The simulation above represents an amino acid (polypeptide) chain. Certain properties are used to characterize amino acids. For example, some amino acids are attracted to water (hydrophilic), while some amino acids are repelled by water (hydrophobic). This attraction and repulsion has to do with hydrogen bonds. Amino acids that are electrically charged (positive or negative), and amino acids that are polar (regions of partial charge), are hydrophilic. Amino acids that are non-polar, meaning they have a balanced electrical charge, do not form hydrogen bonds with water and disrupt existing hydrogen bonds between water molecules. As a result, non-polar molecules are driven to re-arrange themselves to minimize the amount of their surface area that comes into contact with water. Non-polar amino acids are hydrophobic.