2.03 Naming/Writing Formulas

Naming and Writing Formulas Formulas Different methods of naming and writing are used depending on the type of bond in the compound. Different methods of naming and writing are used depending on the type of bond in the compound. Ionically bonded compounds are named and written using the Stock method. Ionically bonded compounds are named and written using the Stock method. Covalently bonded compounds are named and written using the Greek prefix method. Covalently bonded compounds are named and written using the Greek prefix method.

Stock System Naming Write the full name of the cation first. Write the full name of the cation first. Write the root of the anion followed by an –ide ending. Write the root of the anion followed by an –ide ending. If a transition element is used, a charge must be assigned and written in parenthesis as a roman numeral. If a transition element is used, a charge must be assigned and written in parenthesis as a roman numeral. The charge is determined by finding out what is need to neutralize the compound or create its overall charge. The charge is determined by finding out what is need to neutralize the compound or create its overall charge.

Stock System Writing Write the symbol of the cation, followed by anion Write the symbol of the cation, followed by anion Find their oxidation charges on the periodic table and cross the absolute values of each to get the subscripts. Find their oxidation charges on the periodic table and cross the absolute values of each to get the subscripts.

Greek System Naming Write the full name of the least electronegative (bottom left) element first. Write the full name of the least electronegative (bottom left) element first. Write the root of the most electronegative element (top right) second, followed by an –ide ending. Write the root of the most electronegative element (top right) second, followed by an –ide ending. Write a prefix for each element name based on the subscript number. Write a prefix for each element name based on the subscript number. If the prefix for the first element is mono, it does not have to be included in the name. If the prefix for the first element is mono, it does not have to be included in the name.

Greek System Writing Write the symbol for the least electronegative element first followed by the most. Write the symbol for the least electronegative element first followed by the most. Write in subscripts by looking at prefixes for each element. Write in subscripts by looking at prefixes for each element.

Tertiary Compounds Compounds that consist of only two elements are called binary. Compounds that consist of only two elements are called binary. Compounds containing three or more elements are called tertiary. Compounds containing three or more elements are called tertiary. Tertiary compounds can only be formed when a metal bonds with a polyatomic ion. Tertiary compounds can only be formed when a metal bonds with a polyatomic ion. A polyatomic ion is two or more nonmetals that are already bonded covalently to one another. A polyatomic ion is two or more nonmetals that are already bonded covalently to one another. The polyatomic ion has an overall charge therefore allowing it to bond to a metal to form the tertiary compound. The polyatomic ion has an overall charge therefore allowing it to bond to a metal to form the tertiary compound.

Polyatomic ions These are some common polyatomic ions and their charges. They need to be memorized. These are some common polyatomic ions and their charges. They need to be memorized. NitrateNO 3 1- NitrateNO 3 1- AcetateCH 3 COO 1- SulfateSO 4 2- CarbonateCO 3 2- HydroxideOH 1- AmmoniumNH 4 1-

Naming/Writing with Polyatomic Endings of polyatomic ions cannot be changed when naming. Endings of polyatomic ions cannot be changed when naming. When determining subscripts in formulas, the charge on the overall polyatomic ion is what is used when crossing. When determining subscripts in formulas, the charge on the overall polyatomic ion is what is used when crossing. If more than one polyatomic ion is used, parenthesis must be added around it before any subscripts can be added. If more than one polyatomic ion is used, parenthesis must be added around it before any subscripts can be added. All other rules remain. All other rules remain.

Mole Relationships in Compounds In a formula, the subscripts represent the amount of moles of that element in the substance. In a formula, the subscripts represent the amount of moles of that element in the substance. H 2 O contains two moles of hydrogen and one mole of oxygen. H 2 O contains two moles of hydrogen and one mole of oxygen. Subscripts must be multiplied by coefficients to get correct mole counts. Subscripts must be multiplied by coefficients to get correct mole counts. 2H 2 O contains two moles of water, four moles of hydrogen and two moles of oxygen. 2H 2 O contains two moles of water, four moles of hydrogen and two moles of oxygen.

Percent Composition Percent composition is the percentage by mass of a particular element in a compound. Percent composition is the percentage by mass of a particular element in a compound. Percent composition Percent composition To find percent composition, the total mass of the element within a compound must be known. To find percent composition, the total mass of the element within a compound must be known. This is done by multiplying the atomic mass of the element by its total number of moles. This is done by multiplying the atomic mass of the element by its total number of moles. By dividing this total mass of the element by the formula mass of the compound, you are able to get the percentage of that element within the total compound. By dividing this total mass of the element by the formula mass of the compound, you are able to get the percentage of that element within the total compound.

Empirical Formulas Empirical formula is the formula showing the smallest whole-number mole ratio of the atoms in the compound. Empirical formula is the formula showing the smallest whole-number mole ratio of the atoms in the compound. H 4 O 2 could be reduced to an empirical formula of H 2 O. H 4 O 2 could be reduced to an empirical formula of H 2 O.

Writing Empirical Formulas To write an empirical formula, the smallest whole number ratio of atoms must be found. To write an empirical formula, the smallest whole number ratio of atoms must be found. This is done by converting the mass of all elements in the compound to moles and then dividing by the smallest mole. This is done by converting the mass of all elements in the compound to moles and then dividing by the smallest mole.

Molecular Formulas Unlike empirical formula which is the smallest whole number ratio of moles of atoms, the molecular formula is the actual ratio. Unlike empirical formula which is the smallest whole number ratio of moles of atoms, the molecular formula is the actual ratio. H 2 O could have the molecular formula H 4 O 2 or even H 6 O 3. H 2 O could have the molecular formula H 4 O 2 or even H 6 O 3.

Writing Molecular Formulas The empirical formula must be multiplied by an x factor to go from the smallest ratio to the actual ratio. The empirical formula must be multiplied by an x factor to go from the smallest ratio to the actual ratio. That x factor is found by dividing the given experimental formula mass by the calculated empirical formula mass. That x factor is found by dividing the given experimental formula mass by the calculated empirical formula mass. Formula mass is found by adding the mass of all elements together. Formula mass is found by adding the mass of all elements together.