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

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