Transcript Atomic Properties and the Period Table

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
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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 Table
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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
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Transition Metal Ions
Transition 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+
Mo2+
Cu+ ,
Ag+
2+
Zn2+
Cd2+
Au+, 3+ Hg2+
How many 3d electrons do Cu2+, Fe3+, etc ions have?
Period Table
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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
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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 Zeff, the
effective atomic charge (or number).
Thus, the energy of many electrons is
Zeff2
En = – RH ---------;
n2
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.
Period Table
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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 Table
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Atomic radii as Z increases
Period Table
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Trends of Ionic radii
Ions 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
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From Atoms to Ions
Consult a periodic table and arrange the
following lists by increasing atomic radius.
Na+, Li+, K+, Cs+, Xe, IBr– , Cl –, I –, F –
Be2+, Li+, B, C, O–2, F–, N
Period Table
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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–;
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,
Zeff2
Eeff = ---------n2
a positive value
But ionization energy is not Eeff.
Period Table
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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
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The In of Group n
Period Table
Define In. How do I1-to-n+1 change
with elements in group number
n?
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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); EA1= – 141 kJ / mol = – 1.46 eV/atom
O– (g) + e–  O2– (g);
eV/atom
EA2 = 744 kJ / mol = 7.71
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
Period Is.
Table
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Electronegativity
Explain the trend of EN in the periodic table
Period Table
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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, Fe2O3 etc.
Which of these are paramagnetic, H, Na, Mg, Cl, Cl –, Ag, Fe
Period Table
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Metals, Non-metals, Acids and Bases
1s1
Metallic and reducing properties increases along
the arrows, and oxidizing and non-metallic
properties decreases along the arrows.
1s2
2s1-2
2p1 – 2p6
3s1-2
3p1 – 3p6
4s1-2
3d1 – – – 3d10
4p1 – 4p6
5s1-2
4d1 – – – 4d10
5p1 – 5p6
6s1-2
4f1 – – – – – 4f14
5d1 – – – 5d10
6p1 – 6p6
7s1-2
Th Pa U – – – 5f14
6d1 – – – 6d10
7p1 – 7p6
Period Table
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Oxides and Strong Acids
Aside from HCl, other strong acids are derived from oxides of N, S, Cl:
HNO3
H2SO4
HClO4
HClO3
HNO2
H2SO3
HClO2
Some oxides also form weak acids:
HCO3
In contrast, look at some strong bases
NaOH
KOH
RbOH
CsOH
Ca(OH)2
Sr(OH)2
Ba(OH)2
Period Table
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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*1019)
How do the work functions vary:
Down in a group?
Across a period?
Estimate the work function for K. _____*10-19 J
What 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
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Review of energy states
Gaseous 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
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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
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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 Table
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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.
Period Table
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