1. Atoms are the smallest units of chemical elements that enter into chemical reactions. ATOM

2. Hidrogênio Núcleo contem 1 próton 1 elétron em órbita ao redor do núcleo Carbono Núcleo contem 6 prótons 6 nêutrons 6 elétrons em órbita ao redor do núcleo Nêutron Elétron Próton (Carga Positiva)(Sem carga) (Carga negativa)

4. Although the forces holding atoms together to form molecules are electrostatic the application of classical electrostatics to the hydrogen atom failed to predict any of its properties.Although the forces holding atoms together to form molecules are electrostatic the application of classical electrostatics to the hydrogen atom failed to predict any of its properties. The failure of classical electrostatic theory to describe the bonding in simple molecules led to the development of a new theory:The failure of classical electrostatic theory to describe the bonding in simple molecules led to the development of a new theory:

5. ATOMIC ORBITALS The atomic orbitals s, p, d, and f are solutions to the wave function.The atomic orbitals s, p, d, and f are solutions to the wave function. Any linear combination of s, p, d, and f are also solutions to the wave function.Any linear combination of s, p, d, and f are also solutions to the wave function. Schrödinger equation Ĥ  = E  Ĥ is the Hamiltonian operator.  is the wave function. E is the energy.

6. ATOMIC ORBITALS In the ground state, the lowest energy orbitals fill first. Each orbital holds two electrons of opposite spin. First period elements have 1s orbitals. Second period elements have 1s and 2s orbitals, and usually have 2p orbitals.

7. ATOMIC ORBITALS An atomic orbital is an electron cloud describing the probability of the position of electrons. Basically, an electron can be found within the range of an atomic orbital’s shape at any point in time. This, however, does not determine the exact position of an electron because it is constantly moving.

8. ATOMIC ORBITALS

9. HYBRID ORBITALS sp 1 s orbital + 1 p orbital sp2 1 s orbital + 2 p orbitals sp3 1 s orbital + 3 p orbitals Combination of atomic orbital wavefunctions generates a new set of orbitals, Hybrid Orbitals, that better represent the bonding properties observed.

10. Valence Electrons VALENCE ELECTRONS = electrons in the outermost shell (valence shell). The NUMBER of valence electrons determines the atom’s chemical properties. The OCTET RULE –Atoms attempt to acquire an outer orbital with eight electrons through chemical reactions. –This gives them an outer shell configuration like their nearest noble gas and therefore they become stable. ATOMIC ORBITALS Carbon valence: 4 C Hydrogen valence: 1 H Oxygen valence: 2 O Nitrogen valence: 3 N

11. Electrons in atoms exist in atomic orbitals. Electrons in molecules exist in molecular orbitals. Using Schrödinger equation, we can calculate the shapes and energies of the molecular orbitals. MOLECULAR ORBITALS

12. The overlapping of atomic orbitals gives rise to the formation of covalent bonds and involves a change in electronic configuration. One standard quantum mechanical theory of bond formation uses a linear combination of atomic orbitals (LCAO), in which the atomic orbital wavefunctions are mathematically combined to form molecular orbitals. For stable bonds in the ground state, the energy levels of the occupied molecular orbitals are lower than those of the original atomic orbitals. MOLECULAR ORBITALS

13. Overlap of hybrid atomic orbitals can form two types of bonds, depending on the geometry of the overlap.  bonds (strong) are formed by “direct” overlap.  bonds (weak) are formed by “parallel” overlay. MOLECULAR ORBITALS

14.  bonds Overlapping s orbitals / Overlapping s and p orbitals / Overlapping px orbitals

15. MOLECULAR ORBITALS  bonds Overlapping p orbitals,

16. MOLECULAR ORBITALS  bonds

17. The mixing of n atomic orbitals always generates n molecular orbitals. Two 1s atomic orbitals combine to give a sigma (s) bonding (low energy) molecular orbital and a second higher energy MO referred to as an antibonding orbital. Antibonding molecular orbital is a molecular orbital where electron density is concentrated outside the region between the two nuclei. There are two electrons in the bonding molecular orbital and no electrons in the antibonding molecular orbital. MOLECULAR ORBITALS

19. Non-bonding electrons reside in non- bonding molecular orbitals (n). Any two atoms may only form one  bond. Multiple bonds are made up of one  and one or more  bonds.

20. CC bondBond typeBond length Bond energy (kcal/mol) C-Csp 3 -sp 3 1.54 Å88 C=C sp 2 -sp 2 and one p-p 1.34 Å144 C=CC=C sp - sp and two p-p 1.21 Å198 BOND STRENGTH increasing s-character

21. MOLECULAR ORBITAL ARRAY FOR MOLECULES WITH NON-BONDED ELECTRONS (n electrons) 0     n BONDENERGYBONDENERGY There is no such thing as an n* orbital

22. The dipole moment is a measure of the degree of charge separation in a molecule. We can view the polarity of individual bonds within a molecule as vector quantities. Thus, molecules that are perfectly symmetric have a zero dipole moment. These molecules are considered nonpolar. Dipole Moment and Molecular Geometry

24. RESONANCE If you can draw more than one (correct) Lewis structure for a molecule, it is likely that the actual molecule will look more like an average of the different structures. O N O O + __ O N O O + _ _ O N O O + _ _ + O N O O -2/3 The contributing structures do not exist! They are plausible arrangements which, taken together, represent reality.

25. RESONANCE Resonant structures have extra stability. Properties are averaged over the resonance forms. Example: bond length C C single bond 1.54 Å C C double bond 1.34 Å C C aromatic bond1.40 Å