Naming and Writing Formulas for Chemical Compounds

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Naming Chemical Compounds
1
Ions: Naming and Formulas
Naming:
Cations (positive charge)
• Single ion formation
– Metals in groups 1,2,13
– Element Name + ion
– ex. Ca+2  Calcium ion
•
Anions (negative charge)
• Nonmetals
– Root of Element –ide
– ex. S-2  sulfide
Multiple ion formation
- Transition metals, Tin and Lead
- Element Name (RN) + ion
- Roman Numeral (RN) = charge
- ex. Fe+3  Iron (III) ion
• Formulas -- element symbol AND charge
•
Charge is determined by group number or roman numeral
2
Naming Binary Compounds –
2 Elements
• Cation/1st element = name of element (always 1st)
• Anion/2nd element = root of element + ide
– Type I (Ionic) – cation only forms a single ion….
• Nothing added
– Type II (Ionic) - cation forms multiple ions…..
• roman numeral must be added (between cation and anion
names) to indicate charge of the metal
– Type III (covalent) – 1st element is a nonmetal …
• Prefixes are used to indicate number of atoms for 1st and 2nd
element
• Mono- never used on 1st element
3
Type I (binary ionic)
• Characteristics
– 2 elements
– Metal + Nonmetal
– Metal found in groups 1,2,13,Zn+2,Ag+,Cd+2
• Rules
– cation (+) named 1st, anion (-) named second
– cation  element name
– anion  root of element name + (-ide)
*subscripts of chemical formulas are NOT indicated directly in compound name
4
Type II (binary ionic)
• Characteristics
– 2 elements
– Metal + Nonmetal
– Metal found in groups 3-12,Pb,Sn
• Rules
– cation (+) named 1st, anion (-) named second
– cation  element name (roman numeral)
• roman numeral indicates the charge of the cation
– anion  root of element name + (-ide)
*subscripts of chemical formulas are NOT indicated directly in compound name
5
Determining Charge for Roman Numerals
• Total charge of + ions and – ions = 0
(# +ions)(charge +ions) + (# -ions)(charge –ions) = 0
Example:
FeCl2 --- (1) Fe ion + (2 Cl)(-1) = 0
Fe ion + (-2) = 0
Fe ion = 2+
Cr2O3 ----- (2) Cr ion + (3 O) (-2) = 0
2 Cr ions + (- 6)
= 0
2 Cr ions
= 6+
Cr ion
= 3+ = Cr3+
6
Type III (binary covalent)
• Characteristics
– 2 elements
– Nonmetal + Nonmetal
• Rules
– 1st element  element name
– 2nd element  root of element name + (-ide)
– Use prefixes on both elements to indicate the number
of atoms (subscripts)
• 1 (mono)
2 (di) 3 (tri)
4 (tetra) 5 (penta)
6 (hexa) 7 (hepta)
8 (octa) 9 (nona) 10 (deca)
• NEVER use (mono) on the 1st element
• No double vowels with “o” and “a”
7
Non-binary Ionic
• Characteristics
– 3 or more elements
– contains a polyatomic ion
• Rules
– Cation
• Metal (groups 1,2,13,Zn+2,Ag+,Cd+2) element name
• Metal (groups 3-12, Pb, Sn)  element name (roman numeral)
• Polyatomic ion  name on reference sheet
– Anion
• Nonmetal  root of element name + (-ide)
• Polyatomic ion  name on reference sheet
8
Writing Formulas
Elements and Compounds
9
Element Formulas
• Monatomic Elements
– Only the element symbol is used for the formula
• Diatomic Elements
– These elements can NOT exist in nature as single
atoms, they must be paired.
– They include: hydrogen (H2), nitrogen (N2), oxygen
(O2), fluorine (F2), chlorine (Cl2), bromine (Br2),
and iodine (I2).
10
Compound Formulas - Ionic
• Ionic (metal and nonmetal)
– Symbol
• Elements – symbol on periodic table
• Polyatomic ions – reference sheet
– Charges
• Group charges – 1(+1), 2(+2), 13(+3), 15(-3), 16(-2), 17(-1)
• Roman numerals – charge of the transition metal
• Polyatomic ions – reference sheet
– Switch
• total (+) = total (-)
• Charge #’s cross down to become the subscripts on the other
element
– Reduce
• Subscripts must be in smallest ratios
11
Compound Formulas – Covalent
• Covalent (only nonmetals)
– Convert prefixes to subscripts
– place BEHIND the element symbol
• Mono – 1
• Di – 2
• Tri – 3
• Tetra – 4
• Penta – 5
• Hexa – 6
• Hepta -7
• Octa – 8
• Nona – 9
• Deca - 10
12
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