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IV. Chemical Bonding

IV. Chemical Bonding

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IV. Chemical Bonding

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  1. IV. Chemical Bonding

  2. Dots represent valence electrons.Everything else (inner shell electrons and nucleus) is called the Kernel and is represented by the symbol. Phosphorous has 5 valence electrons so we draw 5 dots around the symbol for phosphorous.

  3. The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. 1 2 Ne 3 5 8 6 4 7 It does not matter which side you start from.

  4. The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. 5 8 Ne 1 7 4 2 6 3 This will let you know how many electron pairs and how many unpaired electrons are in the atom’s valence shell

  5. Draw the Lewis Dot Structures of the first 18 elements.

  6. What is a chemical bond? When an atom gains, loses or shares electrons to complete their outer shell (octet)

  7. Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond.

  8. Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetals to form molecular (covalent) compounds. Ionic compounds containing polyatomic ions have both ionic and covalent bonding.

  9. Ionic compounds are formed when a metal combines with a nonmetal. Ionic compounds have ionic bonds. Molecular compounds are formed between two or more nonmetals. Molecular compounds have covalent bonds. Two major categories of compounds are ionic and molecular (covalent) compounds.

  10. Chemical bonds are formed when valence electrons are : • Ionic: transferred of electrons from a metal to a non metal • Covalent: shared between two or more non metals • Metallic: mobile electrons within a metal

  11. Polyatomic ions are groups of atoms covalently bonded together that have a negative or positive charge.

  12. Polyatomic ions are held together by covalent bonds but form ionic bonds with other ions. + Ionic bond H - Covalent bonds H N H Cl H

  13. The bonds holding metals together in their crystal lattice are called metallic bonds. • All metals have metallic bonds • “Positive ions immersed in a sea of mobile electrons” • Bonds are between Kernels, leaving the valence electrons free to move from atom to atom • Mobile electrons give metals the ability to conduct electricity

  14. When metals lose electrons to form ions, they lose all their valence electrons. The Lewis Dot Structure of a metal ion has no dots. The charge indicates how many electrons were lost. Magnesium atom Magnesium ion

  15. When nonmetals gain electrons, they fill up their valence shell with a complete octet (except hydrogen.) The ion is placed in brackets with the charge outside the brackets.

  16. When a bond is formed, energy is released. Energy is needed to break a bond

  17. What is the octet rule? The desire for eight valence electrons in the outer shell

  18. Regents Question: 06/02 #3 Which compound contains ionic bonds? • NO • NO2 • CaO (4) CO2 Nitrogen – nonmetal Oxygen – nonmetal Calcium – metal Carbon – nonmetal þ

  19. Regents Question: 08/02 #11 Which formula represents an ionic compound? (1) NaCl (2) N2O (3) HCl (4 )H2O þ

  20. What type of bonding would sodium and chlorine have? How do you know? IONIC • Sodium is a metal and chlorine is a non metal

  21. Compounds with Ionic bonds have the following properties. - Solids with high melting and boiling points (strong attraction between ions) • Crystalline solids that form regular geometric patterns • Hard • Electrolytes: able to conduct electricity Do not conduct electricity as solids but do when dissolved or molten – ions are charged particles that are free to move

  22. Ionic solids conduct electricity when dissolved or molten. Molecular solids do not. Solution doesn’t conduct electricity Solution conducts electricity Ionic Solid dissolved in water Molecular Solid dissolved in water

  23. Electronegativity values are assigned according to arbitrary scales. (5.2j) Fluorine is assigned the value 4.0 – the highest of any element Nonmetals have high electronegativity – they want to attract electrons so they can fill their valence shell Metals have low electronegativity – they want to lose electrons to get rid of their valence shell

  24. Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond.

  25. Sodium has one valence electron and chlorine has seven. Sodium want to lose 1 electron and chlorine needs to gain 1. Sodium transfers its valence electron to chlorine Forming an Na+ and a Cl- ion – sodium chloride NaCl Ionic bonds are formed when metals transfer their valence electrons to nonmetals.The oppositely charged ions attract each other to form an ionic bond.

  26. A + metal ion is attracted to a – nonmetal ion (opposites attract) forming an ionic compound. We can use Lewis dot structures to represent ionic compounds. The formula for magnesium fluoride is MgF2

  27. Additional atoms may be necessary to insure that all the ions formed have a stable (noble gas) electron configuration. What happens when aluminum combines with oxygen to make aluminum oxide?

  28. Aluminum want to lose its 3 valence electrons. Oxygen needs to gain 2 electrons. The number of electrons lost by the metal must equal the number of electrons gained by the nonmetal

  29. The formula of aluminum oxide is Al2O3.

  30. Regents Question: 06/02 #51-53 Draw the electron-dot (Lewis) structure of an atom of calcium. Draw the electron-dot (Lewis) structure of an atom of chlorine. Draw the electron-dot (Lewis) structure of calcium chloride.

