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Why do we rarely see elements in their purest form in nature? Familiar materials to us such as iron, aluminium, gold are almost all derived from the smelting of ores and minerals. It would make our life easier to simply pick the out off the ground and fashion them for use, no?
But life would be impossible if it was... |
"In the year 1902 (while I was attempting to explain to an elementary class in chemistry some of the ideas involved in the periodic law) becoming interested in the new theory of the electron, and combining this idea with those which are implied in the periodic classification, I formed an idea of the inner structure of the atom which, although it contained certain crudities, I have ever since regarded as representing essentially the arrangement of electrons in the atom"
Gilbert Newton Lewis, 'Valence and the Structure of Atoms and Molecules', 1923
Chemical bonds are what joins atoms together. When two or more atoms are in a chemical bond they stay together unless the needed amount of energy, or more, is transferred to the bond. Something different can then happen.
Chemical bonds can be explained using different theories. Some of these theories try to explain chemical bonds in a simple way that can be used by chemists to imagine what could happen when they try to make molecules. Some explain how the atoms are bonded together with more detail and are used by chemists and physicists. There are two types of bonds; covalent and ionic. Covalent bonds form when atoms share electrons. Ionic bonding is the attraction between oppositely charged ions. Chemical bonds are negatively charged electrons that are pulling protons into each other.
Chemical bonds can be explained using different theories. Some of these theories try to explain chemical bonds in a simple way that can be used by chemists to imagine what could happen when they try to make molecules. Some explain how the atoms are bonded together with more detail and are used by chemists and physicists. There are two types of bonds; covalent and ionic. Covalent bonds form when atoms share electrons. Ionic bonding is the attraction between oppositely charged ions. Chemical bonds are negatively charged electrons that are pulling protons into each other.
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History
American physical chemist Gilbert Newton Lewis (1875-1946) laid the foundation of valence bond theory; he was instrumental in developing a bonding theory based on the number of electrons in the outermost "valence" shell of the atom. In 1902, while Lewis was trying to explain valence to his students, he depicted atoms as constructed of a concentric series of cubes with electrons at each corner. This "cubic atom" explained the eight groups in the periodic table and represented his idea that chemical bonds are formed by electron transference to give each atom a complete set of eight outer electrons (an "octet"). Lewis's theory of chemical bonding continued to evolve and, in 1916, he published his seminal article "The Atom of the Molecule", which suggested that a chemical bond is a pair of electrons shared by two atoms. Lewis's model equated the classical chemical bond with the sharing of a pair of electrons between the two bonded atoms. Lewis introduced the "electron dot diagrams" in this paper to symbolize the electronic structures of atoms and molecules. Now known as Lewis structures, they are discussed in virtually every introductory chemistry book. |
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Shortly after publication of his 1916 paper, Lewis became involved with military research. He did not return to the subject of chemical bonding until 1923, when he masterfully summarized his model in a short monograph entitled Valence and the Structure of Atoms and Molecules. His renewal of interest in this subject was largely stimulated by the activities of the American chemist and General Electric researcher Irving Langmuir, who between 1919 and 1921 popularized and elaborated Lewis's model. Langmuir subsequently introduced the term covalent bond. In 1921, Otto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic particles.
For cases where no sharing was involved, Lewis in 1923 developed the electron pair theory of acids and base: Lewis redefined an acid as any atom or molecule with an incomplete octet that was thus capable of accepting electrons from another atom; bases were, of course, electron donors. His theory is known as the concept of Lewis acids and bases. In 1923, G. N. Lewis and Merle Randall published Thermodynamics and the Free Energy of Chemical Substances, first modern treatise on chemical thermodynamics.
The 1920s saw a rapid adoption and application of Lewis's model of the electron-pair bond in the fields of organic and coordination chemistry. In organic chemistry, this was primarily due to the efforts of the British chemists Arthur Lapworth, Robert Robinson, Thomas Lowry, and Christopher Ingold; while in coordination chemistry, Lewis's bonding model was promoted through the efforts of the American chemist Maurice Huggins and the British chemist Nevil Sidgwick.
For cases where no sharing was involved, Lewis in 1923 developed the electron pair theory of acids and base: Lewis redefined an acid as any atom or molecule with an incomplete octet that was thus capable of accepting electrons from another atom; bases were, of course, electron donors. His theory is known as the concept of Lewis acids and bases. In 1923, G. N. Lewis and Merle Randall published Thermodynamics and the Free Energy of Chemical Substances, first modern treatise on chemical thermodynamics.
The 1920s saw a rapid adoption and application of Lewis's model of the electron-pair bond in the fields of organic and coordination chemistry. In organic chemistry, this was primarily due to the efforts of the British chemists Arthur Lapworth, Robert Robinson, Thomas Lowry, and Christopher Ingold; while in coordination chemistry, Lewis's bonding model was promoted through the efforts of the American chemist Maurice Huggins and the British chemist Nevil Sidgwick.
Covalent bonds
Covalent bonds are chemical bonds between two non-metal atoms. An example is water, where hydrogen (H) and oxygen (O) bond together to make (H2O). As they are both non-metals—which need to gain electrons—they have to share, so their outer shells cross over in order to have a full outer shell. A full outer shell has eight electrons. The electrons in this outer shell are called valence electrons.
The number of valence electrons is decided by the size of the atom. Electrons orbit an atomic nucleus in the same kind of way that planets orbit stars. There are layers of paths around an atomic nucleus. The first layer always contains only two electrons, while the layers after that usually contain up to eight.
