Chemistry (Covalent Bonds and more)

• The electronegativity difference between two atoms determines the polarity of a bond.
• Covalent bonds form when atoms share valence electrons.
• A molecule is a neutral group of atoms joined together by covalent bonds.
• An oxygen molecule is an example of a diatomic molecule - a molecule that contains two atoms.
• The octet rule also applies for covalent compounds. Each atoms wants to be stable when forming a compound.
• A covalent compound is always going to contain non-metals.
• A single bond is a sharing of two electrons.
• A double bond is a sharing of 4 electrons.
• A triple bond is a sharing of 6 electrons.
• Single, double, and triple bonds are all covalent.
• A structural formula represents the covalent bonds as dashes and shows the arrangement of covalent bonded atoms.
• Lone pairs is a pair of electrons that are not shared between atoms (Also called unshared or nonbinding pairs).
• A polyatomic ion is a tightly bound group of atoms that have a positive and negative charge and behaves as a unit.

  Polyatomic ions are covalently bounded.
• Electronegativity is the ability of an atom to steal electrons from another atom.
• Polarity is the uneven distribution of positive and negative charges in a bond or a molecule.
• Electrons are closer to the atom with higher electongativity.
• Differences that are greater than 2.0 are ionic
• Differences less than 0.4 are generally nonpolar covalent.
• Differences between 2.0 and 0.4 are typically polar covalent.
• Dipole moment is the direction of the Polar bond in a molecule.
• For a molecule to be polar, the molecule must contain at least one polar covalent bond and they must be asymmetrical.
• Nonpolar molecules either have no dipole moment or the dipole moments are symmetrical and cancel out.
• Polar molecules have dipole moments that are asymmetrical and don’t cancel out.
• Polar molecules have asymmetrical shape (lone pairs) and asymmetrical bonds, while non-polar molecules have symmetrical shape and symmetrical bonds
• Intermolecular Forces are attractions between molecules

  • molecules can be attached to each other by a variety of different forces
  • These forces are weaker than either ironic or covalent bonds
• what are the three types of Intermolecular forces?

  hydrogen bonds, Dipole interactions, and dispersion forces
• Dipole interactions and dispersion forces are Van der Waals forces.
• Hydrogen bond is when a hydrogen covalently is bonded to a very electronegative atom (O, N, or F) is attracted to a loan pair of electrons of another atom.
• A hydrogen bonding always involves hydrogen not always water
• Hydrogen bonds are about 5% of the strength of the average covalent bond (strongest of the three forces)
• Dipole interactions occur when polar molecules are attracted to one another.

  • The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.
• Dispersion forces are also known as London forces.
• Dispersion forces are the weakest of all molecular interactions, and they occur even between nonpolar molecules.

  • Electrons are always moving so sometimes there are more on one side of a molecule than the other results and temporary change in electronegative difference.
• The more electrons, the stronger, the attractive dispersion force is.
• Some molecules with an even number of valence electrons, such as some compounds of boron, form compounds with less than an octet.

  • A few atoms, especially phosphorus and sulfur, expand the octet to 10 or 12 electrons
• Molecular geometry refers to the arrangement of atoms around a central atom in a molecule.
• VSEPR model predicts the shape of a molecule based on its Lewis structure.
• The energy required to break the bond between two covalently. Bonded atoms is called bond dissociation energies

  • It is expressed in KJ/Mol

  Ex: the covalent bond in H2 is so strong that it would take 435 KJ energy to break apart all of the bonds in one mole of H2
• Resonance structures are structures that occur when it is possible to draw two or more valid electron dot structures for a molecule or ion.
• VSEPR is a theory that molecular geometry is controlled by the fact that electrons around the central atoms (both bonds and lone pairs)

  repel each other.

  • work as a team