Chemical Names and Formulas

Chemical Names and Formulas
The naming of the compounds depends on the type compound: Molecular compounds Ionic compounds Binary ionic compound Containing a transition metal Containing a polyatomic ion Acids Binary acids Oxy Acids

In naming molecular compounds Prefixes are used to indicate the number of atoms in each molecule It would be impossible to determine the formula without the prefixes Value Prefix 1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 Deca

The naming system is straightforward except… We never begin a formula name with mono CS2 – Carbon disulfide We eliminate the –a or –o in the prefix if the element begins with a or o N2O5 – dinitrogen pentoxide We change the second element’s ending to -ide

Ionic compounds are compounds made up of ions of opposite charges A chemical formula is the lowest whole number ratio of the ions present in the compound Na2Cl2 can be reduced to NaCl The ratio of the ions will depend on the charge of those ions

The charge is sometimes referred to as the oxidation number or oxidation state Ions formed from one atom are called monoatomic ions Group Number Charge 1 + 2 2+ 13 3+ 15 3- 16 2- 17 -

Binary ionic compounds are made up of only 2 different elements There can be more than 2 or more atoms though NaCl K2O Al2S3

To name a binary ionic compound Write the name of the cation first (always a metal) Write the name of the anion, but change the ending to –ide Note that any subscripts do not change the name NaCl sodium chlorine → chloride sodium chloride

K2O Al2S3

Name the following compounds KI MgO SrS BeF2 Li2O Al2O3 Cs3N Ba3P2

To write formulas it is important to remember that the charges on the compound must be balanced Same total number of positive and negative charges Determine if the charges are balanced Sodium chloride Lithium oxide Potassium iodide Beryllium bromide Sodium nitride

When charges are not balanced, it is necessary to add subscripts They represent the quantity of each element No subscript equals 1 atom Li+ O2- the charges are not equal There is only one positive and two negatives We need another positive charge to make them equal Li2O

Write formulas for the following compounds Sodium sulfide Potassium iodide Calcium bromide Aluminum oxide Boron bromide Rubidium selenide

Sometimes the metal in a compound is a transition metal Groups 3-12 contain the transition metals Transition metals can move their electrons from the s to the d orbitals This gives them various oxidation numbers or charges For example iron can be either Fe2+ or Fe3+

Since these metals do not have a set charge, we must indicate their charge in the name, using Roman numerals For example look at the three possible compounds that chromium can form with oxygen Cr2+ and O2- yields CrO called chromium (II) oxide Cr3+ and O2- yields Cr2O3 called chromium (III) oxide Cr6+ and O2- yields CrO3 called chromium (VI) oxide

When writing a formula for a transition metal compound remember that the charge of the metal is in the parentheses Write formulas for the following: Lead (IV) chloride Iron (III) oxide Titanium (II) nitride Niobium (V) bromide Tin (II) oxide

Almost all metals get a roman numeral to show the charge The following do NOT use a roman numeral Group 1 metals Group 2 metals Al3+ Zn2+ Ag1+

To write formulas for compounds containing transition metals, we must work backwards: You will always start with a balanced formula: FeO CoCl2 Au3N

Polyatomic ions are ions that contain more than one atom SO42- OH- PO43- NH4+ It is important to note that the charge is distributed throughout all the atoms in the ion Not only on the last atom!

To name a formula containing a polyatomic ion we must first identify it If the ionic compound formula contains more than two elements, you have a polyatomic ion present We do not change the endings of any polyatomic ion

For example, NaOH is Na2SO4 is Ca(OH)2 is We do not include the subscript outside of the parentheses when naming the compound

To write formulas of ionic compounds containing polyatomic ions: Calcium carbonate - Charges are balanced so Calcium hydroxide - Charges are not balanced - we need an additional OH-, but we must use parentheses – Sodium carbonate – Charges are not balanced – we need an additional Na+, but we do not need parentheses – Parentheses are only needed when you add a subscript to a polyatomic ion

Bases (ending in OH-) are named as taught before A common base with a different name is NH3 –ammonia Acids have a completely different naming system There are two types of acids Binary acid – contains H+ and anion(-) Oxy (Ternary) acid - contains H+ and polyatomic ion(-)

To name a binary acid Use a prefix hydro Add the anion name with an –ic ending Finish with acid HCl becomes hydrochloric acid HBr becomes hydrobromic acid H2S becomes hydrosulfuric acid

To write a formula for a binary acid Identify that it’s a binary acid – must start with hydro Write the H+ and the other element with the charge Balance the charges Hydronitric acid becomes H+ N3- H3N

To name an oxy (ternary) acid Start with the polyatomic name If the polyatomic ends in -ate, change the ending to –ic If the polyatomic ends in –ite, change the ending to –ous Finish with acid H2SO4 becomes sulfuric acid H2SO3 becomes sulfurous acid

To write a formula for an oxy (ternary) acid Identify that it’s an oxy acid (no hydro in name) Start with H+ Add name of polyatomic Remember that -ic means it ends in -ate and -ous means it ends in -ite Balance the charges Nitric acid becomes H+ NO3- HNO3

Chemical Names and Formulas

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