2. Unit 4

3. What is matter? n Matter is anything that has mass and volume. n Matter is made up of atoms. n Energy is NOT matter and does not have mass or volume. n Energy and matter are related by E=mc 2

4. Properties of Matter n Properties of matter are characteristics that can be tested or observed and are used to identify matter. n Physical properties are those which can be observed WITHOUT changing the chemical make-up of the matter. Ex: color, density, odor, taste, shape Ex: color, density, odor, taste, shape n Chemical properties can only be observed when matter is involved in a chemical reaction, which CHANGES the chemical composition. Ex: flammable, corrosive, acidic

5. Classifying Matter n Matter can be classified as either pure substances or mixtures. n Pure substances are matter that consists of ONE type of element or compound (ex: gold metal Au, water H 2 O) n Mixtures are either homogeneous (mixed completely and consistently throughout) or heterogeneous (existing in two or more separate phases).

6. MATTER CompoundElement Mixture Pure Substance HeterogeneousHomogeneous

7. How are compounds different from mixtures? n A mixture is not like a compound in that the parts of a mixture are NOT bonded together as in a pure compound. n Examples of compounds: water (H 2 O), sugar (C 6 H 12 O 6 ), carbon dioxide (CO 2 )… n Examples of mixtures: air, steel, orange juice, “Gorp” … n Mixtures may be homogeneous (evenly distributed in a single phase) or heterogeneous (unevenly distributed in different phases).

8. Solutions, Colloids and Suspensions n A solution is a homogeneous mixture of particles so small they cannot be seen with a microscope (transparent). An example is sugar water. n A colloid is a mixture that has particles which are bigger than in a solution, but not large enough to settle out. An example is milk. n A suspension is a solution that has particles large enough to settle out over time. An example is muddy pond water.

9. Separation of Components n The elements in a compound must be separated by CHEMICAL methods. Ex: electrolysis, combustion, decomposition n The parts of a mixture can be separated by PHYSICAL methods. Ex: filtering, evaporation, use of a magnet

10. What is an atom? n An atom is defined as the smallest piece of matter that still has the properties of the element. n Atoms are made up of protons, neutrons, and electrons. n A group of atoms that is chemically joined and acts as a single unit is called a molecule. called a molecule. Ex: Cl, N 2 O 4, CO 2 Ex: Cl 2, N 2 O 4, CO 2

11. How are heavy atoms created? n Nuclear fusion in stars combine smaller nuclei into larger ones. n Requires intense heat and pressure to force nuclei together (plasma state) which cannot be sustained on earth n Very heavy atoms are created in supernova explosions of large stars.

12. Atomic History n The Greek philosopher Democritus (400BC) came up with the idea that atoms make up all substances. n The idea of an indivisible thing that made up all matter was refined by chemist John Dalton in 1803. n Dalton’s model of the atom consisted of a solid, indivisible sphere. Atom

13. Thompsons model n In 1897, English Physicist J. J. Thompson proposed that the atom is a sphere of positive charge with small areas of negative charge -he discovered electrons. n This theory became known as the “plum pudding” model after an English “dessert” of purple bread and raisins.

14. Ernest Rutherford n Physicist Ernest Rutherford found that radioactive alpha particles deflected when fired at a very thin gold foil. n The results of his experiment suggested that the atom was not a hard sphere, but was mostly space, with a small concentration of mass (he found the nucleus).

15. Rutherford’s gold foil exp. and new atomic model

16. The Bohr Model n Physicist Niels Bohr rebuilt the model of the atom in 1903, placing the electrons in rings called energy levels (the “solar system” model). n Energy levels closer to the nucleus were lower in energy than those farther away.

17. The Electron Cloud Model electron probability cloud nucleus The modern model of the atom places electrons in a “cloud” around the nucleus. The cloud shows where electrons are most likely to be found.

18. Particles in an atom NameLocationCharge Mass (amu) proton (p) in nucleus +11 neutron (n) in nucleus 01 electron (e) outside nucleus 1/2000 Protons and neutrons are found in the nucleus and make up most of the mass. Electrons are found outside the nucleus and take up most of the space in an atom.

