UNIT 2: Chemical Reactions

Chapter 3: Chemical Names, Formulas, and Equations Chapter 4: Classifying Compounds and Chemical Reactions UNIT 2: Chemical Reactions

UNIT 2 Chapter 3: Chemical Names, Formulas, and Equations Chapter 3: Chemical Names, Formulas, and Equations Chemical reactions are used in a variety of sometimes surprising places. This photographer is using a breathing apparatus that uses a chemical reaction to recycle the air. Why is the photographer using this type of breathing apparatus? TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations 3.1 Ionic and Molecular Compounds • Many of the chemical compounds in products that people use at home, school, and work have properties that make them both beneficial and potentially dangerous. • Chlorine compounds are both useful and hazardous. • How is chlorine useful inswimming pools? TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations Chemical Compounds • Identify the molecular compounds and the ionic compounds in the objects below. TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations Chemical Compounds • Compounds are made of elements that are chemically combined in specific proportions. • Two classifications that chemists use to categorize compounds are molecular compounds and ionic compounds. Water is composed of molecules. Water molecules consist of two hydrogen atoms bonded to one oxygen atom. TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations Molecular Compounds • A molecule is a particle formed by two or more atoms joined by covalent bonds. • A molecular compound is a compound formed of atoms of two or more elements that share electrons. • The particles in a molecule are held together by covalent bonds. • What properties do molecularcompounds usually have? • What role do electrons havein covalent bonds? TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations Ionic Compounds • An ion is an atom or group of atoms with a positive or negative charge. • An ionic compound is a compound composed of oppositely charged ions held together with strong ionic bonds. • What properties do ionic compounds usually have? • What role do electrons havein ionic bonds? A crystal of sodium chloride is structured so that six chloride ions surround every sodium ion, and six sodium ions surround every chloride ion. TO PREVIOUS SLIDE

UNIT 2 Section 3.1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.1 Review • Some chemical compounds in household products have properties that are both useful and dangerous. • Compounds can be classified as ionic or molecular. Ionic compounds and molecular compounds have characteristic properties that are a result of their structure at the atomic level. TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations 3.2 Names and Formulas of Ionic and Molecular Compounds • Names of Binary Ionic Compounds • A binary ionic compound is a compound composed of ions of one metal element and ions of one non-metal element joined by ionic bonds. • The name of a binary ionic compound comes from the names of its elements. • How is a binary ionic compound named? magnesium sulfide aluminum fluoride sodium chloride TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Interpreting the Chemical Formula of an Ionic Compound • The chemical formula of a binary ionic compound contains element symbols to identify each ion. • The positively charged ion is named first, and the negatively charged ion is named second. • Subscripts are used to indicate the ratio of each type of ion in the compound. • What does each symbol in the formula mean? TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Writing Formulas of Ionic Compounds • Although an ionic compound is made up of ions, the compound itself is electrically neutral. • The periodic table can be used to determine the charges of some ions. What charges do ions in Group 1, Group 2, and Groups 3−7 have? TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Multivalent Metals • Some metals are multivalent metals, which means that they can have more than one charge. • When naming a compound that contains a multivalent ion, you must include a Roman numeral to show which charge the ion has. • How can you use the periodic table to determine if an ion is a multivalent metal? TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Ionic Compounds Containing Polyatomic Ions • Compounds containing polyatomic ions are not binary compounds because they contain at least three elements. • Compounds containing polyatomic ions are named by writing the name of the positive ion followed by the name of the negative ion. CaCO3 O22- NH4+ CO3- Calcium carbonate is an ionic compound, but it is not a binary ionic compound. NO3- Polyatomic ions are made up of more than one atom. The polyatomic ions above are ammonium, nitrate, peroxide, and carbonate. TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Ionic Compounds Containing Polyatomic Ions • Which polyatomic ion is found in seashells? TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Names and Formulas of Binary Molecular Compounds • A binary molecular compound is a compound composed of atoms of two different elements, usually two non-metals, that are joined together with covalent bonds. • What is the name of a binary molecular compound that contains one sulfur atom and six fluorine atoms? TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations IUPAC and Systematic Names • The international system for naming chemicals is maintained by the International Union of Pure and Applied Chemistry (IUPAC). • IUPAC has developed a systematic method for naming chemicals according to their composition. • Why is an international system for naming chemicals important? These calcium sulfate crystals are found in Mexico. Thanks to IUPAC, scientists around the world can share information about them. TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Key Naming Rules: A Summary TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Exceptions to the Rules • Compounds that contain hydrogen are exceptions to the general naming rules. Hydrogen is a non-metal, and hydrogen chloride (HCl) is molecular compound. Binary hydrogen compounds are named as though they are ionic compounds. • Compounds that contain hydrogen and carbon are also named differently. If hydrogen chloride was named according to the naming rules for molecular compounds, it would be called hydrogen monochloride. HCl TO PREVIOUS SLIDE

