Chemistry 1.0: Lewis Structures and Octet Rule

Chemistry 1.0 Competencies

• Draw Lewis structures of ions
• Apply the octet rule in forming molecular covalent compounds

Ion Formation

• Atoms gain or lose electrons to form ions
• Cations are positively charged ions formed by losing electrons, increasing proton count
• Anions are negatively charged ions formed by gaining electrons, increasing electron count
• Example: Magnesium ion (Mg²⁺), Oxide ion (O²⁻)

Octet Rule

• "Octet" from Greek word "okto", meaning "eight"
• Octet configuration is the most stable electron arrangement for atoms
• Noble gases are stable because they have a full octet of valence electrons
• Atoms tend to gain, lose, or share electrons to achieve a stable octet configuration, affecting chemical reactions
• Atoms with fewer than eight valence electrons tend to bond with other atoms to achieve an octet

Octet Rule (Periodic Table)

• Atoms in the periodic table seek a stable noble gas configuration
• Achieving this configuration involves reacting with other elements to form stable compounds

Gilbert N. Lewis (1875-1946)

• In 1916, developed a system for representing valence electrons of atoms
• Called Lewis's electron-dot structures or Lewis structures

Lewis Structure: Hydrogen

• Element symbol (H) surrounded by dots
• Dots represent valence electrons (1 valence electron)
• Two dots are placed on each side of the symbol

Lewis Structure: Oxygen

• Arrangement of dots around oxygen symbol may vary, but represents valence electrons(6 valence electrons)

Lewis Structures and Ions

• Ions are represented by Lewis structures by adding or subtracting dots to reflect lost or gained electrons in the neutral atom
• Example: Sodium (Na) loses a single electron to form a structure with a +1 charge

Example: Sodium Ion (Na⁺)

• Element: Sodium (Na)
• Electron configuration: 1s², 2s², 2p⁶, 3s¹
• Valence electrons: 1
• Neutral atom loses one electron: Na → Na⁺

Activity 3

• Students must find a stained glass example
• Students must create an A4 size paper with the stained glass sample
• Chemistry concepts must be included detailing the sample

Lewis Structure of Ionic Compounds

• In ionic compounds like NaCl, electrons are transferred from one atom to another (NaCl) forming an ionic bond
• Atoms with different electronegativity values are involved in forming an ionic bond
• The atom with lower electronegativity transfers its electron to the atom with higher electronegativity
• Metals have lower electronegativity values than nonmetals.

Example: NaCl

• Sodium (Na) loses one electron to form Na⁺
• Chlorine (Cl) gains one electron to form Cl⁻
• The resulting ions are held together by electrostatic forces forming NaCl

Example: Li₂S

• Lithium (Li) loses one electron to form Li⁺, while Sulfur (S) gains two electrons to form S²⁻
• These ions are held together electrically to form Li₂S

Lewis Structure of Ions

• In a Lewis structure for ions, the element symbol is in brackets with a superscript representing the charge
• Cations lose valence electrons
• Anions gain valence electrons (obtained by cations)

Example: KCl

• Potassium (K) loses one electron (creating a K⁺ ion)
• Chlorine (Cl) gains one electron (creating a Cl⁻ ion)

Example: CaCl₂

• Calcium (Ca) loses two electrons (creating a Ca²⁺ ion)
• Chlorine (Cl) gains one electron to form Cl⁻

Lewis Structure of Covalent Compounds

• Covalent bonding involves sharing electrons between two or more atoms
• This satisfies the octet rule—ensuring chemical stability
• Involves two or more nonmetals
• Shared electrons are called bonding electrons; unshared electrons are lone pairs

Example: HCl

• Hydrogen (H) and Chlorine (Cl) Atoms share electrons to establish a covalent bond

Example: H₂O

• Oxygen (O) and Hydrogen (H) share electrons to form covalent bonds in water

Practice Problem

• Table with spaces for drawing Lewis structures, identifying neutral atoms, and counting lost or gained electrons for elements C, Br, Al, and Rb.

Test your understanding of Lewis structures and the octet rule in molecular chemistry. This quiz covers ion formation, cations, anions, and the significance of achieving a stable electron configuration. Sharpen your skills in recognizing how electrons play a crucial role in chemical bonding.