Unit+One

=A Crash Course in Chemistry=

By: Anne Clayton
In this lesson basic chemistry concepts from grade ten science and grade eleven chemistry were reviewed, such as bonds, polarity, and intermolecular forces.

Intramolecular Forces
- atoms bond in order to have the same number of electrons in their outer valence shell as the closest noble gas. - **ionic bonds** form between a metal and a non metal
 * the metal gives electrons to the non-metal
 * the metal becomes a positively charged **cation**, the non-metal a negatively charged **anion**
 * - covalent bonds** form between two non metals
 * the electrons are not transferred as in an ionic bond - they are shared
 * a **pure** covalent bond occurs when the sharing is completely equal and the two atoms have the same electronegativity value (such as two C atoms)
 * a **polar** covalent bond occurs when there is an unequal sharing of the electrons and the atoms have a different electronegativity value
 * in a polar covalent bond the atom with the higher electronegativity has a slight negative charge and the atom with the lower electronegativity has a slight positive charge.

Polar Molecules
- a molecule that contains polar bonds may or may not be overall polar - in a polar molecule charges are unevenly distributed - polar bonds and asymmetry in the molecule must be present - if the molecule is symmetrical, the charges are cancelled out and the molecule is overall non polar.

Intermolecular Forces
- are the forces of attraction between molecules - weaker than intramolecular forces - physical changes break or weaken these forces - physical properties of a substance are determined by intermolecular forces - **London Dispersion Forces** are based on the simultaneous attraction of the electrons of one molecule and the positive nuclei of neighbouring molecules - **Dipole-dipole** forces occur between polar molecules and are based on the simultaneous attraction of the positive end of one molecule to the negative end of another - **Hydrogen Bonds** are a special type of dipole dipole force that occur between molecules with hydrogen bonded to nitrogen (N), oxygen (O) or fluorine (F)
 * exist in ALL molecules
 * strength is related to the number of electrons and protons in each molecule
 * Are extremely strong due to the immense electronegativity difference between H and the most electronegative elements
 * For a substance to be able to dissolve in water, it must have the ability to hydrogen bond.

[|Here] is a video that talks about molecular polarity in depth. MAKE SURE YOU WATCH IT WITH THE ANNOTATIONS ON!