W on the periodic table

Introduction :
Let us discuss about the symbol ‘W’ on periodic table. Though Peter Woulfe examined the mineral wolframite and concluded the presence of a new substance, it was Juan Jose and Fausto d'Elhuyar from Spain who purified tungsten in 1783. In Swedish tungsten refers to “heavy stone”. Let us explore more on ‘W’ on periodic table.

Fig:- tungsten

Some Properties of 'W' on periodic table:

Tungsten, which is also called Wolfram and denoted by W on periodic table, has an atomic weight of 183.85 with an atomic number of 74 making it a transition metal on the periodic table. This gives it an electronic configuration of [Xe] 6s² 4f¹⁴ 5d⁴ .
Cutting of a pure tungsten can be done with a saw, spun, drawn, forged, and extruded though impure tungsten is very brittle. Tungsten is a lustrous metal grayish-white in color. Tungsten is known to have the highest melting point compared to all other metals and the lowest vapor pressure of the metals. Because of this property, traditional processes such as smelting cannot refine tungsten. It has very high tensile strength at temperatures exceeding 1650°C. Oxidation of tungsten takes place at increased temperatures. It has very low effect on itself when reacted with acids, as it is highly corrosion- resistant. Very few metallic acids have the strength to attack tungsten.
Physical properties

• Density(g/cc) – 19.3
• Melting Point (K): 3680
• Boiling Point (K): 5930
• Appearance: tough gray to white metal
• Atomic Radius (pm): 141
• Atomic Volume (cc/mol): 9.53
• Tensile strength 50000 – 75000 @1000 degree Celsius, psi
• Reflectivity is 62%

Uses of Tungsten:

Filaments of electrical lamps and picture tubes of television are made from tungsten. It is used in multiple high temperature applications like metal evaporation materials, target for X-rays etc. Some compounds of tungsten are also used in fluorescent lighting such as magnesium tungstenates. Some of the tungsten compounds are also used in mixture of paints. Some lubricants used at high temperatures are also made of tungsten compounds.

Conclusion for tungsten that is 'W' on periodic table:

Therefore, from the above discussion, we can conclude that tungsten is one of strategic and indispensible metals and it is represented by the symbol ‘W’ on periodic table.

Breaking atomic bonds

Solids are characterized by incompressibility, rigidity and mechanical strength. This represent the molecules, atoms or ions that make up a solids which are closely packed. They are join together by strong cohesive forces and cannot move at random. Thus, in solids we have well ordered molecular atomic or ionic arrangements. Thus, it is extremely hard to break atomic bonds between these molecules.

Some solids like sodium chloride NaCl₂, sulphur S, and sugar (carbohydrates),  besides being incompressible and rigid, have also characteristic geometrical forms. Such substances are known be a crystalline solids. The X-ray crystallography studies reveal that their ultimate particles such as molecules, atoms or ions are arranged in unusual pattern throughout the entire three-dimensional (3D) network of crystal. This definite and ordered arrangement of molecules, atoms or ions lengthens over a large distance making it extra difficult in breaking atomic bonds.

The natural history of the Inter-atomic Force resulting in the breaking atomic bonds

Basically, an atom consists of a tiny positively charged body, located at its center called as nucleus. The nucleus, though small have all the protons and neutrons. Since the mass of an atom entirely owing to the presence of protons and neutrons, it is evident that almost the entire mass of an atom resides in the nucleus.

Between the atoms or ions or molecules the inter-atomic bonds is present. This type of breaking atomic bonds is set up by equilibrium between attractive and repulsive forces with the remaining force being zero (0). When the breaking atomic bonds is at stabile. It is evident that the atoms are far apart from the attractive forces between these molecules so it will govern and when they are very close packed together the repulsive force will becomes higher; both these help in ruining away as the separation increases. This report proves that the breaking atomic bonds result from inter-atomic force, as a function of atom separation. Fig 1: Representation of bonds between two molecules

Breaking atomic bonds is also characterized by bond energies

Enthalpy formation of the bond.

Bond energy for any particular type of bond in a compound may be defined as the average amount of energy required to dissociate (to break) one mole, viz., Avogadro’s number of bonds of that type present in the compound. Bond energy is also called the enthalpy of formation of the bond.

