Bonds and Models Flashcards
Bonds (3 Types)
-Hold atoms/ions together in a compound
-Formed by the transfer or sharing of electrons
-Types: Ionic, Covalent, Metallic
Ionic Bonds
Formed by the transfer or electrons resulting in a positive (cation) ion and a negative (anion) ion which are held together by attractive forces
Ionic Bond Characteristics (5)
-Usually a metal and nonmetal
-Dissolve in water to form ions
-Will conduct electricity when dissolved
-Have high melting and boiling points (usually solid at room temperature)
-Electronegativity is greater than 1.67
Covalent Bonds
-2 Types (Polar and Nonpolar)
-Formed by the sharing of electrons resulting in either a single or multiple bond
Polar Covalent Bond
-Uneven sharing of electrons
-Electronegativity difference between 1.67 and 0.4
Nonpolar Covalent Bond
-Even sharing of electrons
-Electronegativity difference is less than 0.4
Covalent Bond Characteristics (5)
-Usually between nonmetals
-Do not dissolve to form ions
-Generally do not conduct electricity
-Low melting and boiling points
-Electronegativity difference is less than 0.4 for nonpolar and between 1.67 and 0.4 for polar covalent
Metallic Bond
Formed between metals with delocalized (free to move around) electrons
Metallic Bond Characteristics (2)
-Involve metals
-Free moving electrons allow for conductivity in solid or molten (somewhat melted) state
Hydrogen
Considered a nonmetal when dealing with bonds/ bond types
Octet Rule
Atom gain/lose/share electrons in an attempt to achieve 8 valence electrons (or 2 for hydrogen)
Steps for writing Lewis Dot Models
- Write electron configuration
- Determine the number of electrons (valence electrons) in the highest energy level
- Represent valence electrons as dots around the symbol
- No more than two “dots” per side- start with two on the furthest right side than one per a side in a counterclockwise motion
Shortcut (only works for A Groups)
-Number of valence corresponds with group
-Exception: Helium (He) cannot have 8 valence
Structural Models
-Represent the covalent bonds within a compound
-Bonds are represented by lines and electrons are represented by dots
Steps for writing Structural Models (7)
- Count the total number valence electrons in the compound
- Determine the central element of the compound (if possible) and connect the other atoms using single bonds
- Use remaining electrons to fulfill octet rule. All electrons must be used.
- If necessary, redraw using multiple bonds or a different arrangement
- If a multiple bond exists and it can be in more than one location, draw the resonance structures
- if central atom is in a group 2/3, or period 3-7, and the octet rule can’t be fulfilled, the central atom may break the rule
- If more than one structure is possible, calculate the formal charge to determine the best structure (all zeros, or if not possible, the most electronegative is most negative)
