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NEAR EAST UNIVERSITY ENGINEERING FACULTY CHEM 101-GENERAL CHEMISTRY INSTR : FİLİZ ALSHANABLEH C H E M 1 0 1 CHAPTER 2 ATOMS & MOLECULES Atomic Structure and Mass . Fundamental Concepts of Atom . Atomic Number-Mass Number-Isotopes Ions Compounds and Chemical Bonds . Chemical Formulas . Chemical Bonding The Periodic Table Chemical Nomenclature EARLY HISTORY OF CHEMISTRY Greeks were the first to attempt to explain why chemical changes occur. Alchemy dominated for 2000 years. Several elements discovered. Mineral acids prepared. Robert Boyle was the first “chemist”. Performed quantitative experiments. BP 250,000 : Homo Sapience – Stone Tools. 80,000 : Fire (Cooking) 10,000 : Farming, Neolithic Age 7,000 : Copper 6,000 : Wine 5,000 : Bronze 3,300 : Iron 2,400: Atomic Theory(Democritos) 2,000: (Alchemy) 500: Metallurgy (Bauer), Alchemy (Paracelsus ) 400: Modern Chemistry: (Robert Boyle, Priestley Lavoisier, Proust, Dalton …) DALTON’S ATOMIC THEORY (1808) 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 with each other. A given compound always has the same relative numbers and types of atoms. CONCEPT CHECK Which of the following statements regarding Dalton’s atomic theory are still believed to be true? I. Elements are made of tiny particles called atoms. II. All atoms of a given element are identical. III. A given compound always has the same relative numbers and types of atoms. IV. Atoms are indestructible. EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS (I) J. J. Thomson (1898—1903) Postulated the existence of electrons using cathode-ray tubes . Determined the charge-to-mass ratio of an electron. The atom must also contain positive particles that balance exactly the negative charge carried by particles that we now call ELECTRONS. Copyright © Cengage Learning. All rights reserved 6 EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(II) Robert Millikan (1909) Performed experiments involving charged oil drops. Determined the magnitude of the charge on a single electron. Calculated the mass of the electron. EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(III) Ernest Rutherford (1911) Explained the nuclear atom. Atom has a dense center of positive charge called the NUCLEUS. Electrons travel around the nucleus at a relatively large distance. EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(IV) THE MODERN VIEW OF ATOMIC STRUCTURE(I) The atom contains: Electrons – found outside the nucleus; negatively charged. Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge. Neutrons – found in the nucleus; no charge; virtually same mass as a proton. The nucleus is: Small compared with the overall size of the atom. Extremely dense; accounts for almost all of the atom’s mass. THE MODERN VIEW OF ATOMIC STRUCTURE(II) Nuclear Atom Viewed in Cross Section ATOMIC NUMBER AND MASS NUMBER Atomic Number (Z): The number of protons in a particular atom. Mass Number (A): The total number of protons and neutrons in the nucleus of a particular atom. Atomic symbols Isotopes : Atoms of an element with same atomic number but different mass number. . Show almost identical chemical properties . In nature most elements contain mixtures of isotopes. ISOTOPES OF HYDROGEN: ATOMIC MASSES(I) Atomic Mass Unit (amu) is the standard unit that is used for indicating mass on an atomic scale. It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12. C-12 isotope with 6 proton and 6 neutron has a mass exactly 12amu Relative atomic masses ; . H: 1.008amu . He: 4.003amu . O: 16.00amu . Fe: 55.85amu ATOMIC MASSES(II) AVERAGE ATOMIC MASSES Average Atomıc Mass of Carbon: 98.89% of 12 amu + 1.11% of 13.0034 amu = natural abbundance of C*12 exact