IMF PDF - Activating Prior Knowledge - General Chemistry 2

ACTIVATING PRIOR KNOWLEDGE GENERAL CHEMISTRY 2 Scope: Intermolecular Forces and Liquids and Solids Physical Properties of solutions Thermochemistry Chemical Kinetics Chemical Thermodynamics Chemical Equilibrium Acid-Base E...

ACTIVATING PRIOR KNOWLEDGE GENERAL CHEMISTRY 2 Scope: Intermolecular Forces and Liquids and Solids Physical Properties of solutions Thermochemistry Chemical Kinetics Chemical Thermodynamics Chemical Equilibrium Acid-Base Equilibria and Salt Equilibria Electrochemistry © 2015 Pearson Education, Inc.  Molecular Shape and Polarity Intermolecular Forces of Attraction States of Matter © 2015 Pearson Education, Inc. REVIEW REVIEW Atoms The nucleus contains the p+ and n0. It is very small but dense and massive. The e- move in the energy levels outside the nucleus Most atoms are more stable when they gain, lose or share their valence electrons in chemical bonds = the octet rule © 2015 Pearson Education, Inc.  Nuclear Symbols © 2015 Pearson Education, Inc.  Ionic Bonds make crystalline solids – Form when e- are transferred from one atom to another as they try to complete their outer energy level. – Metal Atom loses e-: gets a positive charge. – Nonmetal Atom gains e-: gets a negative charge. – Positively and negatively charged atoms (or groups of atoms) are known as ions. – Think rocks, salts and minerals in earth’s crust. © 2015 Pearson Education, Inc. Covalent Bonds make molecules When valence e- are shared (in pairs) by atoms instead of being transferred. Equal sharing of e- = nonpolar covalent Unequal sharing of e- = polar covalent The structure that results is called a molecule. Covalent compounds tend to be liquids and gases at room temperature because of weak forces of attraction between molecules. think water, oceans, atmosphere and carbon-based (organic) molecules. © 2015 Pearson Education, Inc. Polar Covalent Bonds: Unequal sharing of electrons results in one side of the molecule being “negative” and the other side being “positive” There is a greater e- density Water molecules areNegativePolar around one atom than there is end around the other Which one in H2O? Oxygen “pulls” e- more strongly (higher electronegativity) Partial charges form!!! Positive end © 2015 Pearson Education, Inc.  (–) O H H (+) (+) Chemists often use arrows to show the PULL of negative charge toward one end of the molecule. A polar molecule is called a DIPOLE. © 2015 Pearson Education, Inc.  Bond Type by Electronegativity Difference You can estimate the bond type by subtracting the ∆EN Bond electronegativity difference in EN difference Type values of the bonding atoms. ≤0.4 Non Polar Covalent Look up EN values & subtract Between Polar EX: H = 2.1, O = 3.5 0.5 to 1.8 Covalent ∆EN = 1.4 = polar ≥1.9 Ionic covalent © 2015 Pearson Education, Inc. Try Some What is the polarity of the bond between: – C and O – C and H Electronegativity – C and C Values – Na and Cl – S and H C = 2.6 Cl = 3.2 – O and H H = 2.2 N = 3.0 – N and O O = 3.4 S = 2.6 – N and H © 2015 Pearson Education, Inc. How strong are they? The greater the difference in electronegativity, the stronger the bond is. Electronegativity – C and O Values – C and C C = 2.6 Cl = 3.2 – C and H H = 2.2 N = 3.0 – C and Se O = 3.4 Se = 2.5 © 2015 Pearson Education, Inc. Ionic vs Molecular & States of Matter Much of chemistry comes down to opposite charges attract and like charges repel. This means that PROPERTIES like physical state and melting and boiling points DEPEND ON HOW STRONGLY THE BASIC UNITS ARE ATTRACTED TO EACH OTHER! Solids melt and liquids boil when the attractive forces between the particles are broken…. Stronger attractive forces result in higher MPts and BPts. © 2015 Pearson Education, Inc. Ionic vs Molecular & States of Matter The force of attraction between ions is quite strong – ionic crystals are hard, brittle solids with high MPts – it takes more energy to break these bonds. The force of attraction between individual molecules are called weak forces – many molecular substances are gases or volatile liquids at room temp. and MPts are low. © 2015 Pearson Education, Inc.  