Presentation on theme: "Period Table1 Atomic Properties and the Period Table Chemical elements: basic matters from which all material are made of. Atoms: natural entities of all."— Presentation transcript:
Period Table1 Atomic Properties and the Period Table Chemical elements: basic matters from which all material are made of. Atoms: natural entities of all matter. Atomic properties: properties of individual atoms. Periodic table of chemical elements: a tool for correlating and organizing chemical properties of elements. The modern periodic tables are results of quantum mechanics, and the study of chemistry has gone through a period highly theoretical to reach this state. Many atomic properties are related to the location of the element on the period table, and you need to know some of the rules and trends.
Period Table2 Mendeleev and Meyer Work Both Mendeleev and Meyer tried to correlate chemical properties of elements with atomic weight, and they found that the properties reoccur every so often as atomic weight increases. For example, Na, K, Rb form compounds with oxygen and water in similar way. So do Mg, Ca, Ba; F, Cl, Br; etc. Mendeleev predicted some element not yet discovered then and elements were discovered as he predicted. This made him much more known than Meyer. Due to the fact that atomic weight has to be inverted in a few places on the old periodic table, the atomic number was assigned after the discoveries of X-ray and Moseley’s law: the frequencies of the characteristic X-rays of elements are proportional to the square of atomic number. Mendeleev & Meyer role models
Period Table3 Main-group Ions Typical ions by groups of elements Li +1 Be +2 BCN 3– O 2– F – Ne Na +1 Mg +2 Al +3 Si P 3– S 2– Cl – Ar K +1 Ca +2 Ga +3 Ge +4 AsSe 2– Br – Kr Rb +1 Sr +2 In +3 Sn +4 SbTeI – Xe Cs +1 Ba +2 La +3 Pb 2-4 Fr +1 Ra +2 Know your main-group elements.
Period Table4 Transition Metal Ions Transition metals have n s 2 ( n – 1) d electrons. They lose n s electrons to form 2+ ions, and few lose ( n – 1) d electrons to form ions of charge +2 and +3, or even +4 ions. What is the electronic configuration for Ti 4+ ? ____ Some typical transition metal ions: Sc 3+ Ti 2+, 4+ V 2+ Cr 2+, 3+ Mn 2+ Fe 2+, 3+ Co 2+ Ni 2+ Cu +, 2+ Zn 2+ Mo 2+ Ag + Cd 2+ Au +, 3+ Hg 2+ How many 3d electrons do Cu 2+, Fe 3+, etc ions have?
Period Table5 Sizes of Atoms and Ions Make sure you can explain these with some examples: Atomic volume: Cu has a density of 8920 kg m -3, find volume occupied by 1 atom.(63.5/ *N A ) = _______ (reasoning) Atomic radii (take 25% of volume off and find the edge of the cube occupied per Cu atom) (illustrate during the lecture, but not giving here) Covalent radii: half of covalent bond lengths Ionic radii: not easy to give accurate value, but consistent set of cat ion and anion radii have been carefully estimated by repeated trials.
Period Table6 Screening and Penetration The effects of other electrons in an atom on an electron is screening the positive charge. Since electrons are waves, they penetrate into space “occupied by other electrons”. No assumption can be made so that we can treat many-electron atoms as H-like atoms. Thus, we assume the charge experienced by an electron as Z eff, the effective atomic charge (or number). Thus, the energy of many electrons is E n = – R H ; R H = – 13.6 eV, the Rydberg costant for H Energies of sub-shells are also affected by the quantum number l, as we have pointed out before, but quantum numbers l and m also affect sizes. Z eff 2 n 2
Period Table7 Atomic Radii in Groups and Period Give reasons to explain the variation of atomic radii on the periodic table: Variation of atomic radii within a group: increase as Z increases (increase number of electrons and number of shells) Variation of atomic radii within a period: generally decrease as Z increases (penetration of electrons, screening and penetration) Variation of atomic radii of transition metals: almost constant, but decrease very slowly ( d -electrons) Consult a periodic table and arrange the following lists by increasing atomic radius. Na, Li, K, Cs Br, Cl, I, F Be, Li, B, C, O, F, N
Period Table8 Atomic radii as Z increases
Period Table9 Trends of Ionic radii Ions usually have the same electronic configuration as an inert gas. He Li + Be 2+ N 3– O 2– F – Ne Na + Mg 2+ P 3– S 2– Cl – Ar K + Ca 2+ Se 2– Br – Kr Rb + Sr 2+ Te 2– I – Xe Cs + Ba 2+ Explain the trend in groups of color and chemical groups and give reasons for the trend. Chieh does this during the lecture, and you do this during your review. Skipping class is your choice.
Period Table10 From Atoms to Ions Consult a periodic table and arrange the following lists by increasing atomic radius. Na +, Li +, K +, Cs +, Xe, I - Br –, Cl –, I –, F – Be 2+, Li +, B, C, O –2, F –, N
Period Table11 Trend in Ionization Energy Ionization energy, I, is the energy required to convert a gaseous atom or ion into a gaseous ion, in eV per ion or in J or kJ per mole. For example, Mg (g) Mg + (g) + e – ; I 1 = 738 kJ / mol = 7.65 eV/atom Mg + (g) Mg 2+ (g) + e – ; I 2 = 1451 kJ / mol = 15.0 eV/atom The effective atomic number Z eff, may be estimated using, E eff = a positive value But ionization energy is not E eff. Z eff 2 n 2
Period Table12 Variation of I 1 as Z Varies How does first ionization energy I 1 vary in a group and in a period and why? Decreases and increases respectively
Period Table13 The I n of Group n Define I n. How do I 1-to-n+1 change with elements in group number n ?
