Whole Earth iron 35% Earth s Crust oxygen 46% oxygen 30% silicon 28% silicon 15% aluminum 8% magnesium 13% iron 6% nickel 2.4% magnesium 4% other

Transcription

1 Elements yu will need t memrize the names and symbls f the fllwing elements: Cmmn Elements Element Symbls Derived Frm Latin Names Aluminum Al Antimny stibnium Sb Argn Ar Cpper cuprum Cu Arsenic As Gld aurium Au Barium Ba Irn ferrum Fe Beryllium Be Lead plumbum Pb Bismuth Bi Mercury hydragyrum Hg Brn B Ptassium kalium K Brmine Br Silver argentums Ag Cadmium Cd Sdium natrium Na Calcium Ca Tin stannum Sn Carbn C Chlrine Cl Chrmium Cr Cbalt C Oxygen O Flurine F Phsphrus P Helium He Platinum Pt Hydrgen H Radium Ra Idine I Radn Rn Lithium Li Selenium Se Magnesium Mg Silicn Si Manganese Mn Strntium Sr Nen Ne Sulfur S Nickel Ni Titanium Ti Nitrgen N Tungsten W (wlfram) Relative abundance f elements (by mass) Universe hydrgen 60.4% Human Bdy xygen 65% helium 36.6% carbn 18% ther hydrgen 10% ther 7% Whle Earth irn 35% Earth s Crust xygen 46% xygen 30% silicn 28% silicn 15% aluminum 8% magnesium 13% irn 6% nickel 2.4% magnesium 4% ther ther Sep 12 8:25 AM Sep 12 8:26 AM Demcritus The Greek philsphers Demcritus first prpsed the idea f the atm back in 400 B.C. Demcritus pstulated that all matter culd be subdivided until sme finite particle was reached. This finite particle he called the atm, frm the Greek wrd atms, which means indivisible. Unfrtunately, this idea was in cnflict with the views f the philspher Aristtle. Aristtle psed that matter was a cntinuus substance which culd nt be divided int a fundamental unit. Since Aristtle was mre widely knwn and held in greater esteem, it was the Aristtelian view f matter that predminated thinking int the late sixteenth century. Jhn Daltn In the perid an English schl teacher and chemist, Jhn Daltn, develped an atmic thery f matter based n experimental evidence. Daltn pstulated the existence f a different kind f atm fr each element. He als pstulated that atms entered int cmbinatin with ther atms t frm cmpunds and that these atms jined in definite whle number ratis. The pstulates f his thery can be summarized as fllws: All matter is cmpsed f atms All atms f the same element are identical; thse f different elements are different Atms f ne element cannt be cnverted int atms f anther element Atms unite in definite ratis t frm cmpunds Daltn based his thery n three laws which had been frmulated during the late 1700 s. By this time chemists had begun using quantitative methds in their experiments. These laws are summarized as fllws: 1. The Law f Mass Cnservatin Mass is neither created nr destryed in any rdinary chemical Antine Lavisier first prpsed this law when he bserved tha elements reacted t frm cmpunds, mass was always cnserved Lavisier heated tin metal in air t frm tin xide and demns the mass f the tin xide was exactly equal t the mass f the plus the mass f the xygen taken frm the air. 2. The Law f Definite Prprtins The prprtin by mass f the elements in a pure cmpund is a the same. Fr example, Sn (s) + 1/2O 2(g) SnO(s) g 16.0 g g In this cmpund, stannus xide, we will always find the mass percentage f each element the same: Sep 12 8:26 AM Sep 12 8:26 AM 1. The Law f Multiple Prprtins If tw r mre different cmpunds cmpsed f the same tw elements is analyzed, the mass f the secnd element cmbines with a fixed ma f the first element in a rati f small whle numbers. Daltn rec the pssibility that tw atms culd cmbine in mre than ne way an mre than ne prprtin Sn (s) + 1/2O 2(g) SnO(s) g 16.0 g g Sn(s) + O 2(g) SnO 2(s) J.J. Thmsn In the early 20 th century Sir William Crkes devised an apparatus cnsisting f a glass tube cntaining tw metal plates (called electrdes) at ppsite ends cnnected t a surce f electricity. When the electricity was turned n, it was always bserved that the end f the tube ppsite the negative electrde glwed with a greenish light. It was first believed this glw was caused by sme kind f either invisible particle r radiatin that riginated frm the negative electrde, which was called the cathde, and passed away frm it t the psitive electrde. These invisible rays were termed cathde rays. Experiments n these mysterius rays resulted in the fllwing bservatins: Cathde rays travel in straight lines rays and riginate at the cathde. When an bstacle is placed in the path f the rays, shadw is cast n the wall ppsite the cathde, displaying a silhuette f the bject. Thus, cathde rays exhibit characteristics f light (waves) g 32 g g Nte in the abve example that when xygen reacts with a fixed mass tin (118.7 g), the rati f xygen in the tw cmpunds frmed is 2: (32g:16g). Nte als in the secnd cmpund, stannic xide, we will always find the mass percentage f elements as 79% tin and 21% xygen: % Sn = X 100 = 79% % O = X 100 = 21% Daltn visualized the atm as a hard sphere cntaining small hcks which it culd cmbine with ther atms t frm cmpunds. When the electrical nature f matter was bserved, Daltn s cncept f the at mdified t accunt fr psitive and negative parts. This was t evidence fr subatmic particles. Sep 12 8:27 AM Sep 12 8:27 AM 1

