2.4 Chemical Formulas
3 min read•june 24, 2024
Chemical formulas are the language of chemistry, allowing us to represent molecules and compounds concisely. They use element symbols and subscripts to show the types and numbers of atoms in a substance, helping us understand its composition and structure.
Different types of formulas serve various purposes. Molecular formulas show exact atom counts, empirical formulas give simplest ratios, and structural formulas depict atom arrangements. These tools help chemists communicate and analyze chemical properties and reactions.
Chemical Formulas
Chemical formula notation
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- Use the periodic table to determine the symbol for each element in the molecule or compound
- Symbols consist of one or two letters (C for carbon, Na for sodium)
- First letter is always capitalized, second letter is lowercase (Co for cobalt, Cl for chlorine)
- Indicate the number of each type of atom present using subscripts after the element symbol
- If only one atom of an element is present, no subscript is needed (HCl for hydrogen chloride)
- For multiple atoms, write the number as a subscript ( for water, for ammonia)
- Arrange the symbols and subscripts in the order that the elements appear in the name
- For binary compounds, write the less electronegative element first ( for sodium chloride)
- For acids, write hydrogen first, followed by the anion ( for sulfuric acid)
- Examples:
- Methane:
- Iron (III) oxide:
- Phosphoric acid:
Types of chemical formulas
- Molecular formulas represent the exact number and type of atoms in a molecule
- Show the actual composition of a compound ( for ethanol)
- Useful for determining the and performing stoichiometric calculations
- Empirical formulas show the simplest whole-number ratio of atoms in a compound
- Can be derived from the by reducing subscripts to their lowest terms
- Example: The of ethanol () is
- Structural formulas depict the arrangement of atoms and bonds in a molecule
- Represent the connectivity of atoms within a molecule
- Can be displayed as or
- Lewis structures use dots for and lines for bonds ( for water)
- Skeletal formulas omit carbon and hydrogen atoms, showing only the backbone ( for ethanol)
Structure and properties of isomers
- are compounds with the same but different arrangements of atoms
- Contain the same number and type of atoms, but differ in connectivity or spatial arrangement
- have the same molecular formula but different bonding patterns
- Atoms are connected in a different order
- Example: Pentane () has three
- n-pentane:
- Isopentane:
- Neopentane:
- have the same molecular formula and bonding pattern but different spatial arrangements
- Atoms are connected in the same order but oriented differently in space
- Example: Lactic acid () has two stereoisomers
- L-lactic acid: Hydroxyl group points to the left when drawn in a specific orientation
- D-lactic acid: Hydroxyl group points to the right in the same orientation
- can exhibit different physical and chemical properties due to their structural differences
- Melting points, boiling points, and solubilities may vary between isomers
- n-pentane (boiling point: 36.1 °C) vs. isopentane (boiling point: 27.8 °C)
- Reactivity and biological activity can also differ, as the arrangement of atoms affects molecular interactions
- L-lactic acid is produced during anaerobic respiration in muscles, while D-lactic acid is less common in nature
- Melting points, boiling points, and solubilities may vary between isomers
Chemical Bonding and Electron Configuration
- involve the sharing of electrons between atoms
- Formed when atoms share to achieve a stable electron configuration
- result from the transfer of electrons between atoms
- Typically occur between metals and non-metals with large differences in electronegativity
- Valence electrons are the outermost electrons of an atom, which participate in chemical bonding
- The number of valence electrons determines an atom's bonding behavior and reactivity
- represent the degree of oxidation of an atom in a compound
- Indicate the hypothetical charge an atom would have if all bonds were ionic
- are charged species composed of two or more covalently bonded atoms
- Examples include ammonium () and carbonate ()
Key Terms to Review (28)
Chemical Formula: A chemical formula is a concise representation of the chemical composition of a substance, using chemical symbols to indicate the types of atoms present and numerical subscripts to show the relative number of atoms of each element.
Coordination isomers: Coordination isomers are a type of structural isomerism in coordination compounds where the composition of the complex ions varies but the overall formula remains the same. These arise when ligands and counterions exchange places between coordination spheres.
Covalent bonds: A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons to achieve a stable electron configuration. These bonds typically form between non-metal atoms with similar electronegativities.
Covalent Bonds: Covalent bonds are chemical bonds formed by the sharing of electrons between two atoms. These bonds are characterized by the stable arrangement of shared electron pairs, which helps to satisfy the valence electron requirements of the participating atoms.
