example: the formation of sodium chloride (NaCl)

Na gives up its only valence e- to form a stable Na+ cation

1s2 2s2 2p6 3s1 1s2 2s2 2p6 [Na] [Na+] + e-

Cl, with only 7 valence e-, acquires that e- to form a stable Cl- anion

e- + 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6

e- + [Cl] [Cl-]

the force of attraction between the 1+ charge on the sodium cation and the 1- charge on the chloride anion creates the ionic bond in sodium chloride (NaCl)

http://visionlearning.com/library/flash_viewer.php?oid=1349&mid=55

salt –(def) an ionic compound that forms when a metal atom replaces the hydrogen in an acid

other common salts are potassium chloride (KCl) and calcium iodide (CaI2)

salts are electrically neutral ionic compounds salts are made up of cations and anions held

together by ionic bonds the ratio of cations to anions is always a simple

whole number ratio example: NaCl is made of sodium cations and

chloride anions bonded in a 1:1 ratio example: CaI2 is made of calcium cations and

iodide anions bonded in a 1:2 ratio

the attraction between cations and anions in ionic compounds creates crystal structures

ionic compounds are not made up of molecules even though the cation to anion ratio in NaCl is

1:1, there is no single cation to anion “bond” each sodium cation [Na+] is surrounded by [Cl-]

anions each [Cl-] anion is surrounded by [Na+] cations this causes the ions to be pulled into a tightly

packed structure called a crystal lattice

ionic compounds have no overall charge the ratio of cations (+) to anions (-) are

balanced so that the compound has no overall charge

example: magnesium oxide (MgO)

each magnesium cation (Mg2+) is balanced by an oxygen anion (O2-)

both attractive and repulsive forces exist within an ionic compound

the repulsive charges arise from like-charged ions

cations repel other cations anions repel other anions attractive forces arise

from oppositely-charged ions

anions attract cations; cations attract anions

attraction extends beyond the single cation/anion pair

each [Na+] cation is surrounded by 6 [Cl-] anions

each [Cl-] anion is surrounded by 6 [Na+] cations

this resulting crystal structure significantly increases the attractive force between ions

overall the attractive forces are much stronger than the repulsive forces making ionic bonds very stronghttp://www.avogadro.co.uk/structure/chemstruc/ionic/g-ionic.htm

the attraction between ions in ionic compounds is not limited to isolated cation/anion pairs

ionic compounds are created from repeating patterns of ions held together by attractive forces

(a) atomic-level view of the crystal lattice structure of NaCl (b) sodium chloride crystals highly magnified

these repeating patterns of bonded ions create a crystal lattice

crystal lattice –(def) the regular pattern in which a crystal is arranged

the crystal lattice is made of repeating units called a unit cell

unit cell –(def) the smallest portion of a crystal lattice that shows the 3-dimensional pattern of the entire lattice

example: NaCl unit cellhttp://www.avogadro.co.uk/structure/chemstruc/ionic/g-ionic.htm

since different salts have different cation to anion ratios, different salts have different crystal structures (see figure 12 p. 174)

this is due to the strong attraction between the ions

a considerable amount of energy (heat) has to be applied to allow the ions to change state from solid to liquid (melting) and liquid to gas (boiling)

as a result, ionic compounds are rarely gases at room temperature

hard---meaning they can resist a large applied force

brittle---meaning a force it can’t resist will cause the crystal to fracture along widespread shatter-lines

2 conditions must exist for a substance to conduct electricity:1) the substance must contain charged particles2) the particles must be free to move

(a) Pure water does not conduct a current, so the circuit is not complete, so the light does not light. (b) Water containing a dissolved salt conducts electricity and the bulb lights.

ionic solids are not good conductors because the ions are not free to move (see fig 11 p. 172)

both molten salts and dissolved salts can conduct electricity because the ions are free to move (see fig 11 p. 172)