2 Cathde rays are capable f imparting mechanical mtin. Frm this evidence it was cncluded that cathde rays are particles f sme kind. J.J. Thmsn discvered the particles cmprising the cathde rays arte negatively charged. He shwed that if a magnet is placed utside a Crke s tube, the rays wuld always be deflected by the magnetic field in the directin that a negatively charged particle wuld be deflected. Thmsn called the cathde ray particle an electrn. Sep 12 8:27 AM Sep 12 8:27 AM Thmsn measured the charge/mass rati f these electrns and fund this value t be the same regardless f what gas was in the tube r what the electrdes were made f. Other experiments with Crke s tubes prvided evidence fr the existence f a fundamental unit f psitive matter with a much greater mass, which was termed the prtn. Thmsn prpsed a Plum Pudding mdel f the atm the atm cnsisted f an equal mix f psitive pudding and negative plum. This was the first mdel f the atm with subatmic particles. Sep 12 8:28 AM Sep 12 8:28 AM Rbert Millikan In 1909 a prfessr at the University f Chicag, Rbert Millikan, was able t determine the charge n an electrn. He did this by way f the classic il drp experiment. Based n Thmsn s charge/mass rati f the electrn, nw the mass f the electrn culd be calculated. With this, the fundamental unit f negative charge in the atm, the electrn, had nw been characterized in terms f mass and charge Hw did the il drp experiment wrk? Sep 12 8:40 AM Sep 12 8:29 AM 2

3 Chapter 3 Ntes.ntebk Zapping the il drps with X rays caused them t becme inized that is the energy f the X ray packed enugh punch t knck ff electrns f the il drps causing them t becme psitively charged. The electrns were picked by ther il drps causing them t becme negatively charged. The psitively charged il drps fell t the negative plate (ppsites attract) while the negatively charged il drps were repelled by the negative plate. By adjusting the electric frce n the plates, Millikan culd get an il drp t be statinary (which he culd bserve thrugh the micrscpe ). At this pint, the electric frce (acting t push the drp up because like charges repel) = the gravitatinal frce (acting t bring it dwn). That is, Frceelectric = Frcegravity Millikan knew all the variables in the equatin except fr the charge n the il drp, which he slved fr. This was the charge f the electrn. Sep 12 8:29 AM Sep 12 8:29 AM Ernst Rutherfrd Ernst Rutherfrd perfrmed the classic Gld Fil experiment with graduate students Ernest Marsden and Hans Geiger that led Rutherfrd t prpse a nuclear mdel f the atm. This ccurred between 1908 and In this experiment, Rutherfrd bmbarded a thin sheet f gld fil with alpha particles. Alpha particles are a 2 prtnm and 2 neutrn unit (a helium nucleus) that is emitted frm the nuclei f unstable atms. These alpha particles thus carry a net psitive charge (2+). The set up is illustrated belw: Sep 12 8:29 AM Rutherfrd s interpretatin: Observatins: Mst alpha particles passed thrugh A few alpha particles were deflected 3

