Covalent Bonding Chapter 6 Section 1

Covalent Bonds Ionic bond – transfer of e- Ionic bond – transfer of e- Covalent bond – a bond formed when atoms share one or more pairs of electrons Covalent bond – a bond formed when atoms share one or more pairs of electrons

Example – H 2 H is diatomic – come in 2’s H is diatomic – come in 2’s The + nucleus of each atom attracts the e- of both atoms The + nucleus of each atom attracts the e- of both atoms The + nucleus of each atom repels each other The + nucleus of each atom repels each other The – e- cloud of each atom repels each other The – e- cloud of each atom repels each other

Hydrogen’s Molecular Orbital

Single Bond 2 atoms share 1 pair of e- 2 atoms share 1 pair of e- Represented by a single line H—H is H 2 Represented by a single line H—H is H 2 The e- cloud is around both H nuclei called a molecular orbital The e- cloud is around both H nuclei called a molecular orbital

Molecular Orbital Molecular orbital – region where e- pair is most likely to exist around 2 nuclei Molecular orbital – region where e- pair is most likely to exist around 2 nuclei Results from overlap of two atomic orbitals. Results from overlap of two atomic orbitals.

Potential Energy Bonds will form when they can be the most stable = low E Bonds will form when they can be the most stable = low E Most atoms have low stability and high potential E until they bond with other atoms Most atoms have low stability and high potential E until they bond with other atoms At 75 pm, the repulsion b/t like charges = the attraction b/t opposite charges. At 75 pm, the repulsion b/t like charges = the attraction b/t opposite charges. E here is -436kJ/mol E here is -436kJ/mol

Potential Energy

Bond Length Bond length – the distance b/t 2 bonded atoms at min. pot. E; the avg. distance b/t the nuclei of 2 bonded atoms Bond length – the distance b/t 2 bonded atoms at min. pot. E; the avg. distance b/t the nuclei of 2 bonded atoms H 2 = 75 pm H 2 = 75 pm Atoms vibrate in bonds and act like a spring so length always changes Atoms vibrate in bonds and act like a spring so length always changes

Bond Energy Bond energy – the E required to break a chemical bond b/t 2 atoms Bond energy – the E required to break a chemical bond b/t 2 atoms Higher the E the stronger the bond and smaller the bond length Higher the E the stronger the bond and smaller the bond length H 2 is kJ/mol – E released when 1 mol of Hydrogen bonds is 436 kJ/mol H 2 is kJ/mol – E released when 1 mol of Hydrogen bonds is 436 kJ/mol

Electronegativity Electronegativity - the tendency of an atom to attract bonding e-’s to itself when it bonds w/ another atom Electronegativity - the tendency of an atom to attract bonding e-’s to itself when it bonds w/ another atom Trend: electronegativity increases going left to right and decreases down a group Trend: electronegativity increases going left to right and decreases down a group Fluorine is the most e-neg. element. Fluorine is the most e-neg. element.

Electronegativity and Bonding Helps to determine if the bond will be ionic or covalent Helps to determine if the bond will be ionic or covalent Greatly different = ionic bond Greatly different = ionic bond Close = covalent bond Close = covalent bond

Types of Covalent Bonds Nonpolar covalent bond – covalent bond where the bonding e- are = attracted to both bonded atoms Nonpolar covalent bond – covalent bond where the bonding e- are = attracted to both bonded atoms Polar covalent bond – covalent bond where a shared pair of e- is held more closely by 1 of the atoms Polar covalent bond – covalent bond where a shared pair of e- is held more closely by 1 of the atoms

Polar Covalent Bond The more e-neg atom has a higher e- density b/c it has a greater attraction for e-’s The more e-neg atom has a higher e- density b/c it has a greater attraction for e-’s

Predicting Bond Character Diff. in e-negBond Type 0-0.5non polar covalent polar covalent >2.1ionic

Predicting Bond Character Consider Al F 3 - The e-neg diff b/t Al and F 3 is 2.4 It is an ionic bond Consider Al F 3 - The e-neg diff b/t Al and F 3 is 2.4 It is an ionic bond The e-neg diff b/t Al and C is 1.6 It is a polar covalent bond. The e-neg diff b/t Al and C is 1.6 It is a polar covalent bond.

Polarity Polarity – having opposite ends, or poles Polarity – having opposite ends, or poles Dipole – a molecule in which one end has a partial positive charge and the other has a partial negative charge Dipole – a molecule in which one end has a partial positive charge and the other has a partial negative charge

HF HF is a polar molecule HF is a polar molecule Use Greek lowercase letter delta – δ + partial positive δ - partial negative Use Greek lowercase letter delta – δ + partial positive δ - partial negative H δ+ F δ - H δ+ F δ -

Polarity It is possible to have polar ends but for the molecule not to be a dipole It is possible to have polar ends but for the molecule not to be a dipole This happens when the polar sides cancel each other out This happens when the polar sides cancel each other out

Dipole Moment Dipole Moment – measures the polarity of a molecule Dipole Moment – measures the polarity of a molecule The larger the dipole moment, the greater the polarity = the stronger the bond The larger the dipole moment, the greater the polarity = the stronger the bond H-F = 1.8 Dipole Moment H-F = 1.8 Dipole Moment H-I = 0.5 Dipole Moment H-I = 0.5 Dipole Moment

Assignment Complete the section review on page 198. Complete the section review on page 198. Turn in this assignment today before you leave class. Turn in this assignment today before you leave class.