Chapter 3: Ionic Compounds, Formulas, and Reactions

Chemical Formulas

• Chemical formulas are shorthand for compounds that use the atomic symbol and subscripts to signify how many are in it
• Parentheses clarify how many compounds exist within that large compound
  • Al(NO3)3
• Hydrates are compounds that contain water molecules within their crystal structure.
  • Hydrates are formed when water molecules become trapped within the crystal structure of a compound.
  • The water molecules in a hydrate are held in place by hydrogen bonds with the compound's ions or molecules.
  • Hydrates are often named by adding a prefix to the compound's name that indicates the number of water molecules present (e.g. copper(II) sulfate pentahydrate).
  • Hydrates can be identified by their physical properties, such as their melting and boiling points, which are often different from the anhydrous (water-free) form of the compound.
  • Hydrates can be formed or decomposed by heating or cooling the compound, which can cause the water molecules to be released or absorbed.
• The simplest formula is the emprical formula
• the actual formula is the molecular formula
• structural formula is the order the elements are in

Chemical Reactions and Equations

• reactants are converted into products in chemical reactions
  • REACTANTS → PRODUCTS
  • Zn + H2SO4 → H2 + ZNSO4

Balancing a Chemical Equation

• a reaction must be balanced by having the same number of elements on both sides of the reaction. Reactions can be balanced by changing the coefficients

• To balance a chemical equation, follow these steps:

1. Write the unbalanced equation using the correct chemical formulas for each reactant and product.
2. Count the number of atoms of each element on both sides of the equation.
3. Determine which elements are not balanced.
4. Add coefficients to the reactants and/or products to balance the number of atoms of each element.
5. Check that the equation is balanced by counting the number of atoms of each element on both sides of the equation.
6. If the equation is not balanced, adjust the coefficients and repeat steps 4 and 5 until the equation is balanced.

• For example, the unbalanced equation for the reaction between hydrogen gas and oxygen gas to form water is:
  • H2 + O2 → H2O
  • To balance this equation, we can add a coefficient of 2 in front of the H2O:
  • H2 + O2 → 2H2O
  • Now the equation is balanced, with 2 hydrogen atoms and 2 oxygen atoms on both sides of the equation.

Simplest Coefficients

• Reaction should be in the simplest coefficients
• For 4 H2 + 2 O2 → 4 H2O, the whole reaction should be divided by two to get 2 H2 + O2 → 2 H2O

Reaction Types

Combustion Reaction

• Combustion reactions are exothermic chemical reactions that involve the reaction of a fuel with an oxidant to produce heat and light.
• The fuel is typically a hydrocarbon, such as methane, propane, or gasoline, while the oxidant is usually oxygen from the air.
• The reaction produces carbon dioxide and water vapor as the primary products, along with other combustion byproducts such as carbon monoxide, nitrogen oxides, and sulfur dioxide.

Single-Replacement

• Single-replacement reactions are a type of chemical reaction.
• In these reactions, one element replaces another element in a compound.
• The general equation for a single-replacement reaction is: A + BC → B + AC.
  • A represents the element that is replacing another element in the compound BC.
  • B represents the element that was originally in the compound BC and is now replacing A in the compound AC.

Double-Replacement

• Double-replacement reactions are a type of chemical reaction where two compounds exchange ions to form two new compounds.
• The general form of a double-replacement reaction is AB + CD → AD + CB, where A, B, C, and D are elements or groups of elements.
• Examples of double-replacement reactions include the reaction between silver nitrate and sodium chloride to form silver chloride and sodium nitrate, and the reaction between hydrochloric acid and sodium hydroxide to form sodium chloride and water.

Neutralization Reactions

• Neutralization reactions occur when an acid and a base react to form a salt and water.
• The reaction involves the transfer of H+ ions from the acid to the OH- ions from the base.
• The resulting salt is usually a compound made up of a metal and a non-metal.
• The pH of the solution is neutralized, meaning it becomes closer to 7 on the pH scale.

