SCIENCE 10: CHEMISTRY,

Transcription

1 , 1 Atmic Thery and Bnding The Nucleus - The particles that make up an atm are called subatmic particles - The three subatmic particles are prtns, neutrns and electrns. - Prtns, which have a +1 (psitive) electric charge, and neutrns which d nt have an electric charge, are lcated in the center f the atm r nucleus f each atm. - The electric charge n any nucleus is always psitive since prtns are psitively charged and neutrns are neutral - The charge n the nucleus is called the nuclear charge - The nuclear charge is therefre equal t the number f prtns (which is als equal t the atmic number) - Electrns, which have a -1 (negative) electric charge surrund the nucleus in regular patterns called rbitals r energy levels. Refer t the Table belw in rder t answer the fllwing questins. Name Symbl Electric Charge Lcatin in the Atm Prtn p +1 Nucleus 1836 Neutrn n 0 Nucleus 1837 Electrn e -1 Surrunding the nucleus 1 Relative Mass Ø Which subatmic particle r particles accunt fr the majrity f the vlume f an atm? electrns Ø Which subatmic particle r particles accunt fr the majrity f the mass f an atm? Prtns AND neutrns Organizatin f the Peridic Table Each element is listed accrding t its atmic number Each rw is called a perid Each clmn is called a grup r family. Elements within a family have similar prperties Metals are n the left side and middle f the table. (i) Alkali metals are very reactive metals (e.g. Na) (ii) Alkaline earth metals smewhat reactive metals (e.g. Ca) Nn-metals are in the upper right crner (iv) Nble gases- very unreactive gaseus nn-metals (e.g. Ne) (iii) Halgens- very reactive nn-metals (e.g. Cl)

2 Metallids/Semi-metals frm a staircase tward the right side. 2 Transitin metals include the elements frm grups (e.g. Fe, Ni, Cu, Ag, Au) Peridic Table and In Frmatin Recall that an atm is electrically neutral because the number f prtns equals the number f electrns. Mst atms are capable f either lsing r gaining electrns. Atms that have gained r lst electrns are electrically charged particles called ins When there are fewer electrns than prtns, the in is psitively charged Metal atms lse electrns t frm psitively charged ins called catins Many metals frm a catin ne way. Eg. Al +3 Sme metals are multivalent meaning they can frm ins in mre than ne way. Eg Fe When there are mre electrns than prtns, the in is negatively charged. +3, +2 Nn metals with very few exceptins, gain electrns t frm negative ins called anins Table 2: Examples f Atms and Ins Symbl Charge Atm r In # f prtns # f electrns C Al +3 S -2 Na Use yur peridic table t cmplete the fllwing: Symbl Charge Atm r In # f prtns # f electrns F I Ar Atm Bhr Diagrams Niels Bhr wh shwed the arrangement f in energy levels (r shells)

3 Bhr diagrams shw hw many prtns, fund in the nucleus and 3 electrns are fund in the shells/ rbits surrunding the nucleus Hw t draw Bhr diagrams: draw a nucleus and identify hw many prtns and neutrns there are draw electrn shells arund the nucleus and add the apprpriate amunt f electrns using 2 rules: in neutral atms (n charge) the number f e- equals the number f p+ a maximum f 2 can be in the first shell. a maximum f 8 can be in shells 2 and 3 Ex.1 Ptassium Atmic number = Atmic mass = # f prtns= # f electrns= # f neutrns= Ex. 2 Chlrine Atmic number = Atmic mass = # f prtns= # f electrns= # f neutrns= 1. Draw Bhr diagrams fr the first fur Alkali Metals (i.e. H, Li, Na, K). What pattern d yu bserve as yu mve frm ne perid t the next? 2. Draw Bhr diagrams fr the first fur elements in the furth perid (i.e. K, Ca, Sc, Ti). What pattern d yu bserve as yu mve frm ne family t the next? 3. Draw Bhr diagrams fr the first three Nble Gases (ie. He, Ne, Ar). What similarity d yu bserve between all three? Patterns f Electrn Arrangement in Perids The perid number f an element equals the number f ccupied shells f its atms

4 Fr ex., the tw elements in perid 1, hydrgen and helium have ne ccupied shell. 4 The elements in perid 2 have 2 ccupied shells and the pattern cntinues as evident in the figure belw. As yu mve frm left t right acrss a perid, ne mre electrn is added t the utermst shell (valence shell) Ntice that nen and argn have eight electrns in their valence shells. This is referred t as a Octet Rule : Alll atms want t achieve this state by gaining r lsing e- Patterns f Electrn Arrangement in Grups Valence electrns, electrns in the valence r uter shell, are invlved in chemical bnding Grup 1 elements have 1 valence electrns Grup 2 elements have 2 valence electrns Grup 13 elemetns have 3 valence electrns Use the table abve alng with yur peridic table t answer the fllwing questins: 1) Based n the patterns f the peridic table, identify the number f ccupied shells fr each f the fllwing elements: a. calcium 4 c. sulphur 2 b. kryptn 4 d. idine 7 2) Based n the patterns in the peridic table, identify the number f valence electrns fr eachf the fllwing elements: a. chlrine 7 c. strntium 2 b. magnesium 2 d. brmine 7 Frming Cmpunds

