Zinc is one of the main components of brass , being used since the 10th century BCE. Zinc is also incredibly important to humans; almost 2 billion people in the world suffer from zinc deficiency. However, too much zinc can cause copper deficiency. Zinc is often used in batteries, aptly named carbon-zinc batteries , and is important in many platings, as zinc is very corrosion resistant.
Gallium Ga is an element in period 4, between zinc and germanium. Gallium is noteworthy because it has a melting point at about kelvins , right around room temperature. For example, it will be solid on a typical spring day, but will be liquid on a hot summer day. Gallium is an important component in the alloy galinstan, along with tin. Gallium can also be found in semiconductors. Germanium Ge is an element in period 4, between gallium and arsenic. Germanium, like silicon above it, is an important semiconductor and is commonly used in diodes and transistors, often in combination with arsenic.
Germanium is fairly rare on Earth, leading to its comparatively late discovery. Germanium, in compounds, can sometimes irritate the eyes, skin, or lungs.
Arsenic As is an element in period 4, between germanium and selenium. Arsenic, as mentioned above, is often used in semiconductors in alloys with germanium. Arsenic, in pure form and some alloys, is incredibly poisonous to all multicellular life, and as such is a common component in pesticides. Arsenic was also used in some pigments before its toxicity was discovered. Selenium Se is an element in period 4, between arsenic and bromine. Selenium is the first nonmetal in period 4, with properties similar to sulfur.
Selenium is quite rare in pure form in nature, mostly being found in minerals such as pyrite , and even then it is quite rare. Selenium is necessary for humans in trace amounts, but is toxic in larger quantities. Bromine Br is an element in period 4, between selenium and krypton. Bromine is a halogen , never existing in pure form in nature. Bromine is barely liquid at room temperature, boiling at about kelvins. Bromine is also quite toxic and corrosive, but bromide ions, which are relatively inert, can be found in halite , or table salt.
Bromine is often used as a fire retardant because many compounds can be made to release free bromine atoms. Krypton Kr is a noble gas , placed under argon and over xenon. Because of the slow but steady increase in ionization potentials across a row, high oxidation states become progressively less stable for the elements on the right side of the d block.
The occurrence of multiple oxidation states separated by a single electron causes many, if not most, compounds of the transition metals to be paramagnetic, with one to five unpaired electrons. This behavior is in sharp contrast to that of the p-block elements, where the occurrence of two oxidation states separated by two electrons is common, which makes virtually all compounds of the p-block elements diamagnetic.
Due to a small increase in successive ionization energies, most of the transition metals have multiple oxidation states separated by a single electron.
Most compounds of transition metals are paramagnetic, whereas virtually all compounds of the p-block elements are diamagnetic. Thus Sc is a rather active metal, whereas Cu is much less reactive. Exceptions to the overall trends are rather common, however, and in many cases, they are attributable to the stability associated with filled and half-filled subshells.
Consequently, all transition-metal cations possess d n valence electron configurations, as shown in Table The second- and third-row transition metals behave similarly but with three important differences:. The highest possible oxidation state, corresponding to the formal loss of all valence electrons, becomes increasingly less stable as we go from group 3 to group 8, and it is never observed in later groups.
Binary transition-metal compounds, such as the oxides and sulfides, are usually written with idealized stoichiometries, such as FeO or FeS, but these compounds are usually cation deficient and almost never contain a cation:anion ratio. Thus a substance such as ferrous oxide is actually a nonstoichiometric compound with a range of compositions.
The acid—base character of transition-metal oxides depends strongly on the oxidation state of the metal and its ionic radius. Conversely, oxides of metals in higher oxidation states are more covalent and tend to be acidic, often dissolving in strong base to form oxoanions.
Identify these metals; predict the stoichiometry of the oxides; describe the general physical and chemical properties, type of bonding, and physical state of the oxides; and decide whether they are acidic or basic oxides. Refer to the trends outlined in Figure Decide whether their oxides are covalent or ionic in character, and, based on this, predict the general physical and chemical properties of the oxides.
Because the heavier transition metals tend to be stable in higher oxidation states, we expect Ru and Os to form the most stable tetroxides. Because oxides of metals in high oxidation states are generally covalent compounds, RuO 4 and OsO 4 should be volatile solids or liquids that consist of discrete MO 4 molecules, which the valence-shell electron-pair repulsion VSEPR model predicts to be tetrahedral. Finally, because oxides of transition metals in high oxidation states are usually acidic, RuO 4 and OsO 4 should dissolve in strong aqueous base to form oxoanions.
Predict the identity and stoichiometry of the stable group 9 bromide in which the metal has the lowest oxidation state and describe its chemical and physical properties. Because the lightest element in the group is most likely to form stable compounds in lower oxidation states, the bromide will be CoBr 2.
The transition metals are characterized by partially filled d subshells in the free elements and cations. In the second- and third-row transition metals, such irregularities can be difficult to predict, particularly for the third row, which has 4f, 5d, and 6s orbitals that are very close in energy.
The increase in atomic radius is greater between the 3d and 4d metals than between the 4d and 5d metals because of the lanthanide contraction. Ionization energies and electronegativities increase slowly across a row, as do densities and electrical and thermal conductivities, whereas enthalpies of hydration decrease.
Anomalies can be explained by the increased stabilization of half-filled and filled subshells. Transition-metal cations are formed by the initial loss of ns electrons, and many metals can form cations in several oxidation states.
Observations of the way that these elements react with water, acids and steam enable us to put them into this series.
The tables show how the elements react with water and dilute acids:. Note that aluminium can be difficult to place in the correct position in the reactivity series during these experiments. This is because its protective aluminium oxide layer makes it appear to be less reactive than it really is. When this layer is removed, the observations are more reliable.
It is useful to place carbon and hydrogen into the reactivity series because these elements can be used to extract metals. Here is the reactivity series including carbon and hydrogen:. Note that zinc and iron can be displaced from their oxides using carbon but not using hydrogen.
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