POLARITY & FORCES ELECTRONEGATIVITY

 Electron Affinity – a measure of the tendency of an atom to accept an electron  Increases across a period  Decreases down a group  This is why your halogens create anions – they have high electron affinities!

 Electronegativity – measure of the tendency of an atom to attract electrons when in a compound and sharing electrons  Increases across a period  Decreases down a group  Most electronegative = F BOND CHARACTER  A chemical bond is never completely ionic or covalent Electronegativity Bond Character  Bond character depends on how strongly the Difference bonded atoms attract electrons > 1.7 Mostly Ionic  Use electronegativity difference between 0.4 – 1.7 Polar Covalent two atoms to determine the type of bond/ bond character < 0.4 Mostly Covalent

Nonpolar  The greater the electronegativity 0 Covalent difference, the greater the percentage of ionic character! BOND CHARACTER

Electronegativity Bond Character Difference

> 1.7 Mostly Ionic

0.4 – 1.7 Polar Covalent

< 0.4 Mostly Covalent

0 Nonpolar Covalent NONPOLAR COVALENT BOND

 Nonpolar covalent bond - nuclei of atoms pull on electrons equally; bonding electrons are shared equally.

 H2, N2, O2, Cl2  No difference in the electronegativity between the atoms. POLAR COVALENT BONDS

 Polar covalent bond - nuclei of atoms pull on electrons unequally  The electrons are shared unequally.

 The more electronegative the atom, the stronger they pull on the electrons and take a partial negative charge.  The less electronegative atom will have a partial positive charge. POLAR COVALENT BONDS POLARITY OF MOLECULES

 Polarity of a molecule depends on the individual bonds and the shape of the overall molecule.

 If the polar bonds are symmetrical, the polarity cancels out and the overall molecule is nonpolar.

 If the polar bonds are asymmetric, the polarity persists in the molecule. INTRAMOLECULAR FORCES

 Intramolecular Forces – attractive forces that hold particles together in ionic, covalent and metallic bonds  Intra – within

 Metallic bond – Strongest  Ionic Bond – 2nd Strongest  Covalent Bonds  Polar Covalent Bond– 3rd strongest  Nonpolar Covalent Bond– 4th strongest INTERMOLECULAR FORCES

 Intermolecular - attractive forces between molecules  Inter – between

 All intermolecular forces are weaker than intramolecular forces

 Dispersion  Dipole-dipole  Hydrogen bonds INTERMOLECULAR FORCES

 Dispersion Forces – weak forces that result from temporary shifts in the density of electrons in electron clouds  Larger molecules experience larger dispersion forces

 Dipole-dipole – attractions between oppositely charged regions of polar molecules

 Hydrogen Bonds – dipole-dipole attraction between molecules with a H bonded to a small, electronegative atom that has one lone electron pair  H bonded to a F, O, or N

 From weakest to strongest: Dispersion  Dipole-dipole  Hydrogen Bonds INTERMOLECULAR FORCES INTER & INTRA MOLECULAR FORCES & PROPERTIES

 Stronger the force, the more energy is needed to break the bond

 Energy needed to break a metallic or an ionic bond will be much higher than the energy needed to break a covalent bond

 Separating NaCl will require more energy than separating CO2  Energy needed to overcome intermolecular forces will increase with an increase in force strength

 Boiling H2O will require more energy than boiling H2S because H2O experiences hydrogen bonding and H2S experiences only a slight dipole-dipole