Language of Chemistry includes chemical symbols of elements, chemical formulas, & chemical equations AllAll knownknown elementselements ((ca.100)ca.100) areare arrangedarranged inin PeriodicPeriodic TableTable.. EachEach elementelement hashas itsits ownown 1stcharacter namename && chemicalchemical symbolsymbol:: is CAPITAL SodiumSodium NaNa SulfurSulfur SS 2nd (if any) is low-key PotassiumPotassium KK PhosphorusPhosphorus PP HydrogenHydrogen HH CopperCopper CuCu OxygenOxygen OO GoldGold AuAu IronIron FeFe MercuryMercury HgHg TinTin SnSn LeadLead PbPb CoCo isis elementelement cobalt,cobalt, whilewhile COCO isis carboncarbon monoxide,monoxide, aa compound.compound. CompoundsCompounds areare formedformed byby combinationscombinations ofof elements,elements, writtenwritten asas aa chemicalchemical formulaformula:: COCO22 HH22OO CHCH44 BNBN CombiningCombining intointo compounds,compounds, atomsatoms changechange theirtheir properties:properties: CarbonCarbon CC isis aa blackblack stone,stone, sulfur,sulfur, SS isis aa yellowyellow powder,powder, butbut carboncarbon disulfide,disulfide, CSCS2 isis aa toxictoxic liquid.liquid. RearrangementRearrangement ofof atomsatoms resultingresulting inin aa newnew chemicalchemical compoundcompound isis aa CHEMICALCHEMICAL REACTION:REACTION: HH22 ++ ClCl22 →→ 22HClHCl ++ →→ STRUCTURESTRUCTURE OFOF ATOMATOM Humphry Davy, by 1808, found that ELECTRICAL CURRENT DECOMPOSES SOME SUBSTANCES TO ELEMENTS: (+/-) CuClCuCl2(aq) →→ CuCu(s) ++ ClCl2(g) Michael Faraday (1791-1867) introduced the concept of IONSIONS as ELECTRICALLY CHARGED ATOMS that move to the battery poles, according to the Coulomb law: + - Anode: + - Cathode: - - 2+ - o 2Cl -2e → Cl2 Cu +2e → Cu Anions ( - ) Cl- Cu2+ Cations (+) travel to, & travel to, & discharge at discharge at anode [+] cathode [-] + Thus: Element Cl can exist either as a neutralneutral atomatom (in free chlorine, ClCl2), - or as a negativenegative chloridechloride ionion,, ClCl , i.e. although Cl atoms do not disappear in a chemical transformation, they somehow change – in their charge. Element Cu can exist as a neutral atom, 2+2+ or as a positive coppercopper ion,ion, CuCu ∴atoms can either be neutral, or be electrically charged. ∴atoms, though never destroyed in chemistry, must have some inner structure, with its subatomic particles. Jacob J. Berzelius put forward The ELECTRIC THEORY OF CHEMICAL BOND: atoms are held together in compounds due to their opposite electrical charges: NaNa+ ClCl- OnlyOnly outerouter electronselectrons areare involvedinvolved inin chemicalchemical rxnsrxns ELEMENTSELEMENTS ININ PERIODICPERIODIC TABLETABLE EachEach elementelement asas postedposted inin thethe Table,Table, has:has: aa NAMENAME,, potassium,potassium, hydrogen,hydrogen, …… aa SYMBOLSYMBOL,, K,K, Na,Na, Cu,Cu, ClCl,, …… anan ATOMICATOMIC NUMBERNUMBER ZZ (integer(integer only)only) && anan atomicatomic massmass AA (usually(usually nonnon--integer)integer) 55.847 26 Fe AtomicAtomic numbernumber ZZ isis thethe positivepositive chargecharge ofof thethe nucleusnucleus && thethe numbernumber ofof protonsprotons inin itit AtomicAtomic massmass isis thethe sumsum ofof massesmasses ofof protonsprotons && neutrons.neutrons. Why is atomic mass non-integer? Because natural elements consist of a mix of isotopes: Atoms with the same atomic number, but different mass number. Neon,Neon, NeNe:: Z=10Z=10 threethree isotopesisotopes pp nn AA NeNe--2020 90.51%90.51% 1010 1010 2020 NeNe--2121 0.21%0.21% 1010 1111 2121 NeNe--2222 9.22%9.22% 1010 1212 2222 TheThe averageaverage AtomicAtomic massmass isis 20.1820.18 Copper,Copper, Cu:Cu: ZZ == 2929 twotwo isotopesisotopes CuCu--6363 69.17%69.17% CuCu--6565 30.83%30.83% At.At. massmass == 63 x 0.6917 + 65 x 0.3083 = == 63.5563.55 a.m.ua.m.u.. ELEMENTS & PERIODIC TABLETABLE To each isotope, besides a symbol, two numbers are associated: atomic number (Z) - position in the Table (element ID#) mass number (A) Mass Symbol number 5959 Atomic number 2727 means cobalt (Z=27) atom with its mass number A=59 SUBATOMICSUBATOMIC PARTICLESPARTICLES Although atoms are not destroyed, or disappear in chemical rxns, they have their inner structure: atom consist of 3 types of subatomic particles, with their known electrical charges & masses. mass charge PROTON p+ 1 +1 NEUTRON n 1 0 ELECTRON e- 0 -1 (1/2000) Masses are in ATOMIC MASS UNITS (amu) ProtonsProtons && neutronsneutrons areare heavyheavy particlesparticles constitutingconstituting atomicatomic nucleus.nucleus. TheThe massmass ofof atomatom isis duedue toto nucleusnucleus whichwhich isis veryvery smallsmall inin sizesize && positivelypositively charged.charged. ThatThat chargecharge isis thethe atomicatomic numbernumber.. ATOMICATOMIC NUMBERNUMBER ZZ isis thethe NUMBERNUMBER ofof PROTONSPROTONS inin thethe NUCLEUSNUCLEUS MASSMASS NUMBERNUMBER AA isis thethe SUMSUM ofof PROTONSPROTONS && NEUTRONS,NEUTRONS, i.e.i.e. AA == ZZ ++ nn Electrons are almost weightless & spread around the nucleus. The size of atom is the size of its electron cloud. Electron cloud: No mass, negative charge Outer (valence) electrons Atomic nucleus: protons & neutrons Positive charge = Inner shell number of protons, (core) electrons mass = sum of protons & neutrons ChemicalChemical propertiesproperties (i.e.