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P-block Elements

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Today we know more than 100 elements which are arranged in the tabular form known as periodic table given by Mendeleev. The periodic table is based on the atomic number of elements, as all the elements are arranged in increasing order of atomic number.


There are total 18 groups and seven periods in the table. Elements present in the same group show similar chemical and physical properties. On the contrary, the elements in the period show regular trends in properties ionization potential, electron negativity and electron affinity.

P Orbital Shape

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We know that in an atom, there is a certain number of electrons around nucleus in a continuous motion. The distance between electrons and nucleus remains fixed, known as orbitals. Each orbital has a certain shape with a certain number of electrons. Like in p orbital diagram, a dumbbell-shaped region accumulated total six electrons i.e. there is the maximum probability of electrons.

The shape and energy of the orbital depends on the quantum numbers. For example; the Azimuthal quantum number for p-orbitals is one with three possible values for m; -1, 0, +1. The first three quantum number; principal, Azimuthal, magnetic quantum number lies zero to +/- integer values.
  1. On the hand the spin quantum number has two possible values; +$\frac{1}{2}$ and -$\frac{1}{2}$.
  2. The principal quantum number shows the energy level of electrons and represented as ‘n’. The value n can be from one to infinite.
  3. The subsidiary or angular quantum number is used to define the shape of the sub-shell orbital and value stands from zero to n -1.
  4. Each orbital is assigned with a certain value of Azimuthal number such as for s orbital the value of l is zero, while for p orbital, it is one and so on.
  5. As we move from s to f the energy of energy of the sub-level increases with increasing the value of principal quantum number.

P Orbitals

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The Azimuthal quantum number for the p-orbital is one and has three values of magnetic quantum number; -1, 0, +1 on the basis of different orientations of the orbitals. The spin quantum number depends upon the number of electrons. Two electrons in an orbital have two different spin quantum numbers +$\frac{1}{2}$ and -$\frac{1}{2}$ with clockwise and anti-clockwise spinning.

Since there are three orbitals in p oriented in three directions; px, py and pz. Each orbital can accommodate maximum two electrons therefore total number of p orbital electrons are six. Remember that each orbital with one electron involves in bonding with other elements. The unhybridized p orbital involves in hybridization to form hybrid orbitals which involves in hybridization to form a bond.
P Orbitals

All the three p orbitals are aligned perpendicular to each other and denoted as 2p, 4p etc, here 2, 4 represents the principal quantum number.

Periodic Table P Block

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  1. In the periodic table, from group 13th to 17th is known as p-block elements.
  2. The name ‘p-block element’ stands that the valance electron of an element enters in p-orbital of element.
  3. The last element that is 18th element is also a part of the p-block element and also called as zero group or Noble gas elements.
  4. In p-block elements, the valence electron fills in p-orbital and has 3 to 7 valence electrons.
  5. Due to the presence of 3 to 7 electrons in the valence shell, they have a tendency to accept electrons to complete the octet configuration.
  6. Therefore, they are electronegative elements and form anions during chemical reactions.
  7. The entire p-block of the periodic table is composed of metals, non-metals and metalloids.
  8. All the known non-metals are placed in p-block of the periodic table.
  9. The metalloids are placed as a zigzag line and separate the metals and non-metals.
  10. Because of the presence of all the three kinds of elements in p-block elements show a great variation in the properties.

P Block Elements Properties

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The general electronic configuration of p-block ns2 np1-6 excluding helium. All the groups of p-block are generally represented with the help of the first element of the group like the 13th group is called as boron family, 14th group named as carbon family, 15th group is called as nitrogen family, 16th group named as oxygen family, 17th is named as halogens while 18th is known as noble gases or rare elements or inter group.

