Naming Compounds Writing Formulas and Equations

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Naming CompoundsWriting Formulasand Equations

• Larry Scheffler
• Lincoln High School

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Naming Compounds

• The chemical formula represents the composition
  of each molecule.
• In writing the chemical formula, in almost all
  cases the element farthest to the left of the
  periodic table is written first.
• So for example the chemical formula of a compound
  that contains one sulfur atom and six fluorine
  atoms is SF6.
• If the two elements are in the same period, the
  symbol of the element of that is lower in the
  group (i.e. heavier) is written first e.g. IF3.

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Naming Ionic Compounds

• Ionic compounds are combinations of positive
  
• and negative ions.
• In writing the chemical formula the positive
  ion is
• written first, It is then followed by the
  name of the
• negative ion.
• Monatomic anions end in ide. Special endings
• apply for polyatomic ions
• Examples
• NaCl Sodium chloride
• BaF2 Barium Fluoride
• ZnO Zinc Oxide

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Names of Polyatomic Ions with Oxygen

• Polyatomic ions usually contain oxygen in
  addition to another element. 
• Normally they have a negative charge. 
• They end in either "ate" or "ite" depending on
  the number of oxygen atoms present.

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Polyatomic Ion -- Exceptions

• Most polyatomic ions contain oxygen
• Their names end in ite or ate.
• There are several exceptions
• OH- hydroxide
• CN- cyanide
• SCN- thiocyanate

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Elements with Multiple Cations

• When an element can form more than one cation a
  Roman numeral is used to distinguish the
  oxidation state of the compound.
• Iron, Tin, Lead, Copper, and are common elements
  with more than one cation.
• Examples
• PbSO4    lead (II) sulfate   This compound is
  formed from Pb2 and  SO42-
• Pb(SO4)2   lead (IV) sulfate   This compound is
  formed from Pb4 and  SO42-
• Fe(OH)2    iron (II) hydroxide   This compound
  is formed from Fe2 and  OH- 
• Fe(OH)3    iron (III)  hydroxide    This
  compound is formed from Fe3 and  OH-

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Examples of Ionic Compounds

• NaCl Sodium chloride
• ZnF2 Zinc fluoride
• KOH Potassium hydroxide
• Ca(NO3)2 Calcium nitrate
• BaSO3 Barium Sulfite
• Al2(SO4) 3 Aluminum sulfate
• Ca3(PO3)2 Calcium phosphite
• NH4Cl Ammonium chloride
• (NH4)2CO3 Ammonium carbonate

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Naming Covalent Compounds

• When naming covalent compounds, the name of the
  first element in the formula is unchanged.
• The suffix -ide is added to the second
  element.
• Often a prefix to the name of the second element
  indicates the number of the element in the
  compound
• Examples
• SF6 sulfur hexafluoride
• P4O10 tetraphosphorous decoxide
• CO carbon monoxide
• CO2 carbon dioxide

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Covalent molecules with multiple possibilities

• A Roman Numeral is used to indicate the state of
  the more positive element
• Examples
• N2O     Nitrogen (I) oxide   Since oxygen has a
  2- charge, the nitrogen must be 1 to  balance
  the charges.    Also known as dinitrogen monoxide
• N2O3   Nitrogen (III) oxide    Since oxygen has
  a 2- charge, the nitrogen must be 3 to balance
  the charges  Also  known as dinitrogen trioxide

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Binary compounds of Hydrogen

• The binary compounds of hydrogen are special
  cases. They were discovered before a convention
  was adopted and hence their original names have
  stayed.

Water H2O is not called dihydrogen monoxide
Hydrogen forms binary compounds with almost all
non-metals except the noble gases. Examples HF
- hydrogen fluoride HCl - hydrogen chloride H2S
- hydrogen sulfide
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Acids

• When many hydrogen compounds are dissolve in
  water they take on the form of an acid. Special
  rules apply to acids. The ite suffix becomes
  ous and the ate suffix becomes ic

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Writing Formulas for Ionic Compounds

• Write the positive ion (cation) first, then the
  negative ion.
• The positive charges must balance the negative
  charges.
• Use subscripts to show how many times each ion
  must appear in order for the charges to balance.
  A subscript is not used if the ion appears only
  once
• Use parenthesis around polyatomic ions that
  appear more than once in the formula