(i.e. abilityability toto undergoundergo chemicalchemical rxnsrxns)) dependdepend onon thethe electronelectron configurationconfiguration (primarily on the # of e-), which itself is equal to the number of pp+ in a neutral atom (but not related to the number of neutrons) ∴∴ atomsatoms withwith thethe samesame numbernumber ofof pp+ (i.e.(i.e. samesame Z,Z, ∴∴ alsoalso thethe samesame numbernumber ofof ee-)) butbut differentdifferent numbernumber ofof nn areare chechemmicallyically indistinguishableindistinguishable,, eveneven thoughthough theirtheir massesmasses differ.differ. Atoms with the same Z (number of protons or nuclear charge) but different number of neutrons (∴ different masses) are ISOTOPES 10 Ne Neon,Neon, NeNe:: 33 isotopes:isotopes: 20.18 ZZ AA nn 20NeNe 90.51%90.51% 1010 2020 1010 21NeNe 0.21%0.21% 1010 2121 1111 22NeNe 9.22%9.22% 1010 2222 1212 TheThe averageaverage atomicatomic massmass A=A= 20.1820.18 29 Copper,Copper, Cu:Cu: 22 isotopesisotopes Cu 63.55 ZZ AA nn 63CuCu 69.17%69.17% 2929 6363 3434 65CuCu 30.83%30.83% 2929 6565 3636 AA == 6363××0.69170.6917 ++ 6565××0.30830.3083 == 63.5563.55 amuamu IsotopesIsotopes belongbelong toto thethe samesame elementelement,, havehave thethe samesame symbolsymbol,, occupyoccupy thethe samesame cellcell inin thethe PeriodicPeriodic Table,Table, && havehave thethe samesame chemicalchemical properties.properties. ““ISOTOPEISOTOPE”” translatestranslates asas ““samesame placeplace””,, i.e.i.e. thethe samesame cellcell inin PeriodicPeriodic Table.Table. MassMass numbernumber ofof eacheach isotopeisotope isis anan integerinteger numbernumber (number(number ofof protons)protons) NaturalNatural elementselements areare mixturesmixtures ofof isotopesisotopes.. AtomicAtomic massesmasses inin thethe TableTable areare notnot integerinteger:: theythey areare averageaverage outout ofof allall thethe naturalnatural isotopesisotopes ofof anyany particularparticular elementelement PeriodicPeriodic TableTable Dmitry Mendeleev, 1869 arranged all known (60 by his time) elements according to their increasing atomic masses & noticed some pattern: Properties of elements repeat each other with a period of 7 elements (8 after the discovery of noble gases, & 18 for heavier elements) He organized the list of elements as a chart, so that elements with similar properties stand under each other in columns – groups. He successfully predicted several elements not yet known, & predicted, very precisely, their properties: they were later discovered in the nature, just where Mendeleev advised to look for them. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 IA VIIIA IIA IIIA IVA VA VIA VIIA PERIODIC TABLE OF ELEMENTS IIIB IVB VB VIB VIIB VIIIB IB IIB HorizontalHorizontal rowsrows areare 77 PERIODSPERIODS.. VerticalVertical columnscolumns areare 1818 GROUPSGROUPS.. TallTall columns:columns: 88 MAINMAIN GROUPGROUPSS (I(IA toto VIIIVIIIA).). TheirTheir elementselements areare REPRESENTATIVEREPRESENTATIVE ELEMENTS.ELEMENTS. ShortShort columns:columns: TRANSITIONTRANSITION METALSMETALS (Numbered(Numbered asas 33 toto 1212 oror IBIB toto VIIIB)VIIIB) TwoTwo cellscells containcontain LANTHANIDELANTHANIDE && ACTINIDEACTINIDE familiesfamilies (which(which areare bothboth INNERINNER--SHELLSHELL TRANSITIONTRANSITION METALS).METALS). METALSMETALS vs.vs. NONMETALSNONMETALS MostMost ofof elementselements areare metalsmetals:: theythey conductconduct electricity,electricity, heatheat,, areare malleable,malleable, easilyeasily releaserelease theirtheir electronselectrons producingproducing negativenegative ionsions whilewhile formingforming compoundscompounds withwith nonnon--metalsmetals.. Example: Metal Zn combines with non-metal sulfur S: Zn -2e- → Zn2+ S + 2e- → S2- Almost all metals are solid (except mercury, Hg). NonmetalsNonmetals areare inin thethe upperupper rightright cornercorner ofof thethe table.table. TheyThey existexist asas gases,gases, liquidsliquids (as(as bromine,bromine, BrBr2)) oror solidssolids (carbon,(carbon, iodine,iodine, phosphorus,phosphorus, sulfur,sulfur, etc.)etc.) TheyThey dodo notnot conductconduct electricity.electricity. TheyThey moremore likelylikely acceptaccept electronselectrons fromfrom metals,metals, butbut alsoalso formform compoundscompounds withwith otherother nonnon--metals:metals: