Chapter 2 PPT PDF

CHEMISTRY Chapter 2 Atoms, Molecules, and Ions Dr. Danzhu Wang Georgia State University Chapter 2: Atoms, Molecules, and Ions 2.1 Early Ideas in Atomic Theory (skip for self reading) 2.2 Evolution of Atomic Theory (skip for self reading) 2.3 Atomic Structure and Symbolism...

CHEMISTRY Chapter 2 Atoms, Molecules, and Ions Dr. Danzhu Wang Georgia State University Chapter 2: Atoms, Molecules, and Ions 2.1 Early Ideas in Atomic Theory (skip for self reading) 2.2 Evolution of Atomic Theory (skip for self reading) 2.3 Atomic Structure and Symbolism 2.4 Chemical Formulas 2.5 The Periodic Table 2.6 Molecular and Ionic Compounds 2.7 Chemical Nomenclature (combined with 2.6) 2 2.1 Early ideas in atomic theory -- self reading Atoms were first proposed by Greek philosophers. Matter is composed of small finite particles called atomos. The term atomos is derived from the Greek word for indivisible. Elements were first proposed by Aristotle. The “elements” were fire, earth, air, and water. 3 2.2 Evolution of atomic theory -- self reading 4 2.3 atomic structure and symbols Information from Atomic Theory The mass of an atom is concentrated in the nucleus and comes from protons and neutrons. Negatively charged particles called e- e- nucleus: electrons circulate around the nucleus e- e- protons but have a very small mass compared to e- and protons and neutrons. neutrons e- Have ZERO net charge e- electrons e- circulate The number of positively charged particles equals the number of negatively charged particles. 5 2.3 atomic structure and symbols Describing the Atom Simple notation is used to depict the contents of an atom. 12 6 C 6 A Z X 7  A 2.3 atomic structure and symbols Z X Atomic Number (Z) Z represents the number of protons in an atomic nucleus. The value of Z determines the identity of an atom. Z is the atomic number on the periodic table. A carbon atom has Z=6. Isotopes of carbon may have different mass numbers, but if Z=6, the atom is carbon. What is the name of the element with: Z=8? Z=14? Z=30? Z=78? Z=86? Z=92? 8  A 2.3 atomic structure and symbols Z X Mass Number (A) The total number of protons and neutrons in an atom is its mass number (A). Z = # protons A = # protons + # neutrons If an atom has 7 protons and 7 neutrons, what is its mass number? Name the element. If an atom has 92 protons and 146 neutrons, what is its mass number? Name the element. Which element has 114 neutrons and a mass number of 190? 9  A 2.3 atomic structure and symbols Z X Atomic Symbols Chemical Symbol (X) An element is represented on the periodic table by its atomic symbol (X). You need to learn the A carbon atom is represented by C. names and symbols An iron atom is represented by Fe. of the elements! A xenon atom is represented by Xe. What is the chemical symbol for an atom with 9 protons? What is the chemical symbol for an atom with A=35 and Z=17? What is the chemical symbol for an atom with a mass number of 31 and 16 neutrons? 10  A 2.3 atomic structure and symbols Z X A, Z, and X can be combined to represent a specific element. What is X for each of the following? 14 24 131 6 X 12 X 52 X Fill in the missing information for each of the following: A A 17 X with 19 neutrons Z Pb with 125 neutrons 59 27 X with ___ neutrons 40 Z X with 22 neutrons 11  Example of calculating numbers of protons, neutrons, and electrons For an atom of zinc, determine the following a. the number of protons ? b. the number of neutrons ? c. the number of electrons ? Solution Step 1: Find zinc in the periodic table (chemical symbol of zinc is Zn), atomic number of Zn is 30. the number of proton = atomic number = 30 Step 2: In the periodic table, the mass number is 65 Mass number = proton number + neutron number, so neutron number = mass number – proton number = 65 – 30 = 35 Step 3: Since the atom is neutral (net charge = 0), electron number (negative charge) = proton number (positive charge), so Electron number of Zn = proton number = 30 Why Neutrons Matter -- Isotopes Different atoms of the same element can have different numbers of neutrons. Isotopes are atoms that have the same number of electrons, the same number of protons, but different numbers of neutrons. Number of neutrons = mass number – number of protons Example: Isotope Symbols Practice writing the isotope symbols for the following isotope pairs. 