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Ch 3. Elements, Compounds and Chemical Reactions

Ch 3. Elements, Compounds and Chemical Reactions. Brady & Senese, 5 th Ed. Index. 2.1. Elements and atoms are described by Dalton’s atomic theory 2.2 Atoms are composed of subatomic particles 2.3. The periodic table is used to organize and correlate facts

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Ch 3. Elements, Compounds and Chemical Reactions

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  1. Ch 3. Elements, Compounds and Chemical Reactions Brady & Senese, 5th Ed.

  2. Index 2.1. Elements and atoms are described by Dalton’s atomic theory 2.2 Atoms are composed of subatomic particles 2.3. The periodic table is used to organize and correlate facts 2.4. Elements can be metals, non-metals, or metalloids 2.5. Formulas and equations describe substances and their reactions 2.6. Molecular compounds contain neutral particles called molecules 2.7. Ionic compounds are composed of charged particles called ions 2.8. The formulas of many ionic compounds can be predicted 2.9. Molecular and ionic compounds are named following a system

  3. + Dalton’s Atomic Theory • Matter consists of tiny particles called atoms. • Atoms are the smallest stable unit of matter. • Chemical reactions rearrange atoms but do not create or destroy them. 2.1. Elements and atoms are described by Dalton’s atomic theory

  4. NaCl has a 1:1 atom ratio on the atomic level and larger Dalton’s Atomic Theory (Cont.): • A sample of a pure element contains atoms of single type. These atoms are more or less identical to each other. • Atoms of different elements differ in mass and other properties. • In a given compound the constituent atoms are always present in the same fixed numericalratio. 2.1. Elements and atoms are described by Dalton’s atomic theory

  5. Chemical Laws • The law of conservation of mass – Mass is not created or destroyed. The total mass before a chemical reaction will be exactly equal to the total mass after a chemical reaction. • Implication: reactions involve the re-organization of materials. • The law of definite proportions- The ratio of each type of atom (and therefore their masses) is fixed for a given compound • Implication: Each atom has a fixed specific mass, thus in unique combinations, the mass ratio is specific 2.1. Elements and atoms are described by Dalton’s atomic theory

  6. The Law Of Multiple Proportions • The same elements may sometimes react to form multiple different compounds with different properties. • The ratio of the elements will be different for the different compounds. • Therefore the masses of each element will be different for the different compounds. 2.1. Elements and atoms are described by Dalton’s atomic theory

  7. sulfur sulfur dioxide trioxide Mass S 32.06 g 32.06 g Mass O 32.00 g 48.00 g Use these data to prove the law of multiple proportions Using The Law Of Multiple Proportions 2.1. Elements and atoms are described by Dalton’s atomic theory

  8. Proof Of Atoms • Since the early 1980’s, we have used the Scanning Tunneling Microscope (STM) • A surface can be scanned for topographical information • The image for all matter shows spherical regions of matter- atoms 2.1. Elements and atoms are described by Dalton’s atomic theory

  9. Rutherford’s Alpha Scattering Experiment Most alpha rays passed right through the Au A few were deflected off at an angle 1 in 8000 bounced back towards the alpha ray source 2.2 Atoms are composed of subatomic particles

  10. Since most of the alpha particles were not deflected, most of the atom is empty space. Since some of the particles were deflected, they encountered small particles of the same charge. Since some particles were reflected, there must be a small dense area. Rutherford’s Nuclear Model of the Atom 2.2 Atoms are composed of subatomic particles

  11. Subatomic Particles 2.2 Atoms are composed of subatomic particles

  12. Atomic Mass • Dalton’s atomic theory states that atoms of an element have a characteristic atomic mass or atomic weightmeasured inamu (u) • Atomic masses units are based on a standard mass: 1/12 of an atom of Carbon-12 (the most common type of carbon atom) 2.2 Atoms are composed of subatomic particles

