Nomenclature A systematic method of writing chemical formulas and naming compounds

Nomenclature

A systematic method of writing chemical

formulas and naming compounds

Chemical symbols Symbols are used to represent

elements Either one capital letter, or a capital

letter with a lower case letter Know names and symbols of elements:

1 – 30, plus Rb, Cs, Sr, Ba, Ag, Au, Cd, Hg, Pt, Sn, Pb,

Br, I, and U

Chemical formulas Formulas are used to represent

compounds All formulas have more than one

symbol Two or more capital letters

All chemical names have two words No need to capitalize words in name

I. Binary Ionic nomenclature Binary = two elements Ionic means cation and anion Cations (+ ions) are usually metals Anions (- ions) are usually nonmetals Therefore:

Two elements, one metal and one nonmetal

a) naming them Name the metal Name the nonmetal, changing the

ending to “ide” Example: name MgCl2 Mg = magnesium

Cl = chlorine, so write “chloride”

Name is magnesium chloride

Name these NaF Na is sodium F is fluorine, so write fluoride sodium fluoride Al2O3

Al is aluminum O is oxygen, so write oxide aluminum oxide

Name these Ca3P2

Ca is calcium P is phosphorus, so write phosphide calcium phosphide K3N K is potassium N is nitrogen, so write nitride potassium nitride

Name these BaS Ba is barium S is sulfur, so write sulfide barium sulfide SrI2 Sr is strontium I is iodine, so write iodide strontium iodide

Name these Mg3N2

Mg is magnesium N is nitrogen, so write nitride Magnesium nitride BeI2 Be is beryllium I is iodine, so write iodide beryllium iodide

Nomenclature



I. Binary Ionic nomenclature Binary = two elements Ionic means cation and anion Cations (+ ions) are usually metals Anions (- ions) are usually nonmetals Therefore:

Two elements, one metal and one nonmetal

a) naming them Name the metal Name the nonmetal, changing the

ending to “ide” Example: name MgCl2 Mg = magnesium

Cl = chlorine, so write “chloride”

Name is magnesium chloride

Name these BaS Ba is barium S is sulfur, so write sulfide barium sulfide SrI2 Sr is strontium I is iodine, so write iodide strontium iodide

b) Writing formulas Notice: subscripts in the name did not effect

the naming of these compounds So, where do the subscripts come from? Why are they there?

1) The subscripts are there to balance charges**ALL IONIC COMPOUNDS ARE NEUTRAL**

2) The subscripts tell us how many of each element are present in the finished formulaExample: Al2S3 means 2 aluminums and three

sulfurs in one “formula unit”

b) Writing formulas1) Write the symbol for each ion

• the element and its charge

2) Balance the charges• The total (+) charge must equal the total

(-) charge• “criss cross”

3) Re-write the formula without any charges

Write the formula for: barium phosphide barium is Ba, the charge is 2+ (column

2A) phosphide was phosphorus, so P;

charge is 3- (column 5A)

Ba2+P3-

Criss-cross to balance charges (2+ with 3-) Ba3P2

Write the formula for: sodium bromide Sodium is Na, the charge is 1+ (column 1A)

Bromide was bromine, so Br; charge is 1- (column 7A)

Na+Br-

Charges are already balanced (1+ with 1-)

Re-write as NaBr

Write the formula for: calcium iodide calcium is Ca, the charge is 2+ (column 2A) iodide was iodine, so I; charge is 1-

(column 7A) Ca2+I- Criss-cross to balance charges (2+ with

-) Ca1I2 Re-write as CaI2

Write the formula for: potassium phosphide potassium is K, the charge is 1+ (column

1A) phosphide was phosphorus, so P; charge

is 3- (column 5A) K+P3-

Criss-cross to balance charges (+ with 3-) K3P1

Re-write as K3P

Write the formula for: magnesium oxide magnesium is Mg, the charge is 2+

(column 2A) oxide was oxygen, so O; charge is 2-

(column 6A) Mg2+O2-

Charges are already balanced (2+ with 2-)

Re-write as MgO

Special case

Zinc (Zn) is always a 2+ ion Silver (Ag) is always a 1+

ion These must be memorized

II. Transition metal ionic nomenclature

Transition metals form several possible cations

Example: manganese (Mn) is found as 2+, 3+, 4+, 5+, 6+ and 7+ ion!