Sub-atomic particles

Introduction

Subatomic particles when considered in physics and chemistry refers to  the smaller particles which makes up the  nucleons and atoms.  Two types of subatomic particles are present in nature. The first one is the elementary particles, which are not composed of other particles, and composite particles. Particle physics and nuclear physics make a study on these particles their interactions. This term describes the behavior of matter and energy at the molecular scales of quantum mechanics. According to uncertainty principle it has been concluded that analyzing of particles at different scales will require a statistical approach.

Types of subatomic particles

Elementary particles

Elementary particles present in the Standard Model include

• Six "flavors" of quarks: up, down, bottom, top, strange, and charm;
• Six types of leptons are present namely electron, electron neutrino,  tau, tau   neutrino, muon, muon neutrino,;
• Twelve gauge bosons (force carriers) are present namely the three W and Z bosons of the weak force, the photon of electromagnetism, and the eight gluons of the strong force.

Composite particles

The bounded states of two or more elementary particles form a composite particle. For instance, two up quarks and one down quark constitute a proton, while two neutrons and two protons make up the atomic nucleus of helium-4. The composite particles consist of all hadrons, a group composed of baryons (e.g., protons and neutrons) and mesons (e.g., pions and kaons). Hundreds of subatomic particles are known till date. The cosmic rays interacting with matter produces the majority of sub atomic particles or they are produced in particle accelerators by scattering processes.

Energy of subatomic particles

According to Einstein’s hypothesis, matter and energy are analogous. Matter can be expressed in terms of energy and vice-versa is also possible. Energy can be transferred by only two types of mechanisms which are known as waves and particles. Light can be expressed both as particles and waves. This type of paradox is termed as Wave-particle Duality Paradox. It has been established that all particles also have an associated wave nature. This is true for both elementary and compound particles. Few laws have been derived which explain how particles collide and interact.

Atomic radii

Atomic  radii  may be defined as  the distance between the nucleus and the outermost  electronic level of the atom. Since electrons are considered as the negatively charged electronic cloud there is no well defined boundary  for an atom.The diffused  nature of the electron cloud  makes it difficult  to give exact definition of  atomic size or atomic radii.

Introduction: Atomic radii

Thus  the atomic radii is an arbitrary  concept and is influenced by the nature of neighbouring atoms.

Types of atomic radii

As  there  is   no exact definition for the atomic radius, a number of radii have been defined for an atom. They are  Covalent radius, Crystal radius (otherwise called as metallic radius)  Vander Waal radius (otherwise called Collision radius). Let us learn one by one.

Covalent radius

 Covalent  Radius:
       Covalent radius  is used to measure the  atomic radii of  non- metals. The atomic  radius of  a non- metal is calculated from the  covalent bond length. In case of  homonuclear diatomic molecules ( type AA) , like F₂, Cl₂,Br₂ ....etc half of the covalent bond length is taken as atomic radius. For example the value of  Cl - Cl  bond idstance is 1.98 A^o  half of the distance 0.99 A^o is taken as the  atomic radius of  chlorine
       Another example: measuring the atomic radius of  carbon in diamond. The value of  C- C bond distance in the diamond is 1.54 A^o half of the  distance 0.77 A^o  is considered as the  atomic  radius of carbon atom.

