- Atoms, Molecules and Ions Atoms, Molecules and Ions.
Atoms, Molecules and Ions Atoms, Molecules and Ions.
Atoms, Molecules and IonsOne of the main challenges of chemistry is to understand the connection between the macroscopic world that we experience and the microscopic world of atoms and molecules. - You must learn to think on the atomic level - Scanning Tunneling Microscope (STM) a special microscope used to "see" individual atoms. it uses an electron from a tiny needle to probe the surface of the substance.Dalton's Atomic Theory Each element is made up of tiny particles called atoms.The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.Chemical compounds are formed when atoms of different elements combine w/each other. A given compound always has the same relative numbers and types of atoms.Chemical reactions involve reorganization of the atoms --changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.The Structure of the AtomAtoms- are really small- are shaped like a sphere but is mostly empty inside.- at it's center is a space called the nucleus that contains 2 types of particles1. proton2. neutron - electron are spread around the nucleus The nucleus is:Small compared with the overall size of the atom.Extremely dense; accounts for almost all of the atoms mass.Nuclear Atom Viewed in Cross SectionNeutrons found in the nucleus; no charge; virtually same mass as a proton.Protons found in the nucleus; positive charge equal in magnitude to the electrons negative charge.Electrons found outside the nucleus;negatively charged.> # of protons = # of electrons* atoms are electrically neutral>Atomic number = # of protons - Defines an element because the atoms of a particular element have a specific number of protons .> Mass number = protons+ neutronsNitrogen Atom Two Isotopes of SodiumIsotopes- Atoms with the same number of protons but different numbers of neutrons.- The elements are arranged by atomic number (the number above the element symbol) in horizontal rows called periods and in vertical columns known as groups or families, according to similarities in their chemical properties.- The periodic table was proposed by the Russian chemist Dimitri MendeleevThe Periodic TableCopyright Cengage Learning. All rights reserved*Special Names for Groups in the Periodic TableCopyright Cengage Learning. All rights reserved*Metals Versus NonmetalsMolecules - formed when atoms react by sharing electrons forming covalent bonds.- most are composed of nonmetallic elements.> a molecule may contain atoms of the same element or atoms of 2 or more elements joined in a fixed ratio.* If the atoms belong to different elements , then the molecule is also known as a covalent compound.An ion is an atom or group of atoms that has a net positive or negative charge (because they have either lost or gained electron)> cations - positive; atoms that lose electrons ; in most cases are derived from metals> anions - negative; atoms that gain electrons; in most cases are derived from nonmetals> Because anions & cations have opposite charges , they attract each other forming ionic compounds. This force of attraction between oppositely charged ions is called ionic bonding.Ions - can be represented in several different ways. The simplest method is the chemical formula, in w/c the symbols for the elements are used to indicate the types of atoms present & subscripts are used to indicate the relative number of atoms.e.g. CO2 => contains 1 atom of carbon & 2 atoms of oxygen Covalent & Ionic CompoundsBinary Ionic CompoundsMetalnonmetalNaming Compounds Binary CompoundsComposed of two elementsIonic and covalent compounds includedBinary Covalent CompoundsNonmetalnonmetal> Review & familiarize yourself w/the names of the elements on the Periodic Table & their corrresponding symbols Flowchart for Naming Binary Compounds (Fig. 3.10)1.The cation is always named first and the anion second.2.A monatomic cation takes its name from the name of the parent element.3.A monatomic anion is named by taking the root of the element name and adding ide.Binary Ionic Compounds (Type I)Examples:KClPotassium chlorideMgBr2Magnesium bromide CaOCalcium oxideMetals in these compounds form more than one type of positive charge.Charge on the metal ion must be specified.Roman numeral indicates the charge of the metal cation.Transition metal cations usually require a Roman numeral.Binary Ionic Compounds (Type II)Examples:CuBrCopper(I) bromideFeSIron(II) sulfidePbO2Lead(IV) oxideReview & familiarize yourself w/the Common Polyatomic Ions (see Table 3.5)Examples of compounds containing polyatomic ions:NaOHSodium hydroxideMg(NO3)2Magnesium nitrate(NH4)2SO4Ammonium sulfatePolyatomic IonsPrefixes Used to Indicate Number in Chemical NamesFormed between two nonmetals.1.The first element in the formula is named first, using the full element name.2.The second element is named as if it were an anion.*A monatomic anion is named by taking the root of the element name and adding ide.*3.Prefixes are used to denote the numbers of atoms present.4.The prefix mono- is never used for naming the first element.Binary Covalent Compounds (Type III)Examples:CO2Carbon dioxideSF6Sulfur hexafluorideN2O4Dinitrogen tetroxideAcids can be recognized by the hydrogen that appears first in the formulaHCl.Molecule with one or more H+ ions attached to an anion.AcidsFlowchart for Naming AcidsIf the anion does not contain oxygen, the acid is named with the prefix hydro and the suffix ic.Examples:HClHydrochloric acidHCNHydrocyanic acidH2SHydrosulfuric acidAcidsIf the anion does contain oxygen:The suffix ic is added to the root name if the anion name ends in ate.Examples:HNO3Nitric acidH2SO4Sulfuric acidHC2H3O2Acetic acidAcidsIf the anion does contain oxygen:The suffix ous is added to the root name if the anion name ends in ite.Examples:HNO2Nitrous acidH2SO3Sulfurous acidHClO2Chlorous acidAcids