Introduction to Chemical Solubility and Bonds

Ions: Chemicals can exist as ions, which are either positively charged (Na^+) or negatively charged (Cl^-).
Polar Molecules: These molecules are soluble in water. They possess a partial charge due to uneven electron distribution. An example is sugar, which is polar because it contains many oxygen atoms, specifically OH (hydroxyl) groups. These OH groups give the sugar molecule a partial charge, making it soluble in water. Even a partial charge is sufficient to allow a substance to dissolve in water.
Hydrophobic Molecules: The term "hydrophobic" means "water-fearing." These are chemicals that are not soluble in water. Consequently, hydrophobic molecules are lipid soluble and are typically found within the lipid bilayer, rather than in the cyclophosphate (assuming this refers to a cellular compartment like cytoplasm where water is abundant). A hydrophobic molecule is characterized by being entirely uncharged and nonpolar; it possesses no charge and no partial charge, rendering it completely insoluble in water.

Chemical bonds are forces that hold atoms together to form molecules.

Nature: An ionic bond forms between oppositely charged ions.
Strength: They are considered to be of medium strength.
Analogy: Think of ionic bonds like magnets. Magnets have a positive pole and a negative pole. When opposite poles come close enough, they attract and "click." Similarly, an ionic bond is always formed between a positively charged ion and a negatively charged ion due to electrostatic attraction.
Example: Table salt, also known as sodium chloride (NaCl), is a classic example. It consists of a positively charged sodium ion (Na^+) and a negatively charged chloride ion (Cl^-). These oppositely charged ions attract each other to form the salt.

Covalent bonds involve the sharing of electrons between atoms.

Electron Sharing: In a nonpolar covalent bond, electrons are shared evenly between the atoms.
Typical Occurrences: These bonds are commonly found between:
- Two carbon atoms (C-C).
- A carbon atom and a hydrogen atom (C-H).
Molecular Characteristics: Molecules primarily containing nonpolar covalent bonds are nonpolar overall, meaning they have no charge and no partial charge.

Electron Sharing: Even though electrons are shared in a polar covalent bond, the sharing is uneven.
Electronegativity: This uneven sharing occurs because one of the atoms involved in the bond is more electronegative (has a stronger pull on shared electrons) than the other.
Example: The water molecule (H_2O) is a prime example of a molecule containing polar covalent bonds.
- Within a water molecule, there is a covalent bond between the oxygen atom (O) and each hydrogen atom (H).
- Oxygen (O) is highly electronegative compared to hydrogen (H).
- Consequently, the pair of electrons shared between the H and O atoms are pulled closer to the oxygen atom. This creates a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms, making the H-O bonds polar covalent and the water molecule itself polar.