Chapter 11 The Chemical Elements

Transcription

1 James T. Shipman Jerry D. Wilson Charles A. Higgins, Jr. Omar Torres Chapter 11 The Chemical Elements

2 Chemistry Chemistry a division of physical science Chemistry deals with the composition and structure of matter and the reactions by which substances are changed into other substances History Egyptian, Chinese, and Mesopotamians wine making, worked metals, dyes, glass, pottery, embalming fluids (as early as 3500 BCE) Intro

3 Major Divisions of Chemistry Physical Chemistry energy of reactions Analytical Chemistry identifies chemicals, modern analytical chemistry is instrumentation driven, lots of industries have analytical chemists for qualitative analysis Organic Chemistry carbon compounds, pharmaceuticals, polymers, some solar cells Inorganic Chemistry non-carbon compounds, synthetic ceramic materials, most common solar cells Biochemistry chemical reactions that occur in living organisms Intro

4 88 Naturally Occurring Elements Either singly or in chemical combination, the 88 naturally occurring elements comprise virtually all matter Their chemical and physical properties affect us continually We discuss the Classification of Matter the Elements the Periodic Table the Naming of Compounds Intro

5 Classification of Matter In Chapter 5 we saw that matter can be classified by its physical phase or state solid, liquid, gas Matter is anything that has mass Chemists use this classification, but also divide matter into several other classifications Pure Substance element or compound Mixture homogeneous or heterogeneous Section 11.1

6 Pure Substance Pure Substance a type of matter in which all samples have fixed composition and identical properties * Element all atoms have same # of protons (gold - Au, sulfur- S, oxygen O 2 ) (any symbol in periodic table) *Compound two or more elements chemically combined in a definite, fixed ratio by mass (salt - Na Cl, water H 2 O ) (combination of at least 2 elements in the periodic table) A compound can be broken into its separate components only by chemical processes Section 11.1

7 Compound vs. Component Elements Compounds are usually different from the individual components Zn S Zn S Section 11.1

8 Mixture Mixture type of matter composed of varying proportions of two or more substances that are only physically mixed and not chemically combined Homogeneous (a solution) uniform throughout (coffee, alloy, tea) Technically, it should be mixed/uniform at the atomic level. Heterogeneous non-uniform (pizza, oil/water, iron filings in sand), at least two components can be observed Formed and broken down by physical processes (dissolving, evaporation) (not by chemical processes) Section 11.1

9 The Classification of Matter Matter can be classified according to its composition: elements, compounds, and mixtures.

10 Heterogeneous Mixtures Section 11.1

11 Liquid Solutions (homogeneous mixture) Solvent the liquid or the substance in the larger quantity Solute the substance dissolved in the solvent Section 11.1

12 Aqueous Solutions Aqueous Solution (aq) a solution in which water is the solvent When dissolved & stirred the distribution of the solute is the same throughout (homogeneous) Unsaturated Solution more solute can be dissolved in the solution at the same temp. Saturated Solution maximum amount of solute is dissolved in the solvent Section 11.1

13 Saturated Solution A dynamic equilibrium exists between the solute dissolving and the solute crystallizing Section 11.1

14 Solubility Solubility the amount of solute that will dissolve in a specified volume or mass of solvent (at a given temperature) to produce a saturated solution If the temperature is raised the solubilities for most solids increase Section 11.1

15 The Effect of Temperature on Solubilities of Salts in Water Usually hotter water will dissolve more solute Section 11.1

16 Supersaturated Solutions When unsaturated solutions are prepared at high temperatures and then cooled, the saturation point may be reached as the solution cools However, if no crystals are present, crystallization may not take place Result Supersaturated Solution contains more than the normal maximum amount of dissolved solute at the given temperature Section 11.1

17 Seed Crystal Added to a Supersaturated Solution of Sodium Acetate, NaC 2 H 3 O 2 Section 11.1

18 Solubility of Gases The solubility of gases increases with increasing pressure Example: in the manufacture of soft drinks, CO 2 is forced into the beverage at high pressure Once the soft drink is opened, the pressure inside the container is reduced to normal atmospheric pressure and the CO 2 starts escaping Section 11.1

19 Robert Boyle In 1661 Robert Boyle proposed that the designation element be applied only to substances that could not be separated into components by any method In addition Boyle initiated the practice of carefully and completely describing experiments so that anyone might repeat and confirm them Due to this procedure (carefully documenting experiments) scientists have been able to build on previous knowledge (background reading don t memorize) Section 11.2

20 Discovery of the Elements The earliest civilizations isolated 12 substances; gold, silver, lead, copper, tin, iron, carbon, sulfur, antimony, arsenic, bismuth, and mercury later all 12 proved to be elements Phosphorus was isolated (from urine) in 1669 P is the first element whose date of discovery is known By 1746, platinum, cobalt, and zinc had all been discovered By 1800, ten more elements were added. background reading: don t memorize Section 11.2

