Review 3.1-3.4

3.1 Fathers of Atomic Theory

  • Element:

    • A pure substance that cannot be broken down by physical or chemical means.

    • Everything is made of various elements.

  • Atom:

    • The smallest particle of an element.

    • Atoms of the same element are identical.

  • Diatomic Elements:

    • Two of the same element bonded together but NOT a compound.

    • Examples: Bromine (Br), Iodine (I), Nitrogen (N), Chlorine (Cl), Hydrogen (H), Oxygen (O), Fluorine (F).

    • Mnemonic: BrINClHOF.

Key Theorists:

  • Democritus:

    • Proposed that everything is made of small indivisible and indestructible particles, which Dalton called "atoms."

Atomic Model Discovery:

  • Thomson:

    • Conducted the Cathode Ray Experiment, found that electricity was attracted to a positively charged plate and repelled by a negatively charged plate.

    • Concluded that particles that are negatively charged (electrons) exist in atoms.

    • Proposed the Plum Pudding Model, depicting the atom as a sponge with electrons throughout it.

  • Rutherford:

    • Conducted the Gold Foil Experiment, firing alpha particles at a thin sheet of gold foil.

    • Observed that:

      • Some alpha particles passed through the foil;

      • Some were deflected;

      • None stuck to the gold foil.

    • Conclusions:

      1. The nucleus is a small, dense, positively charged center.

      2. Electrons move around the nucleus.

      3. Atoms are mostly empty space (electron cloud).

3.2 Atomic Structure & Subatomic Particles

  • Subatomic Particles:

    • Smaller than an atom ("sub" means below/under/within).

  • Atom Information:

    • An atom is neutral (number of protons = number of electrons).

    • Contains a nucleus composed of protons and neutrons (positive charge).

    • Mostly empty space surrounds the nucleus where electrons reside (negative charge).

Properties of Subatomic Particles:

  • Protons (+):

    • Positively charged.

    • Found in the nucleus.

    • Large mass: 1 a.m.u.

  • Neutrons (0):

    • Neutral (no charge).

    • Found in the nucleus.

    • Large mass: 1 a.m.u.

  • Electrons (-):

    • Negatively charged.

    • Orbiting in empty space.

    • Very small mass: almost 0 a.m.u.

Key Concepts:

  • Atomic Number:

    • The number of protons in the nucleus, which identifies the element.

    • It never changes and is written in bold at the bottom left corner of an element’s box on the periodic table.

    • Elements are arranged in order of atomic number from left to right.

  • Mass Number:

    • The total weight of the nucleus (mass number = protons + neutrons).

    • Calculation:

      • Neutrons = mass number - protons

      • Protons = mass number - neutrons.

3.3 Isotopes

  • Definition: Isotopes are atoms of the same element that have different masses due to varying numbers of neutrons.

  • Key Point:

    • Isotopes have the same number of protons but different numbers of neutrons.

  • Examples of Isotopes:

    • Hydrogen–1: mass # 1

    • Hydrogen–2: mass # 2

    • Hydrogen–3: mass # 3

  • Applications of Isotopes:

    • Cobalt–60: Used in cancer treatments.

    • Uranium–238: Used to date organic materials (rocks, fossils, trees, etc.).

    • Carbon–14: Utilized for dating archaeological artifacts.

    • Iodine–131: Used for diagnostic procedures.