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Overview of Electrons in Atoms

  • Atomic Number: The number in the corner represents protons, which is also equal to the number of electrons in a neutral atom.

  • Total Electrons: This is the sum of all electrons in the atom.

  • Valence Electrons: Found at the top of the element symbol, which indicates the electrons available for bonding.

  • Core Electrons: The remainder of electrons not designated as valence electrons.

    • Formula to calculate core electrons: Core Electrons = Total Electrons - Valence Electrons.

Example Calculation: Total and Core Electrons

  • For an Example Element: Calculation using the example provided.

    • Total Electrons = 15

    • Valence Electrons = 5

    • Calculation: Core Electrons = 15 - 5 = 10.

Understanding Lewis Structures

  • Definition: Lewis structures represent the valence electrons around atoms and how they bond.

  • Components:

    • Nonbonding Electrons: Also known as lone pairs, are the electrons that are not shared with other atoms.

    • Shared Electrons: Represented by lines between atoms in the structure.

Method for Calculating Valence Electrons

  • Total Electrons for Xenon: 54 total electrons.

  • Valence Electrons for Xenon: 8.

  • Core Electrons Calculation: Core Electrons = 54 - 8 = 46.

Drawing Lewis Structures

  • Example Structure: $SiH_4$ (Silane)

    • Steps:

    1. Identify the central atom (silicon, Si).

    2. Count total valence electrons:

      • Si = 4 valence electrons.

      • H = 1 valence electron each for 4 hydrogen atoms.

      • Total = 4 (Si) + 4 (H) = 8.

    3. Draw the structure with Si in the center and H atoms surrounding it, each connected by bonds showing bonding pairs of electrons.

Shared and Nonbonding Electrons

  • Calculation:

    • Bonded Electrons for $SiH_4$:

    • 4 bonds count as 8 bonded electrons (counted as pairs).

    • Nonbonded Electrons: No lone pairs in $SiH_4$, therefore zero nonbonding electrons.

Additional Examples of Lewis Structure Calculations

  • For Water (H2O)

    • Valence Electron Count:

      • O = 6, H = 1 (x2) = 2, Total = 6 + 2 = 8.

    • Structure: O in center with two H atoms.

Double and Triple Bonds in Lewis Structures

  • Octet Rule: Atoms tend to form bonds until they are surrounded by eight valence electrons.

    • Example: Oxygen usually forms 2 bonds and can create double bonds if necessary.

    • Carbon: Wants to complete 4 bonds. If the arrangement calls for more bonds, adjust accordingly, ensuring others still meet octet rules.

Practice Problems and Approach

  • Practice with a Partner: Doing practice with another person helps reinforce learning and confidence.

  • Attempt Examples: When you approach a new problem, work through and explain your reasoning aloud to identify mistakes and clarify.

    • Example Problem: Draw the Lewis structure for NH3 (Ammonia)

Understanding Resonance Structures

  • Definition: Structures that can be represented with different electron arrangements.

  • Example: For a structure like CO2, where double bonds can move between atoms.

Final Thoughts on Chemistry

  • Math in Chemistry: Vital for understanding concepts. Example mathematical formulas include lattice energy calculations:

    • $H_{sub} = rac{1}{2}BE - EA$ (where EA is Electron Affinity).

  • Confidence Building: The importance of correctly understanding these concepts leads to better test performance.

    • Connecting course content with practical problems improves retention and boosts performance.