Ionic bonding and compounds

Ionic bonding and compounds - Transcript

Chapter 15
Ionic Bonding and Ionic Compounds

Electron Configuration in Ionic Bonding
Valence Electrons
The electrons in the highest occupied energy level of an element s atoms The of valence electrons determines chemical properties Elements within each group have the same of valence electrons See table 15 1 p 414 Electron dot structures are diagrams that show valence electrons as dots

Electron Dot Structures

Electron Configuration in Ionic Bonding cont
Electron Configurations for Cations
Octet rule In forming compounds atoms tend to achieve the electron configuration of a noble gas an octet is a set of eight The most common cations are those produced by the loss of valence electrons from metal atoms Some transition metals are exceptions to the octet rule

Electron Configuration in Ionic Bonding cont
Electron Configurations for Anions
Nonmetallic atoms have relatively full valence shells and they achieve the octet more easily by gaining electrons Halide ions are the ions produced when the halogens gain electrons All halogen ions have seven valence electrons and need to gain only one electron to achieve the electron configuration of a noble gas

Ionic Bonds
Anions cations have opposite charges and they attract one another by electrostatic forces The forces of attraction that bind these oppositely charged ions are called ionic bonds The total of positive charges must equal the total negative charges The maximum charge an ion is likely to have is 3 Sample problem 15 1 p 421

Properties of Ionic Compounds
At room temperature most ionic compounds are crystalline solids The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal Ionic compounds are salts

Bonding in Metals
Metals often form lattices in the solid state
In such a lattice 8 12 other metal atoms closely surround each metal atom Within the crowded lattice the outer energy levels of the metal atoms overlap This is a unique arrangement that is described by the electron sea model

The electron sea model proposes that all the metal atoms in a metallic solid contribute their valence electrons to form a sea of electrons This sea of electrons surrounds the metal cations in the lattice

Bonding in Metals
The electrons can move easily from one atom to the next Because they are free to move they are often referred to as delocalized electrons When the atom s outer electrons move freely throughout the solid a metallic cation is formed A metallic bond is the attraction of a metallic cation for delocalized electrons

Electron Sea Model

B Free electrons can move rapidly in response to electric fields hence metals are a good conductor of electricity C Free electrons can transmit kinetic energy rapidly hence metals are good conductors of heat D The layers of atoms in metal are hard to pull apart because of the electrons holding them together hence metals are tough But individual atoms are not held to any other specific atoms hence atoms slip easily past one another Thus metals are ductile Metallic Bonding is the basis of our industrial civilization

Properties of Metals
Metals have moderately high melting points boiling points Metals are malleable which means they can be hammered into sheets they are ductile which means they can be drawn into wires Metals are generally durable The delocalized electrons move heat from one place to another much more quickly than the electrons in a material that does not contain mobile electrons Mobile electrons easily move as part of an electric current when an electric potential is applied to a metal As the number of delocalized electrons increases so do the properties of hardness strength

Metal Alloys
An alloy is a mixture of elements that has metallic properties
Due to the nature of metallic bonds it is relatively easy to introduce other elements into the metal crystal Stainless steel brass and cast iron

Properties of alloys
They differ somewhat from the properties of the elements they contain Steel has some properties of iron but has additional properties such as increased strength

Types of Alloys
Substitutional alloys
Some of the atoms in the original metallic solid are replaced by other metals of similar atomic size

Interstitial alloys
Small holes interstices in a metallic crystal are filled with smaller atoms

Commercial Alloys
Alnico magnets
50 Fe 20 Al 20 Ni 10 Co

Brass plumbing hardware lighting
67 90 Cu 10 33 Zn

Bronze bearings bells medals
70 95 Cu 1 25 Zn 1 18 Sn

Cast iron casting cookware
96 97 Fe 3 4 C

Gold 10K jewelry
42 Au 12 20 Ag 37 46 Cu

Lead shot shotgun shells
99 8 Pb 2 As

Pewter tableware
70 95 Sn 5 15 Sb 0 15 Pb

Stainless steel instruments sinks cookware
73 79 Fe 14 18 Cr 7 9 Ni

Sterling silver tableware jewelry
92 5 Ag 7 5 Cu

Everyday Chemistry
Costume jewelry particularly pieces made in developing countries could have high levels of lead When lead gets wet a certain amount of it dissolves becoming lead II ions Inside the body these ions can replace calcium ions and cause learning disabilities coma or death Leaded gasoline was phased out in the mid 1970s and as a result lead levels in Americans blood dropped