  13. Isotopes • All elements in nature are a mixtures of two or more forms with slightly different masses • Atoms of the same element with different masses are called isotopes • For example: there are naturally occurring 3 isotopes of hydrogen and 4 isotopes of iron • Isotopes have virtually identical properties other than mass, density and sometimes radioactivity • Isotopes have the same number of protons but differing number of neutrons 2.2 Atoms are composed of subatomic particles

  14. Atomic Notation • An element is a substance whose atoms all contain the identical number of protons, called the atomic number (Z) • Isotopes are distinguished by mass number(A): • Atomic number, Z = number of protons • Mass number, A = (number of protons) + (number of neutrons) • Note that for atoms, A is greater than Z: the symbol is top-heavy • The term atom indicates neutral charge overall so the number of electrons = the number of protons 2.2 Atoms are composed of subatomic particles

  15. 235 U 92 Mass number, A (protons + neutrons)  Chemical Symbol  Atomic number, Z (number of protons)  Example: uranium-235 This information can be summarized: • Number of protons = 92 ( = number of electrons) • Number of neutrons = 143 • Atomic number (Z) = 92 • Mass number (A) = 92 + 143 = 235 • Chemical symbol = U 2.2 Atoms are composed of subatomic particles

  16. Learning Check: Fill in the blanks: symbol neutrons protons electrons 60Co 81Br 36 29 29 33 27 27 46 35 35 2.2 Atoms are composed of subatomic particles

  17. (75.77×34.9689) + (24.23×36.9659) u 100 Learning Check: Atomic Mass Naturally occurring chlorine is a mixture of two isotopes. In every sample of this element, 75.77% of the atoms are chlorine-35 and 24.23% are chlorine-37. The measured mass of chlorine-35 is 34.9689 u and that of chlorine-37 is 36.9659 u. Calculate the average atomic mass of chlorine. 35.45 u 2.2 Atoms are composed of subatomic particles

  18. Periodic Table • arranged in numbered rows – “periods” • columns called “groups” or “families” 2.3. The periodic table is used to organize and correlate facts

  19. Periodic Table • Mendeleev first arranged atoms by increasing atomic mass. Noted repeating (periodic) properties • Modern table is arranged by increasing atomic number (Moseley) 2.3. The periodic table is used to organize and correlate facts

  20. Some Important Classifications: • A groups = representativeelements or main group elements I A = alkali metals II A = alkaline earth metals VII A = halogens VIII = noble (also inert) gases • B groups = transition elements • Inner transition elements = elements 58 – 71 and 90 – 103 58 – 71 = lanthanide elements 90 – 103 = actinide elements 2.3. The periodic table is used to organize and correlate facts

  21. The modern periodic table 2.3. The periodic table is used to organize and correlate facts

  22. Metals, Nonmetals, And Metalloids 2.4. Elements can be metals, non-metals, or metalloids

  23. Properties Of Metals • reflect light (have metallic luster) • Can be hammered or rolled into thin sheets (are malleable) andcan be drawn into wire (are ductile) • Are solids at room temperature (except Hg) • conduct electricity and heat 2.4. Elements can be metals, non-metals, or metalloids

  24. Nonmetals And Metalloids • Nonmetals • Lack the properties of metals • Dull luster • Tend to pulverize when struck with a hammer (brittle) • Non-conductors of electricity and heat • Many are gases, a few solids, and one liquid (Br) • React with metals to form (ionic) compounds • Metalloids • Have properties between metals and nonmetals 2.4. Elements can be metals, non-metals, or metalloids

  25. Chemical Formulas • Are symbols used to indicate atoms in elements and compounds • Free elements are not combined with another element in a compound. Examples: Fe (iron), Na (sodium), and K (potassium) • Many non-metals occur in groups of 2 (as diatomic molecules)- H2, O2, N2, F2, Cl2, Br2, I2 • Some elements occur as molecules: P4, S8, C60, O3 , etc… 2.5. Formulas and equations describe substances and their reactions