UNIT 2 Section 3.2 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2 Review • Chemical compounds are named according to whether they are ionic or molecular. • The formula of an ionic compound represents the ratio of the positive and negative ions in the electrically neutral compound. • The formula of a molecular compound represents the number of atoms of each element in a molecule of the compound. • Chemical names and formulas are standardized by bodies such as the International Union of Pure and Applied Chemistry (IUPAC). TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations 3.3 Chemical Equations and the Law of Conservation of Mass • A chemical reaction occurs when one or more substances (elements or compounds) change to form one or more different substances (elements or compounds). • The substances that undergo a chemical reaction are called the reactants. • The substances formed in a chemical reaction are called products. • What are some examples of chemical reactions that take place around you? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Word Equations • A chemical reaction can be expressed in a word equation. • The reactants are on the left side of the arrow, and the products are on the right side of the arrow. • When do you use a plus sign in a word equation? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations The Conservation of Mass in Chemical Reactions • Antoine Lavoisier experimentally demonstrated the Law of Conservation of Mass, which means that, in a chemical reaction, the total mass of the products is always the same as the total mass of the reactants. • In his atomic theory, John Dalton stated that each atom present in the reactants is also present in the products. Since atoms are neither created nor destroyed, the mass does not change. • How did Antoine and Marie-Anne Lavoisier work together as a team? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Chemical Equations and the Law of Conservation of Mass • A chemical equation is a representation of a chemical reaction that uses chemical formulas and symbols. • A skeleton equation is incomplete. A balanced chemical equation is complete because it takes the law of conservation of mass into consideration. • A coefficient is a number placed in front of a chemical formula in a balanced equation to show how many atoms, molecules, or ions are involved in a reaction. Coefficients are used to balance a chemical equation. What do the abbreviations (s), (g), (ℓ), and (aq) represent? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Balancing Chemical Equations • When balancing chemical equations, write the skeleton equation and then use coefficients to balance the numbers of each kind of atom on each side of the yield arrow. The skeleton chemical equation above becomes the balanced chemical equation below. When do you change the subscripts to balance a chemical equation? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Tips for Writing and Balancing Chemical Equations • A systematic approach should be used to write and balance chemical equations. • Can you suggest five tips for writing and balancing chemical equations? TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Tips for Writing and Balancing Chemical Equations • Balance equations by adjusting coefficients, never by changing chemical formulas. • Balance metals first. • Add coefficients to any elements last. • Balance hydrogen and oxygen last. They often appear in more than one reactant or more than one product, so it is easier to balance them after the other elements are balanced. • If a polyatomic ion appears in both a reactant and a product, treat it as a single unit. Continued… TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Tips for Writing and Balancing Chemical Equations • Once you think the chemical equation is balanced, do a final check by counting the atoms of each element one more time. • If you go back and forth between two substances, using higher and higher coefficients, double-check each chemical formula. An error in a chemical formula might be preventing you from balancing the chemical equation. • The following elements exist as diatomic molecules: hydrogen, H2(g); nitrogen, N2(g); oxygen, O2(g); fluorine, F2(g); chlorine, Cl2(g); bromine, Br2 (ℓ); and iodine, I2(s). Always write them as shown here in a chemical equation. A diatomic molecule contains two atoms of the same element. TO PREVIOUS SLIDE

UNIT 2 Section 3.3 Chapter 3: Chemical Names, Formulas, and Equations Section 3.3 Review • In a chemical reaction, a reactant or reactants undergo a chemical change, forming a different substance or substances called products. Reactants and products may be elements or chemical compounds. • According to the law of conservation of mass, the overall mass of the reactants is always equal to the overall mass of the products in a chemical reaction. • Chemists use descriptions, word equations, and balanced chemical equations to represent chemical reactions. • In a balanced chemical equation, there is always the same number of atoms of each element on each side of the equation, in accordance with the law of conservation of mass. TO PREVIOUS SLIDE

UNIT 2: Chemical Reactions