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Ionic Compounds

Learn about ions, monatomic ions, polyatomic ions, and naming and writing formulas for ionic compounds in chemistry. Includes a chemistry joke about helium atoms.

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Ionic Compounds

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  1. Ionic Compounds

  2. Chemistry Joke Q: Why do chemists like nitrates so much? A: They’re cheaper than day rates!

  3. A Review • Ion: atom or group of atoms that have a positive or negative charge • Ions form when an atom or group of atoms gains or loses electrons • METALS lose electrons to form positive CATIONS. • NONMETALS gain electrons to form negative ANIONS

  4. Having One Atom! Monatomic Ions • Ions consisting of only 1 atom • The charge for ions formed from representative elements can be determined by looking at the periodic table • Group 1A metals form cations with a 1+ charge • Group 2A metals form cations with a 2+ charge • Group 3A metals form cations with a 3+ charge • Group 5A nonmetals form anions with a 3- charge • Group 6A nonmetals form anions with a 2- charge • Group 7A nonmetals form anions with a 1- charge • Group 8A elements do not form ions

  5. Having Many Atoms! Polyatomic Ions • Tightly bound groups of atoms that behave as a unit and carry a charge • Ex: The 10 you had to memorize. • 1- charge: • 2- charge: • 3- charge: • 1+ charge: NO3- NO2- OH- ClO3- C2H3O2- CO32- SO42- SO32- PO43- NH4+

  6. Naming Monatomic Cations • The name of a cation is the SAME as the name of the element!! • Ex: Na atom forms a sodium cation • Ex: Li atom forms a lithium cation • How would you name the following ion: Al+3 Aluminum ion

  7. Naming Monatomic Anions • The name of a MONAtomic ion ends in “ide” Ex: Chlorine atom gains 1 electron to become the CHLORIDE anion Ex: Oxygen gains 2 electrons to become an anion named OXIDE What would we name the following ion? S-2 Sulfide ion

  8. Practice: • What do we call: • A strontium atom when it loses 2 electrons • An iodine atom when it gains 1 electron • A phosphorus atom when it gains 3 electrons? Strontium ion Iodide ion Phosphide ion

  9. Naming Ionic Compounds • The cation comes 1st and keeps its name. • Monatomic anions end in “ide” • Polyatomic cations and anions keep their names. K2SO4 LiCl Lithium Chloride Potassium Sulfate MgF2 Magnesium Fluoride LiNO3 MgCO3 Lithium Nitrate Be(OH)2 Magnesium Carbonate Beryllium Hydroxide NH4Cl Ammonium Chloride

  10. Writing the Formulas! • Cations and anions combine in a whole number ratio that produces a neutralcompound. • The total positive charge of the cations will equal the total negative charge of the anions. • For example: 1 Al+3 combines with 3 F-1 (1 x +3) cancels with (3 x -1)

  11. Criss Cross Method 3 Step Process for Writing Ionic Formulas • Write the ions with their charges The charges are known from the periodic table or memorized for polyatomic ions. • Cross the charge numbers (dropping the + or -) to form the subscripts. (Subscripts of 1 are not written.) • Simplify the subscripts to the lowest whole number ratio

  12. Writing Formulas for Ionic Compounds • Write the formula for magnesium chloride. • Write the ions with their charges The charges are known from the periodic table. • Cross the charge numbers (dropping the + or -) to form the subscripts. (Subscripts of 1 are not written.) • Simplify the subscripts to the lowest whole number ratio Magnesium is in Group 2A and forms a 2+ charge. Chlorine is in Group 7A and forms a 1- charge. Mg2+ Cl1- Mg Cl MgCl2

  13. Writing Formulas for Ionic Compounds • Write the formula for beryllium oxide. • Write the ions with their charges The charges are known from the periodic table. • Cross the charge numbers (dropping the + or -) to form the subscripts • Simplify the subscripts to the lowest whole number ratio. (If both subscripts are the same, they can be dropped.) Beryllium is in Group 2A and forms a 2+ charge. Oxygen is in Group 6A and forms a 2- charge. Be2+ O2- Be O Be2O2 BeO

  14. Writing Formulas for Ionic Compounds With Polyatomic Ions • Follow the same 3 steps. • Just add parentheses around the polyatomic ion before it gets a subscript

  15. Writing Formulas for Polyatomic Ionic Compounds Calcium is in Group 2A and forms a 2+ charge. Hydroxide is a polyatomic ion that has a 1- charge. • Write the formula for calcium hydroxide. • Write the ions with their charges • Cross the charge numbers (dropping the + or -) to form the subscripts • Subscripts of 1 are not written • Simplify the subscripts • Remember to add parentheses around the polyatomic ion if a subscript has been added! Ca2+ OH1- Ca OH There are 2 Hydroxide ions not just 2 Hydrogen atoms. CaOH2 Ca(OH)2

  16. Try Some Na2CO3 • Sodium Carbonate • Potassium Hydroxide • Magnesium Phosphate KOH Mg3(PO4)2

  17. Chemistry Joke Q: What happened when someone told a joke to two helium atoms? A:They went, “He He!!”

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