Chapter 2 Atoms and Molecules of Life What Are the Building Blocks of Life Basic Atomic Structure Atoms are composed of Protons Neutrons Electrons Protons and neutrons are located in the Electrons are found in Elements Atomic number Defines an element due to characteristic proton number Equal to the number of electrons Mass number Greater than the atomic number Called an amu atomic mass unit Isotopes Equals mass number minus atomic number number of protons Periodic Table Isotope of Carbon 14 6 C Electron Orbitals Electrons arranged around the nucleus in specific regions called orbitals Each orbital can only hold electrons Orbitals are grouped into electron shells Numbered 1 2 3 Lower numbers shells closer to the nucleus Valence shell is outermost shell highest number Each shell can contain up to 4 orbitals 8 electrons Valence Shell outermost electrons called valence electrons Electronegativity High Low O N C H Electronegativity Chemical Bonding Unfilled electron orbitals allow for the formation of and atoms are most stable when each electron orbital is filled Covalent bond Each atom s unpaired valence electrons are by both nuclei to fill their orbitals Substances held together by covalent bonds are called molecules Ionic bond Electrons are completely Nonpolar Covalent Bond Polar Covalent Bond Electron Sharing and Bond Polarity Ionic Bond Ionic Bond I Win Ions and Ionic Bonds An atom or molecule that carries a charge is called an ion Cation An atom that loses and electron and becomes Anion An atom that gains an electron and becomes The resulting attraction between oppositely charged ions is called an Ionic Bonding Chemical Bonding Electron Sharing Continuum How Many Bonds Can an Atom Have The number of determines the number of bonds an atom can make Multiple bonds form from atoms sharing Unpaired electrons in valence shell participate in covalent bonds Summary Covalent bonds are based on Ionic bonds are based on electrical attraction between Covalent bonds can be polar or nonpolar depending on whether electronegativity s of the two atoms are the same or different Water The Most Abundant Molecule in Organisms Life is based on water because water is a great solvent The covalent bonds in water are polar because oxygen has a electronegativity than hydrogen Oxygen has a partial charge Hydrogen has a partial charge Hydrogen Bonds Hydrogen bonds are the between the partially negative oxygen and the partially positive hydrogen of a different water molecule Can also form between a water molecule and another polar molecule Water and Hydrogen Bonding Ions and polar molecules stay in solution because of their interactions with water s partial charges These atoms and molecules are said to be Uncharged and non polar compounds do not dissolve in water and are said to be Water and Hydrogen Bonding Hydrophilic Water and Hydrogen Bonding Hydrophobic
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