Chemistry Ions

Electron Configurations of Noble Gases Write out the electron configuration for the following elements: Neon Argon

Noble Gases Neon can also be written: (He) 2s2 2p6 Argon can also be written: (Ne) 3s2 3p6 Krypton can be written: (Ar) 3d10 4s2 4p6 What do all of the above have in common?

Noble Gases are the Least Reactive Elements The noble gases show almost no reactivity. Because each of the noble gases have a full outer energy level, they are stable. In most chemical reactions, atoms tend to match the s and p electron configurations of noble gases. A xenon atom. Notice that the outer electron shell has 8 electrons and is therefore full. This makes xenon extremely un-reactive.

The Octet Rule The octet rule is a concept of chemical bonding theory that atoms tend to have either empty valence shells or full valence shells of eight electrons. When elements combine, they become more stable if they both achieve an “octet” of electrons.

Ions An ion is an atom (or group of atoms) who has either gained or lost one or more electrons. The number of electrons that are gained or lost depends on the number of valence electrons they have. What are valence electrons?

Group Numbers Are Related to the Number of Valence Electrons The number of valence electrons can be easily determined by looking at the group number (of the Main Group Elements): Which elements would likely lose electrons? Which elements would likely gain electrons?

Atoms May Lose Electrons to Form Stable Cations The Alkali Metals such as Sodium have 1 electron in their outer energy level. Losing this electron will make them have the same electron configuration as a noble gas. They will then be a positive ion called an cation.

Atoms May Gain Electrons to Form Stable Anions Halogens such as Chlorine have 7 electrons in their outer energy level. Gaining one electron will make them have the same electron configuration as a noble gas. They will then be a negative ion called an anion.

Cations (+) and Anions (-) May Form Ionic Bonds Sodium chloride (NaCl) is an example of an ionic compound. Ionic compounds are compounds formed when positive and negative ions are electrically attracted and form a bond. Usually they form when the cation loses its electron to form the anion.