1. carbon-13 and carbon-14 13 14 6 C and 6 C 2. chlorine-35 and chlorine-37 35 37 17 Cl and 17 Cl  A 2.3 atomic structure and symbols Z X Isotope Notation These are carbon isotopes. 12 13 14 6 X 6 X 6 X A 12 13 14 Z 6 6 6 On the periodic X C C C table, why does # protons 6 6 6 carbon have a mass of 12.0107? # neutrons 6 7 8 # electrons 6 6 6 mass number 12 13 14 15 2.3 atomic structure and symbols Ions Ions differ from atoms in that they have a charge; the number of electrons is either greater than, or less than, the number of protons. Cations are positively charged. They have fewer electrons than in the neutral atom. Anions are negatively charged. They have more electrons than in the neutral atom. 2.3 atomic structure and symbols Cations Metals form cations For each positive charge, the ion has one less electron than the neutral atom Na atom = 11 p+ and 11 e−, Na+ ion = 11 p+ and 10 e− Ca atom = 20 p+ and 20 e−, Ca2+ ion = 20 p+ and 18 e− Cations are named the same as the metal sodium Na → Na+ + 1e− sodium ion calcium Ca → Ca2+ + 2e− calcium ion 17  2.3 atomic structure and symbols Anions Nonmetals form anions For each negative charge, the ion has one more electron than the neutral atom F = 9 p+ and 9 e−, F − = 9 p+ and 10 e− P = 15 p+ and 15 e−, P3− = 15 p+ and 18 e− Anions are named by changing the ending of the name to -ide fluorine F + 1e− → F− fluoride ion oxygen O + 2e− → O2− oxide ion 18 Example: Counting Protons and Electrons Write the number of protons and electrons for the following ions: Na+ Cl− O2− Al3+ P3− protons electrons Copyright © McGraw-Hill Education. Permission required for reproduction or display.  Example: Ions Write the symbol for the ion that has the following number of protons and electrons: 1. 20 protons and 18 electrons Ca2+ 2. 16 protons and 18 electrons S2− 3. 26 protons and 23 electrons Fe3+ 2.3 atomic structure and symbols Isotopes and Atomic Mass The atomic mass on the periodic table is a weighted average derived from the masses and abundances of each isotope. What is the atomic mass of carbon? What is the difference between atomic mass and mass number? 12 13 14 6C 6C 6C A 12 13 14 Z 6 6 6 actual mass 12.000000000 13.003354838 14.00324199 % composition 98.9400 1.0605 1.0000 x 10-10 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒎𝒎𝒎𝒎𝒎𝒎𝒎𝒎 = 𝑚𝑚1 𝑎𝑎1 + 𝑚𝑚2 𝑎𝑎2 + 𝑚𝑚3 𝑎𝑎3 + … 21  Example #1 Chlorine has two major isotopes: 35Cl and 37Cl. Calculate the atomic mass of chlorine from the data given. Isotope Mass (amu) Abundance (%) 35Cl 34.97 75.77 37Cl 36.97 24.23 Naturally occurring chlorine consists of 75.77% Cl-35 (mass = 34.97 amu), and 24.23% Cl-37 (mass=36.97 amu). So Atomic mass of Cl = 0.7577 x (34.97 amu) + 0.2423 x (36.97 amu) = 35.45 amu 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒎𝒎𝒎𝒎𝒎𝒎𝒎𝒎 = 𝑚𝑚1 𝑎𝑎1 + 𝑚𝑚2 𝑎𝑎2 + 𝑚𝑚3 𝑎𝑎3 + … Example #2 Gallium has two naturally occurring isotopes: Ga-69 with a mass of 68.9256 amu and a natural abundance of 60.11%, and Ga-71. Use the atomic mass of gallium listed in the periodic table to find the mass of Ga-71. (atomic mass of Ga:69.72 ) atomic mass = 𝑚𝑚1 𝑎𝑎1 + 𝑚𝑚2 𝑎𝑎2 Known: atomic mass, 𝑚𝑚1 , 𝑎𝑎1 , how to calculate 𝑚𝑚2 ? 23 2.4 Chemical formulas Chemical Formulas Molecular Formula A representation of a molecule showing the number and types of atoms present Structural Formula Similar to the molecular formula but shows how atoms are connected in a molecule molecular structural ball-and-stick space-filling formula formula model model 24 2.4 Chemical formulas Chemical Formulas Elements: may be represented by discrete, individual atoms Magnesium Cobalt Silver Mg Co Ag may exist as diatomic molecules may exist as polyatomic molecules 25 2.4 Chemical formulas Chemical Formulas Each sphere represents a hydrogen atom. one hydrogen two hydrogen one hydrogen two hydrogen description atom atoms molecule molecules symbol # atoms # molecules 26 2.4 Chemical formulas Chemical Formulas: Acetic Acid Vinegar is very dilute acetic acid. C2H4O2 CH3COOH Molecular Formula Condensed Formula Structural Formula ratio of atoms indicates connectivity shows bonds C2H4O2 (CH2O) Empirical Formula simplest whole number ratio of Ball and Stick Space Filling atoms shows bonds shows volume 27 2.4 Chemical formulas Isomers Molecules may have the same chemical formula but different molecular structures and different chemical properties. Acetic Acid Vinegar is dilute acetic acid. C2H4O2 CH3COOH Molecular Condensed Structural Methyl Formate Methyl formate can be used as an insecticide. C2H4O2 HCOOCH3 Molecular Condensed Structural 2.5 The Periodic Table Dmitri Mendeleev (1869) –Self reading Mendeleev and others recognized that there were periodic relationships between physicochemical properties of known elements. For example, lithium, sodium, and potassium conduct heat/electricity and react vigorously with water. The halogens, he noted, reacted easily with other elements and were readily available in nature. Mendeleev constantly revised his observations and organized the elements until he arrived at a version of what we now call the periodic table. 29 2.5 The Periodic Table Dmitri Mendeleev (1869) – Self reading Mendeleev predicted the existence of gallium and germanium in 1871, and the elements were discovered, with the properties he predicted, a few years later. Which element is Ga? Which is Ge? 30  Periodic Table Rows are called periods. Columns are called groups. Elements with similar chemical and physical properties are in the same column (family) Elements in a given period do not usually have similar properties to one another. Each period shows the pattern of properties repeated in the next period Major Divisions of the Periodic Table Metals 1. Good conductors of heat and electricity 2. Malleable (can be pounded into flat sheets) 3. Ductile (can be drawn into wires) 4. Often shiny 5. Tend to lose electrons 6. Examples : Chromium and Copper Nonmetals 1. Poor conductors of heat and electricity 2. Tend to gain electrons 3. Examples: Oxygen and Carbon Metalloids 1. Mixed properties 2. Some are semiconductors (intermediate and temperature dependent electrical conductivity) 32 3. Examples: Silicon and Germanium 2.5 The Periodic Table Classification of the Elements 33 34 Ions and the Periodic Table Metals always form positively charged cations. For many main group metals, the charge = the group number. Typically they lose electrons to form a cation with the same number of electrons as the nearest noble gas. Nonmetals form negatively charged anions. For nonmetals, the charge = the group number − 8. They gain electrons to form and anion with 35 the same number of electrons as the nearest noble gas. Predict the charges of the monoatomic (single atom) ions formed by the following main-group elements. Al S N Rb Al3+ S2- N3- Rb+ 36 2.6 Molecular and ionic compounds The Elements in Chemical Reactions In an ordinary chemical reaction: the nucleus of each atom remains unchanged. electrons can be shared between atoms to form chemical bonds. atoms can gain or lose electrons resulting in electrically charged particles called ions. 37 2.6 Molecular and ionic compounds Predicting Ion Formation Main group atoms lose or gain electrons so that the overall electron count is the same as the nearest noble gas. Na atoms lose one electron and become Na+. Na+ has the same overall electron count as Ne. Na+ has a positive charge and is a cation. Cl atoms gain one electron and become Cl-. Cl- has the same overall electron count as Ar. Cl- has a negative charge and is an anion. Transition metals have variable charges and are difficult to predict, but we usually can say that: Zinc is usually Zn2+ Silver is usually Ag+ 38 2.6 Molecular and ionic compounds Predicting Ion Formation For main group elements, use the groups on the periodic table. alkali alkaline pnictogens chalcogens halogens metals earths 3- 2- 1- 1+ 2+ transition metals are variable 39 2.6 Molecular and ionic compounds Predicting Ion Formation Practice prediction ion formation by filling in the table. Cation or Nearest Noble Atom Ion Anion? Gas Mg K F O Sr P Se Cs 40 2.6 Molecular and ionic compounds Polyatomic Ions Thus far, only monatomic ions have been discussed. Groups of atoms bonded together into electrically charged molecules are known as polyatomic ions. These ions are very important and appear repeatedly in general chemistry, organic chemistry, and biology. 