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Covalent Bonding. Covalent Bonds. Occur when atoms of relatively similar EN share electrons. Not good conductors. Solids tend to have low melting points. Generally liquid or gas at room temperature Form molecular substances whose shapes can be predicted using VSEPR.
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Covalent Bonds • Occur when atoms of relatively similar EN share electrons. • Not good conductors. • Solids tend to have low melting points. • Generally liquid or gas at room temperature • Form molecular substances whose shapes can be predicted using VSEPR.
Naming Molecular Compounds Unlike ionic compounds, molecules are named by using prefixes to state the exact number of each atom in the compound. 1= mono 2= di 3= tri 4= tetra 5= penta 6= hexa 7= octa 9 = nona 10 = deca
Name the following compounds: NF3 PCl5 Cl2O7 Write the following formulas: Diboron hexahydride Nitrogen triiodide Carbon disulfide
Formation of Covalent Bonds • Covalent bonds complete the valence shell of nonmetals. • Point of maximum attraction of nuclei for electrons. • Single bonds are the result of sharing two electrons.
Sigma Bonds • Single covalent bonds are sigma bonds. • Result from the overlap of an s-s, s-p, or p-p orbital. • σ
Multiple Bonds • Many molecules need to share more than one pair of electrons to form an octet. • Pi bonds result from the sideways overlap of p orbitals • π
Strengths of Covalent Bonds • As the number of shared pairs increases, bond length decreases. • Triple bonds are the shortest. • Energy needed to break bonds is called dissociation energy. Breaking bonds requires energy to be added. • Higher the bond energy, stronger the bond
Lewis Structures • Used to represent the physical arrangement of atoms in a molecule. • Based on a central atom with enough bonds to complete the octet of each atom.
Draw Lewis structures for the following molecules: CO32- CH2F2 NO3- H3PO4 H2Se
VSEPR • Valence Shell Electron Pair Repulsion Theory • Way to determine shape of molecules in three dimensions. • Shapes will minimize electron pair repulsion. • VSEPR ShapesTable
VSEPR Shapes Draw a table in your notebook with the following column headings: VSEPR Structure Atoms around Lone Ex. shape Central atom Pairs
Draw the Lewis structure and predict the VSEPR shape of each of the following: H2S CO32- PCl3 SiH4 SeBr6
Polar Molecules • Molecules are considered polar when they have polar bonds and there is an uneven distribution of charge. • The polarity of a molecule can be determined by looking at the central atom. • If the molecule has lone pairs on the central atom or it is not symmetric, the molecule is polar.
Determine the polarity of the following molecules: H2S CO32- CCl4 PF3