4 Cnclusins: Atms are mstly empty space mst alpha particles passed thrugh the gld atms Alpha particles deflected came clse t cncentratins f psitive charge (like charges repel). The center f psitive charge was termed the atm s nucleus. Rutherfrd bserved similar results using ther metals. The metals, hwever, needed t be extremely thin. Rutherfrd prpsed that the atm cnsists f a tiny psitively charged center that cntains the mass f the atm which he termed the nucleus. This nucleus was surrunded by electrns which essentially accunted fr the vlume f the atm. This mdel f the atm is ften called the planetary mdel f the atm. An electrstatic frce (electrstatic frces are the attractive and repulsive frces between electrically charged particles). An electrstatic frce f attractin keeps the electrn rbiting arund the nucleus while a centrifugal frce keeps the electrn frm falling int the nucleus (and cllapsing the atm). This presented a perfect explanatin fr the subatmic structure f the atm, but this mdel was shrt lived. Particle Relative mass Relative charge prtn 1 amu* +1 neutrn 1 amu 0 electrn 1/1864 amu 1 Istpes f hydrgen: Istpes are atms f the same element (same number f prtns r atmic number) with a different number f neutrns (r atmic mass/weight). Designatins used fr istpes are: atmic mass (A) (prtns + neutrns) H H H prtium (H 1) deuterium (H 2) tritium (H 3) 27 Al 13 atmic number (Z) (number f prtns) Sep 12 8:31 AM Sep 12 8:31 AM Determining Atmic Masses symbl prtns neutrns electrns net charge mass S Cl 37 The atmic masses listed fr the elements n the peridic table are weighted averages f their istpes. That is why their masses are shwn with decimal places (fractins f masses). The number and percentage f each istpe f an element is determined by a mass spectrgraph. This instrument is illustrated belw: Sep 12 8:31 AM Sep 12 8:31 AM 4

5 A sample f an element is injected int the instrument, heated t vaprize it, and then bmbarded with a beam f electrns. The electrns cllide with atms f the element kncking ff sme f the utermst electrns. The result is vaprized atms that have a net psitive charge psitive gaseus ins. These ins are then accelerated by an electric field t a narrw stream and subjected t the frce f a magnetic field. The ins are deflected by the magnetic field and separatin ccurs n the basis f mass, with the heaviest istpes (thse with the mst neutrns) deflected the least while the lightest istpes (with fewest neutrns) deflected the mst. The atmic masses f the elements are based relative t the deflectin f a carbn 12 istpe in a mass spectrgraph. The C 12 istpe is defined as exactly 12 atmic mass units, r amu. Thus, 1 amu = 1/12 the mass f a C 12 atm. Sep 12 8:32 AM Sep 12 8:32 AM The atmic mass f an element is cmputed frm the masses f its istpes and their fractinal abundances. This is dne by multiplying each istpe s fractinal abundance by its atmic mass, and then adding the results: atmic mass = (atmic mass f istpe1 X % abundance) + (atmic mass f istpe2 X % abundance) + (atmic mass f istpe3 X % abundance) + etc. Sep 12 8:32 AM Sep 16 2:01 PM Prblem: The element silicn cnsists f three istpes: Si 28 ( amu, 92.21%), Si 29( amu, 4.70%), and Si 30 ( amu, 3.09%). a) Why can t we simply add the masses f all three istpes and divide by three t get the average mass? Prblem: The atmic mass fr chlrine is reprted as amu. It cnsists f tw istpes, Cl 35 ( amu) and Cl 37 (36.966). Calculate the percent (fractinal abundance) f each istpe. b) T which istpe will the average mass be clsest t (Si 28, Si 29, r Si 30)? Explain. c) Calculate the atmic mass f silicn as reprted n the Peridic Table. d) Out f 100 atms f a sample f silicn, hw many will be the Si 28 istpe? e) Out f 225 atms f silicn, hw many will be the Si 30 istpe? f) Out f 100 atms f silicn, hw many atms f silicn will have a mass f amu? Sep 12 8:32 AM Sep 12 8:33 AM 5

