy level is d with _______ orbitals and a maximum of _______ electrons. 

The _________________________________ end each period in the periodic table.

The fourth energy level is f with ______ orbitals and a maximum of _______ electrons.

Each horizontal row is called a(n) _________________________.

Each vertical column is called a(n) ________________________.

According to the video, there are three families of elements known as the: ________________________,  ____________________, and ____________________.

The elements are arranged in order by their ___________________________________. 

The second energy level is p with ______ orbitals and a maximum of _______ electrons.