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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 Presentation
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Unit 6:Writing and Naming Chemical FormulasCHEMISTRY I2013-2014
Ions & The Octet Rule
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”
Ion
An ion is an atom or group of atoms that has either a positive or negative charge
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
Cations – Positive Ions
Sodium loses one electron to become stable Results in an ion that has a positive charge
Cations
The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+
Na+
Anions – Negative Ions
Chlorine gains one electron to become stable
Results in an ion with a negative charge
Anion
The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1-
Cl-
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-
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.
Common Charges
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
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”
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
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
Polyatomic Ions
Writing and Naming Ionic Compounds
Ionic Compounds
Cation + anion
Name the cation first (typically a metal) just as it appears on the periodic table
Na+ = Sodium Ca+2 = Calcium
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**
Practice
NaCl Sodium Chloride AlCl3 Aluminum Chloride Na2O Sodium Oxide Al2O3 Aluminum Oxide
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
Practice
CuO
Name: Copper (II) Oxide
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)
Practice
Magnesium Oxide
Copper (I) Phosphide
Mg2O2
**Simplify to MgO
Cu3P
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
Naming Covalent Compounds
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
Covalent Naming uses Prefixes
1.Mono2.Di3.Tri4.Tetra5.Penta
6.Hexa7.Hepta8.Octa9.Nona10.deca
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
Practice
OF2
SO2
SO3
N2O5
N2O4
H2O
Oxygen diflourideSulfur dioxideSulfur trioxideDinitrogen pentoxideDinitrogen tetroxideDihydrogen monoxide
http://www.lhup.edu/~dsimanek/dhmo.htm
Names and Formulas of Common Acids and Bases
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
Naming Bases
Bases are almost always compounds made from hydroxide (HO-) and a cation
Cation + Hydroxide
Mg(OH)2 = Magnesium Hydroxide LiOH = Lithium Hydroxide
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
Empirical and Molecular Formulas
Empirical Formula
The formula that gives the simplest whole number ration of atoms in a compound
Molecular Formula: C6H12O6
Empirical Formula: CH2O
What is the empirical formula of…?
C6H12O6
Fe3O2
C6H10O4
CH2O
Fe3O2
C3H5O2