PERIODIC TABLE, LIGAND AND COMPLEX COMPOUND
CHEMISTRY
SOME REVISION QUESTIONS
1. What
is the meaning of periodic table (P.T) of elements
2. What
information does the periodic table of elements tell us
3. Explain
the classification of elements in the periodic table
4. Which
important property did Mendeleev use to classify the elements in his P. Table
5. State
the Modern periodic law. What is the basic difference in approach between the Mendeleev’s
Periodic Table?
6. What
are the major difference between metals and non metals
7. Explain
trends of chemical and physical properties of representative elements in the
periodic table
8. Outline
general properties of transition
elements
9. Explain
why copper (Cu) is paramagnetic, but Zinc (Zn) is diamagnetic
10. Write
down the group state electronic configuration of:
(i). s-block
elements
(ii). d-block
elements
11. What
do you understand by isoelectronic species? Name a species that will be
isoelectronic with each of the following atoms or ions F, Ar, Mg, Rb
12. Explain
why cations are smaller and anions larger in radii that their parent atoms?
Give examples
13. Use
the periodic table to answer the following questions
1) Identify
an element with five electrons in the outer subshell
2) Identify
an element that would tend to lose two electrons
3) Identify
an element that would tend to gain two electrons
4) Identify
the group having metal, non-metal, liquid as well as gas at room temperature
14. Write
the general outer electronic configuration of s-, p-, d- and f- block elements
15. Define
complex ion and ligand. Give example of each
16. Describe
three types of ligands. How do they form complex ions
1.
What
is the meaning of periodic table (P.T) of elements
The periodic table is a
tabular display of all the chemical elements. The atoms are grouped in order of
increasing atomic number. The elements are arranged in horizontal rows called
PERIOD and vertical Column called GROUP. The element symbol is always almost
accompanied by other information such as atomic number and atomic weight.
Atomic number describes the number of protons in one atom of that element. For
example, an atom of oxygen contains 8 protons. Elements are listed in order of
increasing atomic number from left to right. Each row of the periodic table is
called a period and each column of
the periodic table is called a group
(or family). Some groups have specific names like the halogens or noble gases.
Elements within the same period or group have similar properties.
2.
What
information does the periodic table of elements tell us
Elements are placed in order
of increasing atomic number, which is the number of protons in the nucleus of
the element’s atom. The rows are also organized so that elements with similar
properties are found in the same columns. Within each element square,
information on the element’s symbol,
(i). Atomic
number,
(ii). Atomic
mass,
(iii). Electronegativity,
(iv). Electron
configuration, and
(v). Valence
numbers can be found
3.
Explain
the classification of elements in the periodic table
Alkali
and Alkaline Earth Metals
With the exception of
hydrogen, the first column consists of the soft, shiny alkali metals. These
metals have only one electron in their valence shell. Because of their
explosive reactivity in both air and water, the alkali metals are rarely found
in their elemental form in nature. In the second group, the alkaline earth
metals have two valence electrons, making them slightly harder and less
reactive. However, these metals are still rarely found in their elemental form.
Transition
Metals
The transition metals
lie in the center of the table, spanning groups three through 12. These
elements are solid at room temperature, except mercury, and have the metallic
color and malleability expected of metals. Because the valence shells grow so
large, some of the transition metals are excerpted from the periodic table and
appended to the bottom of the chart; these known as the Lanthanides and
Actinides. Many of the transition metals near the bottom of the periodic table
are rare and unstable.
Metalloids
and Nonmetals
Metalloids, such as
germanium and arsenic, which have some metallic properties. Chemists categorize
all elements to the right of this dividing line as nonmetals, with the
exception of group 18 on the far right. Many of the nonmetals are gaseous, and
all are notable for their tendency to gain electrons and fill their valence
shells.
Noble
Gases
Group 18, on the far
right side of the periodic table, is composed entirely of gases. These elements
have full valence shells, and tend to neither gain nor lose electrons. As a
result, these gases exist almost exclusively in their elemental form. Chemists
classify them as noble or inert gases. All the noble gases are colorless,
odorless and nonreactive.
4.
Which
important property did Mendeleev use to classify the elements in his P. Table
In his periodic table,
Mendeleev arranged elements in rows by increasing atomic mass. Within a row,
elements with lower atomic masses were on the left. Mendeleev started a new row
every time the chemical properties of the elements repeated. Thus, all the
elements in a column had similar properties
5.
State
the Modern periodic law. What is the basic difference in approach between the
Mendeleev’s Periodic Table?
