Chapter 22 Chemical Bonds

22.1 Stability in Bonding Most elements are found combined with other elements because they are not chemically stable (compounds) Noble gases are mono-atomic (6% elements) Chemical stability depends on valence electrons Compounds have different properties than the elements that compose it Ex. Na, Cl, NaCl from chapter 18

Writing Chemical Formulas Chemical Formula: represents a chemical compound Uses symbols for the elements The subscript numbers show the ratio of ions in the compound Formulas are like cooking recipes

Write the Formula For: Sodium chloride Magnesium oxide Aluminum oxide Iron (III) oxide Calcium fluoride Strontium phosphate Barium nitrate

Write the Name for: K2O Al2O3 Mg3N2 CaCO3 NaNO3 Calculate the molecular weight for each of the above:

Stable Electron Configurations When outermost energy level is full - Atom is stable (pg. 690) Not likely to react with other elements Electron dot diagram – model of atom with symbol of element in the center and the valence electrons represented by dots around the symbol Pg. 690, 691

Atmospheric gases exist as molecules Chemical bonding occurs when elements bond with other elements or themselves to achieve stability in their valence levels Atmospheric gases exist as molecules Hydrogen H2 Oxygen O2 Nitrogen N2 Chlorine Cl2

Ionic Bonds Metals combine with Nonmetals Transfer of electrons to become more stable Ions – when an atom gains or loses electrons “charged atom” Electrons no longer equal the protons – the atom becomes charged Draw NaCl, MgO, Al2O3

Anions and Cations Loses electrons – makes positive ion or cation – Ex. Na+ sodium ion “metals” Gains electrons – makes negative ion or anion – add suffix -ide Ex. Cl- chloride ion “nonmetals” Ionic bond – force that holds anions and cations together

Ionic bond: formed when electrons are transferred from one atom to another Ionization Energy: – energy required to remove an electron Ionic Compounds: – Compounds that contain ionic bonds Chemical Formula: – shows the elements and ratio of atoms in a compound Crystal Lattices: – arrangement of ions in a repeating pattern – forms solid crystals

6.2 Covalent Bonding Nonmetals combine with nonmetals Sharing electrons to become stable Covalent Bond – when two atoms share one pair of valence electrons – single bond Two pairs – double bond Three pairs – triple bond

Polar Covalent Bonds Electrons are not shared equally Atom with greater attraction for electrons has a partial negative charge Other atom has a partial positive charge Ex. Water – H2O Ex. Carbon Dioxide – CO2

Polyatomic Ions – a group of covalently bonded atoms with a positive or negative charge and acts as a unit Prefix poly- means “many” Most polyatomic ions are anions Page 707

6.3 Naming Compounds and Writing Formulas Chemical Formula: represents a chemical compound Uses symbols for the elements The subscript numbers show the ratio of ions in the compound

Ionic Compounds Write symbol of cation (metal) first followed by the symbol of the anion (nonmetal) Ex. NaCl Use subscripts to show the ratio Criss cross the oxidation numbers Add the suffix “ide” to the nonmetal when naming these

Covalent compounds Name and formula describe the type and number of atoms in each molecule Prefixes on page 709 Use prefixes to tell how many atoms of each element Ex. N2O4 dinitrogen tetraoxide

6.4 The Structure of Metals Metallic Bond – the attraction between a metal cation and the shared electrons that surround it The more valence electrons in the shared pool, the stronger the metallic bond

Alloys A mixture of 2 or more elements, one of which is a metal – has properties of both metals Copper Alloys – copper + tin = bronze copper + zinc = brass Steel Alloys – iron + carbon = steel iron + chromium = stainless steel