  26. Chemical Formulas (Cont.) • Specify the composition of a substance • Fe2O3 is composed of the elements iron and oxygen in a 2:3 ratio • CO(NH2)2 expands to CON2H4, but parentheses often group atoms to show the compound’s structure 2.5. Formulas and equations describe substances and their reactions

  27. Chemical Equations • 2 HCl(aq) + CaCO3(s) CaCl2(aq) + H2O(l) +CO2(g) • HCl and CaCO3are called reactants • CaCl2,H2O,CO2are called the products • Reactants are separated from products with “” that means “yields” • States matter: for solids use (s), liquids (l), gases (g), and for substances dissolved in water (aqueous solutions) use (aq). 2.5. Formulas and equations describe substances and their reactions

  28. The number of atoms of each type must remain the same on each side of the arrow subscripts must not change- they define the identity of the substances Coefficients- numbers in front of formulas-- indicate the number of molecules Balancing achieved by adjusting coefficientsonly Balanced Equations 2 H2 + O2 →2 H2O 2.5. Formulas and equations describe substances and their reactions

  29. Molecules Form When Nonmetallic Elements Combine • Molecules are neutral particles made of 2 or more atoms. • Many molecular compounds contain hydrogen: Group Noble Period IVA VA VIA VIIA Gas 2 CH4 NH3 H2O HF Ne 3 SiH4 PH3 H2S HCl Ar 4 GeH4 AsH3 H2Se HBr Kr 5 SbH3 H2Te HI Xe 2.6 Molecular compounds contain neutral particles called molecules

  30. Alkanes • Alkanes are hydrocarbons (contain only C and H) • Always have a ratio of atoms CnH2n+2 • Named using a prefix designating the number of C • All have –ane suffix. 2.6 Molecular compounds contain neutral particles called molecules

  31. Learning Check: Name that alkane • ethane • butane • octane 2.6 Molecular compounds contain neutral particles called molecules

  32. Your turn! Which of the following is heptane? • C6H12 • C7H14 • C6H14 • C7H16

  33. Your turn! Which is the correct name for C4H10? • methane • ethane • propane • pentane • none of these butane

  34. Other Organic Compounds Alkenes- hydrocarbons with fewer H than the alkanes. CnH2n. Use the same prefixes, but have the suffix -ene. • C2H4 : ___________ • C3H6: _____________ ethene propene 2.6 Molecular compounds contain neutral particles called molecules

  35. Other Organic Compounds (Cont.) Alcohols- Replace one H in an alkane with an -OH group • Same prefixes, suffix becomes –anol • CH3OH is ____________ • C2H5OH is _______________ methanol ethanol 2.6 Molecular compounds contain neutral particles called molecules

  36. Your Turn! What is the name of CH3CH2CH2CH2OH? • butanol • propanol • pentanol • tetranol • none of these

  37. Your Turn! What is a formula for heptene? • C6 H12 • C7H14 • C6H14 • C7H16 • none of these

  38. Positively charged ions are called cations Negatively charged ions are called anions subscripts in the formula always specify the smallest whole-number ratio of the ions needed to make a neutral combination (formula unit) Ionic Compounds 3 2 Fe3+ O2- FeO 2 3 2.7 Ionic compounds are composed of charged particles called ions

  39. What About Ions? • Number of protons = number of e- if neutral • Number of protons < number of e- if negative • Number of protons > number of e- if positive • The number of protons never changes How does Ca form Ca2+? Ca loses 2 electrons How is N3- formed? N gains 3 electrons 2.7 Ionic compounds are composed of charged particles called ions

  40. Learning Check: Fill in the blanks: Symbol neutrons protons electrons 60Co3+ 81Br- 36 29 27 33 27 24 36 46 35 2.7 Ionic compounds are composed of charged particles called ions

