Atoms, Molecules and Ions Chapter 2 homework 17, 21, 24, 31, 41, 44ab, 47, 51, 53, 56, 59, 63, 67, 71, 72, 75, 78, 89, 91, 105 Summary Atoms Subatomic Particles Isotopes Periodic Table Classifications Diatomic Elements Ions Naming Compounds Dalton’s Atomic Theory 1. Matter is composed of indivisible particles called atoms. 2. Atoms of the same element are identical and have the same properties. A chunk of sodium is made up of a huge number of atoms, each having the same properties. Na + H2O NaOH +1/2 H2 (each Na atom reacts with one molecule of H2O to form Na+). Atoms of one element are different to those of another element (Cu is different than Au). Atoms of one element cannot be changed to form atoms of another element by chemical reactions. Compounds are formed when atoms of more than one element combine. Atomic Theory Compounds are composed of atoms of different elements combined in simple, whole number ratios. 2H2 + O2 2 H2O the ratio of H/O = 2/1 in H2O During chemical reactions, atoms rearrange into different combinations (mass is conserved). Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) Composition of the Atom Subatomic Particles Electron() …. Negatively charged particles with negligible mass with respect to protons and neutrons The charge of an electron is -1.602x10-19 Coulombs Proton(+) positively charged particles that cancel the charge of the electrons The charge of an prtoton is +1.602x10-19 Coulombs Neutron(0) neutral particles that are massive, same mass as the protons Subatomic Particles Particle Mass Relative Charge Proton 1.673x10-24 g (1.0073 amu) +1 Neutron 1.675x10-24 g (1.0087 amu) 0 Electron 9.109x10-28 g (5.486x10-4 amu) -1 atomic mass unit (amu) = 1.66054x10-24 g Atomic mass units are used because the masses of atoms are small and thus cumbersome to express in grams (a heavy atom can be between 10-22-10-23 grams) 1 gram = 6.02 x 10 23 amu,s 1amu is 1/12 of 12 C………this carbon isotope is assigned 12 anu,s Naturally occurring carbon contains: 98.93% of 12C and 1.07% of 13C Average atomic mass of carbon atom is (0.9893) (12) + (0.0107) (13) = 12.01 amu Naturally occurring chlorine contains; 75.78 % of 35Cl and 24.22 % of 37C What is the average mass? (35.45 amu). How many protons and neutrons in 37Cl?? Most of the space in an atom is occupied by electrons The nucleus if very small and extremely dense Rutherford’s Experiment: Alpha particles backscattered or deflected by small nuclei of a gold foil Note here that the size of atoms are expressed in Angstroms 10-10 m, 10-8 cm, 0.1 nm atomic number/ mass number Atomic Number = # Protons Mass number = # protons + #neutrons The atomic number for an element is the number above the element symbol in the periodic table and the mass number is written below the symbol 6 C 12.011 Atomic number Mass number Atomic Number What do we know about the number of protons, neutrons, and electrons in a neutral carbon atom? 6 C 12.011 Isotopes Atoms of the same element with different numbers of neutrons are called isotopes. Can atoms of the same elements have different masses? What is the mass number for a carbon atom with: 6 neutrons? …………..12 7 neutrons?...................13 Carbon 12 and carbon 13 have 6 and 7 neutrons respectively. They have different masses Isotope Symbols Isotope symbols are used to show the number of neutrons in an atom. Mass number Atomic number 13 6 Isotopes of Hydrogen The Periodic Table The Periodic Table The periodic classification of elements was developed in 1869 by Dmitri Mendeleev. Elements are arranged in rows of increasing atomic number Elements in the same column have similar chemical and physical properties The Periodic Table Rows are called Periods Columns are called Groups or Families The Periodic Table Table 2.3 Group IA - Alkali Metals (except H) Group 2A - Alkaline Earth Metals Group 6A - Chalcogens Group 7A - Halogens Group 8A - Noble Gases The Periodic Table The elements can also be classified as metals, nonmetals or metalloids. Metals - left of the stair-step line. Nonmetals - Right of the stair-step. Metalloids - Lie on the stair-step. Metals, Nonmetals, and Metalloids Molecular Elements A molecule is a group of atoms chemically bonded. Molecular elements are composed of only one type of atom. S8 P4 Cl2 Diatomic Elements Diatomic elements are composed of molecules that contain two like atoms. Know these: H2 N2 O2 F2 Cl2 Br2 I2 Structural formula of methane Ball and stick structure of methane Space filling model of methane Molecules, formulas Compounds that are composed of molecules are called molecular compounds Benzene Molecular formula C6H6: indicates the actual number and