Shell Model & Quantum Mechanics

(1) Predict and explain electronic properties of atoms (IE, EA, radius) in terms of the shell model.

Photoelectron Spectroscopy

Photoelectron Spectroscopy is a technique used to determine the ionization energy of an atom, where atoms are bombarded with monochromatic X-rays. The energy of the X-rays is gradually increased until an electron is ejected from the atom.

IE can be found using a similar technique as Hess’s Law. IE is determined by measuring the ejected electron’s kinetic energy.

Successive IEs for multielectrons are defined as followes:

Graphs of Successive IEs

• Groups of 2 for ground state electrons (highest IE)
• Groups of 8 for electron orbits for core electrons
• Between 0-8 for valence electrons (lowest IE)
• IE is increasing on the graph because each orbit has a different IE
• IE is increasing within orbits since as electrons leave, the remaining electrons are less repelled because less electrons are now in the orbit.

IE Trends

IE increases across a period and decreases down a group. That is to say, helium has the highest IE, since it is furthest to the right and highest up on the periodic table.

Electron Affinity

Electron Affinity is the energy change that occurs when an electron is added to a gaseous atom to form a negative ion. EA is kind of the opposite of IE. EA becomes more negative (increases) as you move across a period and becomes less negative (decreases) as you move down a group.

ENC & Shielding

Electrons that are sufficiently far away from the nucleus will not experience the full charge from the nucleus (called 𝑍), because the electrons in orbit around the nucleus will cancel out part of the charge.

The charge that the valence electrons experience is called the Effective Nuclear Charge (ENC). ENC is the charge that the valence electrons experience, which is less than the actual charge of the nucleus, becaeuse of the afformentioned shielding effect.