Chemical Bonds Hydrogen bonds are weak interactions (approximately 5% as strong as covalent bonds) between hydrogen and adjacent electronegative atoms like oxygen or sulfur. Hydrogen bonds result from attraction of oppositely charged parts of molecules—they should not be confused with covalent bonding to hydrogen which involves actual sharing of electrons.

Chemical Bonds Hydrogen bonds are useful in establishing links between molecules or between distant parts of a very large molecule. Large 3-D molecules (like proteins) are often held together by a great many hydrogen bonds. In water, hydrogen bonding provides considerable cohesion which creates a very high surface tension (as this bug demonstrates).

Chemical Bonds Interactions Animation Chemical Bonding You must be connected to the internet to run this animation.

Chemical Reactions Chemical reactions occur when electrons in the valence shell are shared or transferred. New bonds form and/or old bonds are broken. Metabolism is the “sum of all the chemical reactions in the body”. Law of conservation of energy: The total mass of reactants equals the total mass of the products .

Chemical Reactions Energy (the capacity to do work) is transferred in a chemical reaction. Kinetic energy is the energy of matter in motion. Potential energy is energy stored by matter - due to an object’s position in space, or stored in chemical bonds.

Chemical Reactions An exergonic reaction releases energy (usually in the form of heat during catabolism of food) by breaking a bond with more energy than the one being formed. An endergonic reaction requires that energy be added, usually from a molecule called ATP, to form a bond.

Chemical Reactions Activation Energy is the energy required to break chemical bonds in the reactant molecules so a reaction can start.

Chemical Reactions Factors that cause a collision (and a chemical reaction to take place) include the temperature and the concentration of the reactants, and the presence or absence of a catalyst. Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur. Catalysts are neither consumed nor produced in the reaction. They are used over-and-over again, often several million times per second!

Chemical Reactions In a chemical reaction, a catalyst helps to properly orient the colliding particles of matter so that a reaction can occur at a lower collision speed. A catalyst does not alter the difference in potential energy between the reactants and products (it only lowers the amount of energy needed to get the reaction started.)

Chemical Reactions Types of chemical reactions can be broadly classified as: Synthesis reactions – Anabolism A + B ➙ AB Decomposition reactions – Catabolism AB ➙ A + B Exchange reactions AB + CD ➙ AD + CB Reversible reactions AC ↔ A + C

Types of Reactions Interactions Animation Types of Reactions and Equilibrium You must be connected to the internet to run this animation.

Interactions Animation Chemical Reactions Types of Reactions and Equilibrium Interactions Animation You must be connected to the internet to run this animation.

Inorganic & Organic Compounds Inorganic compounds are structurally simple molecules that usually lack carbon - like the salt potassium chloride (KCl) depicted here: Organic compounds always contain carbon and are usually large, complex molecules. Usually contain hydrogen Always have covalent bonds

Inorganic Compounds Water is the most important and abundant inorganic compound in all living systems. Water’s most important property is polarity, the uneven sharing of valence electrons that enables reactants to collide to form products.

Inorganic Compounds Sodium and Chloride ions dissolve in the polar water molecules.

Water Interactions Animation Polarity and Solubility of Molecules You must be connected to the internet to run this animation

Water and Fluid Flow Interactions Animation You must be connected to the internet to run this animation. ,

Inorganic Compounds Water as a solvent: In a solution, the solvent dissolves the solute. Substances which contain polar covalent bonds and dissolve in water are hydrophilic, while substances which contain non-polar covalent bonds are hydrophobic. The polarity of water and its bent shape allow it to interact with several neighboring ions or molecules. Water’s role as a solvent makes it essential for health and survival.

Inorganic Compounds Water has a high heat capacity, meaning it can absorb or release a relatively large amount of heat with only a modest change in its own temperature. This property is due to the large number of hydrogen ions in water. Heat of vaporization (amount of heat needed to change from a liquid to a gas) is also high. Evaporation of water from the skin removes large amounts of heat.

Three Common Mixtures A mixture is a combination of elements or compounds that are physically blended together but are not bound by chemical bonds. In a solution, a substance called the solvent dissolves another substance called the solute. Usually there is more solvent than solute in a solution. In our bodies, the most common solvent is water: We are 65-80% water (depending on age - babies are very “wet”… as anyone who has had one can attest.)

Three Common Mixtures A colloid differs from a solution mainly on the basis of the size of its particles, with the particles in the colloid being large enough to scatter light (milk). In a suspension, the suspended material may mix with the liquid or suspending medium for some time, but it will eventually settle out (blood is a suspension.)

Methods of Measurement The concentration of a molecule is a way of stating the amount of that molecule in solution. Percent gives the relative mass of a solute found in 100 ml of solution (usually water). A mole is just a convenient way of counting large numbers of small things (like atoms or molecules). 1 mole is 6.02 x 1023 of something just like 1 dozen is 12 of something.