19. Elements n We illustrate an element with an atomic symbol. n The atomic number tells the number of protons and identifies the element. n The atomic mass is the total mass of the protons plus the neutrons. (On the P. T. the average atomic mass is given, an average of all isotopes) O OXYGEN 8 15.9994 average atomic mass is not a whole number atomic number

20. Isotopes n When an atom has more or less neutrons than another atom of the same element, we call them isotopes. n For instance, the element carbon has 6 protons, but it could have 6, 7, or 8 neutrons, to form Carbon-12, Carbon-13, and Carbon-14. Each has a different mass. n In nature, there is a mix of different natural isotopes. We use this mix to calculate average atomic mass. 12 C 13 C 14 C

21. Isotope symbols n Isotope symbols give the element symbol, the mass and atomic numbers. From these, the number of protons, neutrons, and electrons can be determined. +2 a charge is shown here for an ion

22. Practice n How many protons, neutrons, and electrons are present in (a) 27 Al 3+ (b) 79 Se 2- n Write the isotope notation for an ion that contains 20 protons, 21 neutrons, and 18 electrons. n Write the isotope notation for an atom of lead that has 128 neutrons. n Write the isotope notation for the following:

23. Periodic Table Development n In1869, Russian chemist Dmitri Mendeleev organized elements into a table based on atomic mass and similar properties. n Mendeleev stated that the properties of elements are a periodic function of their atomic masses.

24. Mendeleev’s Periodic Table pink = “missing ” elements

25. Mendeleev’s Prediction n Mendeleev’s table had several missing elements. When these elements were discovered, they were almost exactly as Mendeleev predicted. n The following is an example of an element that Mendeleev predicted, and we now know as the element Germanium…

26. Germanium is located below silicon. Mendeleev predicted its properties based on its location in his table. Ekasilicon (Es) Germanium (Ge) 1. Atomic mass: 72 1. Atomic mass: 72.61 2. High melting pt. 2. Melting pt: 945° C 3. Density: 5.5g/cm 3 3. Density: 5.323g/cm 3 4. Dark gray metal 4. Gray metal 5. Will obtain from K 2 EsF 6 5. Obtain from K 2 GeF 6 6. Will form EsO 2 6. Forms oxide (GeO 2 ) Predicted….. Actual……

27. Modern Periodic Law n Henry Moseley revised Mendeleev’s periodic table by using atomic number (rather than atomic mass) to organize the elements. n Atomic number is the basis for our current periodic table.

28. Dalton’s Periodic Table Alternative Periodic Tables

29. Organization of the Periodic Table: n Rows on the periodic table are called PERIODS n Columns on the periodic table are called GROUPS or FAMILIES

30. Periodic Table Organization n There are 7 periods and 18 groups. n Elements with similar electron arrangements are placed in the same group. n Elements in groups are also listed in order of their increasing electron energy levels (shells). n The properties of elements are determined by their electron arrangements. Therefore, elements in the same group have similar chemical behavior.

31. Metal Groups

34. Organizing Information on the Periodic Table n Use colored pencils to shade each group or category a different color. n On your handout, draw a stair step dark line starting between B and Al. n Label the right side: nonmetals n Label the left side: metals n Write METALLOID along stair step line (all except for Al and Po!)

35. Basic Properties of Metals, Nonmetals, and Metalloids n Metals: 1. malleable, ductile and shiny solids. 2. Conduct heat and electricity well. 3. Tend to give up electrons in reactions (form + ions). 3. Tend to give up electrons in reactions (form + ions). n Nonmetals: 1. Generally gases or brittle solids. 2. Solids have dull surface. 3. Good insulators. 4. Tend to gain electrons in reactions (form – ions). 4. Tend to gain electrons in reactions (form – ions). n Metalloids: 1. Properties of both metals and nonmetals.

36. Periodic Trends n A periodic trend is a repeating pattern of properties. n We will focus on four trends: 1. metallic character 2. number of valence electrons 2. number of valence electrons 3. predicted charge on ions 3. predicted charge on ions 4. reactivity 4. reactivity

37. Metallic Character Metallic properties increase towards the bottom left (Francium) and decrease towards the top right (Fluorine).

38. Ions n An ion is an atom that has gained or lost one or more electrons. n The octet rule predicts that atoms try to achieve zero or eight electrons in their outer (valence) shell. n When an atom bonds with another atom, it seeks to gain electrons or lose them. For instance: n Cl has 7 and will gain one electron n Na has 1 and will lose one electron ClCl - NaNa + Positive ions are called “cations” Negative ions are called “anions”

39. Using the Periodic Table to Predict Charges of Ions n The basis of the periodic table is the atomic structures of the elements. n Position on the table and properties of these elements arise from the electron arrangements of the atoms. n Properties such as ionic charge can be predicted.

40. Q: What is a cation afraid of? A: A dogion.

42. Valence Electrons and the Octet Rule n Valence electrons are electrons found in the outermost energy level. Valence electrons increase across a period, and are the same within a group. n Atoms with full outer levels (a complete valence octet) are stable and do not react easily (such as noble gases). n For elements other than He, this stable configuration has eight valence e- (two in the outer s sublevels and six in the outer p sublevels).  When atoms react with one another, they do so to obtain a stable electron configuration. Some atoms gain or lose e- (ions), and some share e- (molecules) to achieve this stability.

