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Section 2.3—Chemical Formulas
We need to be able to read the formulas for chemicals in the antacids!
Your Appendix (Page A-2) has lists of:Common polyatomic ionsMultivalent metalsCovalent prefixes
Use your periodic table to determine the charges of common elements when they form ions
Reminders from Section 2.2
Binary Ionic compounds
Definitions
Binary Ionic Compound- compound containing two elements—one metal and one non-metal
+Cation
+Cation
-Anion
-Anion Ionic Compound
Ionic bond- bond formed by attraction between + and - ions
Metals & Non-Metals
Ionic Bonds are between metals & non-metals
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Lr Rf Db Sg Bh Hs Mt Uun Uuu Uub Uut
Metals Metalloids Non-metals
These compounds:End in “-ide” (except “hydroxide and cyanide”)Do NOT contain covalent prefixes
To write these formulas:Write the symbol & charge of the first element (the metal,
cation)Write the symbol & charge of the second element (the
non-metal, anion)Add more of the cations and/or anions to have a neutral
compoundUse subscripts to show how many of each type of ion is
there.
Identifying & Naming Binary Ionic
Example #1
Sodium chloride
Example #1
Sodium chloride
Cation
Anion
Na+1
Cl-1
NaCl
Example #1
Sodium chloride
Cation
Anion
Na+1
Cl-1
NaCl
Na+1Cl-1
+1 + -1 = 0
The compound is neutral…no subscripts are needed.
Example #2
Calcium bromide
Example #2
Calcium bromide
Cation
Anion
Ca+2
Br-1
Example #2
Calcium bromide
Cation
Anion
Ca+2
Br-1
CaBr2
Ca+2Br-1
+2 + -1 = +1
Ca+2Br-1Br-1
The subscript “2” is used to show that 2 anions are needed.
+2 + -1 + -1 = 0
Let’s Practice
Example:Write the following chemical formulas
Cesium chloride
Potassium oxide
Calcium sulfide
Lithium nitride
Let’s Practice
CsCl
K2O
CaS
Li3N
Example:Write the following chemical formulas
Cesium chloride
Potassium oxide
Calcium sulfide
Lithium nitride
Polyatomic Ionic Compounds
Definition
Polyatomic Ion- more than one atom that together have a charge
+Cation
+Cation
Polyatomic Ionic Compound- compound containing at least one polyatomic ion
-Polyatomic
Anion
Polyatomic IonicCompound
These compounds:Do not end with “-ide” (except hydroxide & cyanide)Do not use covalent prefixes
To write these formulas:Write the symbol & charge of the cation & anionAdd additional cations or anions to have a neutral
compoundUse subscripts to show the number of ions
When using subscripts with a polyatomic ion, you must put the polyatomic ion in parenthesis.
Identifying & Naming Polyatomic Ionic
Example #3
Sodium carbonate
Example #3
Sodium carbonate
Cation
PolyatomicAnion
Na+1
CO3-2
Example #3
Sodium carbonate
Cation
PolyatomicAnion
Na+1
CO3-2
Na2CO3
Na+CO32-
+1 + -2 = -1
Na+Na+CO32-
The subscript “2” is used to show that 2 cations are needed.
+1 + 1 + -2 = 0
Example #4
Magnesium nitrate
Example #4
Magnesium nitrate
Cation
PolyatomicAnion
Mg+2
NO3-1
Example #4
Magnesium nitrate
Cation
PolyatomicAnion
Mg+2
NO3-1
Mg(NO3)2 Use parenthesis when adding subscripts to polyatomic ions
Mg+2NO3-
+2 + -1 = 1
Mg+2NO3- NO3
-
The subscript “2” is used to show that 2 anions are needed.
