1. 1.5 Atomic Size Atomic Radius LO: I know what an atomic radius is.

2. There are two types of atomic radius. The radius of an atom is half the distance between the nuclei of two atoms that are bonded together. (1)The radius (r 1 ) is half the distance between the nuclei of two atoms joined by a covalent bond (E-F). (2)The radius (r 2 ) is half the distance between the nuclei of two atoms joined by van der Waals forces (C-G). covalent van der Waals

3. Atomic Size and the Periodic Table LO: I understand trends in atomic radii throughout the Periodic Table.

4. So, the size of the atoms increases. Going down a group: The number of electron energy levels increases. Going across a period: The number of protons in the nucleus increases. The increasing nuclear charge pulls all of the electrons closer to the nucleus. The size of the atoms decreases going across a period from left to right.

5. Atomic Size and Density LO: I understand how density changes with atomic size.

6. So, the density of the atoms increases. Going down a group: The mass of the atoms increases more than the size does. Going across a period: The mass of the atoms increases as the size decreases. So, the density of the atoms increases.