INTERMOLECULAR FORCES: Weak attractive forces between molecules Chemists call intermolecular forces of attraction Van der Waals forces, after the scientist who discovered them. IM forces vary in strength and change the properties of molecular substances. IM forces are due to polarity in molecules – differences depend on whether dipoles are permanent or temporary. IM forces allow molecules to come together and form liquids, like water, and a few covalent solids. © 2015 Pearson Education, Inc.  Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions (bonds) that hold compounds together. Many physical properties reflect intermolecular forces, like boiling points, melting points, viscosity, surface tension, and capillary action. Intermolecular Forces © 2015 Pearson Education, Inc.  States of Matter Retains a fixed Expand to fill their Take shape of shape, rigid. container container Particles locked Particles are fluid, Particles are fluid, into place. move rapidly & can slide past Not compressible. randomly each other Dense-little free VERY Not compressible space between compressible. Dense-little free particles space between Lots of free space particles between particles. © 2015 Pearson Education, Inc.  Polar Molecule Nonpolar 1. High boiling Molecule point 1. Low boiling 2. High melting point point 2. Low melting Properties 3. Soluble in 1. Boiling point point Polar solvent 2. Melting point 3. Soluble in non- 4. Strong 3. Solubility Polar solvent intermolecular 4. Intermolecular 4. Weak forces of forces of attraction intermolecular attraction 5. Surface forces of 5. High Surface tension attraction Tension 5. Low Surface Tension © 2015 Pearson Education, Inc.  Ion–Dipole Interactions Ion–dipole interactions are found in solutions of ions. The strength of these forces is what makes it possible for ionic substances to dissolve in polar solvents. Intermolecular Forces © 2015 Pearson Education, Inc.  Hydrogen Bonds Exist Between Water Molecules ▪ Form between (-) oxygen atom of a polar molecule and (+) hydrogen atom of a H neighboring molecule. ▪ The attractions between polar water molecules are so significant we call them O hydrogen bonds even though they are not as strong as true covalent or ionic bonds. ▪ Without hydrogen bonds water would never be a liquid © 2015 Pearson Education, Inc.  Interaction Between Water Molecules Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of another water molecule to form a HYDROGEN BOND © 2015 Pearson Education, Inc.  Hydrogen bonds are the strongest type of Hydrogen bond intermolecular forces These are covalent bonds intermolecular forces act BETWEEN the molecules. © 2015 Pearson Education, Inc.  Hydrogen Bonds – Why we are here… Hydrogen bonds make water a liquid at room temperature Hydrogen bonds allow DNA to unzip during replication White = H and Red = O © 2015 Pearson Education, Inc.  Hydrogen Bonds Hydrogen bonds, especially strong dipole−dipole attractions, occur between polar molecules containing hydrogen atoms bonded to very electronegative atoms such as fluorine (F), nitrogen (N), and oxygen (O). a hydrogen atom with a partial positive charge attached to a N, O, or F with a partial negative charge. © 2015 Pearson Education, Inc.  Hydrogen Bonding The dipole–dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds. A hydrogen bond is an attraction between a hydrogen atom attached to a highly electronegative atom and a nearby small electronegative atom in another molecule or Intermolecular chemical group. Forces © 2015 Pearson Education, Inc.  What Forms Hydrogen Bonds? Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine. These atoms interact with a nearly bare nucleus (which contains one proton). Intermolecular Forces © 2015 Pearson Education, Inc.  Dipole−Dipole Attractions Polar molecules are attracted to each other by dipole−dipole attractions when the positive end of one dipole is attracted to the negative end of a second dipole, such as the attractive forces between two molecules of H—Cl. © 2015 Pearson Education, Inc.  Dipole–Dipole Interactions Polar molecules have a more positive and a more negative end–a dipole (two poles, δ+ and δ−). The oppositely charged ends attract each other. Intermolecular Forces © 2015 Pearson Education, Inc.  Dipole–Dipole Interactions For molecules of approximately equal mass and size, the more polar the molecule, the higher its boiling point. Intermolecular Forces © 2015 Pearson Education, Inc.  