27.1 Development of the Periodic Table 1st developed by Dmitri Mendeleev (Russia) & Lothar Meyer (Germany) on the basis of the similarity in chemical and physical propertiesMendeleev …started by organizing elements by increasing mass.Recognized a repetition of pattern.Placed elements by same column same propertiesPredicted correctly about the existence of new elementsHenry Moseleyestablished that each element has a unique atomic number, which added more order to the periodic tableIdentified the atomic number with the # of protons in the nucleus of the atom & the # of electrons in the atom.
37.2 Electron Shells and the Sizes of Atoms Atoms aren’t hard spheres with well-defined shells of electronsThe edges of atoms are a bit “fuzzy”The quantum mechanical model of the atom supports the notion of electron shells: certain distances from the nucleus at which there is a higher likelihood of finding an electron
4Atomic SizesThe size of an atom can be gauged by its bonding atomic radius, based on measurements of the distances separating atoms in their chemical combinations with other atomsMeasure the atomic radius from the center of the nucleus to the outermost electron.Atom size increases going down a group.Atomic size decreases going left to right across the period.
57.3 Ionization EnergyIonization energy – the minimum energy required to remove an electron from the ground state of the isolated gaseous atom or ion1st ionization energy (I1) – The energy needed to remove the first electron from a neutral atom, forming a cation2nd ionization energy (I2) – the energy needed to remove the second electronThe greater the ionization energy, the harder it is to remove an electron
67.3 Ionization EnergyHIGH ionization energy means the atom hold onto the electron tightly and a lot of energy is need to pull it offLOW ionization energy means the atom holds onto the electron loosely so breaking it apart doesn’t require much energy
77.3 Ionization Energy Periodic Trends in Ionization Energies Ionization energy decreases as you move down a group.Ionization energy increases as you move from left to right on the periodic table.Representative elements show a larger range of values of I1 than do the transition metal elements
97.4 Electron AffinitiesElectron affinity – the energy change that occurs when an electron is added to as gaseous atomA negative electron affinity = the anion is stableA positive electron affinity = the anion is higher in energy than are the separated atom and electron. The anion is not stable and will not form
107.4 Electron AffinitiesIf the electron affinity is negative, the atom releases energy.Normally, non-metals have a more negative electron affinity than metals. The exception is the noble gases.
117.4 Electron AffinitiesElection affinities become more negative as we proceed from left to rightHalogens have the most negative electron affinitiesThe electron affinities of the noble gases are all positive since the added electron would have to occupy a new, higher-energy subshellElectron affinity doesn’t change greatly as we move down a group. Electron affinity should become more positive (less energy released).
13MetalsNon-MetalsHave a shiny luster; various colors, although most are silveryDo not have a luster; various colorsSolids are malleable and ductileSolids are usually brittle; some are hard, and some are softGood conductors of heat and electricityPoor conductors of heat and electricityMost metal oxides are ionic solids that are basicMost non-metallic oxides are molecular substances that form acidic solutionsTend for form cations in aqueous solutionsTend to form anions or oxyanions in aqueous solutionPg Table Characteristic Properties of Metals and Nonmetals
147.5 Metals, Nonmetals, and Metalloids Metallic Character - The tendency of an element to exhibit properties of metalsMetallic character generally increases going down a column and decreases going from left to right across a period
15Metals Metals conduct heat & electricity They are malleable & ductile Solids at room temp. except mercury(Hg) (it’s liquid)Melt at very high tempsHave low ionization energies & are consequently oxidized (lose electrons) when they undergo chemical reaction.Many transition metals have the ability to form more than one positive ion.
16Chemical Reactions with Metals metal oxide + water metal hydroxideMost metal oxides are known as basic oxidesEx: Na2O (s) + H2O(l) 2NaOH (aq)metal oxide + acid salt + waterEx: MgO (s) + 2HCl (aq) MgCl2 (aq) + H20 (l)
17NonmetalsNot lustrous & generally are poor conductors of heat and electricityNon-metals commonly gain enough electrons to fill their outer p sub-shell completely, giving a noble gas electron configuration.Molecular substances - Compounds composed entirely of nonmetalsEx: oxides, halides, and hydridesMelting points are gen. lower than those of metals
18Chemical Reactions with Nonmetals Nonmetal oxide + water → acidMost nonmetal oxides are acidic oxidesCO2 (g) + H2O (l) H2CO3 (aq)Nonmetal oxide + base salt + waterCO2 (g) + 2NaOH (aq) Na2CO3 (aq) + H2O (l)
19Metalloids (aka Semi-metals) Have properties that are intermediate between those of metals and nonmetals
207.6 Group Trends for the Active Metal Group 1A: The Alkali MetalsCharacteristicsSoft metallic solidsSilverymetallic lusterhigh thermal and electrical conductivitiesLow densities and melting pointsMost active metalsExist in nature only as compounds
217.6 Group Trends for the Active Metal Group 2A: Alkaline Earth MetalsSolids with typical metallic propertiesHarder, more dense, and melt at higher temperatures when compared to alkali metalsVery reactive towards nonmetals, but not as reactive as alkali metalsBoth alkali and alkaline earth metals react with hydrogen to form ionic substances that contain the hydride ion, H-
227.7 Group Trends for Selected Metals HydrogenHydrogen is a nonmetal with properties that are distinct from any of the groups of the periodic tableIt forms molecular compounds with other nonmetals, such as oxygen and the halogens
237.7 Group Trends for Selected Metals Group 6A: The Oxygen GroupMost important element in group 6AExists in several allotropic forms (different forms of the same element in the same state)Oxygen is encountered in two molecular forms, O2 (common form) and O3 (aka ozone)Oxygen has a strong tendency to gain electrons from other elements, thus oxidizing themIn combination with metals, oxygen is usually found as the oxide ion, O2-, although salts of the peroxide ion, O22-, and superoxide ion, O2-, are sometimes formed
247.7 Group Trends for Selected Metals Sulfur!!2nd more important element in group 6AAlso exists in several allotropic formsElemental sulfur is more commonly found as S8 moleculesIn combination with metals, it is more often found as the sulfide ion, S2-
257.7 Group Trends for Selected Metals Nonmetals that exist as diatomic moleculesThere melting and boiling points increase as you go down the columnHave the most negative electron affinities of the elementsTheir chemistry is dominated by a tendency to form 1- ions, especially in reactions with metals
267.7 Group Trends for Selected Metals Group 8A: The Noble Gases aka inert gasesNonmetals that exist as monoatomic gasesVery unreactive since they have completely filled s and p subshells. Have the complete octetHave large 1st ionization energiesOnly the heaviest noble gases are known to form compounds, and they do so only with very active nonmetals, like fluorine