Chemical Bonding What it’s all about

Why do atoms bond together? Why should we bother to study electron configurations? –Helps determine the way atoms bond with others Why do we bother to study the periodic table? –An organizer for categorizing elements by the way they bond. These tools help us understand how atoms bond to form new compounds

Why do atoms bond? Only noble gases have complete s and p orbitals. They are already in a state of atomic “nirvana” Other atoms seek the same electron configuration as noble gases. Why? It’s more stable. They seek “nirvana”. The magic number is 8 electrons in the valence energy level aka the “stable octet”.

Ionic Bonding An ionic bond occurs between a metal and a nonmetal Atoms lose or gain electrons to become charged ions Metals tend to lose electrons to nonmetals and become positively charged cations Nonmetals tend to gain electrons from metals and become negatively charged anions These oppositely charged ions attract each other to form strongly bonded compounds The formation of chemical bonds is always accompanied by a release of energy.

Ionic Bonding II: Nomenclature Metal cations keep the same name as the elemental state. –Elemental Na → Na + –Sodium metal → Sodium ion Nonmetal anions take the suffix -ide –Elemental Cl → Cl - – Chlorine gas → Chloride ion ALWAYS NAME THE METAL FIRST Another name for an ionic compound is salt.

Ionic Bonding III Each part of a binary ionic compound has become isoelectronic with the nearest noble gas, i.e., the same electronic structure. Each part of a binary ionic compound is stable, i.e., has 8 e- in its valence energy level, and has gained or lost e- accordingly, and are electrostatically attracted to each other. In the case of period 2 metals (Li, Be, B) the ion will have the same electron configuration of He.

Ionic bonding IV The Roman numeral group number designates the number of valence electrons Pertains to “main group” elements only Alkali metals lose 1 e - to become + ions Alkaline earth metals lose 2 e - to become +2 ions Group 3 metals lose 3 e - to become +3 ions

Ionic Bonding V Group VII elements gain 1 e- to form ions with 1 – charge. Example: Cl - Chloride Group VI elements gain 2 e- to form ions with 2 - charges. Example: O -2 Oxide Group V nonmetals gain 3 e- to form ions with 3 – charges. Example: N -3 Nitride Group IV nonmetals gain 4 e- to form ions with 4 – charges. Example: C -4 Carbide

Ionic bonding VI Ionic compounds must be electrically neutral. Ions will bond in a ratio which will produce an electrically neutral compound. If charges are uneven, uneven numbers of ions will bond to form the compound. Subscripts denote the number of ions present in a compound If no subscript is present, then 1 is implied.

Examples Na + + Cl - → NaCl Name? Sodium chloride Ca +2 + Cl - → CaCl 2 Name? Calcium chloride Na + + O -2 → Na 2 O Name? Sodium oxide Al +3 + Cl - → AlCl 3 Name? Aluminum chloride Na + + C -4 → Na 4 C name? Sodium carbide

Remember Ca +2 + N -3 → Ca x N x Cross the charges and make them subscripts Ca 3 N 2 6 positive and 6 negative charges make a neutral happy compound What is the name of this compound? Calcium nitride