CHEM 251 EXAM 1 REVIEW

Chapter 1 – 60 points

Definition of organic compounds-two main elements-why carbon is so important

Organic compounds or organic molecule is a chemical which mainly contains carbon, forming carbon-carbon bonds and carbon-hydrogen.

Carbon is the key for:
-Diversity of compounds possible thanks to forms chaims easily
-Forms 4 covalent bounds, especially other carbom atoms and can form chains of carbom atoms with very strong bonds.
-Stabilitu.
-Is a small atom.

Orbitals – s, p, d – shells/ capacities – electron configurations – core vs valence electrons

An orbital is a region in space where an electron has a high probability of being found.
There are four types of atomic orbitals, s, p, d and f. These atomic orbitals can be different shapes (s is a sphere, p a dumbbell,...). Atomic orbitals are organized in shells; up to two electrons are allowed in any orbital, so the first shell can contain up to two electrons (a duet), the second can contain up to 8 electrons (an octet) and the third shell can contain up to 18 electrons. There are infinite number of shells that are definied by the pricipal quantum number, n.

According to the Pauli´s exclusion priciple, no more than two electrons can occupy a single orbital; two electrons in the same orbital must have opposite spins.
And by Hund´s Rule, electrons in degenerate orbitals are more stable in separate orbitals.

Valence electron ae those occupying the lighest energy shell.
Core electrons occupy the remaining lower energy shells of the atom.

Covalent bond – How it forms – simgle/multiple bonds – Bonds length /strenght (trends)

A covalent bond is one of two types of fundamental bonds in chemistry. Is characterized by the sharing of valence electrons between two or more atoms. When some atoms share two or three pairs of electrons form a double or triple bonds, respectively. Double bonds are shorter and stronger than single bonds, and triple bonds are shorter and stronger than double bonds.

Electronegativyty – Scale/trends in Periodic Table – Polar vs Nonpolar covalent bonds – Bond dipoles – use of partial charges or dipole arrows

When two atoms are bond by a covalent bond and exists a inegual sharing is because they have different electronegativities (ability of an atom to attract electrons).

A polar bond is when atoms have different electronegativities and the most electronegativity attracts more strongly the electrons. Asymmetry occurs in the distribution of charges between the two atoms bonded.
A non polar bond is when atoms have the same electronegativity or the difference is compensated.
Bond dipole is the separation of charges along a bond, resulting a partial charges in a molecule with a positive charge in an extrem and a negative charge in the other extrem.

Ionic bonds – polyatomic ions

A ionic bonds occurs when the difference in