Overview
This lecture covers the basics of chemical bonds, focusing on ionic and covalent bonds, valence electrons, and how to represent these concepts visually.
Chemical Bonds Overview
- Chemical bonds are attractive forces between atoms.
- The two main types of bonds covered are ionic and covalent bonds.
Valence Electrons
- Valence electrons are in the outermost orbital of an atom.
- The number of valence electrons determines chemical bonding behavior.
- Group number on the periodic table indicates the number of valence electrons (excluding transition metals).
- Atoms are most stable with eight valence electrons (“octet rule”).
- Atoms gain, lose, or share electrons to achieve a filled outer shell.
Lewis Dot Structures
- Lewis dot structures show the element symbol with dots for each valence electron.
- Dots are placed around the symbol; each side gets one before pairing.
- Exceptions exist (e.g., helium has two paired electrons).
Covalent Bonds
- Covalent bonds form when atoms share pairs of electrons.
- Each line between atoms in structural formulas represents a covalent bond and two shared electrons.
- Bonds can be single, double, or triple, based on the number of electron pairs shared.
Ionic Bonds
- Ionic bonds form when one atom gives (loses) electrons and another takes (gains) them, creating ions.
- Sodium (Na) gives an electron to chlorine (Cl), forming Na⁺ and Cl⁻ ions.
- Ionic bonds are the attraction between positively charged cations and negatively charged anions.
Key Terms & Definitions
- Valence electrons — electrons in the outermost shell of an atom.
- Octet rule — atoms tend to have eight electrons in their outer shell.
- Lewis dot structure — diagram showing valence electrons around an element’s symbol.
- Covalent bond — chemical bond where atoms share electrons.
- Ionic bond — bond formed when one atom transfers electrons to another, creating ions.
- Cation — positively charged ion (loses electrons).
- Anion — negatively charged ion (gains electrons).
Action Items / Next Steps
- Practice drawing Lewis dot structures for common elements.
- Review periodic table groups to identify valence electrons.
- Read textbook section on chemical bonds and types of bonding.