Figure P4.7 provides data for water entering and exiting a tank. At the inlet and exit of the tank, determine the mass flow rate, each in kg/s. Also find the time rate of change ofmass contained within the tank, in kg/s.
Chapter 10: Chemical Bonding Part II VSEPR Theory: Based on the simple idea that electrons groups which we define as long pairs, single bonds, multiple bonds, and even single electron repel on another through columbic forces Valence Shell Electron Pairs Repulsions Lone pair: 1 group Single Bond: 1 group Double Bond: 1 group Objective: Use VSEPR to predict: o Electron geometry: shape made by electron groups that are present o Molecular geometry: Shape made by nuclei that are present o Bond angles: Angle produced between bonds Ideal: 180°, 120°,; i.e. symmetry Non-Ideal: non-symmetrical Two groups of electrons: o BeCl 2Linear Geometry with bond angles of 180° Three groups of electrons: o Electron Geometry: Trigonal Planar with bond angles of 120° Double bonds need more space therefore have greater Four groups of electrons: o Electron geometry is tetrahedral and has bond angles of 109.5° Five groups of electrons: o Electron geometry is a trigonal bi-pyramid o Bond angles: Anything from equatorial to axial is 90°. Anything form axial is 120° Six groups of electrons: o Electron geometry is octahedral with bond angles of 90° But what does resonance do in a particular structure - o NO 3 o Are bond angles equal YES! Effects of Lone Pairs o Key Idea: Lone pairs require more space Lone pair – Lone pair > Lone pair – Bonding pair > Bonding pair – Bonding pair Lone Pairs “Invisible” in molecular geometry o 3 groups of electrons electron geometry that is Trigonal Central Atom A X E The formation of ozone is bent Ozone is a because of the lone pair that is on the central atom repulsing AX 2 model # of bondsthe other bonds further away because lone pairs want to maximize space Planar o 4 groups of electrons electron geometry is Tetrahederal 1 Lone pair: Example/ NH 3 In the electron geometry, this lone pair is visible, but in the molecular geometry they are “invisible” meaning they are there causing difference in the shape. NH3 is a Trigonal pyramid because the lone pair repulses the other bonds. NH3 is an AX3E AX2E2 2 Lone pairs: Example/ H O2 o 5 Groups of electrons Electron geometry is Bi-Pyramid 1 Lone pair: Example/ SF 4 AX4E Since sulfur is in period 3 and can obtain an expanded octect, this lone pair is aloud. REMEMBER TO ALWAYS MAKE SURE THERE ARE THE CORRECT AMOUNT OF ELECTRONS 2 Lone pairs: Example/ BF 3 AX3E2 AX2E 3 Lone pairs: Example/ XeF 2 o 6 Groups of electrons Electron geometry is Octahedral 1 Lone pair: Example/ BrF 5 AX5E 2 Lone pairs: Example/ XeF 4 AX4E2 o Larger Molecules Determining geometry o Summarizing VSEPR Theory Around this Carbon: AX4 Tetrahedral Bent Linear shape around Oxygen Around this Carbon: AX3 Trigonal Planar Around this Nitrogen: Trigonal Pyramid **Be able to notice the geometrical shapes in large molecules** The geometry of a molecule is determine by the number of electron groups on the central atom (or on all interior atoms, if there is more than one) The number of electron groups is determined from the Lewis structure of the molecule. If Lewis structure contains resonance structures, use any one of the resonance structures to determine number of electron groups Each of the following counts as a single electron group: a lone pair, single bond, double bond, triple bond, or a single electron (as a free radical) In general the electron group repulsions vary as follows: Lone pair – Lone pair > Lone pair – Bonding pair > Bonding pair – Bonding pair Molecular Polarity o When the change is electronegativity is 0, it is perfectly nonpolar (no difference in how the atoms are sharing electrons) o Objective: Determine if molecule is polar based on bonds and shape Have a symmetry about that central atom and that symmetry has a cancel of bond polarities making it look nonpolar But because both sides cancel the overall molecule has a change in electronegativity of 0 o Example: CO 2 o Example H O 2 o Example: CCl 4 Everything in this molecule is pulling form the central atom equally because all the atoms around Carbon are the same making this a nonpolar molecule Point of symmetry= nonpolar molecule The electrons come at each other at an angle instead of head on making the electronegativities not cancel making it polar Because there is no symmetry due to the lone pairs in the electron geometry, this molecule is polar Because central atom(which is carbon even though that is not pictured) is not being pulled equally (due to different atoms) this molecule is polar because the electronegativities do not cancel like in CCl4 o Example: CCl F 2 2 o Determining Polarity: 1. Lewis Structure 2. Shape Ozone is an exception to these Polar bonds rules o No nonpolar o Yes is there a point of symmetry Yes Nonpolar No Polar Trigonal Planar Trigonal Planar Point of symmetry (between nitrogen atoms)= nonpolar molecule o Example: N O 2 4