For water in 2 in aqueous solution, the pK a is 10. When hydroxide is needed to carry out hydrolysis reactions, acidic metal ions, like Zn 2 are often used to stabilize the hydroxide nucleophile in order to catalyze the reaction (lower activation energy). As you saw earlier, binding water to a metal ion can change its pK a, and make its protons more acidic by stabilizing the hydroxide ion. The mechanism for this enzyme is shown around structure of the protein. The figure shows the structure of human carbonic anhydrase IV (from PDB 1znc), with a blow up of the Zn active site where Zn is bound to 3 histidine side chains (His). The structure of protein and acitve site were created from PDB 1znc. (CC-BY-SA Kathryn Haas) Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder.\): Formation of carbonic acid from carbon dioxide catalyzed by human carbonic anhydraze IV. In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped. These layers can slide over each other if they are hammered. Metals are also shiny, as well as malleable (bendable) and ductile (can be drawn into wires) as they have regular layers of atoms. The strong electrostatic forces between the ions and electrons mean metals have very high melting points (large amounts of energy are needed to break these forces).īecause the electrons are able to move freely, it means metals are good conductors of electricity and heat. The electrons are free to move around from each atom to atom as they please. Metals have some unique properties - and it's all to do with how they bond! Their structure is formed from positive metal ions held together by a “sea of delocalised electrons” from the outer shells of the metal atoms. No free electrons exist in this structure, so it does not conduct electricity.ĭiamonds are used as cutting tools as they are the hardest naturally occurring substance due to the arrangement of carbon atoms all bonded by strong covalent bonds. Weak forces of attraction hold the layers of graphite together, so they can slide over each other, making graphite a great lubricant.Įvery carbon atom is strongly covalently bonded to four others in diamond, and because of this it forms a 3D lattice, called a tetrahedron. Each atom has a 'spare' electron, not used for bonding, which it contributes to the “sea of delocalised electrons”, thereby being able to conduct heat and electricity well. This is why graphite is often used for electrodes in electrolysis. Graphite is made from layers of hexagonal rings of carbon, with each atom forming three strong covalent bonds to other carbon atoms. These substances are not soluble in water. These bonds have to be broken by large amounts of energy leading to high melting and boiling points. These compounds are solid at room temperature, because all of the atoms in a giant covalent structure are held together by strong covalent bonds. Graphite and diamond are examples of giant covalent structures. Some solids can turn straight into a gas, skipping the liquid phase this is called sublimation. Gases can be turned back into liquids by condensation, lowring the amounf of energy particles have. Liquids can turn into gases by evaporation or boiling (again by increasing the energy of the particles). Liquids can be turned back into solids by freezing, lowering the amount of energy particles have. This involves increasing the energy of the particles normally by heating. Solids can turn into liquids through the process of melting. Changing from one state to another is a physical change as you end up with the same chemical as you began with (whereas a chemical change would lead to different chemicals). Some of the forces need to be broken during melting, whereas all of the forces must be broken during evaporating/boiling. The amount of energy required to change state depends on the strength of the intermolecular forces between the particles of each substance. To get from a solid to a liquid, or a gas, energy has to be supplied - usually through heating. During these changes the particles gain energy, which is used to break or overcome the intermolecular forces of attraction.įluids (liquids and gases) are able to take the shape of their containers, however, only gases can be compressed as their particles are far apart and have space to move into. Particles in solids have less energy than liquids, which in turn have less energy than gases. In these diagrams, particles are represented by solid spheres. Solids (s), liquids (l) and gases (g) can be represented using particle diagrams.
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