ch2_lectureNotes_key_CHM109

Chapter 2 - Atomic Structure & Radioisotopes

• Topics Covered:

  • Atomic Structure

  • Elements

  • Periodic Table

  • Isotopes

  • Radioactivity

  • Electron Orbitals

  • Atomic Radius

  • Electron Dot Structures

Periodic Table

• Created by Dmitri Mendeleev in 1863, organized by atomic masses:

  • Shows repeating chemical properties periodically

  • Accepted structure still holds today

• Arrangement:

  • Periods (Rows): Horizontal arrangement of elements

  • Families (Columns): Elements with similar chemical properties

• Key Groups:

  • Noble gases (Group 18): eg., Helium (He)

  • Alkali metals (Group 1): eg., Lithium (Li)

  • Transition metals: Located in the center of the table

Isotopes

• Definition:

  • Atoms of the same element (same number of protons) with a different number of neutrons.

• Stable vs. Unstable:

  • Most elements have multiple naturally occurring isotopes

  • Example: Carbon has isotopes 12C, 13C, and 14C.

    • 14C is radioactive with a 5,730 years half-life.

Radioactivity

• Definition:

  • The process by which unstable isotopes undergo nuclear decay to become more stable, releasing radiation.

• Types of Radiation:

  • Alpha (α): Consists of 2 protons and 2 neutrons (Helium nucleus)

  • Beta (β): An electron emitted when a neutron transforms into a proton.

  • Gamma (γ): High-energy electromagnetic radiation.

Atomic Orbitals

• Regions of space around nucleus where electrons are likely to be found (electron clouds).

• Types of Orbitals:

  • S-orbital: Spherical shape around the nucleus.

  • P-orbital: Dumbbell-shaped and can hold 6 electrons.

  • Higher energy levels mean larger orbital volume.

Periodic Trends

• Characteristic patterns that can be observed across periods and groups in the periodic table:

  • Atomic Radius:

    • Depends on energy levels of valence electrons and nuclear charge.

    • The effective nuclear charge is less felt by valence electrons due to electron shielding (how inner electrons block outer electrons’ attraction to the nucleus).

  • Trends Examples:

    • Atomic radius increases down a group and decreases across a period.

Electron Dot Structures

• Used to represent the valence electrons of an atom.

• To draw for example:

  • Mg (Magnesium): Includes 2 valence electrons.

  • N (Nitrogen): Includes 5 valence electrons.

  • O (Oxygen): Includes 6 valence electrons.

  • Cl (Chlorine): Includes 7 valence electrons.

  • Br (Bromine): Includes 7 valence electrons.

  • And so forth for other elements.