Modern periodic law
states that the properties of elements are in periodic functions of their
atomic numbers. In the "periodic table", the atoms are arranged in
the manner with respect to their atomic numbers, electronic configuration, and
chemical properties. The seven rows in the "periodic table" are
called periods
Basic
difference in approach between the Mendeleev’s Periodic Table?
Mendeleev's Periodic
Law states that the physical and chemical properties of elements are periodic
functions of their atomic weights. On the other hand, the Modern periodic Law
states that the physical and chemical properties of elements are periodic
functions of their atomic numbers.
6.
What
are the major difference between metals and non-metals
|
|
Metals |
Non-metals |
|
01 |
These
are solids at room temperature |
These
exist in all three states |
|
02 |
These
are very hard except sodium |
These
are soft except diamond |
|
03 |
These
are malleable and ductile |
These
are brittle and can break |
|
04 |
These
are shiny |
These
are non-lustrous |
|
05 |
Electropositive
in nature |
Electronegative
in nature |
|
06 |
Have
high densities |
Have
low densities |
7.
Explain
trends of chemical and physical properties of representative elements in the
periodic table
Major periodic trends
include electronegativity, ionization
energy, electron affinity, atomic radii, ionic radius, metallic character, and
chemical reactivity.
Within a group,
or family, is a vertical column in the periodic table. Elements in the same
group show patterns in atomic radius, ionization energy, and electronegativity.
From top to bottom in a group, the atomic radii of the elements increase: since
there are more filled energy levels, valence electrons are found farther from
the nucleus. From top to bottom, each successive element has a lower ionization
energy because it is easier to remove an electron since the atoms are less
tightly bound. Similarly, from top to bottom, elements decrease in
electronegativity due to an increasing distance between valence electrons and
the nucleus.
Elements in the same
period show trends in atomic radius, ionization energy, electron affinity, and
electronegativity. Moving left to right across a period, from the alkali metals
to the noble gases, atomic radius usually decreases. This is because each
successive element has an additional proton and electron, which causes the
electrons to be drawn closer to the nucleus. The additional proton increases
the effective nuclear charge to a greater extent than the addition of an extra
electron to an already partially-filled shell. The decrease in atomic radius
also causes ionization energy to increase from left to right across a period:
the more tightly bound an element is, the more energy is required to remove an
electron. Electronegativity increases in the same manner as ionization energy
because of the pull exerted on the electrons by the nucleus. Electron affinity
also shows a slight trend across a period: metals (the left side of a period)
generally have a lower electron affinity than nonmetals (the right side of a
period), with the exception of the noble gases which have an electron affinity
of zero.
8.
Outline
general properties of transition
elements
i.
Have
large charge/radius ratio;
ii.
They
are hard and have high densities;
iii.
They
Have high melting and boiling points;
iv.
They
Form compounds which are often paramagnetic;
v.
They
Show variable oxidation states;
vi.
They
Form coloured ions and compounds;
vii.
They
Form compounds with profound catalytic activity;
viii.
They
Form stable complexes.
9.
Explain
why copper (Cu) is paramagnetic, but Zinc (Zn) is diamagnetic
Diamagnetic substances have
a tendency to move from stronger part to the weaker part of the
external magnetic field. We can also say that the diamagnetic substances
get repelled by a magnet.
Paramagnetic substances are those substances that get
weakly magnetized in the presence of an external magnetic field. In the
presence of an external magnetic field, these substances tend to move from a
region of a weak to a strong magnetic field. In other terms, we can say that
these substances tend to get weakly attracted to a permanent magnet.
Ferromagnetic substances are those substances that when it’s placed in an
external magnetic field, get strongly magnetized. Also, they tend to move from
a region of weak to the region of a strong magnetic field and get strongly
attracted to a magnet.
Zn2+ is d10 system. No unpaired electrons,
therefore diamagnetic
Cu+2 is root 3. It has 2 unpaired electrons therefore
paramagnetic
10. Write
down the group state electronic configuration of:
(i).s-block
elements
|
|
Element |
Symbol |
Electronic
configuration |
|
01 |
Lithium |
Li |
1s22s1 |
|
02 |
Sodium |
Na |
1s22s22p63s1 |
|
03 |
Potassium |
K |
1s22s22p63s23p64s1 |
|
04 |
Beryllium |
Be |
[He]2s2 |
|
05 |
Magnesium |
Mg |
[Ne]3s2 |
|
06 |
Calcium |
Ca |
[Ar]4s2 |
(ii).d-block elements
|
Atomic
number |
Element |
Symbol |
E.
