Chapter 2 Atoms Molecules and Life Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 2 At a Glance 2 1 What Are Atoms 2 2 How Do Atoms Interact to Form Molecules 2 3 Why is Water So Important to Life Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms 2 1 What Are Atoms Atoms are basic structural units composed of still smaller particles Electrons orbit the nucleus at fixed distances Life depends on the ability of electrons to capture and release energy Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Atoms smallest particle of an element are the fundamental structural units of matter and are composed of three types of particles In the central atomic nucleus there are positively charged proton and uncharged neutron In orbit around the nucleus are negatively charged particles called electron Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Atoms are electrically neutral because their number of positive protons and negative electrons are equal Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms The number of protons in the nucleus of an atom is known as its atomic number The atomic mass of an element is the total mass of its protons neutrons and electrons Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Elements and isotopes An element is a substance that cannot be broken down by ordinary chemical reactions All atoms belong to one of 92 types of naturally occurring elements Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Elements and isotopes continued However atoms of an element may vary in the number of neutrons they have in the nucleus Variant atomic forms of an element are called isotopes Some isotopes are radioactive meaning that they spontaneously break apart forming different atoms and releasing energy and are used in research At room temperature elements may occur as solids liquids or gases Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Electron shells Larger atoms can accommodate more electrons than smaller ones can Electrons are distributed around the nucleus of an atom in electron shells The first shell or energy level holds 2 electrons The second shell holds up to 8 Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Electron shells continued The roles of the nucleus and the electrons are The nuclei provides stability The electrons interact with other atoms for example to form Chemical Bonds Chemical bonds are the force of attraction between neighboring atoms that holds them together within a molecule Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 1 What Are Atoms Energy capture and release Life depends on electrons capturing and releasing energy Electron shells correspond to energy levels When energy excites an atom it causes an electron to jump from a lower to a higher energy shell jump shells absorbs energy Later the electron falls back into its original shell releasing the energy jumps back to original release energy Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Atoms interact when there are vacancies in the outermost electron shells Highly reactive free radicals can damage cells Chemical bonds hold atoms together in molecules Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Ionic bonds form among charged atoms that are called ions Covalent bonds form between uncharged atoms that share electrons Hydrogen bonds are attractive forces between polar molecules Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Interaction between atoms molecules consist of two or more atoms from the same or different elements that are held together by interactions among their outermost electron shells A substance made of atoms of different elements is a compound Reactions between atoms depend upon the configuration of electrons in the outermost electron shell Cation NA Anion CL Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Interaction between atoms continued Atoms will not react with other atoms if the outermost shell is completely empty or full such atoms are considered inert Example Neon eight electons on outermost shell is full INERT stable Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Interaction between atoms continued Atoms will react with other atoms if the outermost shell is partially full such atoms are considered reactive Example Oxygen with six electrons on outermost shell SUSCEPTIBLE Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Interaction between atoms continued Reactive atoms gain stability through electron interactions chemical reactions To empty the outermost shell electrons can be lost To fill the outermost shell electrons can be gained Electrons can be shared with another atom when both atoms have full outermost shells Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Interaction between atoms continued Hydrogen and oxygen atoms gain stability by interacting with each other Single electrons from each of two hydrogen molecules fill the outer shell of an oxygen atom Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Free radicals Some cellular reactions produce free radicals A free radical is a molecule in which atoms have one or more unpaired electrons in their outer shells Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Free radicals continued Free radicals are highly unstable and reactive Free radicals steal electrons destroying other molecules Cell death can occur from free radical attack Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms Interact to Form Molecules Free radicals continued Free radicals are implicated in heart disease Alzheimer s cancer and aging antioxidants like vitamins C and E render free radicals harmless Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 2 2 How Do Atoms
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