Formation Reaction

• Formation reactions describe the process of forming a compound from its constituent elements. The structure of these reactions typically involves the combination of reactants, sometimes in fractions, to produce a single product.

Addition Reactions

• a simple molecule is added to an element or another molecule
• H2 + Cl2 → 2HCl.

Decomposition Reaction

• Decomposition reactions are chemical reactions that involve the breakdown of a single compound into two or more simpler substances.

• 2H2O2 -> 2H2O + O2

Net Ionic Equations

• Net ionic equations show only the species involved in a chemical reaction.

• AgNO3 + NaCl → AgCl + NaNO3

• The net ionic equation for the reaction between silver nitrate and sodium chloride is: Ag+ + Cl- → AgCl

Half-Reaction Equations

• Half-reaction equations represent the oxidation or reduction of a species in a chemical reaction.
• They are written as either an oxidation half-reaction or a reduction half-reaction.
• The oxidation half-reaction shows the loss of electrons by a species, while the reduction half-reaction shows the gain of electrons by a species.
• Both half-reactions must be balanced in terms of mass and charge before they can be combined to form the overall balanced equation for the reaction.
• Half-reaction equations are useful in determining the oxidation state of a species and in balancing redox reactions.

Oxidation-Reduction Reactions

• Oxidation-reduction reactions involve electron transfer between two species.
• The species that loses electrons is oxidized, while the species that gains electrons is reduced.
• These reactions can be broken down into two half-reactions: oxidation and reduction.
• In the oxidation half-reaction, the species that is oxidized loses electrons and becomes more positive.
• In the reduction half-reaction, the species that is reduced gains electrons and becomes more negative.
• The two half-reactions are then combined to form the overall redox reaction.

Bonding

Ionic Substances

• A positively charged cation is attracted to a negatively charged anion.

Polyatomic Ions

• Polyatomic ions are ions composed of two or more atoms that are covalently bonded and carry a net electric charge. They are often found in ionic compounds and can have either a positive or negative charge.
  • Examples of polyatomic ions include ammonium (NH4+), nitrate (NO3-), and sulfate (SO42-).

Ionic Formulas

• The law of electroneutrality states that in any chemical species, the total charge of the electrons is equal to the total charge of the protons. This means that the species is electrically neutral. In other words, the number of positive charges (protons) in an atom or molecule is equal to the number of negative charges (electrons). This law is important in understanding chemical reactions and the behavior of ions in solution.

Naming Ionic Compounds

• Ionic compounds are named by indicating the cation first, followed by the anion.

• The cation is named first and takes its name from the element.

• If the element can form ions with different charges, the charge is indicated using Roman numerals in parentheses.

• The anion is named second and takes its name from the root of the element name with the suffix "-ide" added.

• For example, NaCl is named sodium chloride, and FeCl2 is named iron(II) chloride.

Ionic Reactions

Ions in Solution

• If an ionic compound dissolves in water, it can be written as:
  • NaBr (s) → Na+ (aq) + Br- (aq)
• Symbols in parentheses indicates the state of the substance
  • solid (s)
  • aqueous (aq)
  • liquid (l)
  • gas (g)
• The principles of dissolution of ionic compounds are based on the fact that the ions in the solid are held together by strong electrostatic forces of attraction. When the compound is dissolved in a solvent, the solvent molecules surround the ions and weaken the electrostatic forces of attraction between them. This leads to the separation of the ions and the formation of a solution.

Solubility Rules

• compounds containing sodium or potassium alkali metal cations or ammonium ion are soluble
• compounds containing NO3- are soluble

Double-Replacement Reactions

Predicting Products

• Identify the reactants and their respective cations and anions.

• Switch the anions between the two reactants.

• Write the new compounds formed.

• Balance the equation.

• Write the states of matter for each compound.

Chemical Driving Forces

• The driving forces of a chemical reaction are the factors that determine the direction and extent of the reaction. These include the formation of a more stable product, the release of energy, the increase in entropy, and the removal of a reactant or product from the reaction mixture.

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