Transcript atom
THE SCOPE OF LIFE The Properties of Life a Order b Regulation c Growth and development d Energy utilization THE SCOPE OF LIFE The Properties of Life f Reproduction e Response to the environment g Evolution Life at Its Many Levels – Biologists explore life at levels ranging from the biosphere to the molecules that make up cells. Biosphere Ecosystems Communities Populations Organisms Organ Systems and Organs Tissues Organelles Nucleus Cells Molecules and Atoms Atom Life in Its Diverse Forms – Diversity is the hallmark of life. • The diversity of known life includes 1.8 million species. • Estimates of the total diversity range from 10 million to over 100 million species. Grouping Species – Biodiversity can be beautiful but overwhelming. – Taxonomy is the branch of biology that names and classifies species. The Three Domains of Life • The three domains of life are – Bacteria – Archaea – Eukarya Chemistry of Life – Matter is anything that occupies space and has mass. – Matter is found on the Earth in three physical states: • Solid • Liquid • Gas Chemistry of Life – Matter is composed of chemical elements. • Elements are substances that cannot be broken down into other substances. Change the number of PROTONS in the nucleus and you change the ELEMENT Atoms – Each element consists of one kind of atom. • An atom is the smallest unit of matter that still retains the properties of an element. 2 Protons 2 Neutrons 2 Electrons Nucleus Nucleus Cloud of negative charge 2 electrons Chemistry of Life – Elements differ in the number of subatomic particles in their atoms. • The number of protons, the atomic number, determines which element it is. • An atom’s mass number is the sum of the number of protons and neutrons. • Mass is a measure of the amount of matter in an object. Periodic Table of the Elements Legend Solid Liquid Gas Synthetic Alkali metals Alkali earth metals Transition metals Rare earth metals Other metals Noble gases Halogens Other nonmetals Atomic number = number of protons within the nucleus Chemistry of Life – Twenty-five elements are essential to life. – Four elements make up about 96% of the weight of Carbon C: 18.5% the human body: • Oxygen Calcium Ca: 1.5% Phosphorus P: 1.0% Oxygen O: • Carbon 65.0% Potassium K: 0.4% Sulfur S: 0.3% • Hydrogen Sodium Na: 0.2% Chlorine Cl: 0.2% • Nitrogen Magnesium Mg: 0.1% Hydrogen H: 9.5% Nitrogen N: 3.3% Trace elements: less than 0.01% Boron B Chromium Cr Cobalt Co Copper Cu Fluorine F Iodine I Iron Fe Manganese Mn Molybdenum Mo Selenium Se Silicon Si Tin Sn Vanadium V Zinc Zn Chemical Properties of Atoms – Electrons determine how an atom behaves when it encounters other atoms. First electron shell can hold 2 electrons Electron Outer electron shell can hold 8 electrons Hydrogen H Carbon C Atomic number = 1 Atomic number = 6 © 2010 Pearson Education, Inc. Nitrogen N Atomic number = 7 Oxygen O Atomic number = 8 Covalent Bonds – A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. – Atoms held together by covalent bonds form a molecule. Name Electron configuration molecular formula Hydrogen gas H2 Structural formula Space-filling model Single bond a pair of shared electrons Oxygen gas O2 Double bond two pairs of shared electrons Methane CH4 Ball-and-stick model Ionic Bonds – When an atom loses or gains electrons, it becomes electrically charged. • Charged atoms are called ions. • Ionic bonds are formed between oppositely charged ions. Outer shell has 1 electron The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Complete outer shells Outer shell has 7 electrons Na Sodium atom Cl Chlorine atom Na Sodium ion Cl Chlorine ion Sodium chloride (NaCl) The attraction between the ions—an ionic bond—holds them together Hydrogen Bonds – Water is a compound in which the electrons in its covalent bonds are shared unequally. • This causes water to be a polar molecule, one with opposite charges on opposite ends. slightly slightly H H O slightly – Hydrogen bonding • Weak bonds formed between hydrogen and another atom – Surface tension of water • Important as intramolecular bonds, giving shape to proteins and other biomolecules