Bonding & Naming & Formula Writing

Chapters 8 & 9Honors Chemistry

Ionic & Covalent Compounds

Chemical Bonds

Atoms rarely exist alone When atoms are bonded together, they

are more stablechemical bond – mutual electrical

attraction between the nuclei and valence electrons of different atoms that binds the atoms together OR the attraction between a positive ion and a negative ion

Ionic Bondsresults from electrical attraction between cations and anions

atoms donate or accept electrons from each other

Covalent Bonds

results from sharing of electron pairs between two atoms

the electrons shared belong to both atoms

Covalent vs. Ionic Bonding

Bonding Patterns

What generally occurs with elements is if you have:

metals + nonmetals = ionic compoundsnonmetals + nonmetals = covalent

compounds

Of course there will be exceptions! We will discuss this more later.

Ionic Compounds

Ionic bonds do NOT form moleculesChemical formulas for ionic compounds

represent the simplest ratio of ion types Made of anions and cationsBinary ionic compounds contain only two

different types elements.Other ionic compounds contain polyatomic

ions they will have more than two different types elements.

Formation of IonsCations - formed when atoms lose electrons

Generally metals and hydrogen All group 1 metals will lose one e- to become 1+

ions (Hydrogen follows this too when bonded to another non-metal)

All group 2 metals will lose two e- to become 2+ ions

Aluminum will lose three e- to become 3+ ion Zinc will lose two e- to become 2+ ion Silver will lose one e- to become 1+ ion

The other metals you will need help to figure out how many e- they will lose because of the d-orbital e-

they can lose 1, 2, 3, or even 4 electrons. You can figure out what their charges are

based on their names they will have roman numerals that indicate their charge.

Ex: Lead(IV) ion means Lead ion with a 4+ charge

Anions - formed when atoms gain electrons Generally nonmetals and sometimes hydrogen when it

is bonded to metals All group 15 nonmetals will gain 3 e- to become 3- ions All group 16 nonmetals will gain 2 e- to become 2- ions All group 17 nonmetals will gain 1 e- to become 1- ions

(Hydrogen follows this too when bonded to metals) In order to tell when we are talking about an

anion, we use the ending –ide on the root name of the element.

Examples:1. Cl - becomes chloride2. O2- becomes _____________3. S2- becomes _____________4. N3- becomes _____________

Ionic Compounds

Ions combine so that amount of positive and negative charge is equal

Usually crystalline solid at room temp.Formula of ionic compound depends on

the charges of the ions combined

Ionic Compounds Continued…

The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s).

Naming Chemical Compounds:

Ionic & Covalent

Classifying Compounds

The system for naming an ionic compound is different from that for naming a covalent compound, so before a compound can be named, it must be classified as ionic or covalent.

Classifying a compound is not an easy task, but for the purposes of naming them, we employ a simple test:

If the answer is yes, use the system for naming ionic compounds.

If the answer is no, use the system for naming covalent compounds.

Is there a metal or a polyatomic ion present?

Naming Ionic Compounds

Examples: KI

MgCl2

AgBr

Answers: Potassium iodide

Magnesium chloride

Silver bromide

Most ionic compounds are named simply by naming the ions present.

There are, however, two complicating factors:

Naming Ionic Compounds (continued)

I. Some metals form more than one ion.

II. Identifying polyatomic ions

I. Metals that form more than one ion, such as iron, add a Roman numeral to the name to indicate the charge:

Fe2+ is called iron (II) and Fe3+ is called iron (III)

Assume a Roman numeral is required for any metal except

1. metals in groups 1 and 2 on the periodic table

2. aluminum (3+), silver (1+), and zinc (2+) always keep the same charge

Naming Ionic Compounds (continued)

If a Roman numeral is required, the charge on the metal ion must be determined from the charge on the negative ion.

Helpful Rules to Remember

Formula Reasoning Name

FeCl2Cl has a 1- charge, and there are 2 of them for a total of 2-, so the Fe must be 2+ iron (II) chloride

Fe2O3

O has a 2- charge, and there are 3 of them for a total of 6-, so the Fe must have a total charge of 6+ split equally between the two iron atoms, so each must have a 3+ charge

iron (III) oxide

PbS2S has a 2- charge, and there are 2 of them for a total of 4-, so the Pb must be 4+ lead (IV) sulfide

Cu3NN has a 3- charge, so the Cu must have a total charge of 3+ split equally between the 3 copper atoms, so each must have a 1+ charge

copper (I) nitride

Examples

A metal ion is always positive. The Roman numeral indicates the charge, not the subscript.

The positive and negative charges must cancel (total charge must = 0).Nonmetals are always negative & can never form more than one monatomic ion.

Naming Ionic Compounds (continued)

II. Polyatomic ions each have specific names which must be memorized so they can be recognized on sight.

(At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.)

You will need to know these ions for quizzes and tests!

Naming Ionic Compounds Examples

Na2SO4 sodium sulfate

Fe(NO3)2 iron (II) nitrate

AlCl3 aluminum chloride

PbI4 lead (IV) iodide

(NH4)3PO4 ammonium phosphate

Mg3N2 magnesium nitride

AgC2H3O2 silver acetate

Naming Ionic Compounds Practice: Na2CO3 sodium carbonate

Ni2O nickel(I) oxide

K2O potassium oxide

Cu3PO4 copper (I) phosphate

CoI3 cobalt (III) iodide

Analysis If “Yes”

* Is the cation a metal? (If so, does it need a Roman numeral?

The compound is ionic: name

each ion present

(DO NOT USE

PREFIXES)

* Is there a polyatomic ion present?

* Are both elements nonmetals?

