Chapter 2.1-2.3

Learning Objectives

  • Define the subatomic particles that make up the atom, along with their properties (e.g., charge)

  • Define radioactivity and list one danger and one benefit

  • Define and provide examples of ionic bonds

  • Specify how electrons participate in chemical bond formation

Introduction to Chemistry

  • Matter: Anything that takes up space and has mass.

    • States of Matter: Solid, liquid, gas.

  • Elements: Substances that cannot be broken down into simpler substances by ordinary chemical means.

    • There are 92 naturally occurring elements, with additional human-made elements that are not biologically important.

Elements That Make up 95% of Organisms (by Weight)

  • O: Oxygen

  • C: Carbon

  • H: Hydrogen

  • N: Nitrogen

  • P: Phosphorus

  • S: Sulfur

Atomic Structure

  • An atom is the smallest part of an element that displays its properties.

  • Subatomic Particles:

    • Protons: Positively charged; located in the nucleus.

    • Neutrons: Uncharged; located in the nucleus.

    • Electrons: Negatively charged; move around the nucleus.

Atomic and Mass Number

  • Atomic Number: Number of protons in the nucleus.

  • Mass Number: Number of protons + number of neutrons.

The Periodic Table

  • Elements are grouped by recurring chemical and physical properties (periodicity).

    • Groups: Vertical columns.

    • Periods: Horizontal rows.

Isotopes

  • Isotopes: Atoms of the same element with different numbers of neutrons.

  • Radioactive Isotopes: Emit energy as they decay.

Uses of Low-Level Radiation

  • Example: Thyroid scan indicates tumors not taking up radioactive iodine.

  • PET Scan: Reveals active brain portions through colors (yellow/red).

Uses of High Levels of Radiation

  • Radiation can kill bacteria and fungi.

    • Irradiated peaches spoil less quickly.

    • Used in radiation therapy for cancer treatment.

Electrons

  • In an electrically neutral atom, positive charges of protons balance negative charges of electrons.

  • Electron Energy Levels: Electrons occupy shells/orbitals around the nucleus.

    • First shell can hold 2 electrons; subsequent shells can hold 8.

  • Octet Rule: Valence shell is stable with 8 electrons.

Molecules and Compounds

  • Molecules: Formed when two or more atoms bond (e.g., O₂).

  • Compounds: Formed when different elements bond (e.g., H₂O).

  • Chemical reactions can release or absorb energy due to bond energy.

Ionic Bonding

  • Ions: Charged atoms formed by the transfer of electrons.

    • Ex: Sodium (Na) tends to donate an electron, becoming Na⁺.

    • Chlorine (Cl) tends to accept an electron, becoming Cl⁻.

  • After electron transfer:

    • Na⁺ and Cl⁻ have stable outer orbitals with 8 electrons.

  • Ionic Compounds: Held together by attraction between oppositely charged ions (ionic bond).

Key Terms

  • Section 2.1: Matter, Element, Essential element, Trace element, Atom, Neutron, Proton, Electron, Atomic number, Mass number, Isotopes, Electron shells, Valence electron, Valence shell

  • Section 2.2: Molecule, Compound, Ions, Ionic bonds