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SCH3U Chemical Bonding Ionic vs. Covalent Compounds Ms. Yusuf
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Formation of Bonds Chemical Bonds are formed between two atoms using shared valence electrons; this is the force that holds atoms together in compounds. Valence Electrons are the electrons that occupies the outermost energy level of an atom
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Type of Bonds Ionic vs. Covalent Ionic bonding occurs between metals and non-metals Covalent bonding occurs between non-metals Note: Bonding between metals is called Metallic bonding Video Clip: Chemical Bonding
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Octet Rule Most Noble gasses have 8 electrons in their outer shell. This is a stable conformation. Thus, the noble gasses do not react with other elements. In other words, noble gasses are very stable.
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Octet Rule (Continued) When atoms form ions or combine in compounds they obtain electron configurations of the nearest noble gas (eight electrons in their valence shells)
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Ionic Bonding Ionic Bonds are formed from the electrostatic attraction of positive and negative ions An atom that can lose an electron to become a positively charged ion, called a cation An atom can gain electrons to become a negatively charged ion, called an anion In each case, the atom attains a noble gas configuration with its valence electrons. A noble gas configuration is defined as a completely filled outer shell, like the noble gases.
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Ionic Bond: Example (Na and Cl)
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Ionic Bond: Example (Al and O) Al O O O
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Examples of Ionic Bonding using Lewis Structures Magnesium and Fluorine Calcium and Oxygen Potassium and Sulfur
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Covalent Bonding Covalent bonding occurs between two non-metals. Covalent bonding is different from ionic bonding because electrons are shared instead of transferred. Each atom has eight shared electrons
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Covalent Bonding: Example (H and F) H FHF
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Covalent Bonding Using Lewis Structures Silicon Oxygen Hydrogen and chlorine Bromine and Bromine
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Elements will not share the electrons in a bond equally The electronegativity (EN) of an element determines its ability to attract electrons in a bond When elements are bonded together, the more electronegative element attracts the electrons Example: HF Flourine is more electronegative. The electrons in the bond are attracted towards the fluorine atom Polar Bond (Dipole Moment) EN H = 2.1 EN F = 4.0 ∆EN H-F = 4.0 - 2.1 = 1.9
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(Continued) This is not a complete transfer of an electron from hydrogen to fluorine; it is merely a drifting of electrons toward fluorine When a charge separation of this type is present, the molecule possesses an electric dipole, so called “dipole moment” and the bond is called a POLAR COVALENT BOND H : FCl : Polar Covalent Covalent
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Polar Covalent Compound 0.5 < Electronegativity difference < 1.7 This difference is great enough for the bonding electron pair to spend more time near the more electronegative atom than the less electronegative atom.
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(Continued) Example: Water (H 2 O) ∆EN = 1.24 (which is between 0.5 and 1.7) Polar Covalent Bond Oxygen = a slightly negative charge Hydrogen = a slightly positive charge Since the hydrogen does not completely transfer its electron to the oxygen, the their respective charges are indicated as + (the indication of partial positive charge) and - (indication of partial Negative charge). O HH + --
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∆EN 3.3 Comparison of Ionic, Non- polar covalent and Polar covalent bonding 1.70.50 [Na] + [Cl] - H + - Cl - Cl - Cl
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Summary Chemical Bonds are formed between the atoms in molecules The bonds are formed from the valence electrons of the atoms and the resulting bond allows each atom to achieve a noble gas configuration (the most stable arrangement of electrons around the atom: Octet Rule) The types of bonding can be classified as: 1. Covalent (non-metal bondin; 0<∆EN<0.5) 2. Polar covalent bonds (non-metal bonding with a dipole moment; 0.5<∆EN<1.7) 3. Ionic (metals + non-metals; 1.7 <∆EN< 3.3)
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Questions Complete the chart: Identify each compounds as ionic or covalent: CCl 4,HCI, MgF 2, H 2 O,NH 3, NaCl, OH, H 2 Show how the bond forms between Li+Cl, Mg +O (Follow the Octet Rule) as well as Li + O
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