5: Molecules and Compounds
- Page ID
- 47419
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)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. In some respects, a molecule is similar to an atom. A molecule, however, is composed of more than one atom.
- 5.1: Sugar and Salt
- This page discusses sodium chloride (NaCl), an ionic compound formed from sodium and chlorine. It highlights salt's essential role in providing ions for fluid balance and nerve function. The page also contrasts salt with sugar, noting their differing chemical compositions and properties, emphasizing the importance of recognizing how compounds differ from their constituent elements in the context of chemical reactions.
- 5.2: Compounds Display Constant Composition
- This page explains that a compound is a pure substance made of two or more elements chemically combined in a fixed ratio, unlike mixtures. Compounds cannot be separated by physical means but require chemical processes for decomposition. An example is table salt, which cannot be physically divided into sodium and chlorine. Compounds tend to have properties distinct from the elements that make them up, as demonstrated by the benign nature of salt compared to its individual components.
- 5.3: Chemical Formulas - How to Represent Compounds
- This page explains the definitions and differences between chemical, molecular, and empirical formulas. A chemical formula shows the elements and their ratios in a compound (e.g., \(\ce{H_2O}\) for water). Molecular formulas provide the actual number of atoms in a molecule, while empirical formulas reflect the simplest ratios of elements, illustrated with glucose's molecular and empirical formulas (\(\ce{C_6H_{12}O_6}\) and \(\ce{CH_2O}\), respectively).
- 5.4: A Molecular View of Elements and Compounds
- This page outlines the classification of substances into four categories: atomic elements (individual atoms), molecular elements (two or more bonded atoms), ionic compounds (metal and non-metal bond), and molecular compounds (non-metals only). It provides definitions, examples, and exercises to enhance understanding of these classifications.
- 5.5: Writing Formulas for Ionic Compounds
- This page covers the formulation and identification of ionic compounds, detailing their crystal lattice structure and the derivation of empirical formulas through charge balancing of cations and anions. It introduces the crisscross method for formula writing and the role of polyatomic ions. Specific examples like potassium sulfate and magnesium carbonate illustrate the concepts.
- 5.6: Nomenclature- Naming Compounds
- This page discusses the importance of nomenclature in chemistry, emphasizing the need for systematic naming of compounds to prevent ambiguity and enhance communication. It highlights the goal of clarity and uniqueness in names, alongside the reflection of a compound's structure or chemistry. While common names may be acceptable in certain contexts, the ideal chemical name should communicate the chemical formula and, if necessary, the three-dimensional arrangement of atoms.
- 5.7: Naming Ionic Compounds
- This page covers the naming rules for ionic compounds, detailing the nomenclature of monatomic cations and anions. Cations are named with "ion" added, while anions use the element stem plus "-ide." The Stock system employs Roman numerals for cations with variable charges, and traditional Latin names are also utilized. It emphasizes balancing positive and negative charges, lists examples, and introduces polyatomic ions.
- 5.8: Naming Molecular Compounds
- This page discusses molecular compounds, which are formed by nonmetal atoms sharing electrons, contrasting them with ionic compounds based on electrostatic attraction. It explains the naming convention for binary molecular compounds using prefixes and the -ide suffix, citing examples like water and ammonia.
- 5.9: Naming Acids
- This page discusses the spot test for gold in the context of the California gold rush, explaining both the definition and properties of acids. It details how acids release hydrogen ions in water and categorizes them into binary acids and oxyacids, providing naming conventions based on anion types along with examples. The page also addresses how to write formulas for acids, focusing on maintaining charge neutrality.
- 5.10: Nomenclature Summary
- Brief overview of chemical nomenclature.
- 5.11: Formula Mass - The Mass of a Molecule or Formula Unit
- This page covers how to calculate the formula mass of ionic and molecular compounds by summing the atomic masses from the periodic table. It includes examples like sodium chloride, calcium fluoride, and potassium nitrate, stressing accurate counting of atoms. The concept of hydrates is also introduced, along with their formulas and applications in health and other fields. Mastery of these calculations is deemed essential for success in future chemistry studies.