There is no compound just called “manganese oxide” – there are at least four compounds that are different manganese oxides

Different charges result in different subscripts


Iron is commonly found as both Fe2+ and Fe3+

Fe2+ is called iron(II) Fe3+ is called iron(III) and,… Cu+ is called copper(I) Cu2+ is called copper(II), etc…


Lead (Pb) and tin (Sn) behave like the transition metals, and therefore follow the same rules

Pb2+ is lead(II) Sn4+ is tin(IV) Zinc and silver DO NOT follow

these rules, because zinc is always Zn2+ and silver is always Ag+

a) Writing formulas Follow the same rules as the other ionic

compounds Iron(II) oxide is Fe2+O2-

Charges balance, so formula is FeO Iron(III) oxide is Fe3+O2-

Criss cross to balance charges Fe2O3

Write the formula for: vanadium(III) oxide vanadium is V, the charge is 3+ (roman numeral III)

oxide was oxygen, so O; charge is 2- (column 6A)

V3+O2-

Criss cross to balance charges (3+ with 2-)

Re-write as V2O3

Write the formula for: Cobalt (II) iodide Cobalt is Co, the charge is 2+ (roman numeral II)

iodide was iodine, so I; charge is 1- (column 7A)

Co2+I-


Re-write as CoI2

Write the formula for: Lead(IV) sulfide lead is Pb, the charge is 4+ (roman numeral IV)

sulfide was sulfur, so S; charge is 2- (column 6A)

Pb4+S2-


Re-write as Pb2S4

Reduce subscripts!! PbS2

b) Writing names Same rules as other ionic

compounds, except… You must write a roman numeral in

parentheses after the name of the metal to show what the positive charge on the metal is

Only do this with transition metals And Pb, Sn But not Zn, Ag

Name these NiCl2 Ni is nickel, and it is a transition metal Cl is chlorine, so write chloride nickel( ? ) chloride But, what is the roman numeral? Note: uncriss cross subscripts to

determine charges Ni2+Cl-

nickel(II) chloride

Name these CuS Cu is copper, and it is a transition metal S is sulfur, so write sulfide copper( ? ) sulfide But, what is the roman numeral? Note: no subscripts, so charges are

balanced S is always 2-, so the copper in this compound

must be 2+ ! copper(II) sulfide

Name these Cu3N Cu is copper, and it is a transition

metal N is nitrogen, so write nitride copper( ? ) nitride But, what is the roman numeral? Note: subscripts, so charges are

not balanced copper(I) nitride

Name these Co3P2

Co is cobalt, and is a transition metal P is phosphorus, so write phosphide cobalt(?) phosphide But, what is the roman numeral? Note: un-crisscross subscripts to

determine charges Co2+P3-

cobalt(II) phosphide

Name these PbO2

Pb is lead, and it behaves like transition metals

O is oxygen, so write oxide lead( ? ) oxide But, what is the roman numeral? Note: subscripts show charges are not

balanced lead(II) oxide, right? NO!

Name these PbO2

Careful - O is oxide – and is always 2- So the total (-) charge is 4-! So, what is the roman numeral? To balance the 4- charge, you need a

4+ charge lead(IV) oxide, right? YES!

Be careful… When the charges become

subscripts that can be reduced Examples: 4+/2- SnO2 is tin(IV) oxide 6+/3- CrP2 is chromium(VI)

phosphide 6+/2- MnS3 is manganese(VI) sulfide

Nomenclature



III. Polyatomic Ionic nomenclature Polyatomic ions are groups of

atoms covalently bonded together, that act as a single ion

Think of them as lego blocks that have been glued together

Each have a name and charge that must be memorized

Nitrate: NO31-

bicarbonate: HCO3

1-

Image source: wikipedia

Polyatomic ions

carbonate: CO32-

acetate: C2H3O21-

or CH3COO-

Image source: wikipedia

Polyatomic ions

Polyatomic ions

1+ ions Ammonium

NH4+

1- ions Nitrate

NO3-

Hydroxide OH-

Bicarbonate HCO3

-

Permanganate MnO4

-

Acetate C2H3O2

-

Polyatomic ions

2- ions Sulfate

SO42-

Carbonate CO3

2-

3- ions phosphate

PO43-

a) Writing names Same as before: Write the name of the cation Write the name of the anion Simply write the polyatomic ion’s

name as it is, without any changes Still only two words in the name

NaNO3

More than two capital letters, so there must be at least one polyatomic ion in the formula

