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TOPIC II: ELEMENTS AND COMPOUNDS

TOPIC II: ELEMENTS AND COMPOUNDS. Nuclear Atom Isotopes Periodic Table of Elements Molecules and Compounds Naming Simple Ionic Compounds Naming Binary Molecules. Kotz & Treichel Ch 2,3. Chapter 2: Atoms and Elements. 1. History of discovery of the atomic nature of

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TOPIC II: ELEMENTS AND COMPOUNDS

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  1. TOPIC II: ELEMENTS AND COMPOUNDS • Nuclear Atom • Isotopes • Periodic Table of Elements • Molecules and Compounds • Naming Simple Ionic Compounds • Naming Binary Molecules Kotz & Treichel Ch 2,3

  2. Chapter 2: Atoms and Elements 1. History of discovery of the atomic nature of all matter and the various particles found within the atom: Kotz, 2.1-2.2, excellent reading on all topics. Saunders CD-ROM: animated film clips Reading, viewing assignment Lecture Topics, Kotz, 2.3-2.8

  3. Atomic Structure, Atomic Number, Mass • All matter (anything that has mass and occupies • volume) can be classified as: • an element (basic building blocks of nature: H, O, Au ) • a compound (made up of two or more elements) • a mixture (any physical combination of the above) Elements, the simplest forms of matter, are composed of unique tiny particles called atoms.

  4. Atomic Structure The atom itself is composed of three types of “subatomic particles”, the proton (p), the neutron (n), and the electron (e). Each element has its own unique pairings of these three particles. It is the number and the placement of these particles which gives rise to the different properties exhibited by each element.

  5. Comparative Mass, Charge: Nuclear Particles

  6. Nuclear Particle Location Within the Atom 1. Protons and Neutrons: “Nucleus of Atom” compact positive mass in center of atom “all” of the mass, negligible volume (10-2 pm) 2. Electrons: “Outside the Nucleus” cloud of negative charge “all” of the volume (103 pm), negligible mass

  7. THE “NUCLEAR” ATOM Nucleus, C atom . Electron cloud

  8. ATOMIC SYMBOLS Each atom of an element can be represented by a symbol that describes how many protons, neutrons and electrons are contained in this basic unit: Mass number, A: total #, p + n A Elemental symbol X Z Atomic Number, Z: #p (equals #e)

  9. The Mass Number, A Because atoms (and the subatomic particles) are so tiny, a relative mass scale was setup to describe atomic weights in a convenient numerical range. The atom of Carbon which contains 6 protons and 6 neutrons in its nucleus is assigned the weight of 12.00 amu (atomic weight units), which essentially makes the mass of each proton and neutron 1.00 amu. Accordingly, A, the mass number of the atom, represents both the total number of nuclear particles (p + n) and the approximate mass of the atom (in amu’s)

  10. Z, The Atomic Number All known elements are listed in the familiar “Periodic Table of the Elements” in order of increasing atomic number, found usually in the upper right hand corner above each element’s symbol. The atomic number represents the number of protons in the nucleus of every atom of that element. Since every atom is electrically neutral, the number of protons in the nucleus represents the total positive charge of the nucleus, which is exactly balanced by the total number of negatively charged electrons outside the nucleus.

  11. Examples, Atomic symbols Atomic Mass #, p + n A X Element Atomic #, p (or e) Z 238 - 92p = 146n 19 - 9p = 10n 19 F 238 U 9 92 9p, 9e 92p, 92e

  12. Group Work 2.1: Atomic Symbols

  13. Isotopes of the Elements For a given element, the number of protons and electrons is a fixed value and determines which element is being described. The number of neutrons in the atom of a given element is not fixed, and several different atoms of a given element are generally found, varying in atomic mass due to differingnumbers of neutrons. The different atoms of a given element which vary by neutron count and by mass are described as “isotopes” of that element.

  14. Isotopic Symbols Isotopic symbols represent specific isotopic forms of an element. Consider hydrogen:

  15. Atomic Mass, revisited: The atomic mass of any isotope of an element can be approximated by a simple addition of the number of p’s and n’s in the nucleus. However, naturally occurring samples of any element generally include several different isotopes of different atomic masses. The atomic mass value given for each element (as found in your Periodic Table) is a weighted average of all the isotopes.

