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- Бұл бет үшін навигация:
- Law of Conservation of Mass
- Metal Ion Reactivity
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In Mendeleev's table, elements with similar characteristics fall in vertical columns, called groups. Molar volume increases from top to bottom of a group3 Example The alkali metals (Mendeleev's group I) have high molar volumes and they also have low melting points which decrease in the order: Li (174 oC) > Na (97.8 oC) > K (63.7 oC) > Rb (38.9 oC) > Cs (28.5 oC) Atomic Number as the Basis for the Periodic Law Assuming there were errors in atomic masses, Mendeleev placed certain elements not in order of increasing atomic mass so that they could fit into the proper groups (similar elements have similar properties) of his periodic table. An example of this was with argon (atomic mass 39.9), which was put in front of potassium (atomic mass 39.1). Elements were placed into groups that expressed similar chemical behavior. In 1913 Henry G.J. Moseley did researched the X-Ray spectra of the elements and suggested that the energies of electron orbitals depend on the nuclear charge and the nuclear charges of atoms in the target, which is also known as anode, dictate the frequencies of emitted X-Rays. Moseley was able to tie the X-Ray frequencies to numbers equal to the nuclear charges, therefore showing the placement of the elements in Mendeleev's periodic table. The equation he used: ν=A(Z−b)2ν=A(Z−b)2 with
νν: X-Ray frequency ZZ: Atomic Number AA and bb: constants 463
Atomic numbers, not weights, determine the factor of chemical properties. As mentioned before, argon weights more than potassium (39.9 vs. 39.1, respectively), yet argon is in front of potassium. Thus, we can see that elements are arranged based on their atomic number. The periodic law is found to help determine many patterns of many different properties of elements; melting and boiling points, densities, electrical conductivity, reactivity, acidic, basic, valance, polarity, and solubility. The table below shows that elements increase from left to right accordingly to their atomic number. The vertical columns have similar properties within their group for example Lithium is similar to sodium, beryllium is similar to magnesium, and so on. 
So, elements in Group 1 (periodic table) have similar chemical properties, they are called alkali metals. Elements in Group 2 have similar chemical properties, they are called the alkaline earth metals. Short form periodic table The short form periodic table is a table where elements are arranged in 7 rows, periods, with increasing atomic numbers from left to right. There are 18 vertical columns known as groups. This table is based on Mendeleev's periodic table and the periodic law. Long form Periodic Table In the long form, each period correlates to the building up of electronic shell; the first two groups (1-2) (s-block) and the last 6 groups (13-18) (p-block) make up the main-group elements and the groups (3-12) in between the s and p blocks are called the transition metals. Group 18 elements are called noble gases, and group 17 are called halogens. The f-block elements, called inner transition metals, which are at the bottom of the periodic table (periods 8 and 9); the 15 elements after barium (atomic number 56) are called lanthanides and the 14 elements after radium (atomic number 88) are called actinides. Law of Conservation of Mass The Law of Conservation of Mass is that, in a closed system, matter cannot be created or destroyed. It can change forms, but is conserved. The Law of Conservation of Mass is a relation stating that in a chemical reaction, the mass of the products equals the mass of the reactants. Antoine Lavoisier 464
reactions,[11] stated, "atoms of an object cannot be created or destroyed, but can be moved around and be changed into different particles". The principle of conservation of mass was first outlined by Mikhail Lomonosov (1711–1765) in 1748. He proved it by experiments—though this is sometimes challenged.[9]Antoine Lavoisier (1743–1794) had expressed these ideas in 1774. Others whose ideas pre-dated the work of Lavoisier include Joseph Black (1728–1799), Henry Cavendish(1731–1810), and Jean Rey (1583–1645).[10] The conservation of mass was obscure for millennia because of the buoyancy effect of the Earth's atmosphere on the weight of gases. For example, a piece of wood weighs less after burning; this seemed to suggest that some of its mass disappears, or is transformed or lost. This was not disproved until careful experiments were performed in which chemical reactions such as rusting were allowed to take place in sealed glass ampoules; it was found that the chemical reaction did not change the weight of the sealed container and its contents. The vacuum pump also enabled the weighing of gases using scales. Once understood, the conservation of mass was of great importance in progressing from alchemy to modern chemistry. Once early chemists realized that chemical substances never disappeared but were