41 2.6 Molecular and ionic compounds Chemical Bonding: Attractive Forces Ionic Bonds Electrons can be transferred from one atom to another. Ionic bonds are formed by the electrostatic forces between anions and cations. Covalent Bonds Alternatively, electrons can be shared between two atoms. Covalent bonds are formed when one or more pairs of electrons are shared between two atomic nuclei. The type of bond formed between two atoms depends upon the chemical properties of the atoms involved. 42  2.6 Molecular and ionic compounds Nomenclature Ionic Compounds cation followed by anion monatomic ions: the name of the nonmetal is changed to –ide polyatomic anions: use the same ending as the ion 43 Naming Ionic Compounds Important!! Write systematic name by simply naming the ions  if cation is:  metal with invariant charge = metal name  metal with variable charge = metal name(charge)  polyatomic ion = name of polyatomic ion NH4+  if anion is:  nonmetal = stem of nonmetal name + ide  polyatomic ion = name of polyatomic ion Metal ion with invariant charge Metal ion with variable charge  metals whose ions can only have one  metals whose ions can have more than possible charge one possible charge Groups 1A1+ & 2A2+, example:Al3+,  determine charge by charge on anion and Zn2+, cation 44  name = metal name with Roman numeral charge in parentheses cation name = metal name 2.6 Molecular and ionic compounds Chemical Bonding: Ionic Compounds Ionic Compounds: can also be formed by using polyatomic ions. the bonds within a polyatomic ion are covalent. Ionic Cation Anion Cation Formula Anion Formula Compound sodium carbonate calcium sulfate lithium nitrate magnesium phosphate barium chromate ammonium hydroxide 45  2.6 Molecular and ionic compounds Nomenclature Transition Metal Ionic Compounds Transition metals may have variable charge. Roman numerals are used to denote the charge in a compound. Note: Older texts and literature may use –ic and –ous endings to designate some charges, but these are considered obsolete. 46 Memorize! 47 Polyatomic Ions Memorize! Naming Ionic compounds Example: Write the name for the ionic compound Mg3N2 Step 1: Name cation and anion Mg2+: Magnesium N3-: Nitride Step 2: A space separates the name of the cation from the name of the anion. Subscripts are not used. Mg3N2 Mg2+: Magnesium N-: Nitride Magnesium nitride Naming ionic compounds with variable charge metal ions Example: What is the name of Cu2O Step 1: Determine the charge of the cation from the anion Metal Nonmetal Formula Cu2O Elements Copper (Cu) Oxygen (O) Groups Transition element 6A Ions Cu(+?) O2- Charge balance 2 x (?) + (-2) = 0 ? = +1 Ions Cu+ (Copper(I)) O2- (Oxide) Naming ionic compounds with variable charge metal ions Example: What is the name of Cu2O Step 1: Determine the charge of the cation from the anion Step 2: Name the cation by its element name, and use a Roman numeral in parentheses for the charge – Copper(I) Step 3: Name the anion by using the first syllable of its element name followed by ide Step 4: Write the name – Copper(I) oxide Writing ionic Formulas from Ionic Charges Example: Write formula for compound containing Mg and N Step 1: Achieve a stable electron configuration of atom. Mg (metal) loses two valence electrons to form Mg2+ N (nonmetal) gains three electron to form N3- Step 2: Need 3 Mg2+ to balance 2 N3- Step 3: Write formulas: Mg3N2 Writing formulas from the name of an ionic compound Example: Write the formula for iron(III) chloride Step 1: Roman numeral (III) indicates that the charge of the iron ion is 3+, Fe3+ Type of Iron Cation Anion Name Iron(III) Chloride Analyze the problem Transition Group 7A (17) element Symbol of ion Fe3+ Cl- Step 2: Balance the charges. Need 3 Cl- to balance the positive charge of Fe3+ Step 3: Write the formula, cation first, using subscripts from the charge balance. – FeCl3 Writing formulas for compounds containing polyatomic ion Example: Write the formula for aluminum bicarbonate. Step 1: Identify the cation and polyatomic ion (anion) Cation: Al3+ Anion (Polyatomic): HCO3- Step 2: Balance the charges. Need 3 HCO3- to balance the positive charge of