Section 7.1

Ion formation

Chapter 7Ionic Compounds and Metals

Chemical Bonds

A chemical bond is the force that holds two atoms together.

• Can form by the attraction between the positive nucleus of one atom and the negative electrons of another

• Can form between positive and negative ions

Valence Electrons

• Electrons in the outermost principal energy level

• Shown in the electron dot structures

• Octet rule – atoms will gain, lose or share electrons to obtain 8 valence electrons

• The valence electrons determine the bonding properties of the atom

Positive Ion Formation

• A positively charged ion is called a cation.

• Positive ions are formed when an atom loses one or more valence electrons

• Metals make positive ions

Negative Ion Formation

• A negatively charged ion is called an anion.

• Negative ions are formed when an atom gains one or more electrons in its valence shell.

• Nonmetals make negative ions.

7.2: Ionic bonds and ionic compoundsFormation of an Ionic Bond

• An ionic bond is the electrostatic force that holds oppositely charged particles together in an ionic compound

• Compounds that contain ionic bonds are called ionic compounds.

• Ionic compounds are formed between metals (+ charge) and nonmetals (- charge).

Binary Ionic Compounds

• Contain a metallic cation and a nonmetallic anion.

• Formation of Binary Ionic Compounds– Electron(s) is/are transferred from metal to

nonmetal – Metal becomes positive, nonmetal becomes

negative– Opposite charges attract

Properties of Ionic Compounds

• Take the structure of a crystal lattice – Many units of positive and negative ions stick together in

a three-dimensional geometric arrangement

• Can conduct electricity when dissolved in water (they are electrolytes and break into ions when dissolved in water), but not in solid form

• Melting point, boiling point and hardness depend upon how strongly the ions are attracted to each other

Formulas for Ionic Compounds

• Monatomic ions are one-atom ions– Examples: Mg2+ , Br-1

• Oxidation numbers are the charges on ions– Note: some elements have multiple oxidation

states – you will have a periodic table to tell this

• Binary ionic compounds are made of two monatomic ions (one positive, one negative)

Formulas for Binary Ionic Compounds

• Symbol for cation is written first, anion second

• Subscripts tell the number of atoms of each element

• What are the following compounds made of?– CaF2 1 calcium, 2 fluorine

– Na2S 2 sodium, 1 sulfur– NaCl 1 sodium, 1 chlorine

Naming Binary Ionic Compounds

• Name the cation first• Name the anion second with –ide at the end

• Examples– CaF2 calcium fluoride

– Na2S sodium sulfide– NaCl sodium chloride

Try Naming a few moreBinary Ionic Compounds

• K2O potassium oxide

• Al2S3 aluminum sulfide

• Na3N sodium nitride

What if the cation has more than one oxidation state?

• You tell which ion was used by putting a Roman Numeral after the name of the cation

• Example:– CuS

• We know S was -2 (that’s the only one it makes)• If there is only one atom of each element, the Cu must

have been +2• So, the name is written as Copper (II) sulfide [the “II”

indicates the charge]• Make sure, especially with transition elements, that you are

checking the oxidation states

Writing Formulas for Binary Ionic Compounds

• Look up the charges for each element• For a compound to form, the total charge

must balance out to zero (positive charges must equal negative charges)

• Example:– Sodium bromide

• Na is +1, Br is -1• Only need one of each to balance• Formula is NaBr

Try writing some more formulasBinary Ionic Compounds

• Potassium Iodide KI

• Aluminum bromide AlBr3

• Magnesium chloride MgCl2

• Cesium nitride Cs3N

Formulas for Polyatomic Ionic Compounds

• Polyatomic ions are ions that are made up of more than one atom

• You will have a chart for these and do not have to memorize them.

• Examples:– SO4

2- = sulfate– CN- = cyanide– NH4

+ = ammonium

Naming Polyatomic Ionic Compounds

• Name the cation first, anion second• Name the polyatomic as is – don’t change its

name at all

• Examples:– Ca3(PO4)2 calcium phosphate

– Mg(CN)2 magnesium cyanide

– NH4Cl ammonium chloride

Now you try naming Polyatomic Ionic Compounds

• NaNO3 sodium nitrate

• Ca(ClO3)2 calcium chlorate

• Al2(CO3)3 aluminum carbonate

Writing formulas for Polyatomic Ionic Compounds

• Same as binary ionic compounds EXCEPT you may not change anything in the polyatomic ion formula

• Put them in a (parenthesis) and put subscripts outside that parenthesis

• Example:– Calcium Nitrate

• Ions are Ca2+ and NO3-

• Formula will be Ca(NO3)2

Now you try writing formulas forPolyatomic Ionic Compounds

• Sodium hydroxide NaOH

• Copper (II) nitrate Cu(NO3)2

• Silver chromate Ag2CrO4

7.3: Metallic bonds and theproperties of metals

• The electron sea model proposes that all the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons

• Since the electrons are free to move, they are called delocalized electrons

• A metallic bond is the attraction of a metallic cation for delocalized electrons

Properties of Metals(revisited)

• Moderately high melting points• High boiling points• Malleable, ductile, durable• Conduct heat and electricity well• Transition metals are harder/stronger than

alkali metals because the transition metals have more delocalized electrons