Acids are H+ donors in water and bases are OH- donors. Acids and bases can also be defined as electron acceptors and donors respectively based on Bronsted-Lowry and Lewis theories. Electron withdrawing groups make substances more stable but less reactive while electron donating groups have the opposite effect. The power of 10 is used to express the concentrations of acids and bases in solutions. The pH scale represents the negative log of the H+ concentration and is used to measure acidity. Acid-base titration curves show the pH change during neutralization reactions.