Molecule Shape

VSEPR Model (Valence Shell Electron Pair Repulsion) The structure around a given atom is determined principally by minimizing electron pair repulsions.

Predicting a VSEPR Structure Draw Lewis structure. Count the number of bonds. (count double and triple bonds as 1 bond) Count the number of lone pair of electrons on the central atom Determine the name of molecular structure from positions of the atoms from the chart. 9/16/2018

# of e- pairs 1 1 1 atom bonded to another atom # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 4 lone pairs 1 linear  

# of e- pairs 2 2 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 2 linear  

# of e- pairs 3 3 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 3 trigonal planar bent / angular linear  

# of e- pairs 4 4 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 4 tetrahedral trigonal pyramid bent / angular linear

# of Bonds 5 5 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 5 trigonal bipyramid sawhorse / seesaw t-shape linear

# of e- pairs 6 6 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 6 Octahedral square pyramid square planar

pentagonal bipyramidal # of e- pairs 7 7 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom. # of e-pairs Basic Geometry 0 lone pair 1 lone pair 2 lone pairs 3 lone pairs 7 pentagonal bipyramidal pentagonal pyramidal

Determine the Molecular Shape of SCl2 3 . Count the number of lone pairs on central atom 1. Draw the Lewis structure Cl S Cl 20 e- total Cl S Cl 4 electron pairs (bonds and lone pairs) 2 lone pairs of electrons 2 . Count the number of bonds 4. Look at the chart and determine the shape! Cl S Cl Bent

Determine the shape of these molecular compounds 1. PF3 2. CO2 26 e- total 16 e- total 3. NH4+ 8e- total H + F P F O C O F N H H Count the double bonds as “one” electron pair 4 electron pairs (bonds and lone pairs) 1 lone pairs of electrons H 2 “electron pairs” 4 electron pairs Linear Trigonal pyramidal Tetrahedral 9/16/2018

Click Below for the Video Lectures Lewis Diagram and VSEPR

Molecular Polarity

Polarity The polarity can tell you many things: How high or low the melting and boiling point of the substance is How easily the liquid form of the substance evaporates Whether the substance will dissolve in water, or in some other solvent

Polar Molecules If the molecule does not have a symmetrical shape (asymmetrical), then there is a greater concentration of electrons on one side of the molecule compared to the other side. This makes one side charged partially negative and the other side partially positive. The oppositely charged ends of these molecules are “poles”, making the molecule polar. Polar molecules can attract each other, δ+ end of one molecule attracting to the δ- end of the other molecule.

How to determine polarity Draw structural formula Check for line of symmetry – mirror image Look up ENs of the atoms on the ends of symmetry Draw an arrowhead on the side with the higher EN The side with higher EN has greater pull of the e-s, so it is charged δ -. The other side is charged δ +. 3.2 2.1 H - Cl δ + δ -

How to determine polarity Cl H δ - Draw structural formula Check for line of symmetry – mirror image Look up ENs of the atoms on the ends of symmetry Draw an arrowhead on the side with the higher EN The side with higher EN has greater pull of the e-s, so it is charged δ -. The other side is charged δ +. 3.2 Cl – C- Cl δ + 2.1

Nonpolar Molecules If the molecule has a symmetrical shape, then the electrons are distributed evenly through the molecule, and the whole molecule is nonpolar (even if it contains polar bonds). Nonpolar molecules have equal pull of electrons on all sides of the molecule, so no side develops a pole. Since the molecule lacks oppositely charged ends, any attractive forces will be extremely weak.

Nonpolar Molecules H H – C- H H– C - H O = O

Molecular Force

Nonpolar molecules form LONDON DISPERSION FORCE attractions. Since there are no permanent positive or negative ends, these attractions are extremely weak. The attractions are a combination of temporary poles due to electron movement around the molecule or, in the case of huge molecules, they actually get tangled up with each other like sticky strands of spaghetti or yarn. London dispersion forces generally get stronger as the size of the molecule increases.

London dispersion force

Polar molecules form DIPOLE attraction: the simple attraction of the oppositely charged ends of two molecules. The partially positive end of one molecule attracts to the partially negative end of a different molecule. This attraction allows these substances to exist as solids and liquids at higher temperatures than are possible for nonpolar molecules of equivalent size.

H - Cl H - Cl H - Cl H - Cl δ - δ + δ + δ - δ + δ - 3.2 2.1 3.2 2.1

Hydrogen Bond Some polar molecules form HYDROGEN BONDS between them. Bonding between hydrogen and more electronegative neighboring atoms; Nitrogen, Oxygen and Flourine (F,O,N) An extremely high melting point, boiling point, heat of fusion and heat of vaporization for a molecule its size

Hydrogen Bonding in Water The attraction between the two molecule is nearly that of ionic attraction. Not only that but the H end of one molecule actually forms temperary covalent bonds with the N,O or F that makes up the end of the other molecule. This gives extra strength that allows water to be liquid at room teperature despite its small size.

Nonpolar molecules Polar molecules London dispersion forces Dipole – dipole Hydrogen bond (F,O,N)

So, what should you be able to do now? 1) Identify whether a compound is molecular, ionic, metallic or network based on its properties 2) Draw dot diagrams of simple molecules 3) Draw structural formulas of simple molecules 4) Determine the shape of simple molecules 5) Determine if simple molecules are polar or nonpolar 6) If polar, draw the dipole moment and identify the partially charged ends 7) Determine the attractive force type that attracts specific simple molecules to each other.