6 The Peridic Table The elements knwn t the ancient wrld included irn (Fe), cpper (Cu), silver (Ag), gld (Au), mercury (Hg), tin (Sn), lead (Pb), carbn (C) and sulfur (S). The alchemists discvered ther elements that included cbalt (C), nickel (Ni), zinc (Zn), antimny (Sb), arsenic (As), and phsphrus (P). These were the elements knwn up t the 18 th century. The first persn t set up a true table f chemical elements was Lavisier. Jhn Newlands fund that when he placed the knwn elements in rder f increasing atmic mass, the first and eighth elements had similar prperties, as did the secnd and ninth elements, the third and tenth elements, and s frth. Early 19 th century chemists began in earnest t classify elements. These chemists based their descriptin f an element n ur current definitin f an element a substance which cannt be further decmpsed by rdinary chemical means. Chemists were interested in seeing hw elements related t each ther. Jhann Dbereiner, fr example, discvered grups f three related elements which he termed a triad. He fund that when three elements in a triad were put in rder f their atmic masses, the difference in mass between the first and secnd elements was abut the same as the difference in mass between the secnd and third elements. Let s cnsider tw f Dbereiner s triads: atmic mass density chlrine brmine idine calcium strntium barium Sep 12 8:33 AM Sep 12 8:34 AM Credit fr the discvery f the mdern Peridic Table is generally given t the chemist Dmitri Mendeleev (1869). Mendeleev arranged the knwn elements n the basis f the atmic masses in rws (perids) in such a way that elements with similar prperties fell int the same vertical clumns (grups r families). Mendeleeev recgnized the cmbining capacities f elements as a fundamental classifying characteristic and cnsidered the peridic arrangement as a natural law with predictive pwers. He placed idine (I) after tellurium (Te), fr example, because it had similar prperties with chlrine (Cl) and brmine (Br) despite the fact that it had a smaller atmic mass. The key t Mendeleev s Peridic Table, and the reasn he is acknwledged as the discverer f the Peridic Table, was that he recgnized that elements may nt yet have been discvered. He left blanks in his Table where they seemed t be missing, and he very accurately predicted the prperties f the yet undiscvered elements gallium (Ga), scandium (Sc) and germanium (Ge). Cnsider the case f germanium as an example: Predicted Fund atmic mass density (g/ml) clr grey grey white valence 4 4 frmula f xide XO2 density f xide 4.7 GeO2 4.7 frmula f chlride XCl4 GeCl4 Mdern Peridic Law: the physical and chemical prperties f the elements are peridic functins f their atmic numbers. Arrangement f Table: 7 Perids the number f each perid indicates the principle energy level in which the utermst r valence electrns f that perid s elements are fund. In each perid the number f valence electrns increases frm left t right. 18 Grups elements within a grup exhibit similar r related prperties because they have the same number f valence electrns. Grup 1 are called the alkali metals Grup 2 are called the alkaline earth metals Grup 17 are called the halgens Grup 18 are called the Nble gases Grups 3 12 are called the transitin metals The elements can be divided int tw majr grups: metals and nnmetals. Mst f the elements are metals. Sep 12 8:34 AM Sep 12 8:34 AM Metals excellent cnductrs f heat and electricity; metallic bnding is such that the kernels f metallic atms (kernel = nucleus plus inner electrns) are held in fixed psitins in a crystalline arrangement and the valence electrns are shared by the entire crystal. all are slids at rm temperature and pressure except fr mercury (Hg). tend t lse electrns t frm psitive ins (called catins) when cmbining chemically with nnmetals. As they tend t give electrns t a nnmetal they cause the nnmetal t be reduced (recall reductin means a gain f electrns). Thus, metals are gd reducing agents. pssess qualities f malleability (can be bent int shape), ductility (can be drawn int a wire) and metallic luster (appear shinny grey because they reflect mst wavelengths f visible light). The elements with the mst prnunced metallic prperties are fund in the lwer left prtin f the Peridic Table. Nnmetals pr cnductrs f heat and electricity mstly gases, a few slids and ne liquid (brmine) at rm temperature tend t gain electrns when they react with metals and share electrns when they react with ther nnmetals. They cause the metals t lse electrns by taking electrns frm them. (Recall a lss f electrns is termed xidatin). Hence they are gd xidizing agents. brittle in the slid phase and lack metallic luster several nnmetals exist as diatmic mlecules in their elemental frms at rm temperature and pressure: hydrgen clrless gas H 2 nitrgen clrless gas N 2 xygen clrless gas O 2 flurine pale yellw gas F 2 chlrinepale green gas Cl 2 brmine reddish brwn liquid Br 2 idine dark purple slid I 2 Sep 12 8:34 AM Sep 12 8:35 AM 6

7 Chapter 3 Ntes.ntebk Alltrpy Metallids (Semi metals) elements that exhibit bth metallic and nnmetallic prperties these include B, C, Ge, Si, As, and Te. Nble Gases have eight valence electrns (except He which has 2). chemically very unreactive althugh heavier kryptn (Kr) and xenn (Xe) have frmed cmpunds by reacting with the highly electrnegative elements flurine and xygen under extreme cnditins. Elements can ccur in different frms. These different frms are termed alltrpes. There are three alltrpes f the element carbn: diamnd carbn atms ccur in a tetrahedral arrangement graphite carbn atms are bnded in a layered structure with weak frces f attractin between the layers buckminsterfullerence 60 carbn atms bnded in a spherical structure Oxygen ccurs in tw alltrpe frms: xygen as a diatmic mlecule, O2 (called xygen) zne, which is a triatmic mlecule O3. Ozne ccurs in ur upper atmsphere and is critically imprtant in absrbing the ultravilet rays released by ur sun. Ozne can als be fund near the grund after it is made during lightning strms. Near the grund zne is a health risk. Sep 12 8:35 AM Sep 12 8:35 AM Ins Let s cnsider the frmatin f simple catins and anins: The Rutherfrd mdel f the atm we have discussed cnsists f a nucleus cntaining the prtns and neutrns surrunded by electrns. In a neutral atm, the number f prtns (psitives) equals the number f electrns (negatives). Thus, a neutral atm is said t have zer net charge. Ptassium We will learn later that when elements react with each ther t frm cmpunds they d s with their utermst r valence electrns. The number f electrns that ccur in each energy level f an atm is given by its electrn cnfiguratin, which appears n yur peridic tables in the lwer left crner f the element s bx. Sdium, fr example, has the electrn cnfiguratin 2 8 1, which means it has 2 electrns in level 1, 8 electrns in level 2, and 1 electrn in level 3. Sdium thus has 1 valence electrn which is fund in the third level. ptassium in Flurine fluride in 1 +1 K prtns (+) 19 electrns ( ) net charge = 0 K prtns (+) 18 electrns net charge = +1 F F prtns (+) 9 prtns (+) 9 electrns ( ) 10 electrns ( ) net charge = 0 net charge = 1 Recall we said that it is the valence electrns f an element that determine its prperties and hw it reacts with ther elements. The mdel that chemists have develped in ur thery f chemical bnding is that elements will gain, lse r share electrns in bnding with ther elements. Fr nw, we will be interested in hw elements lse r gain electrns. In general, metals tend t lse electrns when reacting with nnmetals t frm psitive ins called catins. Nnmetals tend t gain electrns when reacting with metals t frm negatively charged ins called anins. Thus, ins (atms with a net electric charge) are frmed when atms lse r gain electrns. Sep 12 8:36 AM Sep 12 8:36 AM A catin is named using the name f the parent. Thus, K+ is called ptassium in. An anin is named by taking the rt f the name and changing the ending t ide. Thus F is called fluride in. N3 P3 nitride in phsphide in O2 S2 Se2 Te2 xide in sulfide in selenide in telluride in F Cl Br I fluride in chlride in brmide in idide in Sep 12 8:36 AM The figure belw shws the types f ins frmed by atms in several grups n the peridic table: Sep 12 8:37 AM 7

8 Inic Cmpunds The chemist Svante Arrhenius was the first t pstulate that chemical cmpunds culd be made up f ppsitely charged particles. In his research Arrhenius bserved that neither pure water nr a dry salt wuld cnduct an electric current. If the salt was disslved in water, hwever, the slutin wuld cnduct an electric current. He explained his bservatins by suggesting that units f salt brke up int charged particles r ins when disslved in water and this explained the cnductivity f the slutin. The idea f ins was pretty radical back in the1800s (n pun intended) and Arrhenius idea was nt accepted. His peers argued that sdium chlride disslved in water gave n evidence f a greenish chlrine gas which they said shuld accmpany the decmpsitin f sdium chlride. Arrhenius was crrect t pint ut that chlride in has different prperties cmpared t the chlrine atm. His idea eventually became widely accepted and in 1903 Arrhenius was awarded the Nbel Prize in chemistry. Tday we knw that in rder fr a substance t cnduct an electric current ne f tw criteria must be satisfied: the substance must cntain freely mving electrns (as ccurs in metals) the substance must have freely mving ins. Cmpunds cnsisting f ins meet this requirement in the liquid (r mlten) and aqueus (disslved in water) phases. Inic cmpunds meet the secnd criteria. Inic cmpunds frm when a metal reacts with a nnmetal. In the reactin, the metal transfers an electrn(s) t the nnmetal resulting in a psitively charged meal in and a negatively charged nnmetal in. It is the electrstatic attractin between ppsitely charged ins that results in the inic bnd. Mre abut bnding later! Sep 12 8:37 AM Sep 12 8:37 AM Let s try the fllwing examples invlving simple binary inic cmpunds using the criss crss rule: ptassium brmide: In writing the frmulas f inic cmpunds, the net charge must be cnserved. Catins and anins will react in a rati that cnserves charge. When writing the frmulas f inic cmpunds, we adjust the subscripts t btain the crrect rati. In additin, we typically express the chemical frmula f an inic cmpund by using the simplest whle number rati f atms. This is referred t as the empirical frmula. We have discussed the cmmn charges fr nnmetals. Fr metal, the Grup 1 alkali metals all have charges f +1 nly while that f the Grup 2 alkaline earth metals all have charges f +2 nly. lithium xide: magnesium fluride: calcium xide: Sep 12 8:37 AM Sep 12 8:38 AM sdium nitride: aluminum xide: barium phsphide: rubidium sulfide: aluminum idide: Sep 12 8:38 AM 8