Chp 4

Chapter 4: Atoms and Elements

What are Elements?

• Pure substances that cannot be broken down into simpler substances.

• Represented by 1- or 2-letter abbreviations (e.g., C for Carbon, Na for Sodium).

• Older elements may have Latin names with different abbreviations (e.g., Pb for Lead).

• Elements can be named after:

  • People (e.g., Curium, Einsteinium).

  • Places (e.g., Francium, Europium).

  • Planets (e.g., Uranium, Neptunium).

Arrangement of the Periodic Table

• Created by Dmitri Mendeleev in 1869; organizes elements based on:

  • Increasing atomic number.

  • Periodicity of chemical properties.

• Comprises 7 rows (periods) and 18 columns (groups/families).

• Elements grouped as:

  • Representative elements (Groups 1, 2, 13-18).

  • Transition metals (Groups 3-12).

  • Inner transition metals (bottom two rows).

Properties of Elements

• Metals: Columns 1-12 and some of 13, typically good conductors, malleable, and ductile.

• Nonmetals: Generally poor conductors; can be gases, liquids, or solids.

• Metalloids: Have properties of both metals and nonmetals (e.g., Silicon, Arsenic).

Structure of the Atom

• Composed of:

  • Positively charged protons.

  • Neutral neutrons.

  • Negatively charged electrons (orbiting around the nucleus).

• The nucleus contains protons and neutrons and carries a positive charge.

Atomic Number and Mass Number

• Atomic Number (Z): Number of protons in the nucleus; unique to each element.

• Mass Number (A): Total number of protons and neutrons in the atom.

• Atoms of the same element can have different isotopes; isotopes differ by the number of neutrons.

Isotopes

• Atoms of the same element with varying numbers of neutrons.

• Isotopes have different physical properties (mass varies).

Electron Arrangements

• Organization of electrons in energy levels corresponds to periods on the periodic table.

• Electron Configuration: Describes the distribution of electrons in an atom's orbitals.

• Orbital Diagrams: Visual representation of electrons in different orbitals.

Atomic Size and Ionization Energy

• Atomic Size: Tends to decrease across a period and increase down a group due to increasing nuclear charge and distance from the nucleus.

• Ionization Energy: The energy needed to remove an electron; increases across periods and decreases down groups due to electron shielding.

Chapter 4 Objectives

1. Identify chemical symbols of common elements.

2. Write chemical symbols for given element names.

3. Classify elements according to type (representative, transition, etc.).

4. Determine the number of protons, electrons, and neutrons in atoms based on Z and A.

5. Calculate atomic mass based on isotopes' abundance.

6. Write electron configurations and orbital diagrams for elements.

7. Use Lewis symbols to represent valence electrons.

8. Compare periodic properties of elements based on their positions in the periodic table.

Summary of Periodic Trends

• Atomic Radii:

  • Decrease across periods and increase down groups.

• Ionization Energy:

  • Increase across periods and decrease down groups.

• Metallic Character:

  • Decrease across periods, increase down groups.

Homework Assignment

• Chapter 4 Problems: p. 101 (2, 4), p. 106 (10, 12), p. 109 (18), p. 112 (32), p. 116 (44), p. 122 (46, 50, 52), p. 129 (56bd, 62ac, 66), p. 134 (78abc, 80abc, 84a).

• Write the electron configuration for Polonium (Po).