Period Table14 Electron Affinity Electron affinity EA is the energy change when a gaseous atom or ion gains an electron (reverse of ionization), in eV per ion or in J or kJ per mole. For example, F (g) + e – F – (g); EA = – 328 kJ / mol = – 3.4 eV/atom Li (g) + e – Li – (g); EA = – 59.6 kJ / mol = – 0.62 eV/atom O (g) + e – O – (g); EA 1 = – 141 kJ / mol = – 1.46 eV/atom O – (g) + e – O 2– (g); EA 2 = 744 kJ / mol = 7.71 eV/atom The variation of EA is very irregular as Z increases. There is no particular trend in groups and in periods. Note the relationship of EA s and I s.
Period Table15 Electronegativity Explain the trend of EN in the periodic table
Period Table16 Magnetic Properties Materials can be divided into three types according to their magnetic properties. Be able to explain these terms: Diamagnetic material: substance slightly repelled by a magnetic field. There are no unpaired electrons. Paramagnetic material: substance slightly attracted by a magnetic field. There are some unpaired electrons, (single e – in an orbital) Ferromagnetic material: substances strongly attracted by magnetic field. Magnetic domains line up in these type, Fe, Fe 2 O 3 etc. Which of these are paramagnetic, H, Na, Mg, Cl, Cl –, Ag, Fe
Period Table17 Metals, Non-metals, Acids and Bases 1s 1 2s 1-2 3s 1-2 4s 1-2 5s 1-2 6s 1-2 7s 1-2 1s 2 2p 1 – 2p 6 3p 1 – 3p 6 4p 1 – 4p 6 5p 1 – 5p 6 6p 1 – 6p 6 7p 1 – 7p 6 3d 1 – – – 3d 10 4d 1 – – – 4d 10 5d 1 – – – 5d 10 6d 1 – – – 6d 10 4f 1 – – – – – 4f 14 Th Pa U – – – 5f 14 Metallic and reducing properties increases along the arrows, and oxidizing and non-metallic properties decreases along the arrows.
Period Table18 Oxides and Strong Acids Aside from HCl, other strong acids are derived from oxides of N, S, Cl: HNO 3 H 2 SO 4 HClO 4 HClO 3 Some oxides also form weak acids: HCO 3 HNO 2 H 2 SO 3 HClO 2 In contrast, look at some strong bases NaOH KOHCa(OH) 2 RbOH Sr(OH) 2 CsOHBa(OH) 2
Period Table19 Review of trends of properties The work functions of a number of metals are: Al, 6.86; Cs, 3.45; Li, 4.6 Mg, 5.86; Na, 4.40; Rb, 3.46 (J*10 19 ) How do the work functions vary: Down in a group? Across a period? Estimate the work function for K. _____* J What is the work function? Threshold of photoelectric effect. What units is more convenient? 1 eV atom –1 = e-19 J atom –1 = 96.5 kJ mol –1
Period Table20 Review of energy states Gaseous Na atoms [Ne]3s 1 absorb quanta with the energies and excited states shown. 203 kJ mol –1, [Ne]3p 1 ; 308 kJ mol –1, [Ne]4s 1 ; 349 kJ mol –1, [Ne]3d 1 ; 362 kJ mol –1, [Ne]4p 1 ; The ionization energy of the ground state is 496 kJ mol –1. What are the ionization energies of each of the excited states? Estimate Z eff ? Draw an energy level diagram for Na atoms. Explain the meaning of your results.
Period Table21 Review of acid-base property of elements Consult a periodic table and note the locations of the key elements. Then complete and balance these reactions, if it does take place. Rb(s) + H 2 O (l) I 2 (s) + Na + (aq) + Br – (aq) SrO (s) + H 2 O (l) SO 3 (g) + H 2 O (l) CO 2 + H 2 O (l) CaO + H 2 O (l) Which of these produce acids and which produce bases?
Period Table22 Review questions Consult only the periodic table to answer all these questions. How many unpaired electrons are present in Sc, Ti, V, Cr, Mn, Fe, Co, and Ni? What are the chemical formula for the following, lithium nitride, lithium nitrate, germanium bromide, arsenic acid, hydrogen sulfide? Figure out the smallest and the largest atom (by volume or by radius) in these lists: Ba, Ca, As, At, Ar, K, Al, S, As, Br. Write the equation representing the first ionization of Bromine_______ What is the name of the energy for this reaction Cl(g) + e – (g) = Cl – ?
Period Table23 Review questions – cont. Consult only the periodic table to answer all these questions. Which one of these has the largest and smallest first ionization energy, F, Be, B, Mg, H; Li, Be, Mg, Al, B; Be, B, C, Na, Ba. Which of the following has the highest ionzation energy for the removal of the third electron, Mg, Al, Si, Cl, or Ar? Indicate increase or decrease for the following, atomic radius of atoms in the same period ____ Ionization energy of atoms for the group as Z increases ____ metallic character of elements of the 4 th period ____ Hope you have learned some techniques to answer question.