Al3+ Step 3: Write the formula, cation first, using the subscripts for charge balance. – Al(HCO3)3  Summary of Naming Ionic Compounds Flowchart of naming ionic compounds Metal Nonmetal Q: Does the metal form one Q: Is the nonmetal ion formed form positive ion or more? one atom or a group of atoms? Group 1A -3A, Metal in B Monatomic Polyatomic ion Zn, Ag or Cd Group 3B-12B, ion Such as CO32-, Groups 4A or Such as Cl-, S2- SO42- 5A Use the name Use the Use the first Use the name of the element name syllable of the of the element or followed by a element polyatomic ammonium Roman name, ion numeral equal followed by to the charge ide  2.6 Molecular and ionic compounds Chemical Bonding: Molecular Compounds Molecular Compounds are discrete, neutral molecules formed by a combination of nonmetals. form when atoms share electrons between nuclei. are usually gases and liquids with low boiling points or solids with low melting points. Examples: NO2 nonmetals PCl3 CO2 SF6 SiCl4 56  2.6 Molecular and ionic compounds Nomenclature Molecular Compounds Ionic compounds have atomic ratios that are obvious from the charges of the component ions. Inorganic molecular compounds held together by covalent bonds do not have obvious ratios and must be named more specifically. Prefixes are used to specify the number of atoms of each element (Need to memorize ) 57  2.6 Molecular and ionic compounds Nomenclature Molecular Compounds (continued) The more metallic element – the one toward the left/bottom of the periodic table – is named first. The more non-metallic element – the one toward the right/top of the periodic table – is named last with the suffix –ide. Note: There are exceptions for several common compounds. H2O is water, not dihydrogen monoxide. N2O is nitrous oxide, not dinitrogen monoxide. 58 Molecular Compounds: Formulas and Names Important!! Molecular compounds form between two or more NONMETALS. 1 = mono- 1. Write name of first element in formula not used on first nonmetal i. element furthest left and down 2 = di- on the Periodic Table ii. use the full name of the element 3 = tri- 4 = tetra- 2. Writes name the second element in 5 = penta- the formula with an -ide suffix, just 6 = hexa- like for the anions, however, remember 7 = hepta- these compounds do not contain ions! 8 = octa- 3. Use a prefix in front of each name to 9 = nona- indicate the number of atoms 10 = deca-  Never use the prefix mono- on the first element 59  Naming molecular compounds Example: Name the molecular compound NCl3 Step 1: Name the first nonmetal by its element name Symbol N Cl Analyze the Name Nitrogen Chloride Problem Subscript 1 3 Prefix none tri Step 2: Name the second nonmetal by using the first syllable of its element name followed by ide Step 3: Add prefix to indicate the number of atoms (subscripts) – nitrogen trichloride Writing formulas for molecular compounds Example: Write the formula for diboron trioxide Step 1: Write the symbols in the order of the elements in the name Name Diboron Trioxide Analyze the Symbol of B O problem element Subscript 2 (From di) 3 (From tri) Step 2: Write any prefixes as subscripts – B2O3  2.6 Molecular and ionic compounds Nomenclature Binary Acids Some compounds containing hydrogen form an important class of substances known as acids. A mixture of water with binary acids are named as follows: The word “hydrogen” is changed to hydro–. The nonmetallic element is named with the suffix –ic. Add the word “acid” to the name. 62  2.6 Molecular and ionic compounds Nomenclature Oxyacids Some acids contain hydrogen, oxygen, and one other element. To name oxyacids: Omit the word “hydrogen.” Start with the root name of the anion. Replace –ate with –ic or –ite with –ous. Add the word “acid” to the name. 63 Naming Acids (Formula has H as first element) 1. Binary acids – two element acids Example: HCl = hydrochloric acid 2. Oxyacids – contain oxygen Sulfurate ic Nitrate ic If polyatomic ion name ends in –ate, SO42- NO3- then change ending to –ic suffix H2SO4 HNO3 Sulfuric acid Nitric acid If polyatomic ion name ends in –ite, Sulfurous acid Nitrous acid then change ending to –ous suffix H2SO3 HNO2 SO32- NO2- Write word acid at end of all names Sulfurite ous Nitrite ous 64