Empirical formula: An empirical formula represents the simplest whole-number ratio of elements in a compound. It does not show the actual number of atoms, but rather the relative proportions.
Empirical Formula: The empirical formula represents the simplest whole-number ratio of atoms of each element present in a compound. It provides the most basic representation of the composition of a compound without specifying the actual number of atoms present.
Ionic bonds: Ionic bonds are a type of chemical bond formed through the electrostatic attraction between oppositely charged ions. Typically, these bonds form when a metal donates one or more electrons to a non-metal.
Ionic Bonds: Ionic bonds are a type of chemical bond that forms between a metal and a nonmetal through the transfer of electrons. This electrostatic attraction between oppositely charged ions is a fundamental concept in understanding the structure and properties of ionic compounds.
Isomers: Isomers are molecules with the same molecular formula but different structural arrangements. They can have different physical and chemical properties despite having the same number of each type of atom.
Isomers: Isomers are chemical compounds that have the same molecular formula, meaning they are composed of the same types and numbers of atoms, but have different arrangements or structures. This concept is crucial in understanding the properties and behavior of organic compounds, particularly in the context of chemical formulas and hydrocarbon structures.
Lewis Structures: Lewis structures, also known as Lewis dot diagrams, are a visual representation of the bonding between atoms in a molecule. They depict the arrangement of atoms and the sharing or transfer of valence electrons, providing insights into the structure and properties of chemical compounds.
Molar mass: Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the molecular formula.
Molar Mass: Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is a fundamental concept in chemistry that relates the mass of a substance to the number of particles (atoms, molecules, or ions) it contains, and is essential for understanding chemical formulas, stoichiometry, and the behavior of gases.
Molecular formula: A molecular formula indicates the types and numbers of atoms in a molecule of a substance. It shows the actual number of each type of atom present in a single molecule.
Molecular Formula: The molecular formula is a concise representation of the elemental composition and relative abundance of atoms within a chemical compound. It provides the specific number and type of atoms that make up a molecule, conveying the true chemical identity of the substance.
Molecular mass: Molecular mass is the sum of the atomic masses of all atoms in a molecule, typically expressed in atomic mass units (amu). It represents the total mass of a single molecule of a substance.
Oxidation States: Oxidation states are the measure of the degree of oxidation of an atom in a chemical compound. They represent the number of electrons an atom has lost or gained compared to a neutral atom, and are used to describe the chemical bonding in compounds.
Polyatomic Ions: Polyatomic ions are charged chemical species composed of two or more covalently bonded atoms. They exhibit a net positive or negative charge and play a crucial role in the formation of ionic compounds.
Skeletal Formulas: Skeletal formulas, also known as line-angle formulas, are a simplified way of representing organic molecules by focusing on the carbon skeleton and omitting hydrogen atoms. This representation highlights the connectivity and arrangement of atoms within a molecule, making it easier to visualize and understand the structure of organic compounds.
Spatial isomers: Spatial isomers are molecules with the same molecular formula and connectivity of atoms but differ in the three-dimensional arrangement of those atoms. They include both enantiomers and diastereomers.
Stereoisomers: Stereoisomers are a type of isomer where molecules have the same molecular formula and connectivity, but differ in the three-dimensional arrangement of their atoms in space. This spatial arrangement affects the chemical and physical properties of the molecules.
Stoichiometry: Stoichiometry is the calculation of reactants and products in chemical reactions using balanced chemical equations. It involves the use of molar ratios derived from these equations to predict quantities of substances consumed and produced.
Structural formula: A structural formula is a representation of the molecular structure that shows the arrangement of atoms and the bonds between them. It provides more detailed information than a chemical formula, illustrating how atoms are connected within the molecule.
Structural Formula: A structural formula is a graphical representation of the molecular structure of a chemical compound. It shows how the atoms in a molecule are arranged and connected to each other by chemical bonds.
Structural isomers: Structural isomers are compounds with the same molecular formula but different structural arrangements of atoms. These differences can result in distinct physical and chemical properties.
Structural Isomers: Structural isomers are compounds that have the same molecular formula but different arrangements of atoms in space, resulting in distinct chemical and physical properties. This concept is particularly important in the context of chemical formulas and hydrocarbon compounds.
Valence electrons: Valence electrons are the outermost electrons of an atom and are involved in forming chemical bonds. They determine an element's chemical properties and reactivity.
Valence Electrons: Valence electrons are the outermost electrons in an atom that participate in chemical reactions and bonding. They are the electrons in the highest occupied energy level of an atom and are responsible for an element's chemical properties and behavior.