Dispersion Forces Dispersion forces, very weak attractive forces that occur between nonpolar molecules, occur when movement induces a temporary distortion of the electrons in a molecule, creating a temporary dipole. make it possible for nonpolar molecules to exist as liquids and solids. © 2015 Pearson Education, Inc.  Dispersion Forces The figure below shows how a nonpolar particle (in this case a helium atom) can be temporarily polarized to allow dispersion force to form. The tendency of an electron cloud to distort is called its polarizability. Intermolecular Forces © 2015 Pearson Education, Inc.  Factors Which Affect Amount of Dispersion Force in a Molecule number of electrons in an atom (more electrons, more dispersion force) size of atom or molecule/molecular weight shape of molecules with similar masses (more compact, less dispersion force) Intermolecular Forces © 2015 Pearson Education, Inc.  Which Have a Greater Effect: Dipole–Dipole Interactions or Dispersion Forces? If two molecules are of comparable size and shape, dipole–dipole interactions will likely be the dominating force. If one molecule is much larger than another, dispersion forces will likely determine its physical properties. Intermolecular Forces © 2015 Pearson Education, Inc.  Bonding and Attractive Forces © 2015 Pearson Education, Inc.  Learning Check Indicate which major type of molecular interaction, dipole−dipole attractions, hydrogen bonds, or dispersion forces, is expected between each of the following. A. NF3 B. Cl2 C. HF D. N2 E. SO2 © 2015 Pearson Education, Inc.  Solution Indicate which major type of molecular interaction, dipole−dipole attractions, hydrogen bonds, or dispersion forces, is expected between each of the following. A. NF3 dipole−dipole attractions B. Cl2 dispersion forces C. HF hydrogen bonds D. N2 dispersion forces E. SO2 dipole-dipole © 2015 Pearson Education, Inc.  Polarity of Molecules—Nonpolar In a nonpolar molecule, all the bonds are nonpolar, H2, Cl2 and CH4 are nonpolar because they contain only nonpolar bonds. © 2015 Pearson Education, Inc.  Polarity of Molecules—Nonpolar A nonpolar molecule also occurs when polar bonds (dipoles) cancel each other because of a symmetrical arrangement. Molecules such as CO2 and CCl4 contain polar bonds with dipoles that cancel each other out. © 2015 Pearson Education, Inc.  Polarity of Molecules—Polar A polar molecule occurs when the dipoles from individual bonds do not cancel each other out. For molecules with two or more electron groups, the shape (such as bent or trigonal pyramidal) determines whether or not the dipoles cancel. © 2015 Pearson Education, Inc.  Polarity of Molecules—Polar Examples of polar molecules include HCl, H2O, and NH3. HCl is linear and contains a polar bond. H2O is bent and contains two polar bonds as well as two lone pairs on oxygen. © 2015 Pearson Education, Inc.  Polarity of Molecules—Polar NH3 is trigonal pyramidal and contains three polar bonds and a lone pair on nitrogen. © 2015 Pearson Education, Inc.  Polarity of Molecules—Polar CH3F is tetrahedral and contains three nonpolar bonds and a polar bond. © 2015 Pearson Education, Inc.  Polarizability & Boiling Point If something is easier to polarize, it has a lower boiling point. Remember: This means less intermolecular force (smaller molecule: lower molecular weight, fewer electrons). Intermolecular Forces © 2015 Pearson Education, Inc.  What Does This Graph Show Us? In a group, the period 3/4/5 elements have higher boiling points as the group member gets larger. What happens with the period 2 elements? For group 4A, the trend is continued. What about for the other groups? Intermolecular Forces © 2015 Pearson Education, Inc.  Types of Intermolecular Force Weakest to strongest forces: dispersion forces (or London dispersion forces) dipole–dipole forces hydrogen bonding (a special dipole–dipole force) ion–dipole forces o Note: The first two types are also referred to collectively as van der Waals forces. Intermolecular Forces © 2015 Pearson Education, Inc. Summarizing Intermolecular Forces Intermolecular Forces © 2015 Pearson Education, Inc.  Liquid Properties Affected by Intermolecular Forces boiling point (previously discussed) and melting point viscosity surface tension capillary action Intermolecular Forces © 2015 Pearson Education, Inc.  Viscosity Resistance of a liquid to flow is called viscosity. It is related to the ease with which molecules can move past each other. Viscosity increases with stronger intermolecular forces and decreases with higher temperature. Intermolecular Forces © 2015 Pearson Education, Inc.  