Period Table 1

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 Table 2

Mendeleev and Meyer WorkBoth 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 Table 3

Main-group Ions

Typical ions by groups of elements

Li+1 Be+2 B C N3– O2– F – Ne

Na+1 Mg+2 Al+3 Si P3– S2– Cl – Ar

K+1 Ca+2 Ga+3 Ge+4 As Se2– Br – Kr

Rb+1 Sr+2 In+3 Sn+4 Sb Te I – Xe

Cs+1 Ba+2 La+3 Pb2-4

Fr+1 Ra+2

Know your main-group elements.

Period Table 4

Transition Metal IonsTransition metals have n s2 (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 Ti4+? ____

Some typical transition metal ions:

Sc3+ Ti2+, 4+ V2+ Cr2+, 3+ Mn2+ Fe2+, 3+ Co2+ Ni2+ Cu+ , 2+ Zn2+

Mo2+ Ag+ Cd2+

Au+, 3+ Hg2+

How many 3d electrons do Cu2+, Fe3+, etc ions have?

Period Table 5

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/ 8920000*NA) = _______ (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 Table 6

Screening and PenetrationThe 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 Zeff, the effective atomic charge (or number).

Thus, the energy of many electrons is

En = – RH ---------; RH = – 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.

Zeff2

n 2

Period Table 7

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, CsBr, Cl, I, FBe, Li, B, C, O, F, N

Period Table 8

Atomic radii as Z increases

Period Table 9

Trends of Ionic radiiIons usually have the same electronic configuration as an inert gas.

He

Li+ Be2+ N3– O2– F – Ne

Na+ Mg2+ P3– S2– Cl – Ar

K+ Ca2+ Se2– Br – Kr

Rb+ Sr2+ Te2– I – Xe

Cs+ Ba2+

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 Table 10

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 – Be2+, Li+, B, C, O–2, F–, N

Period Table 11

Trend in Ionization EnergyIonization 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–; I1 = 738 kJ / mol = 7.65 eV/atom

Mg+ (g) Mg2+ (g) + e–; I2 = 1451 kJ / mol = 15.0 eV/atom

The effective atomic number Zeff, may be estimated using,

Eeff = ---------- a positive value

But ionization energy is not Eeff.

Zeff2

n 2

Period Table 12

Variation of I1 as Z Varies

How does first ionization energy I1 vary in a group and in a period and why?

Decreases and increases respectively

Period Table 13

The In of Group n Define In. How do I1-to-n+1 change with elements in group number n?

Period Table 14

Electron AffinityElectron 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); EA1= – 141 kJ / mol = – 1.46 eV/atom

O– (g) + e– O2– (g); EA2 = 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 EAs and Is.

Period Table 15

Electronegativity Explain the trend of EN in the periodic table

Period Table 16

Magnetic PropertiesMaterials 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, Fe2O3 etc.

Which of these are paramagnetic, H, Na, Mg, Cl, Cl –, Ag, Fe

Period Table 17

Metals, Non-metals, Acids and Bases

1s1

2s1-2

3s1-2

4s1-2

5s1-2

6s1-2

7s1-2

1s2

2p1 – 2p6

3p1 – 3p6

4p1 – 4p6

5p1 – 5p6

6p1 – 6p6

7p1 – 7p6

3d1 – – – 3d10

4d1 – – – 4d10

5d1 – – – 5d10

6d1 – – – 6d10

4f1 – – – – – 4f14

Th Pa U – – – 5f14

Metallic and reducing properties increases along the arrows, and oxidizing and non-metallic properties decreases along the arrows.

Period Table 18

Oxides and Strong AcidsAside from HCl, other strong acids are derived from oxides of N, S, Cl:

HNO3 H2SO4 HClO4 HClO3

Some oxides also form weak acids:

HCO3 HNO2 H2SO3 HClO2

In contrast, look at some strong bases

NaOHKOH Ca(OH)2

RbOH Sr(OH)2 CsOH Ba(OH)2

Period Table 19

Review of trends of propertiesThe 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*1019)

How do the work functions vary:Down in a group?Across a period?Estimate the work function for K. _____*10-19 JWhat is the work function? Threshold of photoelectric effect.What units is more convenient?

1 eV atom–1 = 1.6022e-19 J atom–1 = 96.5 kJ mol–1

Period Table 20

Review of energy statesGaseous Na atoms [Ne]3s1 absorb quanta with the energies and excited states shown. 203 kJ mol–1, [Ne]3p1; 308 kJ mol–1, [Ne]4s1; 349 kJ mol–1, [Ne]3d1; 362 kJ mol–1, [Ne]4p1; The ionization energy of the ground state is 496 kJ mol–1.

What are the ionization energies of each of the excited states?

Estimate Zeff?

Draw an energy level diagram for Na atoms.

Explain the meaning of your results.

Period Table 21

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) + H2O (l)

I2 (s) + Na+ (aq) + Br– (aq)

SrO (s) + H2O (l)

SO3 (g) + H2O (l)

CO2 + H2O (l)

CaO + H2O (l)

Which of these produce acids and which produce bases?

Period Table 22

Review questionsConsult 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 Table 23

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 4th period ____

Hope you have learned some techniques to answer question.