Configuration |
|
21 |
Scandium
|
Sc |
[Ar]
3d1 4s2 |
|
22 |
Titanium
|
Ti |
[Ar]
3d2 4s2 |
|
23 |
Vanadium
|
V |
[Ar]
3d3 4s2 |
|
24 |
Chromium
|
Cr |
[Ar]
3d5 4s1 |
|
25 |
Manganese
|
Mn |
[Ar]
3d5 4s2 |
|
26 |
Iron
|
Fe |
[Ar]
3d6 4s2 |
|
27 |
Cobalt
|
Co |
[Ar]
3d7 4s2 |
|
28 |
Nickel |
Ni |
[Ar]
3d8 4s2 |
|
29 |
Copper
|
Cu |
[Ar]
3d10 4s1 |
|
30 |
Zinc
|
Zn |
[Ar]
3d10 4s2 |
10. What do you understand by
isoelectronic species? Name a species that will be isoelectronic with each of
the following atoms or ions F-, Ar, Mg2+, Rb
Isoelectronic species are atom that
have same number of electrons but different magnitude of nuclear charge and
belongs to different atoms. The isoelectronic ions with greater nuclear charge
will have small size as compared to the ions with smaller nuclear charge.
Example F−=9+1=10 electrons, Thus, the species isoelectronic with also have 10 electrons.
i.e.,Na+=11−1=10, O2−=8+2=10. Ar =18 electrons. Thus the species isoelectronic
with it will also have 18 electrons. Some of its isoelectronic are S2−=16+2=18, K+=19−1=18. Mg2+=12−2=10 electrons. Thus the species isoelectronic with it will also have 10
electrons. Some of its isoelectronic are F−=9+1=10 , Al3+=13−3=10. Rb+=37−1=36 electrons.
Thus the species isoelectronic with it will also have 36
electrons. Some of its isoelectronic are Br−=35+=36, Kr=36
11. Explain why cations are smaller and
anions larger in radii that their parent atoms? Give examples
Cations are the atoms
or molecules which have lost one or more electrons giving a net posture charge
on the atom or molecule. This is because since now the number of protons is greater
than the number of electrons. Hence, there is a net posture charge, and atom is
not neutral anymore. Therefore, because of this loss of electron in forming a
cation, the size of the cation is smaller than its parent atom
The size of an anion is larger than
its parent atom because anions are formed due to the gain of electrons. When
the electrons increase, there are still the same number of protons. This causes
the electrons to not be bound as tightly to the nucleus resulting in an
increase in size
12. Use the periodic
table to answer the following questions
(i).Identify an element with five electrons in
the outer subshell
Elements which
have five electrons in their outer subshell should have the electronic
configuration of ns2np5.
Here the outermost p subshell has five electrons in them. If you will check the
periodic table this electronic configuration is shown by the halogen family
which belongs to group 17 of the periodic table. Therefore the elements can be
fluorine, chlorine, bromine, iodine, etc.
(ii).Identify an
element that would tend to lose two electrons
Elements in the
periodic table generally lose electrons to attain the stable noble gas
configuration. And the elements which have two electrons in their outermost
subshell can easily lose the electrons so they can attain the stable noble gas
configuration.The electronic configuration of such elements are ns2.And this electronic
configuration is only shown by the group 2 elements of the periodic table. Thus
the elements will be Be, Mg, Ca, Sr, Ba, Ra.
(iii).Identify an
element that would tend to gain two electrons
Elements in the
periodic table are likely to gain two electrons when they need only two extra
electrons to occupy the stable noble gas configuration.. The electronic
configuration shown by such elements should be ns2np4. Here two electrons can easily be
removed from the outermost p orbital. This type of electronic configuration is
shown by the oxygen family thus the elements will be O, S, Se, Te, Po, Uuh.
(iv).Identify the group
having metal, non-metal, liquid as well as gas at room temperature
In the periodic
table group 17 (Halogen family) have metals, Non-metals, liquid and gas at room
temperature. Iodine is a Metal whereas chlorine and bromine are the non-metals.
Fluorides are present in liquid state while chlorine, bromine and Gaseous are
present in the form of gases.
14. Write the general
outer electronic configuration of s-, p-, d- and f- block elements
The
general outer electronic configuration of s block elements is ns(1−2)
.The general outer electronic configuration of
p block elements is ns2np(1−6)
.The general outer electronic configuration of
d block elements is (n−1)d(1−10)ns(0−2)
.The general outer electronic configuration of f− block elements is (n−2)f(0−14)(n−1)d(0−1)ns2
.
15. Define complex ion
and ligand. Give example of each
According
to the Lewis base theory, ligands are Lewis bases since they can donate
electrons to the central metal atom. The metals, in turn, are Lewis acids since
they accept electrons. Coordination complexes consist of a ligand and a metal
center cation. The overall charge can be positive, negative, or neutral.