+2 + -1 + -1 = 0
Let’s Practice
Example:Write the following chemical formulas
Sodium nitrate
Calcium chlorate
Potassium sulfite
Calcium hydroxide
Let’s Practice
NaNO3
Ca(ClO3)2
K2SO3
Ca(OH)2
Example:Write the following chemical formulas
Sodium nitrate
Calcium chlorate
Potassium sulfite
Calcium hydroxide
Multivalent Metals
Definition
Multivalent Metal- metal that has more than one possibility for cationic charge
These compounds:Will have roman numerals
To write these formulas:Same as binary ionic or polyatomic ionic.The roman numerals tell the charge of the
metal (cation)
Identifying & Naming Multivalent Metals
Example #5
Iron (III) oxide
Example #5
Iron (III) oxide
Cation
Anion
Fe+3
O-2
Example #5
Iron (III) oxide
Cation
Anion
Fe+3
O-2
Fe2O3
Fe+3O2-
+3 + -2 = -1
Fe+3Fe+3O2-O2-
The subscript “2” and “3” are used to show the numbers of atoms needed.
+3 + 3 + -2 + -2 + -2 = 0
Example #6
Copper (II) nitrate
Example #6
Copper (II) nitrate
Cation
PolyatomicAnion
Cu+2
NO3-1
Example #6
Copper (II) nitrate
Cation
PolyatomicAnion
Cu+2
NO3-1
Cu(NO3)2
Cu+2NO3-
+2 + -1 = 1
Cu+2NO3-NO3
-
Use parenthesis when adding subscripts to a polyatomic ion
+2 + -1 + -1 = 0
Let’s Practice
Example:Write the following chemical formulas
Iron (II) nitrate
Copper (I) chloride
Lead (IV) hydroxide
Tin (II) oxide
Let’s Practice
Fe(NO3)2
CuCl
Pb(OH)4
SnO
Example:Write the following chemical formulas
Iron (II) nitrate
Copper (I) chloride
Lead (IV) hydroxide
Tin (II) oxide
Binary Covalent Compounds
Definition
Binary Covalent Compound compound made from two non-metals that share electrons
Nonmetal
Nonmetal
Nonmetal
Nonmetal Covalent compound
Covalent bond atoms share electrons
These compounds:Use covalent prefixes
To write these formulas:Write the symbols of the first and second
elementUse the covalent prefixes (assume the first
element is “1” if there’s no prefix) as the subscripts to show number of atoms.
Identifying & Naming Binary Covalent
Atoms do not form charges when bonding covalently…you DO NOT need to worry about charges with this type!
Example #7
Dinitrogen Tetraoxide
Example #7
Dinitrogen Tetraoxide
N
O
“Di-” = 2
“Tetra-” = 4
N2O4
Example #8
Silicon dioxide
Example #8
Silicon dioxide
Si
O
“Mono-” is not written for the first element
“Di-” = 2
SiO2
CAUTION!!!
bi-di-
Stands for “2” in covalent compounds
Means there’s a hydrogen in the polyatomic anion
“di” and “bi” do not mean the same thing!
Carbon dioxide = CO2
Sodium biphosphate = Na2HPO4
Let’s Practice
Example:Write the following chemical formulas
Carbon monoxide
Nitrogen dioxide
Diphosphorus pentaoxide
Let’s Practice
CO
NO2
P2O5
Example:Write the following chemical formulas
Carbon monoxide
Nitrogen dioxide
Diphosphorus pentaoxide
Nomenclature Summary
Writing Chemical Formulas
Does not contain covalent prefixes
Does contain covalent prefixes = Binary
Covalent compound
Ends with “-ide” (except hydroxide &
cyanide) = Binary Ionic
All others = Polyatomic Ionic
Mixed Practice
Example:Write the following chemical formulas
Magnesium hydroxide
Copper (II) nitrate
Iron (III) oxide
Nitrogen dioxide
Sodium bicarbonate
Mixed Practice
Mg(OH)2
Cu(NO3)2
Fe2O3
NO2
NaHCO3
Example:Write the following chemical formulas
Magnesium hydroxide
Copper (II) nitrate
Iron (III) oxide
Nitrogen dioxide
Sodium bicarbonate