Advice 1: How to determine electronegativity

Electronegativity is a measure of ability of atom to attract shared e-pairs. It has long been established that if a chemical bond formed by atoms of different elements, the electron density is always biased towards one of them to a greater or lesser extent. The atom to which it is drawn, the electron density in this pair will be considered electronegative and the other, respectively electropositive.
How to determine electronegativity
You will need
  • Periodic Table.
Instruction
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For the determination of the electronegativity, there are a lot of methods. For example, there is the so-called "scale Milliken", named after the American scientist who is considered electronegativity as the average value of the binding energy of the valence electrons.
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There is also a "dial Polling", which got its name by the name of the chemist, which laid the Foundation of the concept of "electronegativity" binding energy during the formation of complex substances from simple starting materials. The magnitude of the electronegativity on this scale range from 0.7 (alkaline metal France) to 4.0 (gas-halogen fluorine).
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In the "timeline Alred-Rahova" the degree of electronegativity depends on the magnitude of the electrostatic force acting on the outer electron.
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How to determine which element is more electronegative, and some less, with only a periodic table? It is very simple. Note the pattern: the higher and to the right of this table is a chemical element, the more electronegative properties it has. Accordingly, the below and to the left is the element, the more electropositive.
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The absolute record for electonically – halogen fluoride. It is so chemically active the element that it has long been the unofficial nickname of "all razrezami". Pauling believed that its electronegativity is 4.0. According to the latest revised data, it is 3.98. Fluorine is slightly inferior to the familiar oxygen – it is approximately equal to the electronegativity of 3.44. Then comes the gas-halogen chlorine. Slightly less electronegative nitrogen. And so on. Most non-metals, the value of the electronegativity is approximately equal to 2 or slightly above. Accordingly, the active alkali and alkaline earth – metals, this value ranges from 0.7 (France) to 1.57 (beryllium).
Useful advice
Remember that the electronegativity of an atom of element is not constant. It depends on many circumstances, for example, the oxidation state, valence.

Advice 2 : How to determine valence electrons

Valence is the ability of an atom interact with other atoms, forming with them a chemical bond. In the creation of the theory of valence has made a great contribution by many scholars, primarily German and von stradonitz our compatriot Butlerov. The electronsthat participate in the formation of a chemical bond are called valence.
How to determine valence electrons
You will need
  • Periodic Table.
Instruction
1
Remember the structure of the atom. He is like our Solar system: in the center there is a massive core ("star"), and around it revolve electrons ("planet"). The size of the nucleus, although it focuses almost the entire mass of the atom is negligible compared to the distance to the electron orbit. Which electrons of an atom it will be easier to interact with electrons of other atoms? It is easy to understand that those who are furthest from the nucleus on the outer electron shell.
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Look in the periodic Table. For example, the third Period. Go consistently for the main group elements. The alkali metal sodium has one outer shell electron, which participates in the formation of the chemical bond. Therefore, it is monovalent.
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Alkaline earth metal magnesium has on the outer shell two electrons, it is bivalent. Amphoteric (i.e., exhibiting in their connections, both major and acidic properties) metal aluminium has three electrons and the same valence.
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Silicon in its tetravalent compounds. Phosphorus can form different numbers of bonds and its higher valence five, such as in a molecule of phosphoric anhydride P2O5.
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Similarly, sulfur can have different valence, the highest is six. Similarly behaves the chlorine in the molecule of hydrochloric acid HCl, for example, it is monovalent and the molecule of perchloric acid HClO4 –pneumococcal.
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So remember the rule: the higher the valence of the elements in the main subgroups equal to the group number and is determined by the number of electrons in the outer level.
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But what if the item is not in the main and side entry? In this case, are also of valence d-electrons of the previous sublevel. In the periodic table for each element is given a complete electronic composition. For example, what is the highest valence of chromium and of manganese? On the external level chromium have 1 electron in the d-sublevel 5. Therefore, the higher the valence is 6, as, for example, in the molecule of chromic anhydride CrO3. And manganese in the d-sublevel 5 electrons, but on the external level -2. Hence, it is of the highest valence – 7.
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You can see that chrome is in the 6th group to manganese in the 7th. Therefore, the above rule also applies to elements of side subgroups. Remember delisting of Cobalt, Nickel, Palladium, Platinum, Rhodium. Iridium.
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