Chemistry Lecture: Why Atoms Form Ions

“Valence” Electrons …are the electrons in the outer shell …which is also known as the “valence shell”

“Valence” Electrons …are the electrons that participate in chemical bonding

Why do atoms form IONS ? Atoms “want” a full valence shell of electrons This means 8 valence electrons in the outer shell… (only count the “s” and “p” orbitals!) This is also called a “STABLE OCTET”… (more stable = lower energy)

Why do atoms form IONS ? In order to get a full valence shell (to become more stable), atoms will either GAIN or LOSE electrons. Examples: sulfur magnesium becomes an ANIONbecomes a CATION

Chemical Families Atoms in the same FAMILY (column) have the same valence electron configuration, so they form ions with the same charge. Example: Column #1, “Alkali Metals” LiNaK

Chemical Families Atoms in the same FAMILY (column) have the same valence electron configuration, so they form ions with the same charge. Example: Column #6 OSSe

What about the “noble gases”? What do these elements have to do to get a stable octet? Helium NeonArrrr-gon Krypton These elements don’t need to gain or lose electrons to get a full shell! They’re already stable. This means they don’t form ions, and they don’t form bonds. That’s why they’re called the “noble” gases.

Determine the ions that will be formed by the following elements: Lithiumsodiumpotassium Berylliummagnesiumcalcium Oxygensulfurselenium Fluorinechlorinebromine

Determine the ions that will be formed by the following elements: Notice that all of the elements in a chemical family have the same number of valence electrons! This gives them similar chemical characteristics. This is how the Periodic Table was originally developed!