  1. The properties of p-block elements vary with their electronic configuration and their position in periodic table.
  2. For example; the non-metallic characters increase across the periods in p-block elements while it decreases down in the group.
  3. We can also say that metallic characters show variation in the reverse way of non-metallic nature of elements, and that is the reason, the heaviest elements place at the bottom of groups in p-block elements.
  4. As we move down in the group, the atomic density of elements increases due to increment in the size of elements, but decreases from left to right across the period due to same reason.
  5. The melting and boiling points of elements increases with increasing the molecular mass of elements therefore both temperature values increases from top to bottom in groups.
  6. They show variable oxidation states which further increases across the periods.
  7. Generally the oxidation state of elements in p-block elements show a relation with the number of valence electrons present in the element.
  8. Like other blocks, in p-block of the periodic table, the trend of atomic and ionic radii also follows the same trend and increases down in group whereas decreases across the period.
  9. They have high ionization potentials values which again increase across the period because of the reduction in atomic radii with increment in effective nuclear charge.
  10. The trend of the ionization potential in groups is so regular like s-block elements due to atomic radii and inert pair effect.
  11. But compare to s-block elements, the non-metals of p-block elements have a high value of ionization potential as they have less tendency to loss electrons and tend to accept them and form anions.
  12. Because of octet configuration in Noble gases, they have a maximum value of the ionization potential.
  13. On the contrary, some of the metals and metalloids have very low value of it such as bismuth, lead, tin etc.
  14. Some of the elements like tin are paramagnetic while some elements like iodine, radon, and polonium are non-magnetic in nature.

Compare to s-block elements, the elements of p-block have small size and more charge, therefore have more tendency to form complex. But as the size of elements increases down in groups, this tendency decreases continuously. Only metals of p-block can act as the conductor of heat and electricity while non-metals are usually insulators or poor conductors.

The conductivity of metalloids depends upon the conditions like temperature. Like s-block elements, p-block elements also impart a characteristic color to the flame like blue color flame is due to arsenic or indium or selenium, bright green color is because of boron. Halides of copper produce blue- green color to the flame.

Noble Gases

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The last group of the periodic table that is 18th group is known as inert elements or noble gases. These are highly un-reactive elements with octet configuration excluding helium which has only two electrons with 1s2 electronic configuration. They are usually found as colored, gases elements which are found in trace amount in the atmosphere.

Last two elements, xenon and radon are colorless while helium (red), Neon (orange) and Krypton (purple) are colorful.

Reactivity of Noble Gases

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The inert elements with ns2np6 configuration are non reactive elements as they have completely filled octet configuration and very stable for any kind of electron transfer and therefore cannot show addition or substitution reactions. Because of their low reactivity, these elements are widely used to produce the inert environment during chemical reactions and other chemical processes such as welding.

The halogens and the chalcogens group are placed just before the Nobel gases and have high electron affinity, results the formation of anions and show vigorous chemical reactions compare to noble elements. Nobel elements do not involve in chemical bonding with other elements and form compounds.

Only xenon can form some of the halides like XeF2, XeF6 etc. due to similar value of ionization potential of it compare to oxygen and form similar kind of compounds like oxygen.

Solved Example

Question: Why xenon can form compounds with fluorine and oxygen but other Nobel elements form group-18 cannot?
Solution:
The ionization potential of xenon is almost equivalent to that of the oxygen atom which can form compounds with fluorine. Therefore, the reactivity of xenon shows similarities oxygen and form fluorides or oxyfluorides.

Reactivity of Metalloids

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  1. Elements with intermediate properties of metals and non-metals are known as metalloids which are placed in between metals and non-metals as a zigzag line in periodic table.
  2. Some of the examples of metalloids are boron, arsenic, germanium, antimony, tellurium and polonium.
  3. They show intermediate chemical and physical properties like electron negativities, ionization energies.
  4. For example, silicon possesses a metallic luster like metals but not a good conductor of heat and electricity like them.
  5. The chemical reactivity of these elements depends on reactivity of that element with which they react like boron acts as non-metal with sodium but as a metal with fluorine.
  6. The physical properties like boiling points, melting points, and densities do not show any regular trend in group.
  7. The intermediate value of conductivity of metalloids makes then good semiconductors.
  8. They have a low value of electronegativity and easily oxidized during chemical reactions to form amphoteric oxides.

Boron Group

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Boron family starts from boron and have four metals aluminum, gallium, indium, and thallium. Excluding boron, they are silvery solid elements which can directly react with hydrogen gas and form hydrides. They can also react with halogens to form halides like born trihalide.

Because of the presence of three electrons in their valence shell, with ns2np1 valence shell electronic configuration, they show either +1 or +3 oxidation state. In the entire group, thallium has largest radii otherwise; it decreases down in the group with increment in electrode potential. The value ionization energy decreases from top to bottom in the group.