  41. Noble gases are especially stable Main group elements will often gain or lose electrons to have the same number of electrons as the nearest noble gas Metals form cations by losing electrons What is the expected charge on: Ca? Na? Nonmetals form anions by gaining electrons What is the expected charge on: N? O? The Charges On Many Representative Elements Can Be Predicted 2+ + 3- 2- 2.7 Ionic compounds are composed of charged particles called ions

  42. The cation (metal) is listed first in the formula The subscripts in the formula must produce an electrically neutral formula unit The subscripts should be the set of smallest whole numbers possible The charges on the ions are not included in the finished formula of the substance Rules For Writing Formulas Of Ionic Compounds 2.8 The formulas of many ionic compounds can be predicted

  43. Determining The Formula Of An Ionic Compound • The “Criss-cross” rule often works as a shortcut for determining formula subscripts from charges of ions. • If you choose this approach, make sure that the subscripts are reduced to the lowest whole number. Al3+ O2- Mg2+ O2- NH4+ PO43- Al3+ O2- Al2O3 MgO Mg2+O2- (NH4)+ (PO4)3- (NH4)3PO4 2.8 The formulas of many ionic compounds can be predicted

  44. Your Turn! Which of the following is the correct formula for the formula unit composed of potassium and oxygen ions? • KO b) KO2 c) K2O d) none of these Which of the following is the correct formula for the formula unit composed of Fe3+ and sulfide ions? a) FeO b) Fe3O2 c) Fe2O3 d) none of these

  45. Transition Metals as well as Tin (Sn) and Lead (Pb) Generally Multiple Charges Transition Metals: Chromium Cr2+, Cr3+ Copper Cu+, Cu2+ Manganese Mn2+, Mn3+ Iron Fe2+, Fe3+ Cobalt Co2+, Co3+ Gold Au+, Au3+ Mercury Hg22+, Hg2+ etc… Tin and Lead: Tin Sn2+, Sn4+ Lead Pb2+, Pb4+ Exceptions: Zinc Zn2+ Silver Ag+ Cadmium Cd2+ 2.8 The formulas of many ionic compounds can be predicted

  46. Some PolyatomicIons (Ions With Two Or More Atoms): 2.8 The formulas of many ionic compounds can be predicted

  47. The Stock System Of Naming Ionic Compounds • Cations: • If the metal forms only one positive ion, the cation name is the English name for the metal • If the metal forms more than one positive ion, the cation name is the English name followed, without a space, by the numerical value of the charge written as a Roman numeral in parentheses • Anions: • monatomic anions are named by adding the “–ide” suffix to the stem name for the element • polyatomic ions use guide on next slide 2.9 Molecular and ionic comounds are named following a system

  48. Naming Oxoanions • Many nonmetals form two different oxoanions: • The ion with more oxygen atoms has the –ate suffix • The ion with fewer oxygen atoms has the -ite suffix • NO3- = Nitrate and NO2- = Nitrite • SO42- = Sulfate and SO32- = Sulfite Some elements (generally halogens) form more than two oxoanions: • The ion with the greatest oxygens has the per- prefix • The ion with the least oxygens has the hypo- prefix • ClO4- = Perchlorate, ClO3- = Chlorate, ClO2- = Chlorite and ClO- = Hypochlorite

  49. Naming Binary Molecules The first element in the formula is identified by its English name, the second by appending the suffix –ide to its stem Chemical Name as Name as Symbol Stem First Element Second Element O ox- oxygen oxide N nitr- nitrogen nitride P phosph- phosphorus phosphide Cl chlor- chlorine chloride I iod- iodine iodide 2.9 Molecular and ionic comounds are named following a system

  50. Naming Binary Covalent Molecules • Format: number prefix + 1st element name number prefix + stem_ide for 2nd element. • Greek prefixes mono- = 1 (omitted on 1st atom) hexa- = 6 di- = 2 hepta- = 7 tri- = 3 octa- = 8 tetra- = 4 nona- = 9 penta- = 5 deca- = 10 2.9 Molecular and ionic comounds are named following a system

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