CHEM10 Chapter 3 Part 2

Chapter Three Overview

Atomic Structure

Atoms and Subatomic Particles

Definition of Atoms

  • Smallest units of matter

  • Composed of subatomic particles

Subatomic Particles

  1. Protons

    • Positively charged

    • Located in the nucleus

  2. Neutrons

    • Neutral charge

    • Found in the nucleus

  3. Electrons

    • Negatively charged

    • Reside in the electron cloud surrounding the nucleus

Visual Representation

  • Nucleus is tiny compared to the atom's overall size

    • Analogy: football field with an insect at the center representing the nucleus

Determining Atomic Identity

Atomic Number

  • Definition: The number of protons in an atom

  • Determines identity of an atom

Examples:

  • 1 proton = Hydrogen (H)

  • 2 protons = Helium (He)

  • 3 protons = Lithium (Li)

  • 4 protons = Beryllium (Be)

Stability of Identity

  • Changing number of neutrons or electrons does not affect elemental identity

Atomic Number and Charge

Atomic Number (Z)

  • Number of protons in the atom

  • Equal to the number of electrons in a neutral atom

  • Common misconception to say only protons count

Mass Number

Definition (A)

  • Sum of protons and neutrons in the nucleus

  • Not typically listed in the periodic table

    • Periodic table features atomic number and average atomic mass

Isotopes

Definition

  • Atoms of the same element with the same proton counts but different neutron counts

Example: Hydrogen Isotopes

  1. Protium

    • 1 proton, 0 neutrons

  2. Deuterium

    • 1 proton, 1 neutron

  3. Tritium

    • 1 proton, 2 neutrons

Notation

  • Isotopes represented by mass number (e.g., H-1, H-2, H-3)

Average Atomic Mass

Calculation

  • Based on the relative abundance of each isotope

  • Indicated on the periodic table

    • Usually contains decimal places

Calculation Formula

  • Formula:

    [ \text{Average Atomic Mass} = (\text{Mass}_1 \times \text{Fraction}_1) + (\text{Mass}_2 \times \text{Fraction}_2) ]

Example: Carbon

  • Use carbon-12 and carbon-13 to calculate average atomic mass

Quantum Model of the Atom

Electron Behavior

  • Electrons exist as waves rather than particles orbiting like planets

Impact

  • Explains various physical/chemical properties

  • Crucial for technology applications (e.g., solar panels, computers)

Ions

Definition

  • Charged atoms formed when neutral atoms gain or lose electrons

Types of Ions

  1. Cations

    • Positively charged ions (e.g., Li⁺)

    • Formed by loss of electrons

  2. Anions

    • Negatively charged ions (e.g., F⁻)

    • Formed by gain of electrons

Charge Notation

  • Charge displayed in the upper right corner of the symbol

Example: Lithium and Fluorine

  • Lithium (3 protons) loses one electron to become Li⁺

  • Fluorine (9 protons) gains an electron to become F⁻

Summary of Key Points

  • Proton Count: Determines atom identity (atomic number)

  • Mass Number: Total of protons and neutrons

  • Isotopes: Same atomic number, different mass numbers

  • Average Atomic Mass: Weighted average based on isotope abundance

  • Electrons: Gain or lose electrons to form ions, affecting charge but not identity.