Introduction to General Chemistry I Alberto L. Vivoni Alonso Inter Americana University of Puerto Rico Bayamn Campus All about Matter: Classifications and Properties Matter has mass and occupies space (e.g., it has volume). Matter consists of atoms and molecules in motion. Matter Classifications Physical Change of Matter Chemical change or chemical reaction: Chemical change or chemical reaction: Making a NEW compound Making a NEW compound The transformation of one or more atoms or molecules into one or more different molecules Chemical Changes and Properties of Matter Atomic Structure: Composition Isotopes are elements whose atoms differ in mass only. mass numbers. Isotopes are identified by their mass numbers. Protons + neutrons = mass number Isotopic symbol 13 Al Atomic number, Z Atom symbol Atomic weight Isotopes Problem: How many protons, electrons, and neutrons are in the following atoms: protonselectronsneutrons 32 S Cu 29 U-240 Isotopes & Atomic Mass (Weight) Problem: How many protons, electrons, and neutrons are in the following atoms: protonselectronsneutrons 32 S Cu U NOTE: Neutral atoms will have the same number of protons as electrons. Isotopes & Atomic Mass (Weight) Complete the following table: ProtonsNeutronsElectrons Atomic Number Mass Number Atomic Symbol Isotopes & Atomic Mass (Weight) Complete the following table: Answers ProtonsNeutronsElectrons Atomic Number Mass Number Atomic Symbol Isotopes & Atomic Mass (Weight) Example problem: Boron has two isotopes: Boron is 19.9% 10 B and 80.1% 11 B. Boron atomic weight: = (10.0 amu) (11.0 amu) = 10.8 amu Isotopes & Atomic Mass (Weight) Cations A CATION forms when an atom loses one or more electrons from its outer (valence) shell (energy level). more Cations are positively charged because the atom has more protons (+) than electrons (-). Mg atom has 12 protons & 12 electrons. Mg 2+ ion has 12 protons & 10 electrons. Metal elements tend to form cations. Example: Mg Mg e - Anions An ANION forms when an atom gains one or more electrons into its outer (valence) shell (energy level). fewer Anions are negatively charged because the atom has fewer protons (+) than electrons (-). F atom has 9 protons & 9 electrons. F - ion has 9 protons & 10 electrons. Nonmetal elements tend to form anions. Example:F + e - F - Ions: Charged Atoms = Alkali Metals = Alkali Earth Metals = Noble Gases = Halogens = Transition Metals = Lanthanides = Actinides Periodic Table: Families 18 Barium, Ba Iron (III) chloride, FeCl 3 Bromine, Br 2 Ethanol, C 2 H 6 O Nitrogen monoxide, NO Cobalt, Co How are the following classified? 19 Barium, Ba Iron (III) chloride, FeCl 3 Bromine, Br 2 Ethanol, C 2 H 6 O Nitrogen monoxide, NO Cobalt, Co atomic element ionic compound molecular element molecular compound atomic element How are the following classified? 20 Covalent bond formation Formation of an Ionic Compound 1. Write the symbol for the metal cation and its charge followed by the symbol for the nonmetal anion and its charge. Obtain charges from the elements group number in the periodic table (refer to Figure 2.14). 2. Adjust the subscript on each cation and anion to balance the overall charge. 3. Check that the sum of the charges of the cations equals the sum of the charges of the anions. Example 3.3 Writing Formulas for Ionic Compounds Write the formula for the ionic compound that forms between aluminum and oxygen. SOLUTION Al 3+ O 2 Al 2 O 3 cations: 2(3+) = 6+ anions: 3(2) = 6 The charges cancel. Write the formula for the compound formed between potassium and sulfur. For More Practice 3.3 1. Write the symbol for the metal cation and its charge followed by the symbol for the nonmetal anion and its charge. Obtain charges from the elements group number in the periodic table (refer to Figure 2.14). 2. Adjust the subscript on each cation and anion to balance the overall charge. 3. Check that the sum of the charges of the cations equals the sum of the charges of the anions. Example 3.4 Writing Formulas for Ionic Compounds Write the formula for the ionic compound that forms between calcium and oxygen. SOLUTION Ca 2+ O 2 CaO cations: 2 + anions: 2 The charges cancel. Write the formula for the compound formed between aluminum and nitrogen. For More Practice 2.4