D. Compounds
➢ Compound occurs as result of 2 or more individual elements combining in a fixed ratio
- Different properties of individual elements
- Formed by chemical reaction
➢ Bonds that hold compounds together
- Ionic bonds
■ $\text{nonmetal+metal}$
■ One or more electrons is transferred from one atom to another
■ One atom loses electrons (becomes positively charged) while the other gains electrons (becomes negatively charged)
■ Results from attraction of two oppositely charged ions
■ Cation has a positive charge
■ Anion has a negative charge
■ Cation and anion form to create ionic bond - Covalent bonds
■ $\text{nonmetal+nonmetal}$
■ Molecule consists of 2 or more atoms held together by covalent bonds
■ Formed when electrons are shared between atoms
■ In nonpolar covalent bond, electrons are shared equally
■ In polar covalent bond, electrons are shared unequally
■ In a single covalent bond, one pair of electrons is shared
● Double covalent when 2 pairs are shared, etc.
■ Structural formula used to represent atoms and bonding
● Ex. $\text{H-H}$
■ Molecular formula abbreviates structural formula
● Ex. ${H_2}$
● Electronegativity is an atom’s attraction for the atoms in a covalent bond- The more electronegative an atom, the more strongly it pulls shared electrons toward itself
- Hydrogen bonds
■ Hydrogen atom covalently bonds to one electronegative ato is also attracted to another electronegative atom
■ In living cells, hydrogen bonds are usually oxygen or other nitrogen atoms
○ Van der Waals Interactions
■ Weakest
■ If electrons are distributed asymmetrically in molecules or atoms, they can result in “hot spots” of positive or negative charge
■ Attractions between molecules that are close together as a result of these charges
● How geckos climb