Heteronuclear diatomic  molecule:
      In the calse of heteronuclear diatomic  molecule of  AB type (example CCl_{4 ,} SiC ..etc) bond length  distance d_(A-B) is given by
                   d _{(A -B)}    =  r_(A)  + r_(B)
      r_(A)   and  r_(B) are the  covalent radii of  A and  B  respectively.
     Example:    The experimental value of   d_(C-Cl)  in CCl₄  molecule is  1.76 A^o
                  d _(C-Cl)  =  r _(C) + r_(Cl)
                         r_(C) =  d_(C-Cl) - r_(Cl)
                         r_(C)       =  1.76 A^o -  r_(cl)
                         if  r_(cl)  is  given, then the covalent radius of carbon atom  can be calculated by subtracting the  covalent radius of  Cl from the  d_(C-Cl) bond length.The covalent radius of Cl atom can also be obtained, provided that covalent radius of C atom is known
Crystal Radius:
      It is otherwise called as  Atomic or Metallic radius, and defined as  one half of  the distance between the nuclei of two adjacent metal atoms in the metallic close-packed crystal lattice. For example  the internuclear distance between  two adjacent Na atoms in a crystal of sodium  metal is  3.80 A^oand hence the atomic radius of a Na metal is  half of the  distance, that is  3.80 A^o/ 2                  =  1.90 A^o
      since there  are weak  bonding forces between the metal atoms, the metallic radii are higher than the  single bond covalent  radii and at the same time  the metallic radii are smaller than  the vander Waal radii since the  bonding forces in the metallic crystal  lattice  are much staonger than the vaner waals forces
Vander Waal Radius:
      The name is  derived from theVander  Waal forces which is  found in noble gases.This  type of atomic radii is other wise  called Collision Radius. Tthe distance  between the two non-bonded  isolated  atoms  or the distacnce between  two non-bonded  atoms belonging to two adjacent molecules of an element  in the solid state is called Vander Waals distance  while half of  this  is called vader Waals Radius.
 Example :  The vander Waals distance of Cl₂ molecule =   3.6 A^o  half of  this value is  1.8 A^o  and  1.8 A ^o  is the Vander Waal radius of chlorine  atom.
                   It is to be noted  that the vander Waal radius  of an element  is higher than its covalent radius. Example the measured Vander Waal radius of chlorine is 1.8 A^o  and the  covalent radius  is  0.99 A^o
                  The variation in the atomic radii can be explained as follows.
                  When two chlorine  atoms are  just in contact with each other and  there is no bond between them,  now the distance between nuclei of those two chlorine atoms is called  the vander Waals  distance (3.6 A^o) and  half of it ( 1.8 A^o) is called  vander Waals radius.
                 where as when the electron clouds of the two chlorine atoms merge with each other to form chlorine molecule by forming covalent bond between them, the distance (covalent bond length) between them further decreases and  the distance become 1.8 A^o and half of it  0.99 A^o is the covalent radius.
                 Thus while describing  the atomic radii of various atoms, any of the radii described above can be used.

Dalton's Atomic Theory

When scientists started exploring matter, they realised that matter can be divided into smaller and still smaller particles. What was the ultimate particle like? They discovered that the smallest particle of an element that maintains its chemical identity through all chemical and physical changes is called and 'atom'.

John Dalton (1766 - 1844) can rightly be called the father of the Modern Theory on Atoms. He proposed his Atomic Theory in 1808, i.e., almost 200 years back. He did not have the help of sophisticated instruments that are available today to the scientists. Hence, many of his proposals, have been modified and updated. Over the years, substantial changes have taken place regarding the atomic theory, yet some of the assumptions that Dalton made are still held valid.

Dalton's Atomic Theory

John Daltons Atomic Theory provided a simple theory of matter to provide theoretical justification to the laws of chemical combinations in 1805. The basic postulates of the theory are:

• All substances are made up of tiny, indivisible particles called atoms.
• Atoms of the same element are identical in shape, size, mass and other properties.
• Each element is composed of its own kind of atoms. Atoms of different elements are different in all respects.
• Atom is the smallest unit that takes part in chemical combinations.
• Atoms combine with each other in simple whole number ratios to form compound atoms called molecules.
• Atoms cannot be created, divided or destroyed during any chemical or physical change.

Electrolysis of aqueous solutions

Introduction:
Electrolysis is a process of breaking down (or decomposes) a chemical compound into its elements by using an electric current. The electric current is passed through an electrolytic cell, which consists of electrodes and electrolyte. Oxidation or reduction reactions occur in these electrodes. Electrolyte is a substance which contains free ions that make the substance electrically conductive. Electrolyte can be aqueous solution of molten ionic compound or the aqueous solution of ionic compound, alkali, or an acid. Hence electrolysis can be of two types
i) electrolysis of molten ionic compound
ii) Electrolysis of aqueous solutions.
Consider the example of sodium chloride (NaCl). Molten sodium chloride is obtained when we heat it till it melts. Whereas if, sodium chloride is dissolved in water, gives the aqueous solutions of sodium chloride. Solution of water of a substance is called the aqueous solution. Since the aqueous solution contains more than one type of ions, electrolysis of aqueous solutions is entirely different from that of molten electrolyte.

Electrolysis of aqueous solutions:

i)   Electrolysis of aqueous sodium chloride :
In the electrolysis of aqueous solutions, not only sodium chloride will dissociate into Na⁺ and Cl^-, but some of the water molecules will also decompose to give hydrogen (H⁺⁾ and hydroxide ions (OH^-). The reaction of electrolysis of aqueous solutions (of NaCl) can be written as follows,
              NaCl ---> Na⁺ + Cl^-
               H₂O ---> H⁺ + OH^-
In an aqueous solution, there can be more than one positive and one negative ion. There is a selective discharge, which means when there is a movement of ions to cathode or anode, only one negative ion and one positive ion will be selected to be discharged.