Coordination compounds are complex or contain complex ions, for example
1. Complex
Cation: [Co(NH3)6]3+
2. Complex
Anion: [CoCl4(NH3)2]−
3. Neutral
Complex: [CoCl3(NH3)3]
4. Coordination
Compound: K4[Fe(CN)6]
A complex ion is an ion comprising one or more ligands
attached to a central metal cation with a dative bond. A ligand is a species
which can use its lone pair of electrons to form a dative covalent bond with a
transition metal. Examples of ligands are H2O, NH3, Cl–, OH–, CN–.
Example
1. Tetrachloridonickelate(II) ion ([NiCl4]2− )
2. Diamminetetrachloroplatinum(IV) (Pt(NH3)2Cl4)
3. Diamminedichloroplatinum(II) chloride ([Pt(NH3)2Cl2]Cl2.)
16. Describe three types of ligands.
How do they form complex ions
Mono
dentate are Ligands are Lewis base which donates one lone
pairs of electrons to the central metal atom
Bidentate Ligands are
Lewis base which donates two lone pairs of electrons to the central metal atom
is known as bidentate ligands.
Tridentate ligands have
three lone pairs of electrons to the central metal atom or ion. Molecules with
four donor atoms are called tetradentate, five donor atoms are called
pentadentate and six donor atoms are called hexadentate. They are generally mentioned
as polydentate ligands.
But
also ligand can be
1. Positively
charged (Cation)
2. Negatively
charged (anion)
3. Neutral
A complex ion is a species formed
between a central metal ion and one or more surrounding ligands, molecules or
ions that contain at least one lone pair of electrons. Small, highly charged
metal ions have the greatest tendency to act as Lewis acids and form complex
ions
The set of rules for
naming a coordination compound is:
1. When
naming a complex ion, the ligands are named before the metal ion.
2. Write
the names of the ligands in the following order: neutral, negative, positive.
If there are multiple ligands of the same charge type, they are named in
alphabetical order. (Numerical prefixes do not affect the order.)
3. Multiple
occurring monodentate ligands receive a prefix according to the number of
occurrences: di-, tri-, tetra-, penta-, or hexa. Polydentate ligands (e.g.,
ethylenediamine, oxalate) receive bis-, tris-, tetrakis-, etc.
4. Anions
end in -ido. This replaces the final “e” when the anion ends with “-ate” (e.g,
sulfate becomes sulfato) and replaces “-ide” (cyanide becomes cyanido).
5. Neutral
ligands are given their usual name, with some exceptions: NH3 becomes ammine;
H2O becomes aqua or aquo; CO becomes carbonyl; NO becomes nitrosyl.
6. Write
the name of the central atom/ion. If the complex is an anion, the central
atom’s name will end in -ate, and its Latin name will be used if available
(except for mercury).
7. If
the central atom’s oxidation state needs to be specified (when it is one of
several possible, or zero), write it as a Roman numeral (or 0) in parentheses.
8. End
with “cation” or “anion” as separate words (if applicable).
Anionic Ligands
Ligands
that act as anions which end in "-ide" are replaced with an ending
"-o" (e.g., Chloride → Chloro). Anions ending with "-ite"
and "-ate" are replaced with endings "-ito" and
"-ato" respectively (e.g., Nitrite → Nitrito, Nitrate → Nitrato).
TABLE SHOWING ANIONC LIGANDS
|
Molecular Formula |
Ligand Name |
Molecular Formula |
Ligand Name |
|
F- |
Fluoro |
OH- |
Hydroxo |
|
Cl- |
Chloro |
SO42- |
Sulfato |
|
Br- |
Bromo |
S2O32- |
Thiosulfato |
|
I- |
Iodo |
NO2- |
Nitrito-N-;
Nitro |
|
O2- |
Oxo |
ONO- |
Nitrito-O-;
Nitrito |
|
CN- |
Cyano |
SCN- |
Thiocyanato-S-;
Thiocyanato |
|
NC- |
Isocyano |
NCS- |
Thiocyanato-N-;
Isothiocyanato |
Neutral Ligands
Most
neutral molecules that are ligands carry their normal name. The few exceptions
are the first four on the chart: ammine, aqua, carbonyl, and nitrosyl.
TABLE SHOWING NEUTRAL LIGANDS
|
Molecular Formula |
Ligand Name |
|
NH3 |
Ammine |
|
H2O |
Aqua |
|
CO |
Carbonyl |
|
NO |
Nitrosyl |
|
CH3NH2 |
Methylamine |
|
C5H5N |
Pyridine |
|
en |
Ethylenediamine |
|
ox2- |
Oxalato |
|
EDTA4- |
Ethylenediaminetetraacetato |
The Central Metals
When
naming the metal center, you must know the formal metal name and the oxidation
state. To show the oxidation state, we use Roman numerals inside parenthesis.