number natural abbundance of C*12 (0.9889)(12 amu) + (0.0111)(13.0034 amu) = = 12.01 amu EXERCISE An element consists of 62.60% of an isotope with mass 186.956 amu and 37.40% of an isotope with mass 184.953 amu. Calculate the average atomic mass and identify the element. SOLN: (186.956x0.6260)+(184.953x0.3740) = 186.2 amu Rhenium (Re) MOLECULES AND IONS(I) MOLECULE : Two or more atoms joined and acting as a unit. TYPES MOLECULES : . Diatomic Molecule (contains only 2 atoms) HCl, H2, O2, NaCl, CO, CO2 , H2O, Cl2 . Polyatomic Molecule (contains more than 2 atoms) O3, H2SO4, SO3, P4, KMnO4 MOLECULES AND IONS(II) IONS : is a charged species formed from a neutral atom or molecule when electrons are gained or removed from. Ion with a net (+)ve charge........ CATION Na atom 11 proton 11 electron Na + ion 11 proton 10 electron Ion with a net (-)ve charge........ ANION Cl atom 17 proton 17 electron Cl - ion 17 proton 18 electron TYPES IONS : . Monatomic Ion (contains only 1 atom) H+, Cl-, O2-, Na+, Fe2+ , N-3 . Polyatomic Ions (contains more than 1 atoms) COMPOUNDS AND CHEMICAL FORMULAS CHEMICAL FORMULAS . Empirical formula (the simplest formula) . Molecular formula (the true formula) CHEMICAL BONDING(I) Atoms combine to make compounds by forming CHEMICAL BONDS Three broad categories; . Covalent Bonding . Metallic Bonding . Ionic Bonding COVALENT BONDS . Bonds form between atoms by sharing electrons. . Resulting collection of atoms is called a molecule. CHEMICAL BONDING(II) Metallic Bonding Bonds form between positively charged İon cores and free valence electrons Ionic Bonding Bonds form due to force of attraction between oppositely charged ions. THE PERIODIC TABLE(I) Groups or Families – elements in the same vertical columns; have similar chemical properties Periods – horizontal rows of elements THE PERIODIC TABLE(II) CLASSIFICATION OF ELEMENTS I. Metals: Good conductor of heat & electricity, tends to form cations II. Nonmetals: Poor conductor of heat & electricity, tends to form anions III. Metalloids: Properties between those metals & nonmetals NAMING COMPOUNDS Binary Compounds Composed of two elements Ionic and covalent compounds included Binary Ionic Compounds Metal—nonmetal Binary Covalent Compounds Nonmetal—nonmetal BINARY IONIC COMPOUNDS (TYPE I) The cation is always named first and the anion second. A monatomic cation takes its name from the name of the parent element. A monatomic anion is named by taking the root of the element name and adding – ide . Ionic compounds written by their imperical formula. X 2+ + Y 2= X 2 Y 2 = XY Examples: KCl Potassium chloride MgBr2 Magnesium bromide CaO Calcium oxide Examples of compounds containing polyatomic ions: NaOH Sodium hydroxide Mg(NO3)2 Magnesium nitrate (NH4)2SO4 Ammonium sulfate BINARY IONIC COMPOUNDS (TYPE II) Metals 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. Examples: CuBr Copper(I) bromide FeS Iron(II) sulfide Fe2S3 Iron(III) sulfide PbO2 Lead(IV) oxide BINARY COVALENT COMPOUNDS (TYPE III) . . . . Formed between two nonmetals. The first element in the formula is named first, using the element name. The second element is named as if it were an anion. Prefixes are used to denote the numbers of atoms present. The prefix mono - is never used for naming the first element. Prefixes Used to Indicate Number in Chemical Names Examples: CO2 Carbon dioxide CO Carbon monoxide SF6 Sulfur hexafluoride N2O4 Dinitrogen tetroxide FLOWCHART FOR NAMING BINARY COMPOUNDS Copyright © Cengage Learning. All rights reserved 27 EXERCISE Which of the following compounds is named incorrectly? a) KNO 3 b) TiO 2 c) Sn(OH) 4 d) PBr 5 e) CaCrO 4 potassium nitrate titanium(II) oxide tin(IV) hydroxide phosphorus pentabromide calcium chromate 28