Essential Chemistry Studying Life from The Chemical Level Biology is a multidisciplinary science Biology includes the study of life at many levels Living organisms are subject to basic laws of physics and chemistry We will take the reductionist approach We will start at the atomic level and work our way up to the level of cell activity Cells consist of enormous numbers of chemicals that give the cell the properties we recognize as life Matter Elements and Compounds Organisms are composed of matter Matter is anything that takes up space and has mass Matter is found on the Earth in three physical states Solid Liquid Gas Matter is composed of chemical elements Elements are substances that cannot be broken down into other substances There are 92 naturally occurring elements on Earth Elements and Compounds An atom is the smallest unit of matter that still retains the properties of an element it cannot be broken down to other substances by chemical reactions Each element consists of one kind of unique atom A compound is a substance consisting of two or more elements in a fixed ratio Sodium Chlorine Sodium chloride Essential Elements of Life About 25 of the 92 elements are essential to life Carbon hydrogen oxygen and nitrogen make up 96 of living matter Most of the remaining 4 consists of calcium phosphorus potassium and sulfur Trace elements are those required by an organism in minute quantities Elements Essential to Life Four of these make up about 96 of the weight of the human body Trace elements occur in smaller amounts Figure 2 3 Essential Elements of Life SPONCH Subatomic Particles Atoms are composed of subatomic particles Relevant subatomic particles include Neutrons no electrical charge Protons positive charge Electrons negative charge Neutrons and protons form the atomic nucleus Electrons form a cloud around the nucleus Nucleus a b 2 Protons 2 Neutrons 2 Electrons Cloud of negative charge 2 electrons Atomic Number and Atomic Mass Atoms of the various elements differ in number of subatomic particles An element s atomic number is the number of protons The number of protons atomic number determines the element s properties An element s mass number is the sum of protons plus neutrons in the nucleus Atomic mass the atom s total mass can be approximated by the mass number Periodic Chart Atomic number Element symbol Mass number Isotopes Atoms of an element have the same number of protons but may differ in number of neutrons Isotopes are two atoms of an element that differ in number of neutrons Most isotopes are stable but some are radioactive giving off particles and energy Some applications of radioactive isotopes in biological research Tracing atoms through metabolic processes Diagnosing medical disorders Energy Levels of Electrons Energy is the capacity to cause change Potential energy is the energy that matter has because of its location or structure The electrons of an atom differ in their amounts of potential energy An electron s state of potential energy is called its energy level or electron shell Third energy level shell A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons Second energy level shell Energy absorbed First energy level shell Energy lost Atomic nucleus Electron Configuration and Chemical Properties The chemical behavior of an atom is determined by the distribution of electrons in electron shells The periodic table of the elements shows the electron distribution for each element Hydrogen 1H 2 Atomic number He Atomic mass First shell 4 00 Helium 2He Element symbol Electron shell diagram Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Sodium 11Na Magnesium 12Mg Aluminum 12Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Second shell Third shell Electron Orbitals An orbital is the three dimensional space where an electron is found 90 of the time Each electron shell consists of a specific number of orbitals Electron orbitals y x z 1s orbital 2s orbital Three 2p orbitals 1s 2s and 2p orbitals Electron shell diagrams First shell maximum 2 electrons Second shell maximum 8 electrons Neon with two filled shells 10 electrons Electron Shell Significance Each Orbital holds a maximum of 2 electrons each Several orbitals may be the same distance from the nucleus and thus contain electrons of the same energy Such electrons are said to occupy the same energy level or shell The chemical behavior of an atom is mostly determined by the valence electrons Valence electrons are those in the outermost shell or valence shell First electron shell can hold 2 electrons Outermost electron shell can hold 8 electrons Electron Hydrogen H Atomic number 1 Carbon C Atomic number 6 Nitrogen N Atomic number 7 Oxygen O Atomic number 8 Valence and Chemical Reactions Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms Atoms desire full outer orbitals Give up electrons Na Take electrons Cl Share electrons O2 Rule of Eights for filling each shell Noble gases full outer shells inert Chemical Reactions Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones Such changes in the chemical composition of matter are called chemical reactions Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells These interactions usually result in atoms staying close together The atoms are held together by chemical bonds Hydrogen gas Oxygen gas Water Reactants Products Chemical Reactions Are dependent on Concentration Speed Energy energy of activation Orientation Types of Chemical Reactions Synthesis reactions atoms or molecules combine to form a product Decomposition reactions molecules breakdown into smaller molecules or atoms Exchange reactions molecules exchange constituent components swap partners Reversible reactions the product of a previous reaction can revert to the original reactants Chemical Products Element a substance composed of only one type of atom all the atoms have the same number of protons Molecule a unit composed of two or more atoms joined together by chemical bonds Compound a substance composed of 2 or more elements that have been joined by chemical bonds Mixture a combination of 2 or more substances that do NOT chemically bond e g sugar mixed with salt Periodic Chart Ionic Bonds Atoms sometimes strip electrons from their bonding partners An example is the transfer of an