Section_2.1_Structure_of_Atom_post

Section_2.1_Structure_of_Atom_post - Structure of...

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Sec. 2.1 - Atoms and Molecules 1 Lewis structure of the first 18 elements The Formation of Chemical Bonds The “noble” gases, He, Ne, Ar, Kr, Xe, and Ra, are almost inert chemically. The number of electrons for the noble gasses are; 2 for helium, 10 for neon (2+8), 18 for argon (2+8+8), and so on. They are described as having “filled shells” or having filled outer octets. Other elements can achieve such stable electronic configurations by gaining or losing electrons. The driving force behind atoms combining with each other is the tendency for atoms to gain, lose, or share electrons so as to fill their outermost electronic energy levels . For example NaCl. Cl + - Na + [Ne] full outer shell (stable) [Ne] 3s 2 3p 6 full outer shell (stable) - Structure of Atoms (Chem 120 Review)
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Sec. 2.1 - Atoms and Molecules 2 Trends in the Periodic Table Li 1s 2 2s 1 the electron in the 2s orbital is shielded by the two electrons in the 1s 2 orbital. The 2s electron feels +1 rather than the full +3 charge from the nucleus. B 1s 2 2s 2 2p 1 The two electrons in the lower energy level shield the effective nuclear charge of 2 protons in nucleus. Therefore the second energy level feels a +3 charge. C Æ +4 N Æ +5 O Æ +6 F Æ +7 decreasing atomic radii electrons in the second energy level are pulled in closer to the nucleus by the increasing number of protons or by the effective nuclear charge Atomic Radii
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Sec. 2.1 - Atoms and Molecules 3 Ionization Energy Minimum energy required to remove the most loosely bound electron from an isolated gaseous atom to form an ion with a positive charge. The lower the ionization energy the easier it is to remove an electron. Li Li + + e¯ 1s 2 2s 1 Æ 1s 2 same configuration of He As you go down the periodic table the force of attraction by the nucleus decreases because the electrons are farther from the nucleus and the influence of the protons on the outer shell electrons decreases Increases from left to right because atomic radius decreases, effective nuclear charge increases thus electrons are held more tightly and makes it harder to remove an electron. Ionization Energy increases increases
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Sec. 2.1 - Atoms and Molecules 4 Electronegativity Understanding electronegativity is the first step in the understanding organic reactions and bonding Measure of the tendency for an atom in a molecule to attract a pair of electrons. Electronegativity increases increases The greater the number of protons the greater the nuclear charge. Increasing attraction for valence electrons Attraction between oppositely charged particles increases with decreasing distance Li Be B C N O F Tendency to accept electrons Tendency to lose electrons A) electronegativity increases from left to right B) electronegativity increases from right to left Text: Mole-1
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Sec. 2.1 - Atoms and Molecules 5 Electronegativities of Common Elements
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Section_2.1_Structure_of_Atom_post - Structure of...

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