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Writing Ionic Formulas

Writing Ionic Formulas. Ionic Compounds. An ionic compound is always made up of a metal and a nonmetal. Ionic compounds can be binary (made of just two elements), or contain one or more polyatomic ions as part of it (many different elements).

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Writing Ionic Formulas

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  1. Writing Ionic Formulas

  2. Ionic Compounds • An ionic compound is always made up of a metal and a nonmetal. • Ionic compounds can be binary (made of just two elements), or contain one or more polyatomic ions as part of it (many different elements). • To determine the formula for an ionic compound, we will use the criss-cross method.

  3. The Criss-Cross Method • The criss-cross method is an easy way to determine the formula of any ionic compound. • To write an ionic formula, you need the charge of each ion. • The charge is found by looking at your periodic tablefor most ions.

  4. Steps (in order) Write the chemical symbols. Always write the cation+ (metal) first and anion– (nonmetal) second. Write the charge over the symbols. Criss-cross and drop numbers (not + or -). Reduce – if necessary – the same numbers or a 2 & 4 together. Example:calcium + nitrogen Ca N Ca2+ N3- Ca3N2 How to Criss-Cross

  5. Steps (in order) Write the chemical symbols. Always write the cation+ (metal) first and anion– (nonmetal) second. Write the charge over the symbols. Criss-cross and drop numbers (not + or -). Reduce – if necessary – the same numbers or a 2 & 4 together. Example:aluminum + oxygen Al O Al3+ O2- Al2O3 How to Criss-Cross

  6. Steps (in order) Write the chemical symbols. Always write the cation+ (metal) first and anion– (nonmetal) second. Write the charge over the symbols. Criss-cross and drop numbers (not + or -). Reduce – if necessary – the same numbers or a 2 & 4 together. Example:sodium + sulfur Na S Na1+ S2- Na2S How to Criss-Cross 1’s are understood, you do not need to write them!

  7. Steps (in order) Write the chemical symbols. Always write the cation+ (metal) first and anion– (nonmetal) second. Write the charge over the symbols. Criss-cross and drop numbers (not + or -). Reduce – if necessary – the same numbers or a 2 & 4 together. Example:aluminum + nitrogen Al N Al3+ N3- Al3N3 AlN How to Criss-Cross

  8. Ions in Compound Beryllium + bromine Lithium + oxygen Potassium + nitrogen Calcium + sulfur Magnesium + nitrogen Aluminum + phosphorus Lithium + chlorine Magnesium + oxygen Calcium + iodine Chemical Formula BeBr2 Li2O K3N CaS Mg3N2 AlP LiCl MgO CaI2 Try These FormulasUse the criss-cross method to find the formulas for the following.

  9. Formulas With Transition Metals • Transition metals (groups 3-12) can often form more than one type of cation. • Lead (Pb) and Tin (Sn) can also form more than one type of cation. • The charge for these metals is always positive and can be found in the name of the compound that contains them (the Roman numeral indicates the charge). • Examples: • Iron (II)– the iron (Fe) used here has a charge of 2+. • Lead (IV)– the Lead (Pb) used here has a charge of 4+.

  10. Name of Compound Iron (III) and oxgen Tin (II) and sulfur Lead (II) and chlorine Iron (II) and nitrogen Lead (IV) and oxygen Silver (I) and phosphorus Chemical Formula Fe2O3 SnS PbCl2 Fe3N2 PbO2 Ag3P Formulas With Transition MetalsWrite the formulas for each of the following ionic compounds that feature one of the transition metals.

  11. Polyatomic Ionic Compounds • Polyatomic ions are clusters of atoms that stay together as one unit and carry an overall charge. Most polyatomic ions are negatively charged. Parentheses • You may need more than one polyatomic ion in your formula…This means that you will have to use parentheses. Use parentheses whenever you need more than one polyatomic ion in the formula. • Example: Iron (III) nitrate… • Start with symbols and combining charges… Fe3+ NO31- • After the criss-cross, you may get one of two possibilities… FeNO33 OR Fe(NO3)3 • The second option is right because it says you need two nitrate clusters to go with every iron atom. The first option, which did not use brackets, reads as one iron atom with one nitrogen atom and thirty-three oxygen atoms. • Fe(NO3)3 is the correct formula! Use parentheses!

  12. Name of Compound Sodium nitrate Calcium chlorate Lithium phosphate Aluminum sulfate Tin (IV) carbonate Iron (II) hydroxide Magnesium carbonate Lead (II) bicarbonate Potassium chlorate Ammonium phosphate Chemical Formula NaNO3 Ca(ClO3)2 Li3PO4 Al2(SO4)3 Sn(CO3)2 Fe(OH)2 MgCO3 Pb(HCO3)2 KClO3 (NH4)3PO4 Polyatomic Ionic CompoundsWrite the formulas for each of the following polyatomic ionic compounds. Use parentheses when necessary.

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