21 Occurrence of the Elements Human Body = 65% oxygen & 18% carbon Earth s Crust = 47% oxygen & 27% silicon Analyses of electromagnetic radiation from space indicates that the universe consists of: Hydrogen 75% (simplest element) Helium 24% (second most simple element) Others 1% Earth s atmosphere = 78% nitrogen, 21% oxygen, and about 1% argon Earth s core = 85% iron & 15% nickel (do not memorize interesting only) Section 11.3

22 Relative Abundance (by Mass) of Elements in Earth s Crust Note that 74% of the mass of the Earth s crust is composed of only two elements oxygen & silicon (sand is silicon dioxide) (interesting only do not memorize) Section 11.3

23 Molecules Molecule an electrically neutral particle composed of two or more atoms chemically combined If the atoms are the same element, then the molecule is of an element Element examples: H 2 or N 2 If the atoms are different elements, then the molecule is of a compound Compound examples: H 2 O or NH 3 end 8/29W 9am class Section 11.3

24 Representations of Molecules Section 11.3

25 Seven Common Elements that Exist as Diatomic Molecules These atoms (H, N, O, F, Cl, Br, I) are too reactive to exist as independent atoms (memorize these: HON & all halogens) (as in can I have more honey, HON ) When writing formulas w/ these seven elements we use the diatomic form: H 2 +Cl 2 2HCl Section 11.3

26 Allotropes Allotrope two or more forms of the same element that have different bonding structures in the same physical phase Example: diamond, graphite (and fullerenes) Both pure diamond and pure graphite are each 100% carbon (C), and are both solid But the atomic arrangement of the carbon atoms is different Section 11.3

27 Three Allotropes of Carbon Diamond, Graphite, and Buckminsterfullerene (C 60 ) End class 8/29W 11am Section 11.3

28 The Periodic Table The periodic table puts the elements in order of increasing atomic number, into seven horizontal rows, called periods The fifteen vertical columns in the periodic table are called groups Section 11.4

29 The Periodic Table Divided into Periods and Groups group period Section 11.4

30 One Way to Classify the Periodic Table Representative Elements (green) (main group elements) End 8/31 9am Transitional Elements (blue) transition metal elements Inner Transition Elements (purple) lanthanides & actinides Section 11.4

31 Metals & Nonmetals Another Way to Classify the Elements A metal is an element whose atoms tend to lose electrons during chemical reactions (+) A nonmetal is an element whose atoms tend to gain (or share) electrons ( ) Section 11.4

32 Metals/Nonmetals in the Periodic Table NonMetals Metals Section 11.4

33 General Properties of Metals & Nonmetals Do not memorize background reading only. End 11 am 8/31 Section 11.4

34 Electron Configuration & Valence Electrons Electrons are located in energy levels or shells that surround the nucleus Level 1 maximum of 2 electrons (period 1) Level 2 maximum of 8 electrons (period 2) Level 3 maximum of 18 electrons (period 3) The chemical reactivity of the elements depends on the order of electrons in these energy levels Section 11.4

35 We will only discuss the representative elements (main group) Groups 1A 8A Section 11.4

36 Valence Electrons The outer shell of an atom is known as the valence shell The electrons in the outer shell are called the valence electrons The valence electrons are the electrons involved in forming chemical bonds so they are extremely important Elements in a given group all have the same number of valence electrons (and \ similar chemical properties) Section 11.4

37 Guidelines: Shell Electron Configurations The number of electrons in an atom is the same as the element s atomic number (Z) The number of shells that contain electrons will be the same as the period number that it is in For the A group (representative, main group) elements, the number of valence electrons is the same as the group number Let s look at Example 11.1 Section 11.4

38 Example 11.1 Na has Z = 11 and an atomic mass = 23.0 u It is a representative (main group) element, period 3, group 1A It has 11 electrons and 11 protons It has 1 valence electron (group number) 3 shells have electrons (same as period) The electron configuration is 2, 8, 1 (2 electrons in shell 1, 8 in shell 2, and 1 valence electron) Section 11.4

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40 The Periodic Nature of Atomic Size The atomic size of the elements also varies periodically (refer to the Periodic Table) from nm (H) to 0.47 nm (Cs) Atomic size increases down a group Atomic size decreases across a period Section 11.4

41 Relative Atomic Sizes Note the Periodic Table can be used to determine relative atomic size Section 11.4

42 Ionization Energy also Periodic Ionization energy the amount of energy that it takes to remove an electron from an atom Ionization energy increases across a period due to additional protons in the nucleus Ionization energy decreases down a group because of the additional shells situated between the nucleus and the outer electron shell Larger atom, easier to remove electrons Section 11.4

43 Size increases Ionization Energy Trend Size decreases Section 11.4

44 Chemical Formulas In order to easily and conveniently discuss chemistry we can use chemical formulas Chemical formulas are written by putting the elements symbols adjacent to each other usually w/ the more metallic element first A subscript following each symbol designates the number of atoms H 2 O Section 11.5

45 Eleven Compounds with Special Names * * * * * * * * Section 11.5

46 Recognizing ionic vs covalent Ionic compounds metal with nonmetal, combine two elements on opposite side of periodic table ex: NaCl, K 2 S Covalent compounds nonmetal with nonmetal, combine two elements close together on periodic table ex: CO 2, PCl 3