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Examples

• Na and Cl- NaCl
• Zn2 and Br- ZnBr2
• K and OH- KOH
• Ca2 and OH- Ca(OH)2
• Fe2 and SO42- FeSO4
• Fe3 and SO42- Fe2(SO4) 3
• Ca2 and PO43- Ca3(PO4)2
• NH4 and Cl- NH4Cl
• NH4 and CO32- (NH4)2CO3

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Chemical Reactions

• Elements and compounds frequently undergo
  chemical reactions to form new substances
• In a chemical reaction, chemical bonds are
  frequently broken and new chemical bonds are
  formed
• Atoms are neither created nor destroyed in an
  ordinary chemical change

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Chemical Reactions

• A balanced chemical reaction is used to describe
  the process that occurs in a chemical change.
• For example Zinc reacts with hydrochloric acid
  to produce zinc chloride and hydrogen gas.
• This chemical reaction could be written as
• Zn 2 HCl ? ZnCl2 H2

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Reactants and Products

• In the chemical reaction
• Zn 2 HCl ? ZnCl2 H2
• Reactants Products
• This shorthand way of describing a chemical
  reaction is known as a chemical equation
• The starting materials are shown on the left and
  are known as reactants
• The substances formed are shown on the right and
  are known as the products

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Balancing a Chemical Reaction

• A proper chemical reaction must be balanced
• Zn 2 HCl ? ZnCl2 H2
• Reactants Products
• Each element must appear on both sides of the
  arrow and equal number of times
• Chemical reactions can be balanced by inserting
  numbers in front of formulas.
• These numbers are called coefficients

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Balancing Chemical Reactions

• Most simple equations can be balanced by
  inspection
• Example Balance the following equation
• BaCl2 K3PO4 ? Ba3 (PO4)2 KCl
• There are 3 Ba on the right so we need
  coefficient of 3 in front of BaCl2
• There are 2 PO4 on the right so we need a
  coefficient of 2 in front of K3PO4.
• This leaves 6 K on the left so we need a
  coefficient of 6 in front of the KCl on the right
• The balanced equation is
• 3 BaCl2 2 K3PO4 ? Ba3 (PO4)2 6 KCl

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Balancing Chemical Reactions

• An equation is balanced when there are the same
  number and kind of atoms on both sides of the
  arrow
• 3 BaCl2 2 K3PO4 ? Ba3(PO4)2 6 KCl

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State Symbols

• State symbols are often added to chemical
  equations.
• CaCO3 (s) 2 HCl (aq) ? CaCl2 (aq) CO2 (g)
  H2O (l)

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Types of Reactions

• There are many kinds of chemical reactions that
  occur. Some are very simple while others are
  very complex and may occur in multiple steps.
• A number of reactions conform to some relatively
  simple patterns
• Understanding and identifying these patterns can
  be helpful in predicting the products of similar
  reactions

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Direct Combination

• In a direct combination, two elements or
  compounds combine to form a more complicated
  product
• Examples
• CaO CO2 ? CaCO3
• 2 H2 O2 ? 2 H2O
• FeCl2 Cl2 ? FeCl3
• N2 O2 ? 2 NO

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Decomposition

• In a dcecomposition, a single compound is broken
  down into two or more simplier substances
• Examples
• 2 KClO3 ? 2 KCl 3 O2
• ZnCO3 ? ZnO CO2
• Cu(OH)2 ? CuO H2O

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Single Replacement

• In a single replacement, one substance (usually
  an element) takes the place of another in a
  compound
• Examples
• Zn H2SO4 ? ZnSO4 H2
• Cl2 2 KBr ? 2 KCl Br2
• Mg CuCl2 ? MgCl2 Cu

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Double Replacement

• In a double replacement, two substances exchange
  places in their respective compounds
• Examples
• AgNO3 NaCl ? AgCl NaNO3
• 3 CaCl2 2 K3PO4 ? Ca3(PO4)2 6KCl BaCl2
  Na2SO4 ? BaSO4 2NaCl

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Diatomic Molecules

• Certain elements exist as diatomic molecules in
  nature

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Diatomic Molecules

• Certain elements exist as diatomic molecules in
  nature