Group 14 Elements - Basic Inorganic Chemistry PDF

 Group 14 elements - the group with no name ▪ Much of the important chemistry of the group 14 elements can be understood on the basis of their electronic structure. ▪ Since the elements have a [core]ns2 np2 electron configuration, neutral group 14 compounds usually form up t...

 Group 14 elements - the group with no name ▪ Much of the important chemistry of the group 14 elements can be understood on the basis of their electronic structure. ▪ Since the elements have a [core]ns2 np2 electron configuration, neutral group 14 compounds usually form up to four bonds. ▪ This uses all the electrons and orbitals around the atom (a complete octet) around the group 14 atom so such compounds are called “electron-precise”. Elements of Carbon Family Carbon is the first element in this 14th group of elements. It is one of the most plentily available elements present on our earth. We can find it in combined as well as free states. We usually find it in air, polymers, organic compounds, carbonates etc. It has three isotopes, namely, 12C, 13C, and 14C where 14C is radioactive. Silicon is a common element in dust, sand, clay, stone, silica and silicate minerals. We can hardly find it as a pure element. It is neither a nonmetal or a metal. In fact, it is a metalloid. Germanium is a rare element which we use in the manufacturing of semiconductor devices. Pure germanium is an excellent semiconductor. However, it only occurs in traces as it is too reactive to be found in the elemental state. Tin is a soft, malleable metal with a low melting point. It is mainly obtained from the mineral cassiterite. It has two main allotropes at regular pressure and temperature. Lead, also plumbate, is obtained from Galena. We find its common use in the making of lead-acid batteries, oxidizing agents, and alloys. Lead is toxic for us, the humans. Properties and Trends in Element Group 14 1) Covalent Radius As we move down the group, the covalent radius increases. Therefore, there is a substantial increase in radius from carbon to silicon. Post that, the difference is less considerable. The reason can be credited to the d and f orbitals which are completely filled with the heavier members. 2) Ionization Enthalpy Moving down the group, we notice that the ionization enthalpies decrease. This is because of the increase in the distance from the nucleus. There is a substantial decrease of ionization enthalpy from carbon to silicon. Post that, the difference is less considerable. There is a slight increase in ionization enthalpy from tin to lead due to the poor shielding effect of the d and f orbitals. The Anomalous Behavior of Carbon The properties of carbon are very unique. We can attribute this behavior to carbon mainly due to : The small size of the atom High electronegativity High ionization enthalpy Unavailability of d-orbital’s Unique Properties of Carbon 1) The Small Size of Carbon Carbon derives a lot of its properties from its small size. The compounds that carbon forms are highly stable and this is also because of its small size. Due to its small size, the nucleus effectively holds on to the bonded and nonbonded electrons. Hence, in short tetravalency, small size and property of catenation make carbon different from other elements and so we have the whole branch of chemistry dedicated to the study of this kind of compound. 2) Tetravalency of Carbon Carbon exhibits tetravalency. It means it can share four electrons to complete its octet. Thus, we know it bonds to four different monovalent atoms. Carbon forms a large variety of compounds with oxygen, nitrogen, hydrogen, halogens. This results in a different set of compounds which have distinctive characteristics and properties. Carbon has the availability of only s and p orbitals. Therefore, it can hold only four pairs of electrons in its valence shell. Thus, we can restrict the covalence to four. However, the other elements in the group can easily grow their covalence due to the availability of d- orbitals. 3) Catenation One of the unique properties of Carbon is its ability to form long carbon chains. It implies that carbon attaches with other carbon atoms to form long carbon chains. This property is what we call as catenation. This gives rise to a variety of complex compounds. Some of the compounds have a straight carbon chain while some others have branched carbon chain or even rings. The carbon compounds having only single bond are the saturated hydrocarbons. On the other hand, the compounds with double or triple bond are the unsaturated hydrocarbons. As we move down the group, the size of the elements increases. This results in a decreasing electronegativity. Thus, the property to show catenation also decreases. This can be clearly observed from bond enthalpy values. The catenation order is C >> Si > Ge >> Sn. 4) Electronegativity Carbon has an extraordinary capacity to shape pπ – pπ multiple bonds with itself and with different molecules. This can also be related to its smaller size and high electronegativity. Some of the examples would include C = C, C≡C, C = O, C = S and C= N. As a matter of fact, the heavier elements don’t shape pπ – pπ bonds. This is mainly because of the reason that their nuclear orbitals are too vast and diffused to have viable overlapping. For example, lead does not indicate catenation. References: Cotton F and Wilkinson, Basic inorganic Chemistry, terjemahan Sahati Suharto, Kimia Anorganik Dasar, UI Press, Jakarta Rayner-Canham, G., Descriptive Inorganic Chemistry, 2nd edition, W.H Freeman & Co, New York, Shriver, D.F and Atkin, P.W., 2006, Inorganic Chemistry, 4th ed, WH Freeman & Co, New York Suyanta, 2013, Kimia Unsur, Gadjah Mada University Press, Yogyakarta https://www.toppr.com/guides/chemistry/the-p-block-elements/group-14-elements-carbon- family/ http://taladev.com/ebook/products/0-13-190443-4/ddref_chem05_eh06.pdf http://kummelgroup.ucsd.edu/courses/Overheads/Chapter_14/Slidesb.pdf  The Trend from Non-Metal to Metal in Group 4 Elements ▪ The trend from non-metallic to metallic behavior in the Group 4 elements (carbon (C), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb)). ▪ It describes how this trend is evident in the structures and physical properties of the elements, and attempts to explain the trend. Structures of the elements The trend from non-metal to metal down the group is evident in the structures of the elements themselves. Carbon, at the top of the group, forms large network covalent structures in its two most familiar allotropes: diamond and graphite. Diamond has a three-dimensional structure of carbon atoms each bonded covalently to 4 other atoms. This diagram shows a representative portion of that structure:  This structure is also found in silicon and germanium and in one of the allotropes of tin, "grey tin" or "alpha-tin". The more common allotrope of tin ("white tin" or "beta-tin") is metallic, with its atoms held together by metallic bonds. The structure is a distorted close- packed arrangement. In a close-packed structure, each atom is surrounded by 12 neighboring atoms. In lead and the heavier elements, the atoms are arranged in a 12- coordinated metallic structure. From this information, it is clear that there is a trend from the typical covalency found in non-metals to the metallic bonding in metals, with an obvious inflection point between the two common tin allotropes. Physical properties of the elements Melting points and boiling points If the trends in melting and boiling points down Group 4 are examined, it is difficult to comment on the shift from covalent to metallic bonding. The trends reflect the increasing weakness of the covalent or metallic bonds as the atoms get bigger and the bonds get longer. This trend is shown below: The low value for tin's melting point compared with that of lead is presumably due to the distortion in tin's 12-coordinated structure. The tin values in the chart refer to metallic white tin. Brittleness A much clearer distinction between nonmetals and metals is shown when the brittleness of the elements is considered. Carbon in its diamond allotrope is very hard, reflecting the strength of the covalent bonds. However, if a diamond is hit with a hammer, it shatters. Silicon, germanium and grey tin (all with the same structure as diamond) are also brittle solids. However, white tin and lead have metallic structures. The atoms can move around without any permanent disruption of the metallic bonds; this leads to typical metallic properties like malleability and ductility. Lead in particular is fairly soft. Electrical conductivity Diamond does not conduct electricity. In diamond the electrons are all tightly bound and not free to move. Silicon, germanium and grey tin are semiconductors. White tin and lead are metallic conductors. This information shows clear trend between the typically non-metallic conductivity behavior of diamond, and the typically metallic behavior of white tin and lead. Explaining the trends One important characteristic of metals is that they form positive ions. This section examines factors which increase the likelihood of positive ions being formed down Group 4. Electronegativity Electronegativity measures the tendency of an atom to attract a bonding pair of electrons. It is usually measured on the Pauling scale, in which the most electronegative element (fluorine) is assigned an electronegativity of 4. The lower the electronegativity of an atom, the less strongly the atom attracts a bonding pair of electrons. That means that this atom will tend to lose the electron pair towards whatever else it is attached to. The atom we are interested in will therefore tend to carry either a partial positive charge or form a positive ion. Metallic behavior is usually associated with low electronegativity. The trend in electronegativity in Group 4, and its implications for metallic behavior, can be examined using the figure below: Electronegativity clearly decreases between carbon and silicon, but beyond silicon there is no definite trend. There therefore seems to be no relationship between the non-metal to metal trend and electronegativity values. Ionization energies When considering the formation of positive ions, a good start includes describing how ionization energies change down Group 4. Ionization energy is defined as the energy required to carry out each of the following changes (reported in kJ mol-1): First ionization energy: X(g)→X+(g)+e− Second ionization energy: X+(g)→X2+(g)+e− and so on for subsequent ionizations.  None of the Group 4 elements form 1+ ions, so looking at the first ionization energy alone is not helpful. Some of the elements do, however, form 2+ and (to some extent) 4+ ions. The first chart shows how the total ionization energy needed to form the 2+ ions varies down the group. The values are all reported in kJ mol-1.  The ionization energies decrease down the group, although there is a slight increase at lead. The trend exists because: The atoms are getting bigger because of the extra layers of electrons. The farther the outer electrons are from the nucleus, the less they are attracted; therefore, they are easier to remove. The outer electrons are screened from the full effect of the nucleus by the increasing number of inner electrons. These two effects outweigh the effect of increasing nuclear charge.  Examining the ionization energy required to form 4+ ions, the pattern is similar, but not as simple, as shown below (values again reported in kJ mol-1): ▪ Large amounts of ionization energy are required to form 2+ ions, and even more energy is required for 4+ ions. However, in each case there is a decrease in ionization energy down the group; this implies that tin and lead could form positive ions. However, there is no indication from these figures that this is likely. ▪ Carbon's ionization energies are so large that there is essentially no possibility of it forming simple positive ions. Reference: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Desc riptive_Chemistry/Elements_Organized_by_Block/2_p_Block_Elements/Group_14%3A_The_Carbon_Family/1Gro up_14%3A_General_Chemistry/The_Trend_from_Non-Metal_to_Metal_in_Group_4_Elements