5 When tw atms mve clser tgether, their valence electrns interact. 5 A chemical bnd frms between atms if the new arrangement f electrns is stable. Lwer energy states are mre stable. The lwest energy states are achieved when the atms in the cmpund have the same arrangement f valence electrns as the nble gas they are clsest t in the peridic table. Referred t as Nble Gas stability. The nble gases are stable (i.e. unreactive) because their valence shells are cmpletely full Atms acquire stable valence shells, when they frm cmpunds, in ne f three ways: Metal atms may lse electrns t ther atms, frming catins (+). Nn- metal atms may gain electrns frm ther atms, frming anins (-) Atms may share electrns Reactivity f an element is linked t hw clse the atm is t having a full valence shell Therefre we find the mst reactive elements are thse f Grups 1 and 17 Cmpunds are either inic r cvalent An inic cmpund cntains a metal, (+) in, and a nn metal, the (-) in. In an Inic bnd, ne r mre electrns transfers frm each metal atm t each nn-metal In cvalent bnding, the atms f many nn-metals share electrns with ther nn- metal atms A cvalent mlecule is a grup f atms in which the atms are bund tgether by sharing ne r mre pairs f electrns The pair f electrns invlved in a cvalent bnd are smetimes called the Bnding Pair A pair f electrns in the valence shell that is nt used in bnding is called a Lne Pair Bhr diagrams, as seen belw, can be used t describe simple cvalent cmpunds. Lewis Diagrams Gilbert Lewis ( ), an American chemist, invented a methd f shwing bnding

6 A Lewis diagram illustrates chemical bnding by shwing nly an atm s valence/uter electrns and 6 chemical symbl Lewis diagrams are als referred t as Lewis Dt diagrams r Lewis structures. The figure belw cmpares Bhr diagrams t Lewis diagrams: Rules fr drawing Lewis diagrams: Dts representing electrns are placed arund the element symbl at the pints f a cmpass (N,E,S,W) Electrn dts are placed singly until the 5 th electrn is reached, then they are paired. Lewis diagrams f ins: Fr psitive ins, ne electrn dt is remved frm the valence shell fr each psitive charge f the in. (this usually means all f the electrn dts are remved) Square brackets [] must be placed arund the element symbl with the in charge shwn utside f the brackets at the tp right. Fr negative ins, ne electrn dt is added t each valence shell fr each negative charge f the in. (This usually means the element s symbl is surrunded by eight electrn dts) Square brackets are als placed arund the element symbl with the with the in charge at the tp right, utside f the brackets. (refer t figure belw). NaCl à Lewis diagrams f cmpunds: Lewis diagrams can be used t shw inic cmpunds as seen in the figure belw:

7 7 Lewis diagrams are als used t shw cvalent cmpunds as seen in the figure belw: Cvalent mlecules can als be represented by Lewis diagrams: Lewis diagrams are als used t explain why sme f the nn-metal elements exist as diatmic mlecule A diatmic mlecule is a pair f identical atms that are jined by cvalent bnds Diatmic elements frm this way because the tw atm mlecules are mre stable than the individual atms. The diatmic elements include: hydrgen: H 2 nitrgen: N 2 xygen: O 2 chlrine: Cl 2 brmine: Br 2 flurine: F 2 idine: I Names and Frmulas f Cmpunds Inic Cmpunds: Naming Inic Cmpunds frm their Frmula 1. Name the metal in first 2. Name the nn metal secnd, but change the end t ide 3. Cmbine the tw. 4. Ignre the subscripts Examples: a. CaI 2 b. MgCl 2 c. AlCl 3 d. NaCl e.kbr Calcium idide magnesium chlride aluminum chlride sdium chlride ptassium brmide

8 Frmulas f Inic Cmpunds: 8 1. They symbl frm the peridic table is used as is the charge 2. T write the frmula yu must balance the charges f the (+) and the (-) ins by having a different number f atms f each f them 3. There are tw methds t d this. By a. balancing charges r b. criss crss 4. Yu need t indicate the number f atms f each element in the frmula using subscripts. If yu have 1 atm f an element yu d nt need t include the subscript. If yu have mre than ne f an element yu need t include the subscript. *Nte: Yu must reduce subscripts t lwest terms if pssible Ex. magnesium chlride Multivalent Metals A multivalent metal is ne that can have mre than ne in charge Examples: Cu +1 r +2 Pb +2 r +4 Fe Naming: +2 r +3 The charge n the metal is imprtant t its prperties, s we must be specific when we write the **Charge & R.N table name f a cmpund with ne f these metals Rman Numerals are used t say which in charge was used. These are placed between the name f the metal and the nn metal fr inic cmpunds Ex. Cu 2O cpper (I) xide Writing Frmulas: Writing frmulas fr multivalent metals is the same as any ther inic cmpund, yu just need t make sure yu are using the right in charge. Once yu have the crrect charge use the criss crss methd r balancing charges methd Example: Lead (IV) xide Plyatmic Ins: A plyatmic ins 2 r mre f atms jined by cvalent bnds carrying an verall charge. Examples: NH4 +1 r OH -1 r (ClO) -1

