Atomic Radius Jennifer Chiang & Janice Park

1. Atomic Radius Jennifer Chiang & Janice Park

2. Definition For single elements: The atomic radius is the distance from the valence electrons to the nucleus of the atom. i.e. He For bonded elements: The atomic radius is half of the distance between the two bonded nuclei. i.e. Nucleus Nucleus this line divided in half

3. Definition continued… Van der Waals radius: The radius of non-bonding atoms caused by a weak attraction when they are placed adjacent to each other Nucleus Nucleus this line divided in half

4. General Trends Down a family= atomic radius gets larger Across a period= atomic radius decreases

5. Explanations: Going Down • As you go down the periodic table, the atomic radii becomes bigger because more shells of electrons being added (larger number of orbitals). • Even though there is an increase in protons, Z* decreased enough by shielding to limit effect • Electron-electron repulsion causes the atom to also increase

6. Explanations: Going Across • As you go across a period, the atomic radius will get smaller because Z* increases with each proton that is added to the nucleus • Greater pull causes the atom’s size to decrease • There is still electron-electron repulsion, but the charge experienced by the electrons from the additional protons outweighs the addition of electrons

7. Units Atomic radii are usually expressed in terms either the SI unit of nanometers ( m) or picometers ( m). Nowadays, the picometer is becoming more popular.

8. Exceptions • One exception to the trend of atomic radii are the noble gases because they pretty much don’t form bonds. Therefore, only the van der Waals radius can be measured. Other elements are held by strong bonds which cause them to be squished together. Therefore, noble gases are bigger than other elements of the same period. • Another exception to this rule comes because of elements in the d and the f orbitals • Electrons are added into these orbitals with there already being electrons present in higher orbitals • i.e. an element in 3d will generally already have 4s2 filled. • Size generally stays the same • Electron-electron repulsion overrides the addition of a proton and the atomic radius will occasionally increase.