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Transcript
Chapter 6 section 2 • Covalent bonding • Molecular compounds A molecule is a neutral group of atoms that are held together by a covalent bond • A molecular compound is a chemical compound whose simplest units are molecules • A molecular formula show the types and numbers of atoms combined in a single molecule of a molecular compound. • A chemical formula indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. Two H atoms bond with one O atom to form H2O • if we look at the difference in electronegativity, we see that • • • • H is 2.1 and O is 3.5. 3.5 – 2.1 = 1.4 so the bond between H and O is a polar covalent bond. By definition a neutral group of atoms held together by covalent bonds is a molecule. So, the H2O particle is a molecule H2O is a molecule which makes H2O a molecular compound and a molecular formula. But H2O is also a chemical formula because we use atomic symbols and subscripts to describe it. Diatomic molecule • A diatomic molecule is a molecule containing only two atoms of the same element. • There are seven elements that exist as diatomic molecules in nature • Ex: H2 N2 O2 F2 Cl2 I2 Br2 Formation of a covalent bond Bond energy is the energy required to break a chemical bond and form neutral isolated atoms. Octet rule • Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet (8) of electrons in it’s highest energy level. Electron dot notation • On board Lewis Structure • On board Multiple covalent bonds • On board Resonance Structures Resonance Structures • Resonance structures refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure Resonance Structures • For example: NH3 – ammonia has only one correct structure • .. • N • H H H Resonance Structures • But some structures have more than one Lewis Structure; • O3 - Ozone •O O O or O O O Resonance Structures
