Presentation on theme: "Trends in the periodic table:"— Presentation transcript:
1 Trends in the periodic table: 1604/10/99Trends in the periodic table:Ionization Energy Atomic Radius Electron Affinity Electronegativity
2 Objectives Periodic Trends Be able to interpret trends that occur on the periodic tableBe able to predict relative sizes of atomsBe able to predict more electronegative atomBe able to predict relative ionization energy
3 04/10/99IntroductoryThere is a special stability associated with having a full outer shell (8 valence electrons)Half full shells and a full s offer some stabilityAtoms give up and lose electrons in order to gain this special stability (Ionic Ch 4)Atoms also share electrons to gain this outer shell (Covalent Ch 4)
4 Periodic Trends Sizes of atoms and ions. Ionization energy. 04/10/99Periodic TrendsSizes of atoms and ions.Ionization energy.ElectronegativityElectron affinity.
6 Sizes of Atoms Bonding atomic radius tends to… 04/10/99Sizes of AtomsBonding atomic radius tends to……decrease from left to right across a row…increase from top to bottom of a columnWhy? Explain both trends
7 Atomic Radius What gives atoms their size is the electrons 04/10/99Atomic RadiusWhat gives atoms their size is the electronsThe largest atoms are in the bottom left of the periodic tableWhy not the right since there are more electrons?Short answer: more protonsBut why? There are more electrons too?
8 04/10/99Atomic RadiusLong answer: As you more from left to right across the periodic table, you stay at the same principal energy level.The electrons are added to an existing orbital, but now there are more protons to pull them in closerWhen you go from a Noble gas to the next row, then you have a big jump
9 Atomic Radius Li Be B + + + + + + + + + + + + As we add more protons, the electrons in the same shell have more attraction to the centerThis explains higher ionization energies04/10/99Atomic RadiusLiBeB++++++++++++
10 04/10/99Atomic RadiusThis also means that:The 1s shell of Hydrogen (H) is much larger than the 1s shell of Cesium (Cs)
12 Sizes of Ions Ionic size depends upon: Nuclear charge. 04/10/99Sizes of IonsIonic size depends upon:Nuclear charge.Number of electrons.Orbitals in which electrons reside.
13 Sizes of Ions Cations are smaller than their parent atoms. 04/10/99Sizes of IonsCations are smaller than their parent atoms.The bigger the positive charge, the smaller you areThe outermost electron is removed and repulsions are reduced.
14 Sizes of Ions Anions are larger than their parent atoms. 04/10/99Sizes of IonsAnions are larger than their parent atoms.The larger the negative charge, the larger you areElectrons are added and repulsions are increased.
15 04/10/99Sizes of IonsIons increase in size as you go down a column.
16 04/10/99Sizes of IonsIn an isoelectronic series, ions have the same number of electrons.In an isoelectronic series, the most positive charge is the smallest
18 04/10/99Ionization EnergyAmount of energy required to remove an electron from the ground state of a gaseous atom or ion.First ionization energy is that energy required to remove first electron.Second ionization energy is that energy required to remove second electron, etc.
19 04/10/99Ionization EnergyIt requires more energy to remove each successive electron.When all valence electrons have been removed, the ionization energy takes a “quantum leap”.
20 Trends in First Ionization Energies 04/10/99Trends in First Ionization EnergiesAs one goes down a column, less energy is required to remove the first electron.For atoms in the same group, Zeff is essentially the same, but the valence electrons are farther from the nucleus.
21 Trends in First Ionization Energies 04/10/99Trends in First Ionization EnergiesGenerally, as one goes across a row, it gets harder to remove an electron.
22 Ionization Losing an electron is called ionization 04/10/99Losing an electron is called ionizationThis loss can be caused byThe presence of another element that has a tendency to gain electronsEnergy absorbed by the electron causing it to jump out of orbit (High energy photon needed)An ion is an atom that has either a net positive or net negative chargeQ: what would the charge be on an atom that lost an electron? Gained two electrons?A: +1 (because your losing a -ve electron)A: -2 (because you gain 2 -ve electrons)
23 Ionization energy04/10/99Ionization energy is the energy required to remove one outer electron from an atomThis value is dependent on many factors.General trends you find about ionization energy areAtoms in the top right of the periodic table have the largest ionization energiesAs you move down a column the energy required becomes less as the electron is farther away from the nucleusAs you move right across a row the ionization energy becomes larger (atomic radius smaller)
30 04/10/99Electron AffinityTake note of the high Electron Affinity associated with the Halogens (F, Cl, Br, I)Noble Gases as well as some other groups hover at zero due to factors such asPairing up of electrons (Nitrogens group)New principal energy level (Noble gases)Addition of orbital and/or new type of orbital (Alkaline Earth Metals)
32 Electronegativity Summed up as: How bad an atom wants an electron 04/10/99ElectronegativitySummed up as: How bad an atom wants an electronClosely associated with electron affinityIf the atom releases energy by gaining an electron, it will have a high electronegativityA high electronegative corresponds with high desire to grab another electron
33 04/10/99ElectronegativityLinus Pauling is the one who did extensive work with this trend. Also made a simple scale of electronegativityHe used the 2nd row of the periodic table, Li through FHe assigned Lithium 1.0 and Flourine 4.0+0.5 as you move acrossUsed Flourine as standard to set other #’s
36 04/10/99Practice QuestionsWhat atom has the highest ionization energy: F, He, Ar, CsWhat atom has the largest neutral radius: F, He, Cs, BaWhat atom has the highest electronegativity: O, S, N, PWhich group has no electronegativity?
37 04/10/99Practice QuestionsWhat atom has a larger radius: Na with a +1 charge, Mg with a +2 charge?What atom has a larger radius: N with a -3 charge, O with a -2 charge, or F with a -1 charge?What do you think happens when a neutral F and neutral Li come in contact?
38 Practice Questions Which column has the largest electronegative value? Which columns have no electron affinity?