For example, if an atom contained eight total electrons, the first two would orbit very close to the nucleus, the next 6 would orbit a little farther away. Every atom wants a "full" outer shell. That is to say, it wants the number of electrons in the outer-most layer to be as high as they can be. Since most atoms' outer shells can support up to eight electrons, this is the number of electrons most atoms want in their outer shell. In this example, the atom had eight total electrons, and six in the outer shell. Since there are fewer than eight electrons in the outer shell, the atom will want to "fill" the places for two electrons with electrons borrowed from another atom. When an atom "borrows" electrons with another atom, a covalent bond is formed.
With water the oxygen atom shares one electron with each hydrogen atom and the hydrogens also share one: this means that the hydrogen atoms have two each and the oxygen atom has eight. Covalent bonds are weaker than ionic bonds, and have a lower melting point. They are also thought to be poor conductors of electricity and heat.
Covalent bonds are chemical bonds between two non-metal atoms. An example is water, where hydrogen (H) and oxygen (O) bond together to make (H2O). As they are both non-metals—which need to gain electrons—they have to share, so their outer shells cross over in order to have a full outer shell. A full outer shell has eight electrons. The electrons in this outer shell are called valence electrons.
The number of valence electrons is decided by the size of the atom. Electrons orbit an atomic nucleus in the same kind of way that planets orbit stars. There are layers of paths around an atomic nucleus. The first layer always contains only two electrons, while the layers after that usually contain up to eight.
For example, if an atom contained eight total electrons, the first two would orbit very close to the nucleus, the next 6 would orbit a little farther away. Every atom wants a "full" outer shell. That is to say, it wants the number of electrons in the outer-most layer to be as high as they can be. Since most atoms' outer shells can support up to eight electrons, this is the number of electrons most atoms want in their outer shell. In this example, the atom had eight total electrons, and six in the outer shell. Since there are fewer than eight electrons in the outer shell, the atom will want to "fill" the places for two electrons with electrons borrowed from another atom. When an atom "borrows" electrons with another atom, a covalent bond is formed.
With water the oxygen atom shares one electron with each hydrogen atom and the hydrogens also share one: this means that the hydrogen atoms have two each and the oxygen atom has eight. Covalent bonds are weaker than ionic bonds, and have a lower melting point. They are also thought to be poor conductors of electricity and heat.
Ionic bonds
Ionic bond is a type of chemical bonds involving electrostatic attraction between oppositely charged ions. Ions representing the atom that has lost one or more electrons (called cations) and atom that has gained one or more electrons (called anions). In the simplest case, the cation is a metal atom and the anion is a non-metallic atom, but these ions can become more complex nature, such as molecular ions like NH4 + or SO42-. In short, an ionic bond is electron transfer from metal to non-metal atom to two to get the full valence shell
It is important to realize that the net ionic bonds - in which one atom "taking" an electron from another - can not exist: All ionic compounds have a covalent bond, or sharing electrons. Thus, the term "ionic bond" is given when the ionic character is greater than the covalent character - that is, bonds for which the difference in electronegativity that exists between two atoms, the bonding is more polar (ionic) versus covalent bond in which electrons are shared more equal. Bonds with ionic and covalent character partly partly called polar covalent bond.
Ionic compounds conduct electricity when molten or in solution, but usually not as strong. There are exceptions to this rule, such as rubidium silver iodide, in which silver ions can be quite mobile. Ion compounds generally have a high melting point, depending on their ionic charges consist of. The higher the charge stronger cohesive forces and a higher melting point. They also tend to be soluble in water. Here, the opposite trend is roughly hold: the weaker cohesive forces, greater solubility.
Ionic bond is a type of chemical bonds involving electrostatic attraction between oppositely charged ions. Ions representing the atom that has lost one or more electrons (called cations) and atom that has gained one or more electrons (called anions). In the simplest case, the cation is a metal atom and the anion is a non-metallic atom, but these ions can become more complex nature, such as molecular ions like NH4 + or SO42-. In short, an ionic bond is electron transfer from metal to non-metal atom to two to get the full valence shell
It is important to realize that the net ionic bonds - in which one atom "taking" an electron from another - can not exist: All ionic compounds have a covalent bond, or sharing electrons. Thus, the term "ionic bond" is given when the ionic character is greater than the covalent character - that is, bonds for which the difference in electronegativity that exists between two atoms, the bonding is more polar (ionic) versus covalent bond in which electrons are shared more equal. Bonds with ionic and covalent character partly partly called polar covalent bond.
Ionic compounds conduct electricity when molten or in solution, but usually not as strong. There are exceptions to this rule, such as rubidium silver iodide, in which silver ions can be quite mobile. Ion compounds generally have a high melting point, depending on their ionic charges consist of. The higher the charge stronger cohesive forces and a higher melting point. They also tend to be soluble in water. Here, the opposite trend is roughly hold: the weaker cohesive forces, greater solubility.
Ponder this
The noble gasses (such as argon, and neon) are known to be quite inert to the other elements. How and why this whole category of elements are so?
Most elements form bonds with others quite easily. How can we explain the occurrence of elemental (pure) deposits in the Earth, in contrast to their more common mineral forms?
How different would the world be if elements are not so keen on forming bonds? Would it be advantageous to us? Or disastrous?
Discuss
How would the simple act of transferring (ionic bond), or sharing (covalent bond) electrons change the nature of the respective elements? For example, table salt, or sodium chloride, is mostly harmless. However elemental sodium is an extremely reactive metal especially with water; while elemental chlorine in its natural state is an extremely poisonous gas. How do we explain this?
Further readings
Gilbert Newton Lewis, at the Chemical Heritage Foundation.
Lewis' Theory of Bonding, a rather concise and straightforward primer to Lewis' theory, at LibreText
Ionic and covalent bonds, at LibreText.
