1Chapter 2AtomsStudy Goals•The classification of matter•Dalton’s atomic theory•The atomic structure•The periodic table•Electron configuration•The Periodic trendsFigure 2.1Classification of matter.Fig. 2.1 p. 32Classification of MatterA.Element-A pure substance that consists of identical atoms.- the building blocks of matter.- cannot be broken down into simpler substances by ordinary laboratoryprocesses.- There are 116 known elements.•Of these, 88 occur in nature; the others have been made by chemistsand physicists.•Their symbols consist of one or two letters.gold (Au)carbon (C)aluminum (Al)•Names are derived from a variety of sources.p. 32p. 33
2B. Compound-A pure substance that is made up of two or more elements in a fixedratio by mass, e.g., sodium chloride (NaCl), table salt; water (H2O).*Formulaof a compound- tells usthe ratiosof its constituent elements and identifies eachelement by its atomic symbol.- NaCl: the ratio of sodium atoms to chlorine atoms in sodium chlorideis 1:1- H2O: the ratio of hydrogen atoms to oxygen atoms in water is 2:1Example 2.1 Formula of a compound(p. 34)Magnesium fluoride ( MgF2)Mg : F =1 : 2Perchloric acid (HClO4)H : Cl : O = 1 : 1 : 4Problem 2.1Na : Cl : O = 1 : 1 : 3NaClO3Al:F= 1 : 3AlF3p. 32-33A Water Molecule•Figure 2.2Four representations of a water molecule.p. 34C.Mixture-A combination of two or more pure substances.(Air: 78% N2; 21% O2)- The substancesmay be present in any mass ratio.- Each substance has a different set of physical properties.- Mixtures may behomogeneousorheterogeneous(optical microscope).- can be separated into its component parts by physical methods.Fig. 2.4blood cellsNaCl in watersulfur (S) & iron (Fe)Fig. 2.3p. 34-352.3Dalton’s Atomic Theory•John Dalton (1766-1844)•All matter is composed of very tiny particles (atoms).•All atoms of the same element have the same chemical properties. Atomsof different elements have different chemical properties.•In ordinary chemical reaction, no atom of any element disappears or ischanged into an atom of another element.•Compounds (Ionic and Covalent)are formed by the chemicalcombination of two or more of the same or different kinds of atoms. (NaCl)•Amoleculeis a tightly bound combination of two or more atoms that actsas a single unit, e.g.,water H2O, glucose (C6H12O6).
3A.Evidence for Dalton’s TheoryThe Law of Conservation of Mass: Antoine L. Lavoisier (1743-1794)•Matter can be neither created nor destroyed.•As Dalton explained, if matter is made up of indestructible atoms, thenany chemical reaction just changes the attachments among atoms, butdoes not destroy the atoms themselves.p. 36The Law of Constant Composition: Joseph Proust (1754-1826)- Any compound is always made up of elements in the same portion bymass.e.g., If you decompose water, you always get 8 g of oxygen for each 1 gof hydrogen. (H2O: 2 x 1g +16 g )B. Monoatomic, Diatomic and polyatomic elementsMonatomic elements- consist of single atoms; e.g., helium (He) and neon (Ne).