9 They act as unit with a charge and dn t get split int their individual atms 9 Yu will be given a list f these n the back f yur peridic table fr quizzes and tests. All f these are (-) charged, except fr NH 4 +1 and H Frmulas f Cmpunds with Plyatmic Ins: 1. Figure ut which in is (+) and which in is (-).*The first ne in the name must be the +in 2. Use the balancing charges r criss crss methd t cme up with a frmula 3. Use subscripts t shw hw many f each in yu need by adding it afterwards. a. If there is mre than ne plyatmic in, yu must put brackets arund it befre adding yur subscript n the utside. Example: magnesium hydrxide 4. Yu d NOT change the ending f the plyatmic in. Ex. NaNO 3 = sdium nitrate Naming f Cmpunds with Plyatmic ins: Hint: If there is mre than tw capital letters in the fmula there is a plyatmic in present in the cmpund Identify the plyatmic in. Then name the mlecule accrding t the same rules as regular inic cmpunds Example Ca(OH) 2 Calcium hydrxide Prefix Number Mn 1 Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Septa 7 Octa 8

10 Cvalent Cmpunds Naming Binary Cvalent Cmpunds: Nna 9 deca Remember, cvalent means nn-metal + nn metal When yu have tw nn-metals jined tgether, we Name them in a specific way We use prefixes t help us 1. Name the element clsest t the left f the Peridic Table first. 2. Name the ther element secnd and change the ending t ide 3. Add the apprpriate prefix befre the element saying hw many f the element are in the cmpund. 4. If there is ne f the first element, yu d nt write the prefix 5. D nt reduce numbers t lwest terms Example: N 2O 2 dinitrgen dixide Writing Frmulas: 1. Write the element symbls in the rder they appear in the name 2. Add subscripts t the symbls based n the prefixes f each element. Example: Carbn tetrasulfide CS4

11 Summary f Naming 11 Befre yu start t name a cmpund, yu must ask yurself a cuple f questins. TYPE 1. Is this a simple inic cmpund? (metal + nn-metal ) *metal stays the same, nn metal s ending changed t ide ex. ZnS = zinc sulphide TYPE 2. Des the metal have mre than ne ptin fr its charge? (*Check the peridic table ) * Yu must put Rman numerals ( ex: in brackets between the metal and the nn-metal if it des) Ex. irn (II) xide = Fe +2 + O 2- FeO TYPE 3. Is there a plyatmic in in the cmpund? (There are mre than 2 elements in the cmpund r there are brackets in the frmula) *Lk n the back f yur peridic table t find the name f the plyatmic in Ex. lithium acetate= LiCH3COO TYPE 4. Is it a cvalent cmpund? (Nn-metal + nn metal) * Yu must use prefixes (ex. mn- r di-) in the name. Ex. CO2 : Carbn dixide

12 Chemical Equatins: A + B à C Reactants Prducts -bth reactants and prducts are pure substances ( either elements r cmpunds) - reactants and prducts have different prperties - chemical reactin shws chemical changes - scientists use equatins t shw hw the atms are rearranging in the reactin - yu can write an equatin with names r with chemical symbls Wrd Equatin: nitrgen mnxide + xygen à nitrgen dixide Symbl Equatin: 2NO (g) + O 2 (g) à 2NO 2 (g) Writing and Balancing Chemical Equatins The simplest frm f chemical equatin is a wrd equatin. Ptassium metal + xygen gas à ptassium xide A skeletn equatin shws the frmulas f the elements/cmpunds. A skeletn equatin shws atms, but nt quantities f atms K(s) + O2(g) à KO A balanced chemical equatin shws all atms and their quantities Balancing makes sure that the number f each atm is the same n bth sides f the reactin arrw Always use the smallest whle-number rati 2K + O2 à 2KO Cunting atms t balance an equatin Using the law f cnservatin f mass, we can cunt the atms n each side and balance them in chemical equatins Wrd equatin: methane + xygen à carbn dixide+ hydrgen Skeletn equatin: Balanced equatin: Reactants Prducts

13 13 T balance cmpunds, take nte f hw many atms f each element ccur n each side f the reactin equatin. T balance, change the numbers f mlecules invlved by adding a cefficient s the atms n bth sides f the equatin are equal (*T table) Strategic Balancing Tips Balance the atms in cmpunds first Balance ne cmpund at a time Plyatmic ins (i.e. NO 3 ) can ften be balanced as a whle grup Be careful f special cases such as plyatmic ins and the special seven : HOFBrINCl Several cmmn cvalent mlecules cntaining H have cmmn names that yu shuld knw Methane= CH 4 Glucse= C 6H 12O 6 Ethane= C 2H 6 Ammnia= NH 3 Only change cefficients, never subscripts! If H and O appear in mre than ne place, always balance them LAST! Always duble check at the end!