47 Naming a Binary Compound for a Metal and Nonmetal Binary = two-element compound First give the name of the metal and then give the name of the nonmetal, changing its ending to ide NaCl sodium chloride (chlorine + ide) Al 2 O 3 aluminum oxide (oxygen + ide) Ca 3 N 2 calcium nitride (nitrogen + ide) End 9/5 9am & 11 am Section 11.5

48 Don t write down will post. Have rule to do this without memorizing Section 11.5

49 Compounds of Two Nonmetals The more metallic or less nonmetallic element (farther left or farther down periodic chart) is usually written first in the formula and named first (covalent molecule) Given formula left symbol named first, right symbol named second The second element is named using the ide ending Greek prefixes are used to designate the number of atoms in the molecule Section 11.5

50 Examples: HCl hydrogen chloride CS 2 carbon disulfide PBr 3 phosphorus tribromide IF 7 iodine heptafluoride Section 11.5

51 Polyatomic Ions Ion an atom or chemical combination of atoms having a net electric charge Monatomic ion an ion formed from a single atom (Cl ) Polyatomic ion an electrically charged combination of atoms (CO 3 2 ) Name the metal and then the polyatomic ion: ZnSO 4 zinc sulfate NaC 2 H 3 O 2 sodium acetate Mg(NO 3 ) 2 magnesium nitrate K 3 PO 4 potassium phosphate Section 11.5

52 Common Polyatomic Ions * * * * * ** Also related to acid names -- ic acid H = -- ate ex: nitric acid H = nitrate HNO 3 NO 3 - Section 11.5

53 Naming Compounds Example H 2 SO 4 sulfuric acid (special name) ZnCO 3 zinc carbonate (metal + polyatomic ion) Na 2 S sodium sulfide (binary compound of metal + nonmetal) SiO 2 silicon dioxide (binary compound of two non-metals) NH 3 ammonia (special name) NH 4 NO 3 ammonium nitrate (ammonium ion + polyatomic ion) Section 11.5

54 Flowchart: Naming Compounds End 9/7 9am & 11 am END EXAM I Section 11.5

55 Alkali Metals know these Noble Gases Alkaline Earth Metals Halogens Section 11.6

56 Noble (Inert) Gases Group 8A They exist as single atoms (monatomic) Almost never react and form compounds Noble gases have 8 electrons in their outer shells (except He that has a full shell with 2) Eight electrons in the outer shell is VERY stable Neon signs contain minute amounts of various noble gases electric current glow! Argon gas is used inside light bulbs because even at high temps. it will not react with the tungsten filament (W) Section 11.6

57 Alkali Metals Noble Gases Alkaline Earth Metals Halogens Section 11.6

58 Alkali Metals Group 1A (not H) Each alkali metal atom has only one valence electron \ tends to lose this electron ( +) and readily react with other elements active metals, very reactive Na & K are abundant (Li, Rb, Cs are rare) So reactive w/ oxygen and water that they must be stored in oil info only do not memorize NaCl, K 2 CO 3 (potash), Na 2 CO 3 (washing soda). NaOH (lye), NaHCO 3 (baking soda) You can now predict formulas KCl (potassium chloride), LiCO 3 (lithium carbonate) Section 11.6

59 Alkali Metals Noble Gases Alkaline Earth Metals Halogens Section 11.6

60 Halogens Group 7A Each halogen atom has seven valence electrons \ tends to gain ONE electron and readily react with other elements very reactive nonmetal Only occur in nature as a compound, but when purified occur as a diatomic molecule (as element) (F 2, Cl 2 ) generally poisonous F is the most reactive will corrode Pt, and cause wood, rubber, water to burn on contact info only Iodine is necessary for proper thyroid function AlCl 3 (aluminum chloride), NH 4 F (ammonium fluoride), CaBr 2 (calcium bromide) Section 11.6

61 Halogens Chlorine Bromine Iodine Section 11.6

62 Alkali Metals Noble Gases Alkaline Earth Metals Halogens Section 11.6

63 Alkaline Earth Metals Group 2A This group contains two valence electrons, and tend to lose two electrons ( +2) Not as chemically active as (calcite) alkali metals (1A), and are generally harder and stronger Be 2 Al 2 (SiO 3 ) 6 (beryl), Mg(OH) 2 (milk of magnesia), CaCO 3, Ca 3 (PO 4 ) 2 (bones & teeth), BaSO 4 (barite), Sr (red) & Ba (green) give color in fireworks for info only do not memorize Ra is radioactive RaCl 2 was used on watch dials (glowed in dark) until it was understood that radioactivity was an issue. Section 11.6

64 Hydrogen Group 1A Usually (sometimes Group 7A) Although a nonmetal, H usually reacts like a alkali metal (HCl, H 2 S) Sometimes reacts like a halogen NaH, CaH 2 At room temp. colorless, odorless, diatomic Lightest element was used in early dirigibles Will burn in air to form water Section 11.6

65 Hindenburg, Lakehurst, NJ; 5/6/37 Flammable H was used for buoyancy. Airships today use He. Section 11.6