Chemical Bonds

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1. Each element has a different number of electrons

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2. Electrons move around the nucleus in levels of energy.

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5. 3. Energy levels of electrons depend on the distance from the nucleus a.         a.   The closer, the less energy Th b. The farther away, the more energy

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4. There is a limited number of electrons for each energy level or they repel each other

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5. Electrons per energy level Level 1 = 2 e- Level 2 = 8 e- Level 3 = 18 e- Level 4 = 32 e- (use formula 2n2 where n = Energy level, and e- = electrons)

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6. The Octet Rule: Atoms will gain, lose or share electrons until they have 8 in the outer shell www.micromountain.com

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7. Electron dot diagram: the chemical symbol for an element with dots representing the outer electrons

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8. To write an electron dot diagram you need to know the group number Example: Phosphorus (group 15, so 5 e-)

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Outer energy shell electrons (Valence electrons)

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119. If atoms don’t have all their outer energy level electrons, they form chemical bonds by either: a.        A. Sharing them (covalent bond)

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B. Sharing more than 1 pair of electrons 1. Double bond = 2 pairs of electrons 2. Triple bond = 3 pairs of electrons

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10. Atoms sometimes don’t share equally and become POLAR molecules + -

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11. Or by B. Losing electrons to other atoms or gaining electrons from other atoms (ionic bonding)

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Ionic Bond

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Na Cl

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Na Cl

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Na Cl + -

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Na Cl

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Comparing Ionic and Covalent bonds

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13. Metallic Bond: type of bond in which electrons move among nuclei

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14. Properties of metal due to metallic bonding: a. Conduct electricity well b. Conduct heat well c. Easy to shape

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15. Properties may also depend on structure of bonds

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16.Chemical formula: a combination of chemical symbols of the elements present and how many atoms of each there are   a. Symbols are used for elements, compounds and molecules. b. Subscripts tell the number of atoms in a chemical formula c. Coefficients tell number of molecules Example: H2O (one water molecule) 2 hydrogens,1 oxygen   2H2O (two water molecules) 4 hydrogens, 2 oxygens

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17. Chemical bond: a force that holds two or more atoms together