C CHEMIC CAL CHA ANGES aand STRU S UCTU URE E Atom mic Structu ure – SSumm mary N Notess ELEM MENTSS and tthe PEERIODIIC TAB BLE • Th here are 92 naaturallyy occurring ele ementss and arround aabout aanotherr 25 wh hich havve bee n made e by sccientistss. hese eleementss are arrranged d by their atom mic • Th nu umber and the eir chemical p propertties on the Peeriodic Table. • All the ellementts have their o own ind dividua l symbol. he chem mist maainly reesponsible for the waay the • Th elementss are organiseed was Dmitri Mendeeleev. PERIODIC TABLE INFORMATION • ALKALI METALS – These are the metals making up Group 1 e.g. Sodium, Potassium etc. They are very reactive. • HALOGENS – These are the reactive non‐metals making up Group 7 e.g. Fluorine, Chlorine etc. • NOBLE GASES – These are very unreactive gases making up Group 8 e.g. Helium, Neon etc. • TRANSITION METALS – These are metals found between Group 2 and Group 3 e.g. Iron, Copper and Platinum. They have many uses and many of them and their compounds are used as catalysts in industrial processes. A Atomss All eleementss are m made o of veryy small particcles callled ATOM MS. At thee centrre of evvery attom is the NUCLEU US containing b both PROTONS and d NEUT TRONSS. The us is su urroun nded b by fast movin ng ELECCTRON NS. nucleu how 2 ways of dra awing aatomss ‐ Thesee diagrrams sh More about atoms – The following table shows important differences between the 3 particles – PARTICLE Proton MASS 1 CHARGE +1 LOCATION Nucleus Neutron Electron 1 0 0 ‐1 Nucleus Outside the nucleus In an atom there are always the same number of positive protons as negative electrons. This means that they have no overall charge i.e. ATOMS ARE NEUTRAL. ELECTRON A ARRAN NGEME ENTS Electrons arre arranged in ENERGY LE EVELS or SHEELLS undingg the n nucleuss – surrou n arran ngemeents off the e elemen nts are e The electron e data book given in the E.g. Sod dium’s eelectron n arranggement is 2,8,1 which m means Sodium m has 2 eelectron ns in thee 1st ene ergy leve el, 8 in tthe seco ond and 1 in n the 3rd. Electrrons in tthe enerrgy leve el furtheest from the nucleuss are called OUTER ELEECTRON NS. Sodiu um has 1 outerr electron. TA ARGETT DIAG GRAMSS Electrron arrrangem ments can be e show wn as ttarget diagraams E.g. Liithium m 2, 1 Phosphoru us 2, 88, 5 The outer electron ns are very im mportant. El ementts in the saame grroup of the PPeriodiic Table havee the same numb ber of o outer eelectro ons and for tthis reason havee simila ar chemical properties. IMPORTANT NUMBERS 1. ATOMIC NUMBER Each element has its own Atomic Number and they are arranged on the Periodic Table in order of increasing Atomic Number. The Atomic Number gives the number of PROTONS present in an atom of the element. E.g. Element number 11 is Sodium Sodium has Atomic Number 11 Each sodium atom contains 11 protons and its nucleus has a charge of +11 Since the atom is neutral, it must also have 11 electrons. 2. MASS NUMBER This is the total number of PROTONS + NEUTRONS in an atom E.g. a Sodium atom with Mass Number 23 will contain – 11 protons 11 electrons 12 neutrons NUCLIDEE NOTTATIO ON Chemiists use e nuclid de notaation to o show w the nu umberss of sub‐attomic p particle es in an n atom or ion. mber of p protonss = 10 Num Num mber of p protonss = Num mber of e electron ns = 10 Num mber of n neutron ns = 22 –– 10 = 1 12 ISOTOPES Isotopes are atoms with the same Atomic Number but different Mass Number. This means they are atoms of the same element but they have different numbers of neutrons. Eg. Chlorine has 2 isotopes 35Cl and 37Cl Number of protons Number of electrons Number of neutrons 35 37 Cl 17 17 18 Cl 17 17 20 Eg. Hydrogen has 3 isotopes, 1H, 2H and 3H Number of protons Number of electrons Number of neutrons 1 H 1 1 0 2 H 1 1 1 3 H 1 1 2 R RELAT TIVE A ATOM MIC M MASS The Reelative Atomicc Mass of an e element is thee AVERA AGE MASS OF ALLL THE ISSOTOP PES pressent taking intto acco ount the rellative aabundance of each. Eg. Ch hlorine Chlo orine haas 2 iso otopes ‐ 35Cl a and 37CCl In Chlo orine 75 5% of tthe atoms havve Masss Numbber 35 and 25% haave Maass num mber 377. Avverage mass = (75 X X 35) + + (25 X X 37) 10 00 = = 2625 + + 925 10 00 = 35.5 he Relative Atomic M Mass wiill always be cclosest to • Th th he masss of the e most abundaant isottope. • Reelative Atomicc Massees are rrarely w whole nnumbers. Th hey aree used in calcu ulationss later in the ccourse.
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