Drawing covalent bonds Draw the following covalent compounds in your notebooks now: NH3 CH4 CO2 Draw the following covalent compounds in your notebooks now: NH3 CH4 CO2

2/8/11 – “E” Day Objective: To understand how structure of compounds determines their function Do Now: What is the shape of the following molecules: CH 4, H 2 O, O 2 Today: Review of Ionic & Covalent Compounds Polarity Objective: To understand how structure of compounds determines their function Do Now: What is the shape of the following molecules: CH 4, H 2 O, O 2 Today: Review of Ionic & Covalent Compounds Polarity

Three dimensional chemistry REMEMBER electrons = same charge = repel each other unshared electrons also repel because electron pairs repel, molecules adjust their shape so that the valence electron pairs are as far apart as possible = VSEPR theory REMEMBER electrons = same charge = repel each other unshared electrons also repel because electron pairs repel, molecules adjust their shape so that the valence electron pairs are as far apart as possible = VSEPR theory

Molecular geometry linear triatomic (carbon dioxide, CO2) trigonal planar tetrahedral (methane, CH4) all possible bonds are attached to atoms (no lone pairs on central atom) bent triatomic (water) pyramidal (ammonia, NH4) lone pairs on central atom in these two linear triatomic (carbon dioxide, CO2) trigonal planar tetrahedral (methane, CH4) all possible bonds are attached to atoms (no lone pairs on central atom) bent triatomic (water) pyramidal (ammonia, NH4) lone pairs on central atom in these two

Bent (water, H2O)

Pyramidal (ammonia, NH4)

Methane (tetrahedral, CH4)

Daily Agenda: Bonding Overview Notes - Polarity CW – IF Polarity WS, Models Lab HW – 8.3 Guided Reading Bonding Overview Notes - Polarity CW – IF Polarity WS, Models Lab HW – 8.3 Guided Reading

Bonding Overview Atoms bond to satisfy the octet rule… Ionic Bonding… Metals + Nonmetals Form Ions BECAUSE of HUGE difference in electronegativity! Molecular Bonding… Nonmetals/metalloids –SHARE e- BECAUSE of SMALL difference in electronegativity! Atoms bond to satisfy the octet rule… Ionic Bonding… Metals + Nonmetals Form Ions BECAUSE of HUGE difference in electronegativity! Molecular Bonding… Nonmetals/metalloids –SHARE e- BECAUSE of SMALL difference in electronegativity! Blue – Metals Yellow – NonMetals/metalloids Electronegativity Increases!

Bonding Overview Octet Rule… Atoms gain/lose/share electrons to become like their nearest NOBLE GAS When atoms satisfy octet rule they BECOME MORE STABLE Results in a DECREASE of potential energy It is easier to lie down than to stand up, bonding is Nature’s way of allowing elements to lie down. Octet Rule… Atoms gain/lose/share electrons to become like their nearest NOBLE GAS When atoms satisfy octet rule they BECOME MORE STABLE Results in a DECREASE of potential energy It is easier to lie down than to stand up, bonding is Nature’s way of allowing elements to lie down.

Bonding Overview Ionic Bonding… Formulas are definitive Metals/nonmetals ALWAYS gain or lose fixed numbers of electrons, so charges are ALWAYS the same Criss cross charges to make formulas Name compounds: metal + nonmetal + “ide” or metal + polyatomic ion Ionic Bonding… Formulas are definitive Metals/nonmetals ALWAYS gain or lose fixed numbers of electrons, so charges are ALWAYS the same Criss cross charges to make formulas Name compounds: metal + nonmetal + “ide” or metal + polyatomic ion

Ionic Bonding Review Structures are definitive Cations (+ metal ions) and anions (- non metal ions) ATTRACT Arrange themselves into highly organized 3-D structures called CRYSTALS High MP & Conduct electricity when molten or dissolved in water Structures are definitive Cations (+ metal ions) and anions (- non metal ions) ATTRACT Arrange themselves into highly organized 3-D structures called CRYSTALS High MP & Conduct electricity when molten or dissolved in water

Bonding Review Molecular Bonding… Formulas are not set Nonmetals/metalloids have similar Electronegativity values, so electrons are shared NO IONS FORMED We have to be GIVEN either formula or name Formulas: use prefixes to determine subscripts Naming: use prefixes to show # atoms of each element Molecular Bonding… Formulas are not set Nonmetals/metalloids have similar Electronegativity values, so electrons are shared NO IONS FORMED We have to be GIVEN either formula or name Formulas: use prefixes to determine subscripts Naming: use prefixes to show # atoms of each element

Bonding Review Molecular Bonding… Structures are not set Nonpaired valence electrons will ALWAYS form bonds Each elements will form enough bonds in order to satisfy the octet rule Single, double or triple bonds (Needed – Available)/2 = # bonds formed by each element (OR THE NUMER EQUALS THE CHARGE!) Molecular Bonding… Structures are not set Nonpaired valence electrons will ALWAYS form bonds Each elements will form enough bonds in order to satisfy the octet rule Single, double or triple bonds (Needed – Available)/2 = # bonds formed by each element (OR THE NUMER EQUALS THE CHARGE!)