only transformed into other substances with the same weight, these scientists could for the first time embark on quantitative studies of the transformations of substances. The idea of mass conservation plus a surmise that certain "elemental substances" also could not be transformed into others by chemical reactions, in turn led to an understanding of chemical elements, as well as the idea that all chemical processes and transformations (such as burning and metabolic reactions) are reactions between invariant amounts or weights of these chemical elements. Following the pioneering work of Lavoisier the prolonged and exhaustive experiments of Jean Stas supported the strict accuracy of this law in chemical even though they were carried out with other intentions. His research[12][13] indicated that in certain reactions the loss or gain could not have been more than from 2 to 4 parts in 100,000.[14]The difference in the accuracy aimed at and attained by Lavoisier on the one hand, and by Morley and Stas on the other, is enormous. What is the Law of Conservation of Mass? When elements and compounds react to form new products, mass cannot be lost or gained. "The Law of Conservation of Mass" definition states that "mass cannot be created or destroyed, but changed into different forms". So, in a chemical change, the total mass of reactants must equal the total mass of products. The law of conservation of mass can also be stated "no atoms can be lost or made in a chemical reaction", which is why the total mass of products must equal the total mass of reactants you started with. By using this law, together with atomic and formula masses, you can calculate the quantities of reactants and products involved in a reaction and the simplest formula of a compound 465
One consequence of the law of conservation of mass is that In a balanced chemical symbol equation, the total of relative formula masses of the reactants is equal to the total relative formula masses of the products. 2.3 reactivity series of metals. In chemistry, a reactivity series (or activity series) is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest.[1][2][3] It is used to summarize information about the reactions of metals with acids and water, double displacement reactions and the extraction of metals from their ores. Table
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Going from the bottom to the top of the table the metals: increase in reactivity; lose electrons (oxidize) more readily to form positive ions; corrode or tarnish more readily; require more energy (and different methods) to be separated from their ores; become stronger reducing agents (electron donors). Defining reactions[edit] There is no unique and fully consistent way to define the reactivity series, but it is common to use the three types of reaction listed below, many of which can be performed in a high-school laboratory (at least as demonstrations).[4] Reaction with water and acids[edit] The most reactive metals, such as sodium, will react with cold water to produce 467
hydrogen and the metal hydroxide: 2 Na (s) + 2 H2O (l) →2 NaOH (aq) + H2 (g) Metals in the middle of the reactivity series, such as iron, will react with acids such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a metal salt, such as iron(II) sulfate: An iron nail placed in a solution of copper sulfate will quickly change colour as metallic copper is deposited and the iron is converted into iron(II) sulfate: Fe (s) + CuSO4 (aq) → Cu (s) + FeSO4 (aq) Similarly, magnesium can be used to extract titanium from titanium tetrachloride, forming magnesium chloride in the process: 2 Mg (s) + TiCl4 (l) → Ti (s) + 2 MgCl2 (s) However, other factors can come into play, such as in the preparation of metallic potassium by the reduction of potassium chloride with sodium at 850 °C. Although sodium is lower than potassium in the reactivity series, the reaction can proceed because potassium is more volatile, and is distilled off from the mixture. Na (g) + KCl (l) → K (g) + NaCl (l) Comparison with standard electrode potentials[edit] The reactivity series is sometimes quoted in the strict reverse order of standard electrode potentials, when it is also known as the "electrochemical series":
the same as the reverse order of the (gas-phase) ionization energies. This is borne out by the extraction of metallic lithium by the electrolysis of a eutectic mixture of lithium chloride and potassium chloride: lithium metal is formed at the cathode, not potassium.[6] In a reactivity series, the most reactive element is placed at the top and the least reactive element at the bottom. More reactive metals have a greater tendency to lose electrons and form positive ions. A reactivity series of metals could include any elements. For example: 468
A good way to remember the order of a reactivity series of metals is to use the first letter of each one to make up a silly sentence. For example: People Say Little Children Make A Zebra жүктеу/скачать 18,66 Mb. Достарыңызбен бөлісу:
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