  31. Covalent bonds can be divided into two categories molecular and network

  32. Properties of molecular compounds • Low melting and boiling points (weak attraction between molecules) • Nonelectrolytes: Do not conduct electricity as solids or when dissolved or molten – no charged particles (ions) to move • Solids are soft • Examples: Wax and sugar C6 H12 O6

  33. Network solids • High melting and boiling points • Hard • Non electrolytes • Examples: sand SiO2 and diamond (carbon compound)

  34. The stronger the intermolecular forces, the higher the boiling points and melting points. Strongest Weakest • Ionic Solids • Molecules with Hydrogen bonds • Polar molecules • Nonpolar molecules For nonpolar molecules, the greater the mass, the greater the force of attraction.

  35. Regents Question: 08/02 #33 The table below shows the normal boiling point of four compounds. Compound Normal Boiling Point (°C) HF (l) 19.4 CH3Cl (l) –24.2 CH3F (l) –78.6 HCl (l) –83.7 Which compound has the strongest intermolecular forces? (1) HF(l) (2) CH3Cl(l) (3)CH3F(l) (4)HCl(l) þ

  36. When nonmetals combine with nonmetals, they share electrons.The attraction of two atoms for a shared pair makes a covalent bond. • Electrons are always shared in pairs. • Sharing electrons fills the valence shell with 8 electrons (2 for hydrogen.) Hydrogen chloride water ammonia methane

  37. Regents Question: 06/02 #61-63 Testing of an unknown solid shows that it has the properties listed below. (1) low melting point (2) nearly insoluble in water (3) nonconductor of electricity (4) relatively soft solid State the type of bonding that would be expected in the particles of this substance. Explain in terms of attractions between particles why the unknown solid has a low melting point. Explain why the particles of this substance are nonconductors of electricity. Covalent The attraction between particles is weak because there are no charged particle. Molecular substances are non-electrolytes – they do not form ions.

  38. Regents Question: 01/03 #35 Which of the following solids has the highest melting point? (1) H2O(s) (2) Na2O(s) (3) SO2 (s) (4) CO2 (s) þ

  39. Regents Question: 08/02 #53 Draw an electron-dot diagram for each of the following substances: A calcium oxide (an ionic compound) B hydrogen bromide C carbon dioxide

  40. Regents Question: 06/03 #12 Which type of chemical bond is formed between two atoms of bromine? • Metallic (2) Hydrogen (3) ionic (4) covalent þ

  41. In a multiple covalent bond, more than one pair of electrons are shared between two atoms. (5.2e) • Diatomic oxygen has a double bond O=O (2 shared pairs) because oxygen needs 2 electrons to fill its valence shell • Diatomic nitrogen has a triple bond NN (3 shared pairs) because nitrogen needs 3 electrons to fill its valence shell • Carbon dioxide has two double bonds

  42. Regents Question: 08/02 #17 Which molecule contains a triple covalent bond? (1) H 2 (2) N 2 (3) O 2 (4) Cl 2 þ

  43. The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond. (5.2k) • Polar covalent bonds form between two different nonmetals • Polar bonds have a negative side and a positive side • The electrons are attracted more to the atom with the higher electronegativity. • The atom with the higher electronegativity is the negative side of the bond.

  44. Symmetrical (nonpolar) molecules include CO2 , CH4 , and diatomic elements. .. Symmetrical molecules are not dipoles.

  45. Asymmetrical (polar) molecules include HCl, NH3 , and H2 O. (5.2l) The negative side of the molecule is the side that has the atom with the higher electronegativity.

  46. Three types of bonds Ionic bonds– transfer of electrons- occur between a metal and a nonmetal Polar bonds– unequal sharing- occur between two different nonmetals Nonpolar bonds– equal sharing- occur between two of the same nonmetals

  47. Molecular polarity can be determined by the shape of the molecule and the distribution of charge. • Possible shapes • Linear (X2 HX CO2) • Bent (H2O) • Pyramidal (NH3) • Tetrahedral (CH4 CCl4) A polar molecule is called a dipole. It has a positive side and a negative side – uneven charge distribution.

  48. Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point. (5.2n)

  49. Regents Question: 01/03 #10 The strength of an atom’s attraction for the electrons in a chemical bond is the atom’s (1) electronegativity (2) ionization energy (3) heat of reaction (4) heat of formation þ

  50. Regents Question: 06/03 #13 Which of these formulas contains the most polar bond? (1) H–Br (2) H–Cl (3) H–F (4) H–I þ