length bond strength bond Triple Covalent Bond Each atom shares pairs ( ) of electrons

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1 CP NT Ch 8 & 9 Covalent Compounds Why do atoms bond? Atoms want to achieve a noble gas configuration ( ) For bonds there is a of electrons to get an octet of electrons For covalent bonds there is a of electrons to get an octet What is a covalent bond? Covalent bond the chemical bond that results from sharing of electrons Occurs with elements to each other on the periodic table Between a nonmetal and a nonmetal Molecule is two or more atoms are bonded Examples of Molecules F 2 H 2 O NH 3 ( ) CH 4 ( ) Notice there are no, only non- metals Diatomic molecules Some atoms do not exist as a atom Atoms that exist as two: H 2, O 2, N 2, Cl 2, Br 2, I 2, F 2 HONClBrIF Magnificent - don t forget H 3 Types of Covalent Bonds: Single, double, triple Strength of Covalent Bond Several factors control bond strength o of shared electrons the electrons shared, the shorter the bond, and the greater the bond strength o of the atoms Single Covalent Bonds Each atom shares one ( ) of electrons bond bond of the three Double Covalent Bonds Each atom shares pairs ( ) of electrons length bond strength bond Triple Covalent Bond Each atom shares pairs ( ) of electrons bond bond Carbon, nitrogen, oxygen, and sulfur can form double and covalent bonds Covalent Molecule Properties Tend to be solids, liquids, or gases at room temperature melting and boiling points conductors of heat and electricity Non- electrolytes do not conduct electricity in water 1

2 Naming Binary Molecular Compounds 3 Rules to Name 1. Name the first element using the name 2. Second element in the formula- use the root word and in ide ex: Oxygen Oxide Sulfur Sulfide Hydrogen 3. Add a prefix to words to indicate the of atoms 1. mono- 6. hexa- 2. di- 7. hepta- 3. tri- 8. octa- 4. tetra- 9. nona- 5. penta- 10. deca- Exceptions to the Rules 1. When the formula contains one atom of the element, omit (leave out) mono ex: CO 2, not Monocarbon Dioxide 2. Drop the final letter in the prefix if the element begins with a - For prefixes 1 & 4-9 ex: CO, not Carbon monooxide Example 1 S 4 N 2 Example 2 SO 3 Example 3 P 4 S 5 Example 4 CO Example 5 NH 3 common name: Example 6 CH 4 common name: Example 7 As 2 O 3 Example 8 N 2 O 5 Example 9 P 4 O 10 5 rules for Lewis Structures Lewis Structures 1. Find the total # of electrons for the molecule 2. Find the center atom (the element with the # of atoms) 3. Draw bonds. Connect the other atoms to the center atom. Then subtract electrons from the total # of valence electrons for each bond drawn. 2

3 4. Distribute electrons around each atom to give a total of electrons except H, Al, B, & Be 5. If there are not enough to give 8 around each atom, create & triple bonds. Example 1: CF 4 Example 2: NH 3 Example 3: H 2 S Ions: With Ions we add or take away. Put ions in and the charge on the outside Example 4: NH 4 + Double Bonds Example 5: CO 2 Triple Bond Example 6: CO Incomplete Octet Example 7: BCl 3 Boron does not have 8e- around it. It is but it is okay; it is one of our exceptions. 3

4 NT: VSEPR- V S E P R Lewis Structures are, whereas VSEPR Molecules are VSEPR predicts the or of the molecule pairs of electrons influence the shape by pushing other atoms as far apart from each other as possible Molecular Shape Molecule Lewis Structure Number of (shared) bonding pairs of electrons H 2 Number of lone pairs of electrons Total Number of electron pairs Molecular Shapes (look at lone & bond pairs) Linear Ball and Stick Model Bond Angle CO 2 Linear BH 3 Trigonal planar SiF 4 Tetrahedral PH 3 Trigonal Pyrimidal SCl 2 Bent 4

5 Electronegativity Electronegativity and Polarity Relative ability of an atom to electrons in a chemical bond has the highest e.n. value. Trend: across (left to right) a period and down a group Types of Covalent bonds Non- polar covalent Polar covalent Non- polar covalent sharing of electrons Polar covalent unequal of electrons Sharing of electrons Usually occurs when two atoms are bonded together. Examples: H 2, O 2, N 2, Cl 2, Br 2, I 2, F 2 sharing of electrons unequal sharing caused by 2 elements with different (different abilities to attract electrons) The bond is called a dipole (two poles) Creates a molecule with charges Partial charges symbolized by (delta) δ + and δ - The electronegative atom is located at the partially negative end Example: δ + δ - H Cl or H Cl Polar molecule or not? The of a molecule usually tells if a molecule is polar or not If the VSEPR shape is it is usually non- polar If the molecule is asymmetric it is 5

6 Name Polar example VSEPR Model Non- polar example VSEPR Model Linear HCl CO 2 Trigonal planar CH 2 O AlH 3 Tetrahedral CH 3 OH CH 4 Trigonal pyramidal (Always polar) Bent (Always polar) NH 3 N/A N/A H 2 O N/A N/A Intermolecular Forces The force that exists between molecules This force attracts molecules to each other 3 Types Dispersion force or induced dipole moment between molecules; only force in molecules; force (caused by the motion of electrons) (Ex: CH 4 ) Dipole- dipole the force between two molecules; force (Ex: HCl) Hydrogen bond forms between the hydrogen end of one dipole and fluorine, oxygen, or nitrogen (that have at least one lone pair) end of another dipole; force (Ex: H 2 O) molecules have dispersion forces All molecules have dipole- dipole forces and dispersion forces Molecules that hydrogen bond have all 3 Solubility of polar molecules are due to intermolecular forces Like dissolves like Polar substances will dissolve molecules (and ionic compounds) substances will dissolve non- polar molecules 6