Chapter 8 Chemistry 1L Cypress Creek High School Unit 8: Ionic Bonds Chapter 8 Chemistry 1L Cypress Creek High School

Part 1: Introducing Ionic Bonds

Chemical Bonds A bond is a force that holds atoms together; creates a compound with new properties which differ from the individual elements Chemical bonds form because of attractions between oppositely charged atoms, called ions Octet Rule Atoms bond because they are trying to achieve stable electron configurations like the noble gases (8 valence electrons)

Ionic Bonds Table salt, represented by the formula NaCl, is an example of a compound formed by an ionic bond +  Na Cl NaCl Element Metal or Nonmetal? Number of valence electrons? Oxidation number? Sodium Chlorine Metal 1 1+ Nonmetal 7 1-

Common Ionic Compounds Sodium bicarbonate (NaHCO3) is baking soda used in food, cleaning products, and antacids Sodium chloride (NaCl) is table salt used in food Potassium nitrate (KNO3) is saltpeter used in fertilizer, gunpowder, and food preservatives Sodium hydroxide (NaOH) is lye used in soaps and drain cleaner

Common Ionic Compounds Magnesium sulfate (MgSO4) is epsom salt used medically as a soak for aches & pains Potassium bromide (KBr) is used to prevent epilepsy (seizures) in dogs Sodium fluoride (NaF) is an ingredient in toothpaste used for cavity prevention Calcium carbonate (CaCO3) is found in rocks (limestone and marble), shells, chalk; primary cause of hard water

Ionic Compound Properties Also known as salts A single entity is called a formula unit Exist as solids at room temperature Easily dissolve in water Exhibit a crystal structure

Ionic Compound Properties Possess high melting / boiling points Considered an electrolyte – a compound that conducts electricity in solution (dissolved in water) Have high electronegativity differences between ions

Ionic Bonding & Electronegativity Ionic bonds are composed of cations and anions bonded together Atoms actually bond according to the difference in their electronegativity (ability to attract valence electrons) Look at table of EN values and find the difference between the two atoms involved (absolute value) Subscripts do not affect this calculation If EN difference is > 1.7 = ionic bond >1.7

Ionic Bonding & Electronegativity

Ionic Bonding & Electronegativity Try to predict the bond type (ionic or not ionic) using your EN table: Formula EN values EN Difference Bond Type LiCl Li = 1.0 Cl = 3.0 2.0 ionic CO2 MgO B3P2 NF3 C = 2.5 O = 3.5 1.0 not ionic Mg = 1.2 O = 3.5 2.3 ionic B = 2.0 P = 2.1 0.1 not ionic N = 3.0 F = 4.0 1.0 not ionic

Formation of Ionic Bonds Ionic bonds occur when valence electrons are transferred from one atom to another – usually between a metal and a nonmetal Cations donate/give/lose electrons Anions accept/take/gain electrons Opposite charges make them attracted (bonded) to each other by electrostatic forces

Formation of Ionic Bonds What is the charge of… A sodium ion? ____ A chlorine ion? ____ NaCl? ____ The overall charge of any ionically bonded compound is zero - this means stability! 1+ 1-