The compound is

covalent: use

prefixes (NO

CHARGES EXIST)

PbI3 Lead(III) iodide

metal present ionic no prefixesNa group I no Roman numeral

metal present ionic no prefixesNi tranistion metal use Roman numeral (O is 2-, each Ni must be 1+)

metal present ionic no prefixesK group I no Roman numeral

metal present ionic no prefixesCu not group I, II, etc. add Roman numeral (PO4 is 3-, each Cu must be 1+)

metal present ionic no prefixesCo not group I, II, etc. add Roman numeral (I is 1-, total is 3-, Co must be 3+)

metal present ionic no prefixes

Pb not group I, II, etc. use Roman numeral (each I is 1-, so the Pb must be 3+)

NH4Br ammonium bromideNH4 polyatomic ion present ionic no prefixes

Writing Formulas for Ionic Compounds

Writing Formulas for Ionic Compounds

Formulas for ionic compounds are written by balancing the positive and negative charges on the ions present.

The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s).

Polyatomic ion names must still be recognized from memory (e.g. ammonium nitrate), but metals will have a Roman numeral associated with them if there is the possibility of more than one ion (e.g. copper (I) chloride or copper (II) chloride). The Roman numeral indicates the charge on the ion not the number of ions in the formula.

Writing Formulas for Ionic Compounds (continued)

Helpful Rules to Remember

Name Reasoning Formula

ammonium sulfateNH4 has a 1+ charge & SO4 has a 2- charge, so 2 ammonium ions are required for each sulfate.

(NH4)2SO4

zinc chlorideZn has a 2+ charge & Cl has a 1- charge, so 2 chloride ions are required for each zinc ion.

ZnCl2

copper (II) phosphate

Cu has a 2+ charge & PO4 has a 3- charge, so 3 copper (II) ions are required for every two phosphate ions.

Cu3(PO4)2

Examples

A metal ion is always positive. The Roman numeral indicates the charge, not the subscript.

The positive and negative charges must cancel (total charge must = 0).If more than one polyatomic ion is needed, put it in parentheses, and place a subscript outside the parentheses.

Writing Ionic Compound Formulas

sodium chloride

iron(III) oxide

magnesium hydroxide

lithium carbonate

NaCl

Fe2O3

Mg(OH)2

Li2CO3

Naming Covalent Compounds

Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names.

The compounds named in this way are binary covalent compounds.

‘Binary’ means that only two atom are present.

A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.)

A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘-ide’.

Naming Covalent Compounds

Prefixes Used

Subscript Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

Subscript Prefix

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Naming Binary Covalent Compounds: Examples

N2S4 dinitrogen tetrasulfide

NI3 nitrogen triiodide

XeF6 xenon hexafluoride

CCl4 carbon tetrachloride

P2O5 diphosphorus pentoxide

SO3 sulfur trioxide

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

• Second element in

‘-ide’ from

* Drop –a & -o before ‘oxide’

Writing Formulas for Covalent Compounds

Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number of atoms of each element present.

Remember: The compounds named in this way are binary covalent compounds (they contain only two elements, both of which are nonmetals). When in covalent compounds, atoms do not have charges.Subscripts are determined directly from the prefixes in the name.

If no prefix is present on the name of the first element, there is only one atom of that element in the formula.

A prefix will always be present on the name of the second element. The second element will use the form of its name ending in –ide.

Writing Formulas for Binary Covalent Compounds: Examples

nitrogen dioxide NO2

diphosphorus pentoxide P2O5

xenon tetrafluoride XeF4

sulfur hexafluoride SF6

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

* Second element in ‘ide’ from

* Drop –a & -o before ‘oxide’

dihydrogen monoxide H2O

What about these????

Some elements and compounds look as though they should be named as covalent compounds but we don’t:

‘SUPER 7’ N2, O2, F2, Cl2, Br2, I2, and H2

Diatomic elements Named by using the elements name only

Commonly named compounds: H2O = water

NH3 = ammonia

CH4 = methane Methane is an organic compound and they have

completely different rules for naming

Common Acids

There are only 5 Acids that you are Required to Know HCl = hydrochloric acid HNO3 = nitric acid

H2SO4 = sulfuric acid

H2CO3 = carbonic acid

H3PO4 = phosphoric acid

Writing Chemical Formulas: A Review

I. Ionic Compounds

II. Covalent Compounds

Classifying Compounds Using Names

Classifying a compound using its name is not as difficult as using its formula.

The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.).

If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes, such as dichromate, but those will be memorized and recognized as ions.)

If there is an H- in front the compound will usually be an acid.

Writing Formulas Practice:carbon tetrafluoride CF4

Na3PO4sodium phosphate

Cu2SO4copper(I) sulfate

Analysis If “Yes”

The compound is covalent: the prefixes

give the subscripts.

* Are there prefixes present?

Is there a roman numeral or name of an ion?

The compound is ionic: subscripts must be

determined by

balancing charges

prefixes covalent prefixes indicate subscripts

metal ionic balance charges 3 Na1+ needed for 1 PO43-

metal present ionic balance charges 2 Cu1+ needed for 1 SO42-

Al2S3aluminum sulfidemetal present ionic balance charges 2 Al3+ needed for 3 S2-

N2O5dinitrogen pentoxideprefixes covalent prefixes indicate subscripts

NH4NO3ammonium nitratepolyatomic ion present ionic balance charges

1 NH41+ needed for 1 NO3

1-

PbO2lead(IV) oxidemetal present ionic balance charges 1 Pb4+ needed for 2 O2-

Fe2(CO3)3 iron(III) carbonatemetal present ionic balance charges 2 Fe3+ needed for 3 CO3

2-