NOTES: 7.1 - Ions

Valence Electrons:

● Knowing electron configurations is important because the number of valence electrons determines the chemical properties of an element.

● Valence Electrons: The e- in the highest occupied energy level of an element’s atoms.

Valence Electrons:

● All elements in a particular group or family have the same number of valence electrons (and this number is equal to the group number of that element)

Examples:

● Group 1 elements (Na, K, Li, H): 1 valence e-.

● Group 2 elements (Mg, Ca, Be): 2 valence e-.

● Group 17 (7A) elements (Cl, F, Br): 7 valence e-.

LEWIS STRUCTURES:

● Electron dot structures show the valence electrons as dots around the element’s symbol:

● Li

● B

● Si

● N

● O

● F

● Ne

LEWIS STRUCTURES:

● Electron dot structures show the valence electrons as dots around the element’s symbol:

● Li

● B

● Si

● N

● O

● F

● Ne

Which elements form ionic compounds and which elements form covalent (molecular) compounds??

General Rule of Thumb:

metal + nonmetal = IONIC

metal + polyatomic anion = IONIC

polyatomic cation + anion = IONIC

nonmetal + nonmetal(s) = COVALENT

Why are ionic compounds so stable?

● IONIC BONDS:

-metal plus a nonmetal

-cations plus anions

-opposite charges attract

● Examples:

Na+ and Cl- form NaCl

Al3+ and Br- form AlBr3

Ionic Bonds:Isn’t it ionic that opposites attract?

OCTET RULE:

● Noble gas atoms are very stable; they have stable electron configurations. In forming compounds, atoms make adjustments to achieve the lowest possible (or most stable) energy.

● Octet rule: atoms react by changing the number of electrons so as to acquire the stable electron structure of a noble gas.

Formation of Cations and Anions

● can be predicted using the octet rule (not always followed, but a good general rule to follow for the representative elements)

-full outer energy level

-eight electrons (s2p6)

**explains formation of both cations and anions

CATIONS:

● Na: 1s2 2s2 2p6 3s1

● Na+:

● Mg: 1s2 2s2 2p6 3s2

● Mg2+:

CATIONS:

● Na: 1s2 2s2 2p6 3s1

● Na+: 1s2 2s2 2p6

● Mg: 1s2 2s2 2p6 3s2

● Mg2+: 1s2 2s2 2p6

OCTET RULE:

● Atoms of METALS obey this rule by losing electrons.

Na:

Na+:

OCTET RULE:

● Atoms of METALS obey this rule by losing electrons.

Na:

Na+:

ANIONS:

● Cl: 1s2 2s2 2p6 3s2 3p5

● Cl-:

● O:1s2 2s2 2p4

● O2-:

ANIONS:

● Cl: 1s2 2s2 2p6 3s2 3p5

● Cl-: 1s2 2s2 2p6 3s2 3p6

● O: 1s2 2s2 2p4

● O2-: 1s2 2s2 2p6

OCTET RULE:

● Atoms of NONMETALS obey this rule by gaining electrons.

Cl:

Cl-:

OCTET RULE:

● Atoms of NONMETALS obey this rule by gaining electrons.

Cl:

Cl-:

OCTET RULE:

● Transition metals are exceptions to this rule.

Example: silver (Ag) Ag+

By losing one electron, it acquires a relatively stable configuration with its 4d sublevel filled (pseudo noble-gas)

OCTET RULE:

● Transition metals are exceptions to this rule.Example: silver (Ag) Ag+

By losing one electron, it acquires a relatively stable configuration with its 4d sublevel filled (pseudo noble-gas)