<em>The energy level diagram is used to represent the energy states available in each atom. When an electron is in an energy state, it emits nor absorbs radiation. A photon is emitted or absorbed when an electron transitions from one energy state to another.</em>
The first row of elements fits in period <u>6</u>, after the element <u>lanthanum (La)</u>. The second row of elements fits in period <u>7</u>, after the element <u>actinium (Ac). </u>