Writing ionic formulas
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WRITING IONIC FORMULAS PowerPoint PPT Presentation


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WRITING IONIC FORMULAS. Write the symbol for the cation, then the symbol for the anion. Balance the charges - use the crisscross method - by placing subscripts and “( )” for polyatomic ions if needed. Monatomic ions don’t need “( )”.

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WRITING IONIC FORMULAS

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WRITING IONIC FORMULAS

  • Write the symbol for the cation, then the symbol for the anion.

  • Balance the charges - use the crisscross method - by placing subscripts and “( )” for polyatomic ions if needed.

  • Monatomic ions don’t need “( )”.

  • Net charges must be zero. Use ion sheet to get charges.


DETERMINING THE CHARGE

Monotomic Ions

  • An ion with only one atom; Mg+2, Na+1, O-2

  • Most of the charges can be determined by the atom’s position on the periodic table.

  • It is the atom’s oxidation number.

  • Most transition elements have more than one oxidation number (see back of PT or cover of textbook)


DETERMINING THE CHARGE

Polyatomic Ions

  • An ion made up of more than one atom NH4+1, SO4-2, C2H3O2-1;

  • The charges given to polyatomic ions apply to the whole group of atoms.

  • NEVER change the subscripts of a polyatomic ion.

  • If more than one ion is needed, a parenthesis is placed around the ion and the subscript is written outside; Example: Al(OH)3


Criss Cross for writing formulae

  • Determine the charges on the atoms in the formula

  • +ve Cation listed first and –ve Anion listed second

  • Criss Cross the charge each and use the charge as the subscript of the other.


Ex. Aluminum chloride. Al and Cl.

  • What charge does Al get? +3 Cl ? -1

  • Let’s write them down

    Al3+ Cl1- Al3 Cl1 Don’t need to record “1”s

  • Step 2 to get the neutral formula AlCl3

  • Check to see if formula is neutral

    +3 -1 -1 -1 = 0

  • Remember that if you have a polyatomic ion there will be a few atoms grouped together that have a charge together. So use parenthesis.


MULTIPLE OXIDATION NUMBERS

Cations can have more than one oxidation number.

Example: Cu+1 and Cu+2.

It is important to distinguish which ion is in the compound.

There are two ways used in chemistry.


MULTIPLE OXIDATION NUMBERS

Stock SystemClassical (Latin)

Cu+1 copper (I)cuprous

Cu+2 copper (II)cupric

Sn+2 tin(II)stannous

Sn+4 tin (IV)stannic

Hg2+2 mercury (I)mercurous

Hg+2 mercury (II)mercuric

The lower charge ends in –ous and the higher charge ends in –ic.


MULTIPLE OXIDATION NUMBERS

You are only responsible for only the Stock system but I just wanted you to see the other.


MULTIPLE OXIDATION NUMBERS

You are only responsible in class for the Stock system but I wanted to make you familiar with the classic.


Examples

cupric sulfate/copper (II) sulfateCuSO4

ferrous oxide/iron (II) oxide

FeO

cobaltic chloride/cobalt (III) chloride

CoCl3

mercurous nitrate/mercury (I) nitrate

Hg2(NO)2


PRACTICE

  • lithium fluoride

  • magnesium chloride

  • calcium bromide

  • lithium iodide

  • lithium oxide

  • calcium sulfate

  • barium cyanide

  • Iron (II) oxide

  • barium sulfate

  • aluminum oxide


PRACTICE

  • sodium nitrate

  • iron(III) sulfate

  • copper (II) sulfite

  • tin (IV) fluoride


PRACTICE

  • lithium fluorideLiF

  • magnesium chlorideMgCl2

  • calcium bromideCaBr2

  • lithium iodideLiI

  • lithium oxideLi2O

  • calcium sulfateCaSO4

  • barium cyanideBaCN

  • Iron (II) oxideFeO

  • barium sulfateBaSO4

  • aluminum oxide Al2O3


PRACTICE

  • sodium nitrateNaNO3

  • iron(III) sulfateFe2(SO4)3

  • copper (II) sulfiteCuSO3

  • tin (IV) fluorideSnF4


WRITING FORMULAS

  • Potassium fluoride

  • Potassium iodide

  • Potassium iodate 11. Iron (II) hydroxide

  • Beryllium chloride 12. Iron (III) oxalate

  • Beryllium oxide.

  • Beryllium nitride

  • Beryllium hydroxide

  • Sodium acetate

  • Sodium sulfate

  • Copper (II) sulfate


Putting It Altogether

You need to make sure that you can distinguish between ionic, covalent, and acid compounds.


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