Formula writing

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# Formula writing - PowerPoint PPT Presentation

Formula writing. IONS. Cation ion – usually metals positive ion (+) loses electrons Anion ion – usually nonmetals negative ion (-) gainies electrons. Ionic Compounds - transfer of electron(s). Ionic compound must be neutral (total + = total -) Write symbol of each ion

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### Formula writing

IONS

Cation ion – usually metals

positive ion (+)

loses electrons

Anion ion – usually nonmetals

negative ion (-)

gainies electrons

Ionic Compounds- transfer of electron(s)

Ionic compound must be neutral (total + = total -)

• Write symbol of each ion
• See if the charges balance out

If yes, write formula

If no, then criss-cross number (ONLY) of charges (lowest whole number ratio)

Sodium chloride calcium chloride

Na + Cl -

Ca 2+ Cl 1-

Same (1+ = 1-)

2+ = 1-

NaCl

CaCl2

We do not show 1’s in formulas

More examples

Sodium oxide calcium nitrate

Aluminum sulfate iron (III) chloride

You need the () since your ion contains more than one element and you need 2 or more of them to balance the formula

Na 1+ O 2-

Ca 2+ NO31-

Ca(NO3)2

Na2O

Al 3+ SO42-

Fe 3+ Cl 1-

Transition metals will usually have roman numerals. They tell you the CHARGE of the cation

FeCl3

Al2(SO4)3

Nomenclature of ionics(naming)
• Id the cation.
• Ask if it is a transition metal, Sn, or Pb?

-If no then just name each ion.

-If yes, then name each ion leaving a space after the cation for roman numerals.

CaCl2FeCl2

See next slide on how to determine the roman numeral

Iron ( ) chloride

Calcium chloride

How to figure out the charge of the cation?

Remember the total number of positives must equal the number of negatives. We know the charge of the anion, so do the math.

FeCl2

So what charge must the Fe have to cancel out the 2-’s?

Cl 1-

2+

Fe

Cl 1-

Therefore it is iron (II) chloride. The roman numeral tells us the charge on the iron.

Let’s try some more.

Co(NO3)3 Ni2(SO4)3

What is the charge for each anion?

2-

1-

How many anions are present?

3

3

Total number of negatives

(1-)(3) =3-

(2-)(3)=6-

What charge must the cation have to cancel the negatives out?

3+ = 3-

6+ = 6-

Charge of cation

(6+)/2= 3+

3+

Name of each ionic compound

Nickel(III) sulfate

Cobalt(III) nitrate

Molecular compounds

Contains all nonmetals and use prefixes

Mono- 1 (used sparingly with oxygen)

Di – 2 tri -3 tetra – 4 penta- 5

Hexa – 6 hepta – 7 octa – 8 nona – 9

Deca- 10

Nitrogen trichloride diphosphorus tetraoxide

P2O4

NCl3

Acids – Contain H’s listed first

Remember the following

Focus on anion and then add appropriate number of H’s

Binary acid (HX) only 2 elements

Hydro--ic acid

Tertiary acid (3 elements)

Hypo- -ite  hypo- -ous acid

-ite  -ous acid

-ate  -ic acid

Per- -ate  per- -ic acid

Remember you ate it and it tasted icky

Naming and formula writing for acids

H2SO4 H2CO2 HF

Nitric acid sulfurous acidhydrochloric acid

Sulfate so the –ate becomes -ic

Carbonite so the –ite becomes -ous

Binary so hydro--ic acid

Sulfuric acid

Hydrofluoric acid

Carbonous acid

nitrate

sulfite

H 1+ NO31-

H 1+ SO32-

H 1+ Cl 1-

HNO3

H2SO3

HCl