Surface Tension Water acts as if it has a “skin” on it due to extra inward forces on its surface. Those forces are called the surface tension. Intermolecular Forces © 2015 Pearson Education, Inc.  Cohesion and Adhesion Intermolecular forces that bind similar molecules to one another are called cohesive forces. Intermolecular forces that bind a substance to a surface are called adhesive forces. These forces are important in capillary action. Intermolecular Forces © 2015 Pearson Education, Inc.  Capillary Action The rise of liquids up narrow tubes is called capillary action. Adhesive forces attract the liquid to the wall of the tube. Cohesive forces attract the liquid to itself. Water has stronger adhesive forces with glass; mercury has Intermolecular stronger cohesive forces Forces with itself. © 2015 Pearson Education, Inc.  Phase Changes Conversion from one state of matter to another is called a phase change. Energy is either added or released in a phase change. Phase changes: melting/freezing, vaporizing/condensing, subliming/depositing. Intermolecular Forces © 2015 Pearson Education, Inc.  WHAT IS A PHASE DIAGRAM? It is a “map” that tells us which state(s) of matter (solid, liquid, gas) exist for a given set of temperature and pressure conditions. Intermolecular Forces © 2015 Pearson Education, Inc.  Temperature A measure of the average kinetic energy (energy of motion) of particles (atoms or molecules) in matter in Intermolecular Celsius, Kelvin, or Fahrenheit. Forces © 2015 Pearson Education, Inc.  Pressure A measure of how tightly matter is squeezed together in units of atmospheres (atm), bars, torrs, Pascals (Pa) or even pounds/in2 (psi). Intermolecular Forces © 2015 Pearson Education, Inc.  Which one is Two “stable” Allotropes depends on of Carbon both temperature and pressure! Intermolecular Forces © 2015 Pearson Education, Inc.  Phase Diagram for Carbon Dioxide (CO2) 10 atm ⚫In a 1 phase field, only one state is possible. ⚫On a phase boundary, two states 1atm will coexist. ⚫At a triple point, Intermolecular 25 three states coexist Forces. © 2015 Pearson Education, Inc. C  Intermolecular Forces © 2015 Pearson Education, Inc. Triple Point: A unique temperature and pressure at which three phases (usually solid, liquid, and gas) can exist together. Critical Point: The temperature and pressure at which gas and liquid merge together to form a supercritical fluid. Beyond this temperature, no amount of pressure will condense the gas to a liquid. Normal Melting Point – At 1 atm pressure, the temperature at which the solid melts to liquid. Intermolecular Normal Boiling Point – At 1 atm pressure, the temperature at which the liquid vaporizes to Forces become a gas. © 2015 Pearson Education, Inc.  Dry Ice – CO2 (s) vs. CO2 (g) -78 °C, 194.7 K, - 109 °F Intermolecular Forces © 2015 Pearson Education, Inc. In general, 1) High pressures favor liquids and solids because the atoms are packed closer together (more dense). 2) Low pressures and high temperatures favor gases (less dense). 3) High temperatures favor liquids and gases because the atoms are less tightly packed, and are more mobile and Intermolecular Forces energetic. © 2015 Pearson Education, Inc.  In other words….for most cases Pressure Solids Liqui ds Gases Intermolecular Forces Temperature © 2015 Pearson Education, Inc.  The H2O Phase Diagram  = 1.00 g/ml  =.92 g/ml  =.0006 g/ml Intermolecular Forces © 2015 Pearson Education, Inc.  H2O Phase Diagram - continued Note the negative slope of the ice-water phase boundary! What phase is most dense? Two ways to vaporize water….?? Intermolecular Forces © 2015 Pearson Education, Inc.  Energy Change & Change of State The heat of fusion is the energy required to change a solid at its melting point to a liquid. The heat of vaporization is the energy required to change a liquid at its boiling point to a gas. The heat of sublimation is the energy required to change a solid directly to a gas. Intermolecular Forces © 2015 Pearson Education, Inc.  Heating Curves A plot of temperature vs. heat added is called a heating curve. Within a phase, heat is the product of specific heat, sample mass, and temperature change. The temperature of the substance does not rise during a phase change. For the phase changes, the product of mass Intermolecular Forces and the heat of fusion of vaporization is heat. © 2015 Pearson Education, Inc.  