Copy of Copy of Lesson 3 - Bonding and the Periodic Table (1)

Vocabulary

  • Compound: A substance formed when two or more elements bond together.

  • Valence Electron: Electrons in the outermost energy level of an atom that participate in chemical bonding.

  • Reactivity: The tendency of a substance to undergo chemical reactions.

  • Malleable: The ability of a substance to be hammered or rolled into sheets.

  • Ductile: The ability of a substance to be stretched into wires.

  • Luster: The way a surface reflects light; shininess.

  • Semiconductors: Materials that conduct electricity under certain conditions but not others.

Objectives

  1. Distinguish between elements and compounds.

  2. Develop and use models to explain the role of valence electrons in the structure and function of atoms.

  3. Compare the properties of metals, nonmetals, and metalloids.

Introduction to Elements and Compounds

  • Element: A substance that cannot be broken down into simpler substances; made up of one type of atom.

    • Chemical symbols: First letter capitalized; second letter lowercase if present (e.g., H for Hydrogen, Na for Sodium).

  • Compound: Formed when atoms from two or more elements bond together (e.g., H2O for water, NaCl for table salt).

Electron Arrangement in Atoms

  • Electrons exist in different energy levels:

    • First energy level: Closest to nucleus; holds up to 2 electrons.

    • Second energy level: Holds up to 8 electrons.

    • Higher energy levels have electrons with more energy.

  • Valence Electrons: Electrons in the outermost energy level; involved in bonding.

Understanding Valence Electrons

  1. Valence electrons are the outermost electrons.

  2. The number of valence electrons varies among elements (1 to 8).

  3. Represented visually with:

    • Electron Energy Levels Diagram and Electron Dot Diagram.

Electron Dot Diagrams

  • Developed by Gilbert Lewis in 1916.

  • Represents valence electrons as dots around the element's symbol:

    1. Start with the element's group number.

    2. Place dots in a manner that places one on each side before pairing.

    3. Paired dots indicate stability; unpaired dots participate in bonding.

The Periodic Table and Valence Electrons

  • Columns (groups) show similar characteristics in valence electron count.

  • Different groups indicate varying reactivity and types of bonding behavior.

Properties of Metals, Nonmetals, and Metalloids

Metals

  • Characteristics:

    • Shiny (luster).

    • Good conductors of heat and electricity.

    • Ductile and malleable (can be formed into wires and sheets).

  • Found on the left and middle of the periodic table.

  • Generally possess higher density and greater melting/boiling points than other elements.

Nonmetals

  • Often gaseous or dull solids at room temperature.

  • Poor conductors of heat and electricity; good insulators.

  • Referred to as "The Elements of Life."

Metalloids

  • Exhibit properties of both metals and nonmetals; all are solids at room temperature.

  • Typically brittle and can be somewhat reactive.

  • Used in making semiconductors (e.g., silicon and germanium).

  • Conduct electricity at high temperatures but not at low temperatures.