Announcements: DO NOW Q: Use the Lewis dot diagram to show how hydrogen and chlorine bond covalently.

Review: Octet Rule Most all atoms want 8 electrons in their valence shell to be stable. 2) Ionic bonds are bonds between a (circle one) giver / taker and a giver / taker. 3) What if you had a compound made of “takers” of differing strengths? Hydrogen and Fluorine are both strong “takers”. Diagram what happens when hydrogen and fluorine react.

Polarity of Covalent Bonds •electrons are not always shared equally in a covalent bond •different atoms share more or less equally depending only their electronegativity (an atom’s attraction for electrons) nonpolar bond: a bond in which… the electrons are shared evenly Examples: Oxygen Gas (Electronegativity difference less than 0.4) polar bond: a bond in which… the electrons are shared unevenly Examples: Hydrogen Chloride and Water (Electronegativity difference between 0.5 and 1.9) ionic bond: note that an ionic bond can be thought of as a situation where electrons are shared so unequally that an electron is essentially given/taken Examples: Sodium Chloride (table salt) (Electronegativity difference greater than 2.0)

Polar Molecules If there is an imbalance of charge for the whole molecule, the imbalance leads to a polar molecule.

Polar Molecules Notice that polar bonds in a molecule can give rise to an overall charge of zero for the whole molecule. While there are polar bonds present in the molecule, the molecule itself is non-polar.

Solubility of Polar Molecules ionic compounds dissolve in water and other polar liquids because of attraction between the dipoles and the ions Likewise, polar molecules easily dissolve in water because of the attraction between the dipoles in the polar molecule and water. It looks something like this… (on whiteboard) The general rule of solubility is…”like dissolves like”. Polar compounds will dissolve polar compounds Non-polar compounds will dissolve non-polar compounds

Determining Polarity Polarity of the molecule depends on the polarity of its bonds AND the shape of the molecule (in other words, a molecule that contains polar bonds is not necessarily polar)

Determining Polarity Draw a skeleton structure. A skeleton structure is a rough map showing the arrangements of atoms within a molecule. - Central atom is generally one that is least electronegative - or…central atom(s) is the one you have less of - Hydrogen and halogens are usually outside atoms. Example: Silicon Dioxide (SiO2)

Determining Polarity 2) Count total valence electrons 3) Connect the structure by drawing a bond between the central atom and each outside atom 4) Place electrons around outermost atoms 5) Place remaining electrons around the inner most atom

You try! Ammonia (NH3) Water (H2O)

Using your knowledge of electronegativity, draw dipole vectors between the different bonds in your diagrams above. Do you notice an overall charge in the molecule, or do the dipoles of each bond cancel out? If the dipoles cancel each other out, you have a non-polar molecule.

Exceptions to Octet Rule

Exceptions to Octet Rule or