Supercritical Fluids Gases liquefies when pressure is applied. The temperature beyond which a gas cannot be compressed is called its critical temperature. The pressure needed to compress the liquid at critical temperature is called critical pressure. The state beyond this temperature is called a Intermolecular supercritical fluid. Forces © 2015 Pearson Education, Inc.  Vapor Pressure At any temperature, some liquid molecules have enough energy to escape the surface and become a gas. As the temperature rises, the fraction of molecules that have enough energy to break free increases. Intermolecular Forces © 2015 Pearson Education, Inc.  Vapor Pressure As more molecules escape the liquid, the pressure they exert increases. The liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate. Intermolecular Forces © 2015 Pearson Education, Inc.  Vapor Pressure The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. The normal boiling point is the temperature at which its vapor pressure is 760 torr. Intermolecular Forces © 2015 Pearson Education, Inc.  PROPERTIES OF WATER High boiling point High specific heat High density in its liquid form High surface tension High heat of vaporization Intermolecular Forces © 2015 Pearson Education, Inc.  Classification of Solids Crystalline Amorphous Solids with highly Solids with regular arrangement considerable of components disorder in their structure. Intermolecular Forces © 2015 Pearson Education, Inc.  X-ray Diffraction X-ray Diffraction is commonly used to determine the structure of a solid. Intermolecular Forces © 2015 Pearson Education, Inc.  Crystalline Solids A Lattice represents the regular positioning of the components of a crystal. A Lattice is the three dimensional system of points designating the positions of the components. The smallest repeating unit of the lattice is called the Intermolecular Unit Cell. Forces © 2015 Pearson Education, Inc.  Unit Cell-Simple Cubic, Body centered cubic & Face centered cubic. Intermolecular Forces © 2015 Pearson Education, Inc.  Intermolecular Forces © 2015 Pearson Education, Inc.  Types of Crystalline Solid Ionic Solids: metal and non metal Covalent solids: made up of atoms and are joined by covalent bonds Molecular solids: non metal and non metal Atomic solids: single element Metallic solids: joined by metallic bond Intermolecular Forces © 2015 Pearson Education, Inc.  Ionic Solids: metal and non metal Ionic substances have ions at the point of the lattice that describe the structure of the compound. Examples: NaCl, FeSO4, Al2S3 Intermolecular Forces © 2015 Pearson Education, Inc.  Molecular solid: non metal and non metal chemistryicevoet2 Molecular solids have discrete covalently bonded molecules at the end of each of its lattice points. See ice → Intermolecular Forces © 2015 Pearson Education, Inc.  Atomic solids: single element Atomic solids all have atoms at the points of the lattice that describes the structure of the solid. This example is diamond a network covalent solid. Other examples include, boron, silicon and all Intermolecular metals. Forces © 2015 Pearson Education, Inc.  Atomic solids: Three types Metallic Solids Network Solids Group VIIIA solids Intermolecular Forces © 2015 Pearson Education, Inc.  Metallic Solids These have a type of delocalized non- directional covalent bonding. Examples are Cs and Au Intermolecular Forces © 2015 Pearson Education, Inc.  Network Solids The atoms bond to each other with strong directional covalent bonds that lead to macromolecules or networks of atoms. Intermolecular Forces © 2015 Pearson Education, Inc.  Group VIIIA solids Noble gases are attracted to one another at low temperatures with weak London dispersion forces. The examples are Kr and Xe. Both are cubic close packed. Intermolecular Forces © 2015 Pearson Education, Inc.  Types of solids Intermolecular Forces © 2015 Pearson Education, Inc.  Summary Classification of solids Molecular Ionic Atomic Solids Solids Solids Metallic Network Group VIIIA Components that ocupy Group the lattice Nonmetal VIIIA Discrete points Metal Ions atoms atoms molecules Ions Dipole-dipole Directional London and/or London Delocalized Covalent Dispersion dispersion Bonding covalent (marcomolecules) Forces forces Ionic Intermolecular Forces © 2015 Pearson Education, Inc.