  16. The given atomic mass for any element will be closest to the most abundant element in most cases. Consider below the calculation of the atomic mass of magnesium, 24.305 amu: General Method of Calculation: Average Mass Element, amu = (mass, isotope A X % abundance A) + (mass, isotope B X % abundance B) + (mass, isotope C X % abundance C)......

  17. Calculation of average atomic mass of Magnesium: (23.9850 x .7899) + (24.9858 x .1000) + (25.9826 x .1101) = (18.95) + (2.499) + (2.861) = 24.31 amu

  18. Note: You may detect a discrepancy between the mass, in amu’s, of individual protons and neutrons (as given in the first table presented, lecture 3) and the given masses of the Mg isotopes: Mass, proton: 1.007 amu Mass, neutron, 1.009 amu Mass, 24 Mg , 23.9850 amu 12 1.007 amu X 12 = 12.084 1.009 amu X 12= 12.108 24.192

  19. Why Don’t the Numbers Add Up? The mass of the individual particles, p and n, were determined by methods which measured individual particles not bound up in the nucleus. When these particles are packed into the nucleus of an atom, a mass loss (or “mass defect”) always occurs. This loss is thought to be the result of a matter to energy conversion which holds together the nucleus, called the “binding energy”... (See Chapter 24, p 1099) In the nucleus of atoms, p’s and n’s show a mass very close to 1.00 amu rather than 1.007 or 1.009.

  20. The Periodic Table • Lists all known elements in order of increasing • atomic number, left to right and top to bottom • Arranged so that elements of similar chemical • properties fall into the same column (called a group • or family) • Each horizontal line(called a period) represents • elements of a complete range of chemical properties.

  21. The beginning of each “period” features a very active metal • The middle of the period includes increasingly • less active metals • The right hand side of the period includes elements • becoming increasingly non-metallic • The end of the period features an inert, unreactive • element found only in the gas state

  22. Each line of the table features a complete swing from reactive metal to non metal to inert gas. The action is repeated in each successive period, named after the action of a pendulum, in which each revolution or swing is also called a period or “repeated occurrence , from beginning to end and then back again”

  23. metalloids metals Non metals Noble gases

  24. Main Group or “Representative Elements” Noble gases inert gases rare gases 8A (0) Halogens 7A Alkaline earth metals 2A Alkali metals 1A (except H)

  25. Transition Metals 3 columns 8B: more alike “across” than “down” Non- naturally occurring, newly found in lab

  26. The inner Transition Metals: Found beneath the main body of the PT, but belonging to Period 6 and 7: #58 #71 “Lanthanides” #90 #103 “Actinides”

  27. solids liquids gases Note the seven common elements found in nature as “diatomic molecules”

  28. Molecules and Compounds, Chapter 3 Lecture Topics, Kotz, 3.1-3.5 Atoms of the elements come together to form molecules and compounds. Molecules are made by the bonding of two or more atoms together into a independent, uncharged unit. The simplest molecules are the “diatomic elements”: H2 N2 O2F2 Cl2 Br2 I2

  29. Compounds of the elements may be described as “molecular” or “ionic” in nature, depending on the nature of the elements involved: Molecular compounds are typically formed between non-metals, bonded together in a single “molecular” unit: CO2 H2O NH3 PBr3 CH4 SO3 Ionic compounds are formed when metalsbond to nonmetals. The metal and the nonmetal components exist as individual charged units called “ions”: NaCl (Na+Cl-) Fe(OH)3 [Fe3+,3(OH)- ] CuSO4 (Cu2+SO42- )

  30. Formulas for Molecules and Compounds All compounds and molecules are represented by a formula which summarizes number of atoms of each element present: H2SO4CH3CH2OH NaCl C12H22O11 F2 Fe2(SO4)3 (NH4)2CO3H2O MOLECULAR: formula representsall atoms in formula bonded together in a single unit called a molecule... IONIC: formula represents the simplestratio of positive to negative ions found in a sample of the compound...