Na is sodium, so… The entire “NO3 part” must have a

one word name: Nitrate is NO3

-

sodium nitrate

Al2(SO4)3

More than two capital letters, so there must be at least one polyatomic ion in the formula

Al is aluminum, so… The entire SO4 part must have a

one word name: Sulfate (SO4

2-) aluminum sulfate

(NH4)3PO4

Obviously more than two elements Look for polyatomic ions “NH4” is ammonium “PO4” is phosphate Ammonium phosphate

b) Writing formulas Follow the same rules as the other

ionic compounds Iron(II) sulfate is Fe2+SO4

2-

Charges balance, so formula is FeSO4

b) Writing formulas Iron(III) sulfate is Fe3+ SO4

2-

Criss cross to balance charges But: we don’t want Fe2SO43

There aren’t 43 oxygens! Use parentheses around polyatomic

ion Fe2 (SO4)3

Write the formula for: Chromium(III) carbonate Cr3+ CO3

2-

Crisscross to balance charges Cr2(CO3)3

Write the formula for: Magnesium hydroxide Mg2+ OH-

Crisscross to balance charges Mg(OH)2

you need parentheses around the hydroxide because it is a polyatomic ion, even though it has no subscripts of it’s own.

Now – the trickiest ones Name the formula FeSO4

Iron(IV) sulfate? No – the subscript 4 is not from

balancing charges! So, how do you know? Look for subscripts from balancing

charges to “uncrisscross”

FeSO4

If the 4 were from balancing charges, the formula would have parentheses around the SO – Fe(SO)4

There is no subscript on the Fe – or on the SO4 – from balancing charges

So, the charges are balanced Use the “SO4” part to determine the

charge on the iron – sulfate has a 2- charge

Iron(II) sulfate

Must be memorized… Ag+, Zn2+, no roman numeral when

naming Sn, Pb get roman numerals when

naming Cr, Mn, Sn, Pb – the total negative

charge must be determined to get the positive charge Cannot “uncrisscross” these

Nomenclature



Types of compounds All compounds are made of two or more

elements held together by chemical bonds

Ions of opposite charges are held together by ionic bonds

Ionic bonding is non-directional There are no “ionic molecules” Formulas of ionic compounds show the ratio

of cation to anion Ionic compounds only exist in the solid

state, in a 3-D crystal lattice

Covalent compounds are made of elements two or more held together by covalent bonds

Covalent bonding is directional Between two individual atoms

A group of covalently bonded atoms is referred to as a “molecule”

Covalent compounds are also referred to as “molecular” compounds

Types of compounds

Binary Molecular Nomenclature

Two nonmetals no charges to balance multiple subscripts possible ex: N2O, NO, NO2, N2O4, N2O5

Use prefixes to represent subscripts

mono = 1 di = 2 tri = 3 tetra = 4 penta = 5

hexa = 6 hepta = 7 octa = 8 nona = 9 deca = 10

NEVER, EVER, EVER, EVER, EVER, EVER,

EVER,

USE PREFIXES WITH A METAL!

Rules, continued.. Change second name to end

in “ide” do not use prefixes on the first

word if the prefix is “mono” always use prefixes on the

second name

Examples... CO2

carbon = first word subscript = 1, so no prefix oxide = second word subscript = 2, so prefix = di carbon dioxide

Examples... CO carbon = first word subscript = 1, so no prefix oxide = second word subscript = 1, so prefix = mono carbon monoxide

Try to name these…

N2O

dinitrogen monoxide

NO nitrogen monoxide NO2

nitrogen dioxide

N2O4

dinitrogen tetroxide

N2O5

dinitrogen pentoxide

Writing formulas... Dinitrogen tetroxide di = 2, so two nitrogen’s tetra = 4, so 4 oxygens N2O4

Note: do NOT reduce subscripts for molecular compounds

Documents

Nomenclature A systematic method of writing chemical formulas and naming compounds