Química inorganica temas, Diapositivas de Química

¡Descarga Química inorganica temas y más Diapositivas en PDF de Química solo en Docsity! ChemMatters | www.acs.org/chemmatters 15 The Mesmerizing Pull of D o you remember being fascinated by magnets as a kid? Using a magnet from your fridge, you could pick up small metal objects such as paper clips, as if by magic. But other metal objects, including pennies, wouldn’t budge under a magnet’s pull. One idea you might have tried is to draw a liquid to a magnet, which would have been even cooler to see. You might not have succeeded, but it is possible! And, surprisingly, such liquids can be found within familiar items, such as dollar bills, ball bearings, and increasingly, in artwork. These intriguing liquids are called ferrofluids. Ferrofluids are always jet black and mesmerizing to look at. If you hold a powerful magnet close to a ferrofluid, it forms liquid spikes. The spikes reveal the otherwise invisible magnetic field lines surrounding the magnet. So, what are these substances anyway? You might notice that the term ferrofluids is similar to the Latin word for iron, ferrum. This is where the symbol Fe comes from. While not pure iron, ferrofluids do contain iron, usually in the form of iron oxide (Fe3O4), which is usually called magnetite. Magnetite is commonly found in nature. The easiest way to find it is to make a slurry of soil and water and then stir it with a powerful magnet. The bits of hard material that collect on the magnet are likely magnetite. Lodestone, a naturally occurring magnetic mineral, is a type of magnetite that was used in the world’s first-known compasses. THE NATURE OF ATTRACTION To understand why magnetite is attracted to a magnet, we have to first look at the electron configuration of iron. An electron configuration is the arrangement of electrons around the nucleus of an atom. Electrons occupy shells around a nucleus corresponding to specific energy levels. Shells closest to the nucleus are lower in energy than those that are farther from the nucleus. Each shell is assigned a number and letter. The number, or coefficient, refers to the principal energy level. The letter (s, p, d, and f) refers to the subshell within the energy level. A superscript refers to the number of By Brian Rohrig 1s 2s 3s 4s 5s 6s 7s 3d 4d 5d 6d 2p 3p 4p 5p 6p 7p 1s 4f 5f The periodic table’s arrangement is based on electron configurations, and is divided into blocks that correspond to the type of subshell being filled. electrons within a subshell. So, a configuration of 1s2 means there are two electrons in the s subshell of the first major energy level. Iron atoms have an electron configuration of 1s22s22p63s23p63d64s2. In magnetite, Fe3O4, some of the electrons from the iron have been donated to oxygen to form oxide, O2-. To balance the eight electrons received by the four oxygens in Fe3O4, one of the iron atoms has given up two electrons, to form Fe2+ or Fe(II), while the other two iron atoms have each given up three electrons to form Fe3+ or Fe(III). Fe(II) loses its 4s electrons and has a configuration of SH U TT ER ST O CK KE LS EY C A SS EL BU RY 1s22s22p63s23p63d6, while Fe(III) loses an additional 3d electron and has a configuration of 1s22s22p63s23p63d5. Each subshell is further divided into orbitals, which are regions of space in which electrons are most likely to be found. Any orbital can hold a maximum of two electrons. The d subshell contains five orbitals and can hold a maximum of 10 electrons. Within an orbital, electrons create tiny magnetic fields as if they’re spinning. One electron creates a magnetic field oriented in one direction, and the other electron’s mag- netic field is oriented in the opposite direction. The two opposite directions, called spins, are denoted by an upward or downward arrow. According to Hund’s rule, each orbital within a subshell must be filled by one elec- tron before a second electron can be added. Since electrons are negatively charged, they repel one another, so it is more energetically favorable for an electron to occupy its own space than for two electrons to crowd into a single orbital. An orbital-filling diagram depicts the arrangement of electrons within their orbitals. For example, the diagram below shows electrons’ orientations and distribution in iron’s d-subshell in an Fe(II) ion: In the diagram, each horizontal line represents an orbital. With six electrons fitting into five orbitals, only one orbital is completely filled, while the others are partially filled. This arrangement influences a material’s magne- tism because when two electrons are in the same orbital, they will have opposite spins that cancel out each other’s magnetic fields. The other unpaired electrons on an atom all line up in the same direction, so their magnetic fields reinforce each other. Iron(III) has one fewer electron than iron(II), so it actually has one more unpaired electron and thus a larger magnetic field: In most materials that contain iron(II) or iron(III), the atoms act like tiny magnets, but each atom’s magnetic field is oriented randomly relative to the nearby atoms. If you place it near a permanent magnet, there is only a slight tendency to line up the atoms’ fields relative to the external magnet, resulting in a slight attraction to the magnet (usually 16 DECEMBER 2021 | ChemMatters a a a a a a a a a a a In paramagnetic substances, electron spins are randomly oriented. In ferromagnetic materials, spins are parallel. And in ferrimagnetism, spins are parallel and in opposite directions, but don’t cancel each other out. PARAMAGNETIC FERROMAGNETIC FERRIMAGNETIC Magnetite contains iron atoms in two different environments. Some (in pink) are surrounded by four oxygen atoms forming the vertices of a tetrahedron. Others (in black) are surrounded by six oxygen atoms in an octahe- dral environment. a a a a a a a a a a a aaaa a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a Not only are ferrofluids useful, they are also captivating to look at. Artists use the fluids and magnets, along with colorful mixtures of other liquids such as milk and food coloring, to create abstract works of art. SH U TT ER ST O CK RS G R A PH X , L LC KE LS EY C A SS EL BU RY