3: Molecules, Compounds and Chemical Equations
- Page ID
- 369181
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- 3.1: Hydrogen, Oxygen, and Water
- Qualitative description of substances (such as water), the types of bonds present in the substances, and quantitative aspects of the composition of substances are the subject of this chapter.
- 3.2: Representing Compounds- Chemical Formulas and Molecular Models
- A chemical formula is a format used to express the structure of atoms. The formula tells which elements and how many of each element are present in a compound. Formulas are written using the elemental symbol of each atom and a subscript to denote the number of elements. The most common elements present in organic compounds are carbon, hydrogen, oxygen, and nitrogen. With carbon and hydrogen present, other elements, such as phosphorous, sulfur, silicon, and the halogens, may exist in organic co
- 3.3: Lewis (Dot) Representation
- Lewis diagrams are graphical representations of elements and their valence electrons.
- 3.4: A Molecular View of Elements and Compounds
- Most elements exist with individual atoms as their basic unit. It is assumed that there is only one atom in a formula if there is no numerical subscript on the right side of an element’s symbol. There are many substances that exist as two or more atoms connected together so strongly that they behave as a single particle. These multi-atom combinations are called molecules. A molecule is the smallest part of a substance that has the physical and chemical properties of that substance.
- 3.5: Formation of Ions and Ionic Compounds
- Metals (particularly those in groups 1 and 2) tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. By this means, a positively charged ion is formed. Similarly, nonmetals (especially those in groups 16 and 17, and, to a lesser extent, those in Group 15) can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table.
- 3.6: Ionic Compounds- Formulas and Names
- Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to –ide. For example, K2O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge.
- 3.7: Summary of Inorganic Nomenclature
- Chemical nomenclature is the names we use for chemicals. For instance, H2O is called "water", and CH4 (the gas you burn in a stove) is called "methane." You should learn the chemical nomenclature here on this page now, so that you will be able to understand when it is used.
- 3.8: Molecular Compounds- Formulas and Names
- Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF6, sulfur hexafluoride, and N2O4, dinitrogen tetroxide. Acids are an important class of compounds containing hydrogen and having special nomenclature rules. Binary acids are named using the prefix hydro-, changing the –ide suffix to –ic, and adding “acid;” HCl is hydrochloric acid.
- 3.9: Formula Mass and the Molar Mass
- The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass. A convenient amount unit for expressing very large numbers of atoms or molecules is the mole. Experimental measurements have determined the number of entities composing 1 mole of substance to be \(6.022 \times 10^{23}\), a quantity called Avogadro’s number.
- 3.10: Composition of Compounds
- Molecular formulas tell you how many atoms of each element are in a compound, and empirical formulas tell you the simplest or most reduced ratio of elements in a compound. If a compound's molecular formula cannot be reduced any more, then the empirical formula is the same as the molecular formula. Combustion analysis can determine the empirical formula of a compound, but cannot determine the molecular formula (other techniques can though).
- 3.11: Determining a Chemical Formula from Experimental Data
- In this section, we will explore how to derive the chemical formulas of unknown substances from experimental mass measurements.
- 3.12: Organic Compounds
- Organic chemistry is the study of carbon compounds, nearly all of which also contain hydrogen atoms.