Chemistry Practice: Orbitals, IMFs, and Nuclear Charge

Nuclear Stability

• A nucleus is stable when the number of protons is equal to the number of neutrons, or when the sum of protons and neutrons is greater than 82

Effective Nuclear Charge

• Defined as protons minus shielding electrons
• Increases across a period due to more protons per energy level

Atomic Radius

• Defined as the distance of an atom's nucleus to another atom's nucleus divided by 2
• Periodic trend: decreases across a period, increases down a group

Ionic Radius

• Defined as the distance of an ion's nucleus to its outermost electron
• Periodic trend: decreases across a period, increases down a group

Electronegativity

• Defined as an atom's ability to attract and hold electrons
• Periodic trend: increases across a period, decreases down a group

Metallic and Non-Metallic Character

• Metallic Character: defined as how easy it is for a metal to lose an electron
• Non-Metallic Character: defined as how easy it is for a nonmetal to gain an electron
• Periodic trend for Metallic Character: decreases across a period, increases down a group
• Periodic trend for Non-Metallic Character: increases across a period, decreases down a group

Ionization Energy

• Defined as the energy required to remove an electron from an atom

Spectroscopy

• λ (lambda) represents wavelength in meters
• ν (nu) represents frequency of a photon, often in HZ or S^-1
• When wavelength increases, frequency and energy decrease
• When wavelength decreases, frequency and energy increase
• When an electron drops from a higher energy level to the second energy level, visible light is produced
• When an electron drops from a higher energy level to the first energy level, UV light is produced

Orbital Rules

• Aufbau's principle: an electron occupies the lowest-energy orbital that can receive it
• Creepy-bus rule (Hund's rule): electrons fill up each suborbital before being placed in a suborbital with another electron
• F orbitals start with atoms #59 (Pr, Praseodymium) and #91 (Pa, Protactinium)

Isotopes and Atomic Mass

• Mass number: number of protons plus neutrons (P+N)
• Percent Abundance: percentage of atoms of a particular isotope in a natural sample of a pure element
• AMU (Atomic Mass Unit): calculated by weighted average of isotopic masses based on percent abundance