Checking for understanding Explain the difference between polar and nonpolar molecules Explain London dispersion force Explain dipole attraction forces including hydrogen bond

Click Below for the Video Lectures Intermolecular forces Dipole Forces London Disperson forces

Chemical Formula

Click Below for the Video Lectures Molecule and Elements

Molecular Formula Molecular Formula - indicates the total number of atoms of each element needed to form the molecule. MOLECULES ARE PARTICLES FORMED BY THE COVALENT BONDING OF NONMETAL ATOMS. A molecule of methane contains one atom of carbon and four atoms of hydrogen, so the molecular formula is CH4.

Empirical Formula Empirical Formulas represents the simplest ratio in which the atoms combine to form a compound. Empirical formulas are used to represent ionic compounds which form crystals of alternating + and – charge instead of separate molecules. CaCl2 is ionic, and the formula represents a ratio of 1 ion of Ca+2 to every 2 ions of Cl – Empirical formulas of covalent compound show the smallest ratio of atoms possible formula C3H8 may represent molecular formula C3H8 or C6H16

Interpreting chemical formula The subscript tells you how many moles of that particular ion you have in one mole of the compound. A Mole is to chemistry what a “dozen” is to donuts or eggs. Chemical formulas and reactions are written by the mole. 1 mole = 6.02 X 1023 of anything. The mole is a unit of measurement for amount of a substance 1 mole = 6.02 X 1023 of anything If there is no subscript, then the number of moles of that ion is 1. When Interpreting Formulas, if there are (parentheses) around the element, any subscript outside the parentheses multiplies all of the elements inside the parentheses by that amount.

Ca(NO3)2 Ca(NO3)2 1 mol Ca , 2 mol N, 6 mol O 6.02x1023 atoms of Ca 2 outside the parentheses, so double the number of atoms inside to get the total number of atoms of that element (2 N’s and 6 O’s). Since Ca is not inside the parentheses, it is not doubled. There is only 1 Ca in the formula. 1 mol Ca , 2 mol N, 6 mol O 6.02x1023 atoms of Ca 2 x (6.02x1023 ) atoms of N 6 x (6.02x1023 ) atoms of O

Checking for understanding Complete the chart bellow, an example was done for you BaCO3 1mol Ba 1mol C 3mol O Na3PO4 Al2(SO4)3

Molar Mass

Molar Mass of an Element Here are the elements that are in the compounds in the examples of how to determine the gram formula mass. Molar Mass of CO2 = 1 x 12.01 g/mol 44.01 g/mol + 2 x 16.00 g/mol =

Mole Conversion

Mole Map moles grams atoms Circle the numbers Molar Mass atoms 6.02x1023 Circle the numbers Underline what you are looking for Start with what you circled Check your answer with number of sig figs.

Mass to Mole Conversion How many moles of carbon is 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C Molar Mass moles grams

How many moles is 5.69 g of Na? 5.69 g Na 1 mol Na 22.99 g Na moles Molar Mass moles grams 47

How many grams are in 9.45 mol of nitrogen atoms? 9.45 mol N 14.01 g N 1 mol N = 132.39 =132 g N Molar Mass moles grams 48 48

Remember… 1 Mole = 6.02 x 1023 atoms or molecules

Molar Conversion Examples How many atoms are in 2.50 moles of C? 6.02  1023 atoms 1 mol 2.50 mol 1.51  1024 =atoms C 6.02x1023 atoms moles

Calculate the number of atoms in 0.500 mol of Al. 3.01  1023 =atoms Al 6.02x1023 atoms moles

Calculate the number of moles of 1.80 x 1024 Na atoms. 1.80 x 1024 atoms = 2.99 moles 6.02x1023 atoms moles

dinitrogen trioxide, N2O3 ? How many grams are in 1.20 x1024 molecules of dinitrogen trioxide, N2O3 ? 1.20  1024 molecules 1 mol 6.02  1023 molecules 76.02 g 1 mol = 151.53g =152 g N2O3 Molar Mass 6.02x1023 atoms moles grams 53 53 53 53

Find the mass of 2.1  1024 molecules of NaHCO3. 2.1  1024 molecules 6.02  1023 molecules 84.01 g 1 mol = 290 g NaHCO3 Molar Mass 6.02x1023 atoms moles grams 54 54 54 54 54

Checking for understanding 1. How many atoms are in 5g of Ca? 2. How many atoms are in 1.2 mol K? 3. Calculate the mass of 1.4x1024 molecules of CaCO3

Click Below for the Video Lectures The Mole

Percent Composition

Percent Composition by Mass Part X 100 % Whole The proportion by mass of the elements in a compound Experimental Percent Composition given mass of element in sample X 100 % given mass of total sample

Total = 80.0 g O = 56.0 g N = 24.0 g % O = (56.0g/80.0g) X 100 = 70.0% A compound containing nitrogen and oxygen has a mass of 80.0 grams. Experiments show that the 80.0 grams is made up of 56.0 grams of oxygen and 24.0 grams of nitrogen. What is the % composition, by mass, of each element in the compound? Total = 80.0 g O = 56.0 g N = 24.0 g % O = (56.0g/80.0g) X 100 = 70.0% %N = (24.0g/80.0g) X 100 = 30.0%

X 100 % Percent Composition 2) Determination by formula: You need the periodic table to do this. mass of element in compound X 100 % mass of compound

What is the % composition, by mass, of each element in SiO2? Molar mass of SiO2 = 28.1 g + (2 x 16.00g ) = 60.1 g %Si = (28.1g/60.1g) X 100 = 46.8% %O = ( 32 g / 60.1 g) X 100 = 53.2%

Checking for understanding Calculate the % composition, by mass, of each element in Al(OH)3