type of atoms Empirical formula CH// (relative number of atoms, smallest whole ratio) SiO2 vs. CO2 empirical molecular formulas One is a molecule the other is not Both are compounds SiO2 consists of Si atoms surrounded by four oxygens and each oxygen is shared by two silicon atoms CO2 Ions Ions are atoms or groups of atoms that have an electrical charge. Ions Loss of electrons results in cations: Na Na+ + e- 11 protons/11 electrons 11 protons/10 electrons (loss of an electron) Gain of electrons results in anions: Cl + e- Cl- (gain of the electron released from Na) 17 protons/17 electrons 17 protons/18 electrons Na + Cl + e- Na+ + e- + Cl- Na + Cl NaCl Na + Cl NaCl NaCl structure the small atoms are the cations and the large (blue are the anions. Both schematics shown represent the smallest repeating units Common Monatomic Ions Ag+ Cd2+ Zn2+ Ion_Charges Figure 2.22 in your text Ions Predict the charge on each monatomic ion: Ca? O? Br? Cs? Ions Predict the charge on each monatomic ion: Ca2+ O2 Br Cs+ Ions How are cations and anions named differently? Ca2+ calcium ion O2 oxide ion Br bromide ion Cs+ cesium ion Ions How are cations and anions named differently? Ca2+ calcium ion O2 oxide ion Br bromide ion Cs+ cesium ion Polyatomic ions are like molecules but with a charge: Examples: OH-, NH4+, CO32-, PO43- NO3 nitrate ion NO2 nitrite ion SO42 sulfate ion SO32 sulfite ion ClO3 chlorate ion ClO2 chlorite ion Formation of Ionic Compounds Ionic Compounds Ionic compounds are composed of cations and anions. Most consist of a metal cation and a nonmetal anion or polyatomic ion. Examples: NaCl Cu(OH)2 Ca3(PO4)2 Ionic Compounds Compounds are neutral, so the ion charges add to zero. Ca3(PO4)2 Writing Ionic Formulas What is the formula for: Aluminum hydroxide (Al3+ , OH-)______ Calcium nitride (Ca 2+, N-3)________ Magnesium oxide (Mg2+ , O-2)________ Mg__ Al___ O_4__ Hint: four oxygen ions are needed The latter is a common mineral known as “spinel” Naming Binary Ionic Compounds When Metal forms a Single Cation Simply name the cation first and then the anion. The monatomic anion name retains the root name and adds the suffix -ide. Examples: MgCl2: Magnesium chloride Li3N: Lithium nitride Naming Ionic Compounds When an ion is a polyatomic ion, the name of the ion is used in the name. Examples: AgNO3: Silver nitrate Ca3(PO4)2: Calcium phosphate Naming Binary Ionic Compounds When Metal forms Several Cations: Stock System 1. Determine the charge on the metal from the formula: eg. CuO (Cu2+) Cu2O (Cu+) 2. Write the cation name followed by the roman numeral positive charge in parentheses, and then the name of the anion with the -ide ending. Copper(II) oxide Copper(I) oxide Naming Binary Ionic Compounds When Metal forms a Several Cations: Classical System 1. Determine the charge on the metal from the formula: eg. CuO (Cu2+) Cu2O (Cu+) 2. Write the cation name with the suffix (-ic or -ous) that corresponds to the charge, and then anion name with the -ide ending. Cupric oxide Cuprous oxide Name the following compounds using the Stock System. FeS Fe2S3 PbO2 PbO CrO3 Write the formula for the following Copper(II) nitrate Iron(III) phosphate Types of Substances Which of the following are composed of ions? MgCl2 CO2 Cl2 Li3N Which of the following are composed of ions? MgCl2 magnesium chloride CO2 carbon dioxide Cl2 chlorine Li3N lithium nitride Molecular Compounds Molecular compounds are usually composed of nonmetals and are NOT composed of ions. Examples: N2O, NO, NO2, N2O4, N2O5 CO2, CO, SF4, SF6 Naming Molecular Compounds Greek prefixes are used to show the number of each element in the compound. CCl4 is named carbon tetrachloride. Prefixes: 1 mono 5 penta 2 di 6 hexa 3 tri 7 hepta 4 tetra 8 octa Common Molecular Compounds that Retain Old Name Water H2O Ammonia NH3 Hydrogen peroxide H2O2 Acids (HX) Some molecular substances give acidic properties when dissolved in water. When they are dissolved in water we call them acids. For example: HCl(g) - hydrogen chloride HCl(aq) - hydrochloric acid Binary Acids Binary acids are composed of hydrogen and a single nonmetal. HF hydrofluoric acid HCl hydrochloric acid HBr hydrobromic acid HI hydroiodic acid H2S hydrosulfuric acid Oxyacids Oxyacids are composed of hydrogen and an oxyanion (oxygen containing polyatomic ion). Examples: HNO3 Nitric acid HNO2 Nitrous acid H2SO4 Sulfuric acid H2SO3 Sulfurous acid Oxyacids Polyatomic Ion (X) Acid (HX) - ate -ic - ite -ous Examples: HNO3 Nitric acid HNO2 Nitrous acid H2SO4 Sulfuric acid H2SO3 Sulfurous acid Organic compounds Methane, ethane, propane, butane, pentane, hehane Benzene, cyclohexane, ethanol ….. Alcohols etc.