Bonding Review Molecular Bonding… Structures are NOT definitive Bonded/nonbonded pairs of electrons REPEL each other Bonded/nonbonded pairs of electrons will spread out AS FAR AWAY as possible to form shapes – VSEPR Theory Molecular Bonding… Structures are NOT definitive Bonded/nonbonded pairs of electrons REPEL each other Bonded/nonbonded pairs of electrons will spread out AS FAR AWAY as possible to form shapes – VSEPR Theory

Bonding Review Non central bonding atom OR no lone pairs around CBA - LINEAR Four bonded/nonbonded electron pairs around CBA - TETRAHEDRAL –Tetrahedron –Pyramidal –Bent Three bonded electron pairs around central bonded atom - TRIGONAL Non central bonding atom OR no lone pairs around CBA - LINEAR Four bonded/nonbonded electron pairs around CBA - TETRAHEDRAL –Tetrahedron –Pyramidal –Bent Three bonded electron pairs around central bonded atom - TRIGONAL

Ionic vs. Covalent bonds and electronegativity What if one atom has a greater electronegativity than the other but not enough strength to pull the electron away all together (form an ionic bond)? We land somewhere in the middle with polar covalent bonds non polar covalent bonds What if one atom has a greater electronegativity than the other but not enough strength to pull the electron away all together (form an ionic bond)? We land somewhere in the middle with polar covalent bonds non polar covalent bonds

Polar vs. Nonpolar Covalent Bonds Electronegativtiy measures the nucleus’ ability to attract electrons When bonding atoms approach each other a tug of war begins Example: HCl Cl nucleus is stronger so bonding e- are closer to Cl Electronegativtiy measures the nucleus’ ability to attract electrons When bonding atoms approach each other a tug of war begins Example: HCl Cl nucleus is stronger so bonding e- are closer to ClH Cl H :Cl

Dipole In a polar molecule, one end is slightly negative and the other end is slightly positive In chemistry, this type of molecule is referred to as a dipole. EXAMPLE – Water! In a polar molecule, one end is slightly negative and the other end is slightly positive In chemistry, this type of molecule is referred to as a dipole. EXAMPLE – Water!

Non polar covalent bonds Forms when atoms share electrons equally (like in the H 2 example) Each atom has equivalent electronegativity values OR molecule is symmetrical! linear (CO 2, CS 2 ) trigonal (BF 3 ) tetrahedron (CF 4, CCl 4 ) Forms when atoms share electrons equally (like in the H 2 example) Each atom has equivalent electronegativity values OR molecule is symmetrical! linear (CO 2, CS 2 ) trigonal (BF 3 ) tetrahedron (CF 4, CCl 4 )

Non polar covalent bonds

Polar vs. Non-polar vs. Ionic Online Text Video C 2 H 6 – non-polar Water – polar Na + and Cl - Online Text Video C 2 H 6 – non-polar Water – polar Na + and Cl -

Intermolecular Forces Molecular solids exist because of attractive forces between MOLECULES Dipole-Dipole - between polar molecules. MIDDLE Dispersion - between non-polar molecules. WEAKEST Hydrogen Bonding - between molecules with H, N or O or F. STRONGEST Molecular solids exist because of attractive forces between MOLECULES Dipole-Dipole - between polar molecules. MIDDLE Dispersion - between non-polar molecules. WEAKEST Hydrogen Bonding - between molecules with H, N or O or F. STRONGEST

Daily Agenda Submit Completed Lab Packet Molecular Review - Questions? HW - Molecular Exam tomorrow! Submit Completed Lab Packet Molecular Review - Questions? HW - Molecular Exam tomorrow!

Daily Agenda Submit 8.3 Guided Reading VSEPR Quiz Molecular Models Lab Molecular Review - Questions? HW - Molecular Exam tomorrow! Submit 8.3 Guided Reading VSEPR Quiz Molecular Models Lab Molecular Review - Questions? HW - Molecular Exam tomorrow!