Chapter 2: Chemistry of Life

Living Things Consist of Atoms of Different Elements An atom is the smallest basic unit of matter. Are made up of: Protons Found in the center of the atom Have a mass of 1 AMU Have a charge of positive 1 Neutrons Have no charge (neutral) Electrons Found in orbits surround the protons & neutrons Mass is 1/1837 AMU so we count it as 0 Have a charge of negative 1

An element is one particular type of atom, and it cannot be broken down into a simpler substance by ordinary chemical means Carbon (C), Sodium (Na), Sulfur (S),… Oxygen (O2), Hydrogen (H2), ... Differ in the number of protons they have. This is their Atomic Number and no two elements have the same Atomic number The number of protons (which equals the number of electrons), gives the element its physical and chemical properties

Elements on the Periodic Table Atomic Number: # of protons = # of electrons 6 protons and 6 electrons Atomic mass: # of protons + # of neutrons 6 protons + 6 neutrons = 12 Element name Carbon Element symbol C

Elements in the Human Body Symbol Atomic Number (# of Protons = # of Electrons) Atomic Mass (# of Protons + # of Neutrons) Carbon  C  6 12  Hydrogen H  1  Oxygen O  8  16  Nitrogen N  7 14 Phosphorus P  15 31 Sulfur S 16 32 Sodium Na 11 23 Chlorine Cl 17 35 Potassium K 19 39 Calcium Ca 20 40

Bohr Model of an Atom First orbital gets a maximum of 2 electrons The next two get 8 electrons Protons and Neutrons go in the middle P = 6 E = 6 N = 6

Do Oxygen (16O8), Hydrogen (1H1), and then Nitrogen (14N7),

Let’s Combine Atoms together Compounds are substances made up of atoms of different elements bonded together in a certain ratio. H2O CO2 NaCl CH4 C6H12O6 Compounds have different properties than the elements that make it up. Sodium + Chlorine = Sodium Chloride (Salt)

Bohr Model of Sodium Chloride Na+Cl-

Ionic Bonding Ionic bonding occurs when electrons are transferred from the outermost energy levels of two atoms Form ions – Atoms that have gained or lost electrons and now have a charge instead of being neutral The number of protons no longer equals the number of electrons Li+Cl-

Still with Ionic Bonding Elements in Column 1A will easily bond ionically with elements in Column 7A. The Column 1A elements will donate an electron and therefore have an extra positive charge and become a positive 1 ion The Column 7A elements will gain an electron and therefore have an extra negatively charged electron and become a negative1 ion What about Column 2A. Which column will it easily bond ionically with? Column 6A and form either a +2 ion or a -2 ion.

4 Covalent bonds are present in Methane. Covalent Bonding Let’s make Methane (CH4) C has 6 electrons 2 in the first energy level 4 in the second H has 1 electron only in its only energy level Will it bond ionically or covalent with Hydrogen? A Covalent bond forms when atoms share a pair of electrons 4 Covalent bonds are present in Methane.

Now let’s make a molecule of H2O and then CO2

Strength of Bonds Covalent bonds are the strongest bonds making up the compounds found in living organism Need a lot of energy to break the bond Or pressure Or chemicals called enzymes Double and triple bonds are even stronger

Life Depends on the Hydrogen Bonds in Water Properties of water: Water is less dense as a solid Ice floats and covers the water’s surface Ice acts as an insulator and does not let the water below freeze or the organisms in the water Water is a polar molecule The oxygen end has a slightly negative charge The hydrogen ends have a slightly positive charge

Hydrogen Bonds Due to water’s polarity, the opposite charges of another water molecule can interact to form hydrogen bonds Hydrogen bonds are attractive forces between a slightly positive atoms and a slightly negative atom These bonds are weak bonds but when you add them all up, they are strong Found holding water molecules together Found between the two sides of a DNA molecule

Properties of Water due to Hydrogen Bonds High Specific Heat: The amount of heat needed to raise the temperature of a substance 1`C Since water has so many hydrogen bonds, it takes a lot of energy to break the bonds to raise its temperature Once it has absorbed the heat, it takes a lot of energy and time to lower the temperature Why a watched pot never seems to boil!! Why it takes a long time in the summer for the ocean or lakes to heat up. Why water stays warmer in the fall Why it takes a while for our body temperature to lower

Cohesion Like molecules being attracted to each other. There is an attractive force holding adjacent water molecules together called hydrogen bonds Water beading up on leaves or your window Surface tension allowing the water strider to “walk on water”

Adhesion The attractive force between unlike molecules Water molecules stick to other molecules IF they are also polar Water molecules sticking to glass or a web Water molecules sticking to roots The meniscus in a graduated cylinder How water molecules (or our blood since its basically water) can easily be transported through our capillaries (really thin blood vessels)

Water as the Universal Solvent Water makes up about 70% of the mass of living things. For us, its closer to 60%. In order for chemical processes to occur, molecules and ions need to be able to dissolve or go into solution with water. Sugars, oxygen, Vit B & C, minerals such as salt, … Polar compounds or ionic compounds can go into solution with water Non-polar molecules like lipids (fats and oils), fat soluble vitamins like A, D, E, & K can’t. Oil and water do not mix!! They can only dissolve in other nonpolar solvents

Solutions Solutions are a mixture of substances that is the same throughout (Homo gen eous) Solvent is the substance that is present in the greatest amount that dissolves the solute Water Blood – 95% water Solute is the substance going into solution in the solvent. It is being dissolved Salt Glucose

Ionic Compounds in Water When ionically formed compounds go into solution with water, their ions dissociate or separate from one another They remain as ions but are attracted to the opposite poles on the polar water molecules Na+Cl- when placed in water, will break into: Na+ ions which will surround the large Oxygen atom Cl- ions which will cluster around the small hydrogen atoms

To reform the ionic bonds, just remove the water by evaporation!!

Acids and Bases Acids are compounds that when placed in water, release a proton or Hydrogen ion (H+) into the water. HCl, H2SO4, Citric Acid Sour tasting Corrosive

Bases or alkaline compounds remove H+ ions when in solution and have an excess of OH- ions (hydroxide ions) Ammonia, Bleach, Blood, Bile, Soap… Bitter tasting Slimy to touch

Measuring pH or the Acidic or Alkalinity pH or percent H+ ion concentration measures the amount of H+ ions in a solution

Every step on the pH scale is a 10X increase or decrease in H+ concentration. Pure water has a pH of 7 and therefore, the H+ and OH- concentrations are equal

Buffers Our body’s pH overall is about 6.5-6.8. We can not withstand huge shifts in pH. Buffers are chemicals which regulate the pH of the body, preventing sharp changes in pH