7Chemical Substances; Formulas and Names Naming simple compoundsChemical compounds are classified as organic or inorganic.Organic compounds are compounds that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen; they do not contain metals.Inorganic compounds are compounds composed of elements other than carbon and usually contain at least one metal atom.2
8Chemical Formulas; Molecular Substances Organic compoundsAn important class of molecular substances that contain carbon is the organic compounds.Organic compounds make up the majority of all known compounds.The simplest organic compounds are hydrocarbons, or compounds containing only hydrogen and carbon.Common examples include methane, CH4, ethane, C2H6, and propane, C3H8.2
9Naming Covalent Compounds Naming Covalent CompoundsA covalent compound as we said before is formed by sharing electrons between 2 nonmetals or metalloids.These compounds are usually molecular and are named using a prefix system.When naming these compounds name the element further to the left (in the periodic table) first, then the one on the right.2
10Naming Covalent Compounds You name the first element using the exact element name.Name the second element by writing the root of the element’s name and add the suffix “–ide.”If there is more than one atom of any given element, you add the Greek prefix denoting how many atoms of that element are present. Table lists the Greek prefixes used.If only one atom of the second element is present it gets the prefix “mono”2
11Naming Covalent Compounds Here are some examples of prefix names for binary molecular compounds.PF5 phosphorus pentafluorideSO2 sulfur dioxideSF6 sulfur hexafluorideN2O4 dinitrogen tetroxideCO carbon monoxide2
12Naming AcidsAcids are traditionally defined as compounds that could donate an H+; however, they are acids only in the presence of water. In other words before they enter the liquid they are covalent compounds and they are NOT acids.There are two main types of acids:Binary acids consist of a hydrogen ion and any single anion. For example, HCl is hydrochloric acid.An oxoacid is an acid containing hydrogen, oxygen, and another element. An example is a HNO3, nitric acid. (see Figure 2.23)2
13Naming Acids Binary Acids Oxoacids Start with the prefix “Hydro” which represents the Hydrogen, followed it with the root of the name of the second element and append the ending –oic acid.OxoacidsUse the root of the “E” element if the ion taking part in the acid had an ending in –ate to the root append the ending –ic acid, if it ends on –ite then append the ending –ous acid. If the ion had a prefix use the same prefix.
15Ionic Compounds Formulas Ionic Compounds FormulasHow do we know how many atoms of each ion we need?A simple crossing of the charges can answer that question about 90% of the time.Example: Mg2+ and PO43-Mg3(PO4)2Check the charges… 3 x (+2) = +62 x (-3) = -6When they combined they cancel to yield a neutral compound.
16Ionic Compounds Formulas Ionic Compounds FormulasThe crossing technique does not work if the magnitude of the charges is the sameExample: Mg2+ and CO32-Mg2(CO3)2This is incorrect since we want the lowest ratio possible which is 1:1 to yield MgCO3
17Ionic Compounds Properties Ionic compounds have properties completely different from their component elements.Example: Table Salt (NaCl)Sodium (Na) in the presence of water reacts violently heating up the water and producing hydrogen if the temperature of the water is high enough the hydrogen can ignite explosively.Chloride (Cl) Green poisonous and corrosive gas. If inhaled will destroy the nasal passages then dissolve in the stomach producing high concentration of hydrochloric acid which will destroy the stomach lining producing ulcers.Salt (NaCl) posses none of the properties mentioned above.
18Ionic Structure Ions form a 3-D lattice. The coulombic (electrostatic) attraction is so high that in order to separate one ion from the lattice requires a lot of energy (DHlatt).The lattice energy depends on charge and size of the ions.
19Lattice EnergySince the lattice energy is an electrostatic interaction the more separated the charges are the weaker the interaction is.Bigger ions have lower lattice energiesThe higher the charge of the ions the stronger they will attract ions of the opposite charge.When size and charge point to opposite trends the charge will outweigh the size.From smallest atom to biggest atom there is only 1.7x factor. From a +1 to +2 that is already a 2x factor.
20Properties of Ionic Substances Dues to the charged interaction a blow to a crystal leads to the possibility of splitting the crystal since we will force like charged particles to interact.Ionic compounds have high melting/boiling points since in order to move the ions from their respective spots it will require breaking the lattice.
21Ionic SolutionsHowever, if we do melt an ionic compound it will be able to conduct current.When ionic compounds are placed in a solvent the produced solution conducts electricity. The higher the number of ions the higher the conductivity.More when we cover chapter 4.
22Naming HydratesA hydrate is a compound that contains water molecules weakly bound in its crystals.Hydrates are named from the anhydrous (dry) compound, followed by the word “hydrate” with a Greek prefix to indicate the number of water molecules per formula unit of the compound.For example, CuSO4. 5H2O is known as copper(II)sulfate pentahydrate. (see Figure 2.24)2
23Determining Chemical Formulas Determining both empirical and molecular formulas of a compound from the percent composition.The percent composition of a compound leads directly to its empirical formula.An empirical formula (or simplest formula) for a compound is the formula of the substance written with the smallest integer (whole number) subscripts.2
24Determining Chemical Formulas The percent composition of a compound is the mass percentage of each element in the compound.We define the mass percentage of “A” as the parts of “A” per hundred parts of the total, by mass. That is,2
25Mass Percentages from Formulas Let’s calculate the percent composition of butane, C4H10.First, we need the molecular mass of C4H10.Now, we can calculate the percents.2
26Determining Chemical Formulas Determining the empirical formula from the percent composition.Benzoic acid is a white, crystalline powder used as a food preservative. The compound contains 68.8% C, 5.0% H, and 26.2% O by mass. What is its empirical formula?In other words, give the smallest whole-number ratio of the subscripts in the formulaCx HyOz2
27Determining Chemical Formulas Determining the empirical formula from the percent composition.For the purposes of this calculation and making calculations simpler, we will assume we have grams of sample benzoic acid.Then the percentage of each element equals the mass of each element in the sample.Since x, y, and z in our formula represent mole-mole ratios, we must first convert these masses to moles.2
28Determining Chemical Formulas Determining the empirical formula from the percent composition.Our grams of benzoic acid would contain:This isn’t quite a whole number ratio, but if we divide each number by the smallest of the three, a better ratio might emerge.2
29Determining Chemical Formulas Determining the empirical formula from the percent composition.Our grams of benzoic acid would contain:now it’s not too difficult to see that the smallest whole number ratio is 7:6:2. The empirical formula is C7H6O2 .2
30Determining Chemical Formulas Determining the “true” molecular formula from the empirical formula.An empirical formula gives only the smallest whole-number ratio of atoms in a formula.The “true” molecular formula could be a multiple of the empirical formula (since both would have the same percent composition).To determine the “true” molecular formula, we must know the “true” molecular weight of the compound.2
31Determining Chemical Formulas Determining the “true” molecular formula from the empirical formula.For example, suppose the empirical formula of a compound is CH2O and its “true” molecular weight is 60.0 g/mol.The molar weight of the empirical formula (the “empirical weight”) is only 30.0 g/mol.This would imply that the “true” molecular formula is actually the empirical formula doubled 2(CH2O) orC2H4O22
32Molecular and structural formulas and molecular models. Return to Lecture
33A model of a portion of a Sodium Chloride crystal. Return to Lecture
34Common Ions of the transition metals Return to Lecture
35List of Polyatomic Ions List of Polyatomic IonsReturn to Lecture
36Greek Prefixes for Covalent Compounds Nomenclature Return to Lecture