Bohr-Rutherford Diagrams Study Guide

Overview of Bohr-Rutherford Diagrams

• Definition: Bohr-Rutherford diagrams serve as specific models of the atom that provide a visual representation of its subatomic structure.
• Scientific Origin: These models are named "Bohr-Rutherford" because they represent the synthesis of theoretical ideas developed by two prominent scientists: Niels Bohr and Ernest Rutherford.
• Scope of Utility: These diagrams are primarily utilized to explain the chemical and physical properties of the first $20$ elements of the Periodic Table.

Step-by-Step Procedure for Drawing Diagrams

• Step 1: The Nucleus   - Construct a small central circle to represent the nucleus of the atom.   - Inside this circle, you must explicitly record the number of protons and the number of neutrons.   - Protons are often denoted as $p^+$ and neutrons as $n^0$.

• Step 2: The Orbits and Electrons   - Draw concentric "circles" surrounding the nucleus to represent electron orbits (shells).   - Place dots on these circular orbits to represent the total number of electrons ($e^-$) belonging to the atom.

Orbital Occupancy Rules

• There are strict maximum capacities for each electron shell that must be followed when drawing the diagrams:   - First Orbit: This is the shell closest to the nucleus and can hold a maximum of $2\,e^-$.   - Second Orbit: This shell can hold a maximum of $8\,e^-$.   - Third Orbit: This shell can hold a maximum of $8\,e^-$.
• Sequential Filling Rule: You are required to completely fill one energy level (orbit) before proceeding to draw or place electrons in the next level.

Mathematical Calculations for Atomic Components

• To accurately populate the diagram, specific values must be calculated using periodic table data:   - Number of Protons ($p^+$): This value is equal to the atomic number of the element.   - Number of Electrons ($e^-$): In a neutral atom, the number of electrons is equal to the number of protons.   - Number of Neutrons ($n^0$): This is calculated using the formula: $\text{Number of Neutrons} = \text{Atomic Mass} - \text{Atomic Number}$.

Case Study: Magnesium ($Mg$)

• Element Data: Magnesium has an atomic number of $12$ and a provided atomic mass of approximately $24.305$.
• Subatomic Particle Breakdown:   - Protons: $12$ (derived from the atomic number).   - Neutrons: Calculated as $24 - 12 = 12$.   - Electrons: $12$ (matches the number of protons).
• Diagram Visualization: The nucleus of a Magnesium atom would contain $12\,p^+$ and $12\,n^0$.

Case Study: Potassium ($K$)

• Based on the diagram provided for Potassium, the subatomic composition is as follows:   - Protons: $19\,p^+$.   - Neutrons: $20\,n^0$.

Periodic Trends and Reactivity

• Electron Trends in Groups: When moving down a specific family or group in the periodic table, the total number of electrons increases.
• Valence Consistency: Within each specific family, every atom possesses the same number of electrons in its outermost orbit (valence electrons).
• Reactivity Explanation: The consistency of electrons in the outer shell helps explain why elements within the same family exhibit similar chemical reactivity and properties.

Practical Application

• Task: One must be able to draw the Bohr-Rutherford diagram for an atom of Sulphur using the established rules and calculations.