  31. TYPES OF FORMULAS • CONDENSED FORMULAS: summation of all atoms in formula,alcohol: C2H6O • STRUCTURAL FORMULAS: clue to connectivity in compound,alcohol: CH3CH2OH

  32. NAMING MOLECULES AND COMPOUNDS There are many rules for naming many types of compounds: To name any compound, you must first recognize its “type.” “Guidelines”: If the compound formula starts with a nonmetal or metalloid,it is a molecular type compound If the formula starts with a metal, consider it an ionic compound, If the formula starts with H, it is an acid

  33. We’ll name in this lesson two specific types: • “ionic salts and bases” ( cation / anion • combinations) • cation: some metal ion or NH4+ • anion: OH- or O2- (a “base”) • all other anions: (“salts”) • K2SO4 NH4Cl NaOH MgO FeBr3 • “binary molecules” (two non-metals in formula ) • CO2 PCl3 SO3 AsF3 Acids (H written first) will be done later...

  34. GROUP WORK 2.2: Type of Compound Acid, Base, Salt, or Molecular?

  35. Before naming ionic compounds, let’s review cations and anions, and examine charges and formulas we need to know.....

  36. POSITIVE IONS:Cations CATIONS:positively charged ions; monoatomic cations are formed from metals which have LOST one or more electrons in compound formation: - 1 e Na (11p, 11e) --------> Na+ (11p, 10e) (all Group 1A) -2e Ca (20p, 20e) --------> Ca2+(20p,18e)(all Group 2A)

  37. Common Metals, Fixed vs Variable Charge Metals which form single cation Metals which form several cations

  38. Naming Cations: Fixed Charge Metals When the metal in the salt or base exhibits only onecharge and forms only one cation, the name of the cation is identical with that of the metal: Na+ sodium cation Mg2+ magnesium cation Al3+ aluminum cation Ag+ silver cation

  39. “One Charge Only” 3+ 3+ 2+ 2+ 1+ 1+

  40. Metals Forming Several Cations All other common metals form cations resulting from the loss of a variablenumber of electrons (depending on the circumstances of the reaction). An examination of electronic structure (Unit 3) will justify all charges, single or multiple; now we simply must recognize “which is which”.........

  41. Naming Cations: Metals with Variable Charges When a metal is known to form several different cations of different charges, then the name of the cation must include a Roman Numeral indicating the charge of the ion: Fe2+ Iron(II) cation Cu+ Copper(I) cation Fe3+ Iron(III) cation Cu2+ Copper(II) cation Sn2+ Tin(II) cation Bi3+ Bismuth(III) cation

  42. Typically Encountered Cations, Variable Charge Metals Cr2,3+ Fe2,3+ Co2,3+ Ni, Mn 2+ Cu1,2+ Hg2+, Hg22+ Sn, Pb 2+ Bi3+ Maximum (if not always common) charge on all metals is given by group number...

  43. NEGATIVE IONS: Anions Monoatomic ANIONS: Single nonmetallic atoms which have gained one or more electrons in a chemical reaction and become negatively charged ions : +3e N (7p, 7e) --------> N3- (7p,10e) (all Group 5A) +2e O(8p, 8e) --------> O2- (8p,10e) (all Group 6A) +1e F (9p, 9e) --------> F1- (9p,10e) (all Group 7A)

  44. Monoatomic Anions: Name, Charge 3- 2- 1- Fluoride Chloride Bromide Iodide Hydride Nitride Oxide Phosphide Sulfide Selenide “ide”

  45. FORMING IONIC COMPOUNDS Make sure chargesbalance; cross multiply when cation and anion charges are different: Na+Cl- NaCl Na+S2- Na2S Na+P3-Na3P Ba2+Cl- BaCl2 Ba2+S2- BaS Ba2+P3-Ba3P2

  46. CATION, ANION Mg2+ H - Fe3+ S2- Al3+ P3- Cd2+ F - Mn2+ I - FORMULA, NAME GROUP WORK 2.3:Form Compound, Name

  47. POLYATOMIC IONS CATIONS: only one common, ammonium ion, NH4+ ANIONS: negatively charged ions containing two or more elements; the knowledge of the formula and charge of the most common are basic to naming compounds and writing formulas. One of the elements usually involved is oxygen; the ion names end in “ate” or “ite” as follows...

  48. Key Polyatomic Anion Formers:Know these! Permanganate (7B) like Perchlorate Br, I same as Cl Chromate (6B) like Sulfate

  49. Polyatomic Anions of C, 4A Most common: CO32- carbonate HCO31- hydrogen carbonate, “bicarbonate” Others: CH3CO2-acetate (“C2H3O2-”) CN-cyanide

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