Electrolysis of aqueous solutions:

ii)  Electrolysis of Aqueous Sulphuric Acid
It is one of the examples of electrolysis of aqueous solutions.
The aqueous sulphuric has three types of ions. They are hydrogen ions (H⁺), sulphate ions (SO₄^2-), and also hydroxide ions (OH^-) from the water. The equation can be written as follows,
H₂SO₄ + H₂O --> 2H⁺ + SO₄^2- + H⁺ + OH^-
Diagram showing electrolysis of water:

The apparatus used for the Electrolysis of Aqueous Sulphuric Acid
There is more than one type of ion moving to the electrode, there is preferential discharge (also called as selective discharge) takes place.
The chemical reactions occur at anode and cathode is given in the table below.

At cathode	At anode
Here, each hydrogen ion (H+) gains electron and becomes hydrogen atom. Two of the hydrogen atom will combine and produce hydrogen gas molecule. Equation: 2H+ + 2e ---> H2	Here there is a choice of sulphate ions (SO42-) or hydroxide ions (OH-) Oxygen is gives off at anode, because of hydroxide ion is easier to discharge. Equation: OH- + 4e ---> O2 + H2O

Note:
When the electrolysis of aqueous solutions of dilute acids or alkalis is done, the volume of hydrogen given off at the cathode is approximately twice that of the oxygen gas at the anode.

Aqueous hydrogen fluoride

Introduction:
Electrolysis is a process of breaking down (or decomposes) a chemical compound into its elements by using an electric current. The electric current is passed through an electrolytic cell, which consists of electrodes and electrolyte. Oxidation or reduction reactions occur in these electrodes. Electrolyte is a substance which contains free ions that make the substance electrically conductive. Electrolyte can be aqueous solution of molten ionic compound or the aqueous solution of ionic compound, alkali, or an acid. Hence electrolysis can be of two types
i) electrolysis of molten ionic compound
ii) Electrolysis of aqueous solutions.
Consider the example of sodium chloride (NaCl). Molten sodium chloride is obtained when we heat it till it melts. Whereas if, sodium chloride is dissolved in water, gives the aqueous solutions of sodium chloride. Solution of water of a substance is called the aqueous solution. Since the aqueous solution contains more than one type of ions, electrolysis of aqueous solutions is entirely different from that of molten electrolyte.

Electrolysis of aqueous solutions:

i)   Electrolysis of aqueous sodium chloride :
In the electrolysis of aqueous solutions, not only sodium chloride will dissociate into Na⁺ and Cl^-, but some of the water molecules will also decompose to give hydrogen (H⁺⁾ and hydroxide ions (OH^-). The reaction of electrolysis of aqueous solutions (of NaCl) can be written as follows,
              NaCl ---> Na⁺ + Cl^-
               H₂O ---> H⁺ + OH^-
In an aqueous solution, there can be more than one positive and one negative ion. There is a selective discharge, which means when there is a movement of ions to cathode or anode, only one negative ion and one positive ion will be selected to be discharged.

Electrolysis of aqueous solutions:

ii)  Electrolysis of Aqueous Sulphuric Acid
It is one of the examples of electrolysis of aqueous solutions.
The aqueous sulphuric has three types of ions. They are hydrogen ions (H⁺), sulphate ions (SO₄^2-), and also hydroxide ions (OH^-) from the water. The equation can be written as follows,
H₂SO₄ + H₂O --> 2H⁺ + SO₄^2- + H⁺ + OH^-
Diagram showing electrolysis of water:

The apparatus used for the Electrolysis of Aqueous Sulphuric Acid
There is more than one type of ion moving to the electrode, there is preferential discharge (also called as selective discharge) takes place.
The chemical reactions occur at anode and cathode is given in the table below.

At cathode	At anode
Here, each hydrogen ion (H+) gains electron and becomes hydrogen atom. Two of the hydrogen atom will combine and produce hydrogen gas molecule. Equation: 2H+ + 2e ---> H2	Here there is a choice of sulphate ions (SO42-) or hydroxide ions (OH-) Oxygen is gives off at anode, because of hydroxide ion is easier to discharge. Equation: OH- + 4e ---> O2 + H2O

Note:
When the electrolysis of aqueous solutions of dilute acids or alkalis is done, the volume of hydrogen given off at the cathode is approximately twice that of the oxygen gas at the anode.