43. GROUPS IN THE TABLE

44. Valence electrons by Group 1 2 3 4567 8 2 (d electrons are also used)

45. Common Ion Formation by Group +1 +2 +3 ions not common -3-2 0 +1 or +2 (however, many other charges Are possible –up to +7) positive, but varies

46. Reactivity Trends n The metallic reactivity trend follows the same pattern as metallic character –the greater the metallic character, the more reactive the metal. n The nonmetallic reactivity trend follows the same pattern as nonmetallic character –the greater the nonmetallic properties, the more reactive the nonmetal. REMEMBER the Noble Gases are not reactive! n Therefore, Fluorine is the most reactive nonmetal, and Francium is the most reactive metal. Noble gases are not reactive.

47. Reactivity Trends Metal and Nonmetal Reactivity

48. MAIN GROUPS IN THE PERIODIC TABLE

49. Organizing Information on the Periodic Table n Use a pen to label the following: Group 1 Alkali metals Group 2 Alkaline earth metals Group 16 Oxygen Family Group 17 Halogens Group 18 Noble gases Group 3-12 Transition metals La – LuLanthanoids Ac – Lr Actinoids Rare Earth Elements

50. Alkali Metals n Soft n Very reactive (react with water!) n Always found combined in nature n Form +1 ions n Cesium is the most reactive of the common alkali metals alkali metals Lithium pellets coated in lithium oxide Lithium and Sodium stored under mineral oil K flame Technically, francium is the most reactive and least common alkali metal, but since it is highly radioactive with an estimated 550 grams in the entire Earth’s crust at one time, its abundance can be considered zero in practical terms.) Cesium 1111 1H1H1H1H 2222 3 Li Li 3333 11 Na Na 4444 19 K K 5555 37 Rb Rb 6666 55 Cs Cs 7777 87 Fr Fr

51. Alkaline Earth Metals n Less reactive than alkali metals (react with acid) n Form +2 ions Due to its small nucleus, Be is highly transparent to X-rays and can be used as a “window” barrier between a vacuum chamber and an x-ray microscope. Mg can be used as a fire starter. Radium paint was used in the mid 1900s to paint the hands and numbers of some clocks and watches. The paint was composed of radium salts and a phosphor and glowed in the dark. 2222 4 Be Be 3333 12 Mg Mg 4444 20 Ca Ca 5555 38 Sr Sr 6666 56 Ba Ba 7777 88 Ra Ra

52. Transition Metals n Less reactive than groups 1 and 2 n Form ions with a range of charges (+1 to +7) n Many will form colored solutions when dissolved From left to right, aqueous solutions of: Co(NO 3 ) 2 (red); K 2 Cr 2 O 7 (orange); K 2 CrO 4 (yellow); NiCl 2 (green); CuSO 4 (blue); KMnO 4 (purple). Co(NO 3 ) 2K 2 Cr 2 O 7K 2 CrO 4NiCl 2CuSO 4KMnO 4 Co glass

53. Rare Earth Metals n These metals have very similar properties and are difficult to separate n Found in small quantities in nature n The Actinium series are all radioactive Rare Earth Metals uranium Am-241 A ring of weapons-grade electrorefined plutonium, with 99.96% purity. This 5.3 kg ring is enough plutonium for use in a modern nuclear weapon.

54. Oxygen Family n Somewhat Reactive n Can gain 2 electrons n Form -2 ions Liquid O 2 Sulfur melts to a blood-red liquid. When burned, it emits a blue flame. selenium 2222 8O8O8O8O 3333 16 S S 4444 34 Se Se 5555 52 Te Te 6666 84 Po Po 7777 116 Uuh Uuh

55. Halogens n Group 17 n Very reactive nonmetals n Form -1 ions n Form diatomic compounds (Cl 2, F 2, Br 2 …) (Cl 2, F 2, Br 2 …) n F 2 and Cl 2 gases Group 17 is the only group that exhibits all three states of matter. CaF 2 fluorite 2222 9F9F9F9F 3333 17 Cl Cl 4444 35 Br Br 5555 53 I I 6666 85 At At 7777 117 Uus Uus

56. Noble Gases n Group 18 n Do not react easily n Do not form ions n The non-reactivity is why the gases are called inert Group 18 Period 1111 2 He He 2222 10 Ne Ne 3333 18 Ar Ar 4444 36 Kr Kr 5555 54 Xe Xe 6666 86 Rn Rn 7777 118 Uuo Uuo

57. THE END

58. SOME REVIEW TOPICS: n Describe the structure of an atom. n How are the properties of elements related to their atomic structures? n How are electrons arranged within an atom? n What makes metals good conductors of heat and electricity? n Why is potassium more reactive than copper?