unit 6: writing and naming chemical formulas
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Unit 6: Writing and Naming Chemical Formulas. Chemistry I 2013-2014. Ions & The Octet Rule. Ion – an atom or bonded group of atoms with a positive or negative charge Anion – a negatively charged ion Cation – a positively charged ion - PowerPoint PPT PresentationTRANSCRIPT
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Unit 6:Writing and Naming Chemical FormulasCHEMISTRY I2013-2014
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Ions & The Octet Rule
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Vocabulary
Ion – an atom or bonded group of atoms with a positive or negative charge
Anion – a negatively charged ion Cation – a positively charged ion Octet Rule – “atoms lose, gain, or share electrons
in order to acquire the stable electron configuration of a noble gas”
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Ion
An ion is an atom or group of atoms that has either a positive or negative charge
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Atoms form ions by gaining or losing electrons
Atoms gain or lose electrons to become stable
An atom is stable when the valence shell is full
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Cations – Positive Ions
Sodium loses one electron to become stable Results in an ion that has a positive charge
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Cations
The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+
Na+
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Anions – Negative Ions
Chlorine gains one electron to become stable
Results in an ion with a negative charge
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Anion
The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1-
Cl-
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The Octet Rule
Both ions have a full valence shell containing the maximum number of electrons possible (8)
This new arrangement of valence electrons has less energy than the previous arrangement and is stable
Na+ Cl-
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Noble Gases
A metal atom that has lost electrons (cation) and a nonmetal atom that has gained electrons (anion) will have the same number of electrons as its nearest noble gas.
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Common Charges
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Naming Ions
Cations: A metal that has lost electrons to become an ion has the same name as the element
Ca2+ = calcium ion
Anions: A nonmetal that has gained electrons to become an ion has the same name as the element but with the ending changed to –ide
S2- = sulfide ion
Nitrogen Nitride Phosphorous Phosphide Oxygen Oxide Flourine Flouride
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Roman Numerals for Multivents
Multivents – an element that can form an ion in more than one way
Naming: Always include the ion charge as Roman numerals in brackets
Cu+ copper (I) “copper one” Cu2+ copper (II) “copper two”
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Transition Metals to Know
Scandium column: always +3, no Roman numeral needed
F-block: always +3, no Roman numeral needed Ag: always +1, no Roman numeral needed Cd & Zn: always +2, no Roman numeral needed Sn & Pb: either +2 or +4
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Charges Oxidation Number
An oxidation number is the positive or negative charge of an ion
Element Oxidation # Li +1 Be +2 O -2 F -1
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Polyatomic Ions
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Writing and Naming Ionic Compounds
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Ionic Compounds
Cation + anion
Name the cation first (typically a metal) just as it appears on the periodic table
Na+ = Sodium Ca+2 = Calcium
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Ionic Compounds
Write the anion next (typically a nonmetal) Change the ending to –ide
**If the anion is a polyatomic ion, the name stays the same**
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Practice
NaCl Sodium Chloride AlCl3 Aluminum Chloride Na2O Sodium Oxide Al2O3 Aluminum Oxide
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How to determine the Oxidation Number of Transition Metals
Identify the metal as a Transition with multiple oxidation numbers (ex. Fe)
Uncross the “criss-cross”
If nothing to uncross, identify the charge of the anion. The charges have been simplified
Transition metals will be the same just +
Fe2O3
+3 -2
FeS+2 -2
Iron (III) Oxide
Iron (II) Sulfide
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Practice
CuO
Name: Copper (II) Oxide
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Writing Ionic Formula
Identify the ions and their charges
Criss-Cross the charges The sum of the
oxidation numbers must equal zero, so by writing the subscripts we are able to balance the charge
Example: Calcium Chloride
Ions: Ca+2 and Cl-1
+2 -1Ca Cl
Formula = CaCl2
(Don’t write 1’s)
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Practice
Magnesium Oxide
Copper (I) Phosphide
Mg2O2
**Simplify to MgO
Cu3P
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Polyatomic Ions
You can’t change the subscripts in Polyatomic Ions
Put the Polyatomic Ion in brackets and place the subscripts outside those
Calcium PhosphateCa+2 PO4
3-
Ca3(PO4)2
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Naming Covalent Compounds
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What’s the difference between covalent and ionic?
Ionic compounds have a metal and a nonmetal, a cation and an anion
Covalent compounds are called molecules They are made from elements that are similar in
electronegativity
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Covalent Naming uses Prefixes
1.Mono2.Di3.Tri4.Tetra5.Penta
6.Hexa7.Hepta8.Octa9.Nona10.deca
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Rules
If you have more than one atom of that element in the compound, you will need a prefix before it’s name.
Always put a prefix before the name of the second element
Change the ending of the second element to -ide
P2O5
Diphosphorous pentoxide
CO
Carbon monoxide
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Practice
OF2
SO2
SO3
N2O5
N2O4
H2O
Oxygen diflourideSulfur dioxideSulfur trioxideDinitrogen pentoxideDinitrogen tetroxideDihydrogen monoxide
http://www.lhup.edu/~dsimanek/dhmo.htm
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Names and Formulas of Common Acids and Bases
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Naming Acids
Acids are almost always compounds made from hydrogen and an anion
Hydrogen + Halogen = hydro________ic acid HCl = hydrochloric acid
Hydrogen + Polyatomic ion –ate = _______ic acid HNO3 = nitric acid
Hydrogen + Polyatomic ion –ite = _______ous acid H2SO3= sulfurous acid
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Naming Bases
Bases are almost always compounds made from hydroxide (HO-) and a cation
Cation + Hydroxide
Mg(OH)2 = Magnesium Hydroxide LiOH = Lithium Hydroxide
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Practice
Hydroiodic acid HBr H2CO3
Lead (II) Hydroxide
Sn(OH)4
Zn(OH)2
HI Hydrobromic
Acid Carbonic Acid
Pb(OH)2
Stannic Hydroxide
Zinc Hydroxide
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Empirical and Molecular Formulas
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Empirical Formula
The formula that gives the simplest whole number ration of atoms in a compound
Molecular Formula: C6H12O6
Empirical Formula: CH2O
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What is the empirical formula of…?
C6H12O6
Fe3O2
C6H10O4
CH2O
Fe3O2
C3H5O2