Carbon Group

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Carbon group starts from carbon and composed of six elements. The first element of the group is most important on Earth and involve in the formation of many organic compound in living and non-living systems.
  1. Many of the carbon compounds like carbon dioxide, methane play an important role in biochemical reactions.
  2. Carbon is usually found in black color whereas silicon and germanium are reddish brown and lead has a bluish-white color.
  3. They have four electrons in their valance shell therefore have a strong tendency to form four covalent bonds with same or other elements.
  4. They are good oxidizing agent with +4 oxidation state and can reduced to +2 oxidation state.
  5. The higher oxidation state forms covalent compounds while lower tends to form ionic compounds.
  6. Tin and lead have wide applications in various industries such as in dental cares, lead-acid storage batteries and automobile fuel.

Nitrogen Group

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The first element of this group is a colorless gas and found in atmosphere around 78%. Rest of the elements are found in solid state such as phosphorus has white color, arsenic and antimony are found in yellow or grey solid form while bismuth is silvery white solid.

All elements of nitrogen group can show +5 oxidation state and form trihydrides with hydrogen. The reactivity and other physical properties show a regular trend in group from top to bottom. They can form either trioxides or pentoxides with oxygen and halides with halogens. They also have tendency to form binary compounds with metals and have many commercial uses.

Solved Example

Question: Ammonia molecule can involve in hydrogen bonding but phosphorus compounds like PH3 cannot. Why?
Solution:
 
For the formation of a a hydrogen bond, the electro negativity of the element must be high which is only with oxygen, nitrogen and fluorine. Other electrons due to less electro negativity, cannot involve in hydrogen bonding. therefore ammonia which has a nitrogen atom as central atom can form hydrogen bond with another molecule of ammonia but PH3 cannot.
 

Chalcogens

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  1. Like 15th group, this group also starts with a colorless gas; oxygen composed of 21% gaseous part of atmosphere.
  2. Rest all elements of group-16 are found in solid state like sulfur is a pale yellow color solid while tellurium has silvery-white color.
  3. They are placed at the right side of periodic table therefore more electronegative compare to other groups which are placed at the left side of table.
  4. They have strong tendency to combine with electropositive metals to form compounds like oxides, sulphides, sulphates etc.
  5. They show variable oxidation states but -2 are much more common among all the elements. 
  6. They are usually exit in various allotropes in environment like ozone is an allotrope of oxygen which is found in stratosphere layer of atmosphere and protect the living bodies to the harmful effects of ultraviolet radiations as they can absorb those radiations.

Solved Example

Question: The oxygen molecule is found in gaseous state while sulphur is a solid. Why?
Solution:
The oxygen molecule is formed due to pp-pp bond formation of two oxygen atoms which have small atomic radii and high electro negativity. These molecules are held together with weak Van Der Wall force of attraction and can easily overcome at normal temperature conditions. Therefore, oxygen molecules exist in gaseous form. On the contrary, sulphur cannot form the same type of bonding due to bigger atomic radii and less electron-negativity and exist in solid state.

Halogens

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All halogens have a certain color like pale yellow fluorine, greenish yellow for chlorine, brown for bromine and violet for iodine. The reactivity of halogens is more compare to 16th elements also as they are most electronegative elements in entire periodic table.
  1. The electrode potential values for halogens decreases from the top to bottom, therefore iodine shows minimum value.
  2. Because of the high electron negativity of elements, they can easily combine with metals to form ionic compounds.
  3. The reactivity decreases from fluorine to iodine in the group.
  4. They are good oxidizing agents and can oxidize other substances.

Solved Examples

Question 1: Identify the factors which make the halogens good oxidizing agents.
Solution:
halogens are placed at the left side of the periodic table and have smallest radii in their period. Due to this they have high value of electron negativity and electron affinity. Therefore, they have strong tendency to accept electrons and get reduced which make them good oxidizing agents.

Question 2: Why halogens are colorful in nature?
Solution:
A molecule can show any color only when it can absorb the visible light from electromagnetic spectrum. This absorption excites the valence shell electrons and moves them to higher energy state with the transmission of remaining light. The color of object is because of this transmitted light only. As the atomic radii of an element increases, the amount of light for the excitation of the valence electron decreases ,therefore iodine shows intense color compare to fluorine.