Ch 3. Elements, Compounds and Chemical Reactions

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. 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

4. Learning Check: Magnesium burns in oxygen to form magnesium oxide. If 16.88 g of Mg are consumed and 28.00 g of MgO are produced, what mass of oxygen was consumed? 2.1. Elements and atoms are described by Dalton’s atomic theory

5. + 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

6. 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

7. 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

8. 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

9. 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

10. Cathode Ray Tube (CRT) A gas filled glass tube that has electrical charge applied at both ends. Such a tube glows with light and is the precursor of the modern-day television screen. 2.2 Atoms are composed of subatomic particles

11. Discovery Of The Electron By JJ Thomson • In 1897, Thomson placed a magnet near CRT and noted deflection of the beam • Repeated experiment with an electrical field and noted that the discharge was deflected by an electrical field toward the (+) plate • Announced discovery of (-) particle, later named “electron” by Stoney 2.2 Atoms are composed of subatomic particles

12. Determining The Charge On An e-: Millikan 2.2 Atoms are composed of subatomic particles

13. 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

14. 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

15. Discovery Of The Proton • Discovered in 1918 in Ernest Rutherford’s lab • Detected using a Mass Spectrometer 2.2 Atoms are composed of subatomic particles

16. Discovery Of The Neutron • Chadwick determined that the nuclei of light atoms could be caused to disintegrate by being bombarded by alpha particles. • In collision of alpha particles with Be, a free neutron was created • the presence of the neutron confirmed in 1932 2.2 Atoms are composed of subatomic particles

17. Subatomic Particles 2.2 Atoms are composed of subatomic particles

18. Atomic Mass Unit • 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

19. 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

20. 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

21. 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

22. 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

23. Your Turn! How many neutrons are there in 52Fe? A) 52 B) 55 C) 26 D) none of these 2.2 Atoms are composed of subatomic particles

24. (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

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

26. 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

27. 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 2.3. The periodic table is used to organize and correlate facts

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

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

30. 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

31. 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

32. 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 larger molecules: P4, S8, C60, O3 , etc… 2.5. Formulas and equations describe substances and their reactions

33. 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

34. Hydrates • Hydrates are crystals that contain water molecules, for example plaster: CaSO4•2H2O • When all the water is removed (by heating), the solid that remains is said to be anhydrous (without water) CuSO4 •5H2O CuSO4 2.5. Formulas and equations describe substances and their reactions

35. 1 2 3 2 8 1 4 8 3 2 1 1 10 9 Learning Check: Count The Atoms In A Chemical Formula • Na2CO3 • (NH4)2SO4 • Mg3(PO4)2 • CuSO4•5H2O • ___Na, ___C, ___ O • ___N, ___H, ___S, ____O • ___Mg, ___P, ____O • ___Cu, ___S, ___O, ___H 2.5. Formulas and equations describe substances and their reactions

36. 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

37. 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

38. Note that the number of each type of atom balances and that the coefficient applies to the entire formula Balanced Equations 2.5. Formulas and equations describe substances and their reactions

39. 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

40. 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

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

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

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

44. 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

45. 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

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

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

48. 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

49. Naming Binary Covalent Molecules • Format: number prefix + 1st element name number prefix + stem_ide for 2nd element. • Greek prefixes mono- = 1 (generally omitted) 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

50. Learning Check: Name The Following • PF5 = • HCl = • N2O5 = • phosphorus pentafluoride • hydrogen chloride • dinitrogen pentaoxide • or dinitrogen pentoxide 2.9 Molecular and ionic comounds are named following a system