For example, in the problems above, chromium and cobalt have the oxidation
state of +3, so that is why they have (III) after them. Copper, with an
oxidation state of +2, is denoted as copper(II). If the overall coordination
complex is an anion, the ending "-ate" is attached to the metal
center. Some metals also change to their Latin names in this situation. Copper
+2 will change into cuprate(II). The following change to their Latin names when
part of an anion complex:
LATIN TERMS FOR
SELECT METAL ION
|
Transition Metal |
Latin |
|
Iron |
Ferrate |
|
Copper |
Cuprate |
|
Tin |
Stannate |
|
Silver |
Argentate |
|
Lead |
Plumbate |
|
Gold |
Aurate |
What is the name of
this complex ion: [CrCl2(H2O)4]+ ?
Solution
Let's
start by identifying the ligands. The ligands here are Cl and H2O. Therefore,
we will use the monodentate ligand names of "chloro" and
"aqua". Alphabetically, aqua comes before chloro, so this will be
their order in the complex's name. There are 4 aqua's and 2 chloro's, so we
will add the number prefixes before the names. Since both are monodentate
ligands, we will say "tetra[aqua]di[chloro]".
Now
that the ligands are named, we will name the metal itself. The metal is Cr,
which is chromium. Therefore, this coordination complex is called
tetraaquadichlorochromium(III) ion. See the next section for an explanation of
the (III).
What is the name of
this complex ion: [CoCl2(en)2]+ ?
Answer
We
take the same approach. There are two chloro and ethylenediamine ligands. The
metal is Co, cobalt. We follow the same steps, except that en is
a polydentate ligand with a prefix in its name (ethylenediamine), so
"bis" is used instead of "bi", and parentheses are added.
Therefore, this coordination complex is called
dichlorobis(ethylenediamine)cobalt(III) ion.
What is the name of
[Cr(OH)4]- ?
Solution
Immediately
we know that this complex is an anion. There is only one monodentate ligand,
hydroxide. There are four of them, so we will use the name
"tetrahydroxo". The metal is chromium, but since the complex is an
anion, we will have to use the "-ate" ending, yielding "chromate".
The oxidation state of the metal is 3 (x+(-1)4=-1). Write this with Roman
numerals and parentheses (III) and place it after the metal to get
tetrahydroxochromate(III) ion.
What is the name of
[CuCl4]2- ?
Answer
tetrachlorocuprate(II)
ion
A
last little side note: when naming a coordination compound, it is important
that you name the cation first, then the anion. You base this on the charge of
the ligand. Think of NaCl. Na, the positive cation, comes first and Cl, the
negative anion, follows.
What is the name of
[Pt(NH3)4)][Pt(Cl)4] ?
Solution
NH3
is neutral, making the first complex positively charged overall. Cl has a -1
charge, making the second complex the anion. Therefore, you will write the
complex with NH3 first, followed by the one with Cl (the same order as the
formula). This coordination compound is called tetraammineplatinum(II)
tetrachloroplatinate(II).
What is the name of
[CoCl(NO2)(NH3)4]+ ?
Answer
This
coordination complex is called tetraamminechloronitrito-N-cobalt(III). N comes
before the O in the symbol for the nitrite ligand, so it is called nitrito-N.
If an O came first, as in [CoCl(ONO)(NH3)4]+, the ligand would be called
nitrito-O, yielding the name tetraamminechloronitrito-O-cobalt(III). Nitro (for
NO2) and nitrito (for ONO) can also be used to describe the nitrite ligand, yielding
the names tetraamminechloronitrocobalt(III) and
tetraamminechloronitritocobalt(III).
Amminetetraaquachromium(II)
ion would be written as [Cr(H2O)4(NH3)]+2. Both ligands are neutral, so they
are ordered alphabetically with H2O before NH3. Their order in the formula is
the opposite of that in the complex's name since one uses their chemical
symbols and the other uses the names of the ligands.
Amminesulfatochromium(II)
is written as [Cr(SO4)(NH3)]. SO4 is an anion, so it comes before NH3.
Amminetetraaquachromium(II)
sulfate -> Try this on your own. Did you get
[Cr(H2O)4(NH3)]SO4? If you did, you are correct.
Potassium
hexacyanoferrate(III) -> Try this on your own. Did you get
K3[Fe(CN)6]?
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