Unit 5Ionic Bonding

Pure Substances & NomenclaturePure substances can exist in several forms: I)

Atomic Elements & Molecular Elements, II) Ionic Compounds and III) Molecular Compounds (studied in next unit)

I. - Atomic Elements & Molecular Elements: Some elements can exist as single atoms such as He, Ne, Cu, Hg, Au, Pb, U- Molecular Elements: Some elements exist in nature as diatomic molecules: H2 N2 O2 F2 Cl2 Br2 I2

Know theseTheir names are the same as the element

names

Two elements are commonly polyatomic. Sulfur S8

Phosphorous P4

II. Ionic Compounds

II. Ionic Compounds: These are compounds formed between ions. The metal loses electrons to become a + ion

(Cation), and the nonmetal gains electrons to become a – ion (Anion).

The + and – ions are attracted to each other in a ratio so that the resulting compound is neutral in charge; NaCl MgF2 are examples.

The formula unit is the simplest ratio of ionsThese have unique names formed from

naming the + ion followed by the – ion with an “ide” ending.

“Perhaps one of you gentlemen would mind telling me just what is outside the window that you find so attractive..?”

Image courtesy NearingZero.net

Valence electrons

Are electrons in highest occupied energy level of an atom.

For representative elements, number of valence electrons is the same as its group number.Ex. Lithium is in group 1A: has 1 valence

electronSome transition metals form more than one

ion.Ex. Fe2+ and Fe3+

Octet rule: atoms tend to achieve the electron configuration of a noble gas (8 electrons in outer energy level)by gaining or losing electrons.

elements of Group 2A have a

+2 charge

elements of Group 5A have a

-3 charge

elements of Group 6A have a

-2 charge

elements of Group 7A have a

-1 charge

The charge on an ion can be predicted from its position in the periodic table.

Elements in Group 1A have a +1 charge

→

remove e-

neutral atom cation

If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation.

Atom sodium (Na)

calcium (Ca)

lithium (Li) strontium (Sr)

Cation Na+ Ca+2 Li+ Sr+2

Name of Cation

Sodium ion

calcium ion

Lithium ion

strontium ion

Naming Cations

Cations are named the same as their parent atoms.

If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion.

→neutral atom

add e-

anion

An anion consisting of one element has the stem of the parent element and an –ide ending

Naming Anions

Atom

Anion

Name of Anion

fluorine (F)

F-

fluoride ion

stem

Atom

Anion

Name of Anion

chlorine (Cl)

Cl-

Chloride ion

stem

Atom

Anion

Name of Anion

bromine (Br)

Br-

bromide ion

stem

Atom

Anion

Name of Anion

nitrogen (N)

N3

-

nitride ion

stem

Atom

Anion

Name of Anion

phosphorous (P)

P3

-

phosphide ion

stem

Atom

Anion

Name of Anion

oxygen (O)

O2-

oxide ion

stem

A chemical compound must have anet charge of zero.

Writing Formulas FromNames of Ionic Compounds

If the compound contains ions, then the charges on all of the ions must add to zero.

Example: Aluminum ChlorideStep 1:

Step 2:

Step 3: 1 3

Step 4: AlCl3

Criss-Cross Method

Al Cl

Al Cl

3+ 1-

write out name with space

write symbols & value of charge of ions

criss-cross charges as subsrcipts

combine as formula unit(“1” is never shown)

Aluminum Chloride

Example: Aluminum OxideStep 1: Aluminum Oxide

Step 2: Al3+ O2-

Step 3: Al O2 3

Step 4: Al2O3

Criss-Cross Rule

Example: Magnesium OxideStep 1: Magnesium Oxide

Step 2: Mg2+ O2-

Step 3: Mg O

2 2

Step 4: Mg2O2

Step 5: MgO

Criss-Cross Rule

Use simplest ratios

Naming ionic compounds

To name an ionic compound first write the name of the cation (+ ion) followed by the name of the anion (- ion)

Naming Binary CompoundsFormula Name

1 BaO ____________________

2 ________________ sodium bromide

3 MgI2 ____________________

4 KCl ____________________

5 ________________ strontium fluoride

6 ________________ cesium fluoride

barium oxide

NaBr

magnesium iodide

potassium chloride

SrF2

CsF

Classwork: handout ionic binary compounds (single charge cations.)

A polyatomic ion is an ion that contains two or more elements.

-3NO

Naming Compounds Containing Polyatomic Ions

Al2(SO4 )3

subscripts

superscripts

ALUMINUM SULFATE

SO42- Al3+

Rules for ParenthesesParentheses are used only when the following two condition are met:

1. There is a polyatomic ion present and…2. There are two or more polyatomic ions in the formula.

Examples:

NaNO3 NO31- is a polyatomic ion, but there is only one of it.

Co(NO3)2 NO31- is a polyatomic ion and there are two of them

(NH4)2SO4 NH41+ is a polyatomic ion and there are two of them;

SO42- is a polyatomic ion but there is only one of it.