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Introduction to General Chemistry I Alberto L. Vivoni Alonso Inter Americana University of Puerto Rico Bayamón 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 Changes and Properties of Matter • Chemical change or chemical reaction: • Making a NEW compound • The transformation of one or more atoms or molecules into one or more different molecules Atomic Structure: Composition Isotopes • Isotopes are elements whose atoms differ in mass only. • Isotopes are identified by their mass numbers. Protons + neutrons = mass number • Isotopic symbol 13 Al 26.981 Atomic number, Z Atom symbol Atomic weight Isotopes & Atomic Mass (Weight) Problem: How many protons, electrons, and neutrons are in the following atoms: protons electrons 32 S 16 65 Cu 29 U-240 neutrons Isotopes & Atomic Mass (Weight) Problem: How many protons, electrons, and neutrons are in the following atoms: protons electrons neutrons 32 S 16 16 16 Cu 29 29 36 U-240 92 92 148 16 65 29 NOTE: Neutral atoms will have the same number of protons as electrons. Isotopes & Atomic Mass (Weight) Complete the following table: Protons Neutrons 6 7 Electrons Atomic Number 42 Mass Number 96 55 133 Atomic Symbol Isotopes & Atomic Mass (Weight) Complete the following table: Answers Protons Neutrons Electrons Atomic Number Mass Number 6 7 6 6 13 42 54 42 42 96 13 14 13 13 27 55 78 55 55 133 Atomic Symbol Isotopes & Atomic Mass (Weight) –Example problem: •Boron has two isotopes: –Boron is 19.9% 10B and 80.1% 11B. •Boron atomic weight: = 0.199 (10.0 amu) + 0.801 (11.0 amu) = 10.8 amu Ions: Charged Atoms Cations Anions • A CATION forms when an atom loses one or more electrons from its outer (valence) shell (energy level). • An ANION forms when an atom gains one or more electrons into its outer (valence) shell (energy level). • Cations are positively charged because the atom has more protons (+) than electrons (-). – Mg atom has 12 protons & 12 electrons. – Mg2+ ion has 12 protons & 10 electrons. • 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. • Metal elements tend to form cations. • Example: • Example: Mg Mg2+ + 2 e- F + e- F- Periodic Table: Families = Alkali Metals = Halogens = Alkali Earth Metals = Transition Metals = Noble Gases = Lanthanides = Actinides How are the following classified? Barium, Ba Iron (III) chloride, FeCl3 Bromine, Br2 Ethanol, C2H6O Nitrogen monoxide, NO Cobalt, Co 18 How are the following classified? Barium, Ba atomic element Iron (III) chloride, FeCl3 ionic compound Bromine, Br2 molecular element Ethanol, C2H6O molecular compound Nitrogen monoxide, NO molecular compound Cobalt, Co atomic element 19 Covalent bond formation 20 Formation of an Ionic Compound Example 3.3 Writing Formulas for Ionic Compounds Write the formula for the ionic compound that forms between aluminum and oxygen. SOLUTION Al3+ 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 element’s 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. O2– Al3+ O2– ↓ Al2O3 cations: 2(3+) = 6+ anions: 3(2–) = 6– The charges cancel. For More Practice 3.3 Write the formula for the compound formed between potassium and sulfur. Example 3.4 Writing Formulas for Ionic Compounds Write the formula for the ionic compound that forms between calcium and oxygen. SOLUTION Ca2+ 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 element’s 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. O2– Ca2+ O2– ↓ CaO cations: 2+ anions: 2– The charges cancel. For More Practice 2.4 Write the formula for the compound formed between aluminum and nitrogen.