IB SL Chemistry Unit 4

University:
Kentucky State University
Course:
CHE 101 | General Chemistry I
Academic year:

2023
Views:

88

Pages:

4
Author:

Nesbyenvkk

UNIT FOUR ● Bonding ○ Ionic Bonding 1. Occurs between metals and nonmetals 2. In order to be ionic, the difference in electronegativity between the two elements must be greater than 1.8 3. Formed by a lattice structure of the elements 4. Non Directional bonding- the attraction forces go all ways 5. Coordination numbers- amount of ions that one element is touching. For example in Sodium Chloride’s lattice structure, a sodium ion touches 6 chloride ions, so its coordination number is 6. ○ Covalent bonding 1. Occurs between two nonmetals 2. For covalent bonding to occur, electronegativity is less than 1.8 ○ Coordinate Covalent Bond Different from a normal covalent bond, has an arrow to show the movement of electrons from one ion to the other. ● Lewis Structures ○ A method to visualize the interactions between 2 or more atoms. ○ Helps to visualize bonding electrons ○ There are pi and sigma bonds. Sigma bonds are single bonds, a pi bond is any bond attached. ■ For example, a double bond is made of one sigma and one pi bond. ■ A triple bond is one sigma and two pi bonds. ○ Octet Rule- Most elements want 8 electrons bonded to it ○ Duet rule- Hydrogen and Helium share two electrons ○ Incomplete Octet Rule- Boron and Beryllium don't need 8 electrons. Boron needs 6, Beryllium needs 4. ○ Some atoms have an expanded octet. Phosphorus, Sulfur, Arsenic can all have more than 8 electrons. ○ Resonance Structures ■ Different ways to draw the same molecule ■ It looks like Ozone has two different possible structures. ■ That’s not the case. Resonance works in a hybrid resonance. That means the bonds in ozone are a cross between the two. Both Oxygens share the double bond. Neither one actually has it. ● VSEPR Theory ○ Theory that allows us to assume the shape of a molecule based on its regions of bonding and lone pair electrons. ● Giant Covalent Structures/ Allotropes of Carbon- Specific IB example ○ Diamond ■ Hard tetrahedral shape of carbons bonded together. Poor conductor ○ Silicon dioxide ■ Tetrahedral shape, strong bonds ○ Graphite ■ Soft, good conductor, weak intermolecular forces that slide over each other. ○ Fullerene ■ Soccer ball shape ○ Graphene ■ 1000x better tensile strength than steel ■ Peels off in layers ■ Conducts electricity ● Intermolecular forces ○ Bonds between different molecules. ○ Nonpolar molecules are generally symmetrical ○ Larger mass usually makes a molecule more polar ○ London Dispersion Force ■ Weakest force ■ Consists of induced and instantaneous dipole ● Instantaneous ○ Molecule has weak polarity that causes dipoles ● Induced ○ Molecules create dipoles when near other more polar molecules that pull charges to one side. ■ Larger molecules have stronger london dispersion forces ○ Dipole-Dipole ■ Between two permanent dipoles. Both molecules have to be polar. ■ Hydrogen is the positive dipole, chloride is negative dipole. ■ Second strongest dipole force ○ Hydrogen Bonding ■ Hydrogen bonds between Fluorine, Nitrogen, and Oxygen make strongest covalent intermolecular forces. ■ Mnemonic to remember easily- Hydrogen just wants to have FON. ■ These hydrogen bonds will increase polarizability, boiling and melting point. ■ They are responsible for the unique shape of water in its ice form.