1. Molecular Shapes and VSEPR Model
1.1. Molecular Shape
1.1.1. Determined by the arrangement of its valence shell electron pairs around its central atom
1.1.1.1. The six basic molecular shapes are: Linear Trigonal planar Angular (bent) Tetrahedral Trigonal pyramidal Trigonal bipyramidal
1.2. VSEPR Model
1.2.1. Valence Shell Electron Pair Repulsion (VSEPR) model is a chemistry model that predicts the 3D geometry of molecules and ions based on the number of electron pairs surrounding their central atoms
1.2.1.1. Example: predicts that ammonia (NH3) has a trigonal pyramidal shape, and water (H2O) has a bent shape
2. Bond Strength (Bond Enthalpy) and Multiple Bonds
2.1. Bond Strength
2.1.1. The force that holds atoms or materials together, and is measured by the amount of energy required to break the bond
2.1.1.1. Type of Bond Strength (kcal/mole) Covalent -50 to -100 Ionic approx. -80 or -1 Hydrogen -3 to -6 Van der Waals -0.5 to -1
2.2. Multiple Bonds
2.2.1. A chemical bond where two atoms share more than one pair of electrons
2.2.1.1. Example: Ethylene (C2H4) Nitrogen gas (N2)
3. Hybrid Orbitals and Molecular Orbitals
3.1. Hybrid Orbitals
3.1.1. Orbitals that are created when atomic orbitals mix, or hybridize, to form chemical bonds in molecules
3.1.1.1. Examples: sp hybridization sp2 hybridization sp3 hybridization
3.2. Molecular Orbitals
3.2.1. Spaces around two or more bonded nuclei where electrons with a specific energy are likely to be found
3.2.1.1. Molecular orbitals can have: Antibonding orbitals Bonding orbitals Frontier orbitals Linear combination of atomic orbitals (LCAO) Molecular orbital energy diagram
4. Bond Polarity and Electronegativity
4.1. Bond Polarity
4.1.1. A measure of how electrons are shared between atoms in a bond
4.1.1.1. Factors that affect bond polarity: Relative electronegativity Spatial arrangement Molecular geometry
4.2. Electronegativity
4.2.1. A measure of an atom's tendency to attract shared electrons towards itself when forming a chemical bond
4.2.1.1. Key points about electronegativity: Periodic trend Most electronegative element Impact on bonding
5. Chemical Bonds
5.1. Metallic bonds
5.1.1. Metallic bond is a chemical bond that occurs when metal atoms share valence electrons, creating a "sea of electrons" that holds the metal together
5.2. Hydrogen bonds
5.2.1. Hydrogen bonds are electrostatic forces of attraction that occur between a hydrogen atom and an electronegative atom
5.3. Van der Waals bonds
5.3.1. Very weak intermolecular force that occurs between molecules due to temporary fluctuations in electron distribution, creating temporary dipoles which then induce dipoles in neighboring molecules, resulting in a weak attractive force between them
6. Ionic and Covalent Bonding
6.1. Ionic Bonds
6.1.1. An ionic bond when oppositely charged ions are attracted to each other, forming a neutral compound such as:
6.1.1.1. Sodium chloride: NaCl
6.1.1.2. Magnesium bromide: MgBr2
6.2. Covalent Bonds
6.2.1. covalent bond occurs when atoms share electrons to form molecules, crystals, and other structures ex.:
6.2.1.1. Nonpolar covalent bond Polar covalent bond Single bond Double bond Triple bond
7. Lewis Structures and Resonance Structures
7.1. Lewis Structure
7.1.1. Also known as a Lewis dot structure, is a diagram that shows how atoms are bonded together in a molecule and how valence electrons are arranged around the atoms
7.1.1.1. Drawing Lewis structures: Determine the number of electrons Draw the skeleton structure Add electrons to the outer atoms Count the electrons Add remaining electrons to the central atom
7.2. Resonance Structure
7.2.1. A set of Lewis structures that describe the delocalized electrons in a molecule or polyatomic ion
7.2.1.1. Example: Ozone (O3) is an example of a molecule that uses resonance structures
8. Lewis symbols and Octet Rule
8.1. Lewis Symbol
8.1.1. Diagrams to show how elements chemically bond
8.1.1.1. Lewis Symbol is constructed by placing dots representing electrons in the outer energy around the symbol for the element
8.2. Octet Rule
8.2.1. A chemical rule that states that atoms are most stable when they have eight electrons in their valence shell
8.2.1.1. Octet rule is most applicable to the main group elements in the s-block and p-block of the periodic table, elements such as carbon, nitrogen, oxygen, and the halogens are known to obey the octet rule, with the exception of hydrogen, helium, and lithium.