Home > Chemistry > Chemistry 1A Part Deux: Lecture 35 Notes

Chemistry 1A Part Deux: Lecture 35 Notes

Overview

This is a 48 minute lecture on the electronic shell model.  There is quite a bit of spectroscopy today.  Ionization energy is completely removing the electron from the atom.  This is quite different from hitting an atom with some energy and the electron moves between discrete energy values.

Details

High energy photons can be used to eject electrons from atoms.

Periodic trends and the octet rule suggest the correctness of a shell model for atoms.

For the light detector, light strikes the cathode, electrons are emitted, and current is detected.  These are found on automatic doors, like in your local supermarket.

For light as a particle, take a photo of a dim light.  Turn it down, you’ll see individual photon strikes.  Turn it down even further, you’ll see very individual photons.  Electrons are emitted only if the energy of light exceeds a threshold value.  This is difficult to explain with a wave model for light.

Intensity = number of photons

Color is a measure of energy per photon

The kinetic energy of the ejected electron varies linearly with the energy of the impinging light.

KE electron = E photon – Ionization Energy

E = hc/w = hf

Hydrogen atoms have an ionization energy of +1312 kJ/mol.  The electronic configuration of hydrogen is 1s1.

If photons of sufficiently high energy are used, an electron may be ejected from any of the shells of an atom.  Each atom can lose only one electron, but every electron in the atom has approximately equal probability of being ejected.  The kinetic energy of the ejected electron is equal to the energy of the incident photon minus the binding energy of the electron in the atom.

Helium has an ionization energy of 2372 kJ/mol.  It’s electronic configuration is 1s2.

Lithium is 1s2 2s1.  To eject a 2s electron, you need 520 kJ/mole.  To eject a 1s electron, you need a 6260 kJ/mol.  Note the difference; 1s is closer and requires more energy.  Also, each s shell can hold two electrons, which is why there are not two separate IEs.

Boron is 1s2 2s2 2p1.  To eject a 2p, 800 kJ/mol.  To eject a 2s, 1360.  Finally, a 1s orbital costs 200 MJ/mol.

The shell model does not explain anything past Boron.  For that, we need to start in on subshells.

Photoelectron Spectra

Oxygen is 1s2 2s2 2p4 and has IEs of 1310/3120/52600 kJ/mol.

Neon is 1s2 2s2 2p6 and has IEs of 2080/4680/8400 kJ/mol.

Revised Model of the Atom

The n=2 shell is divided into two subshells; the 2s can hold 2 electrons.  The 2p subshell can hold 6 electrons.  Electron in atoms have quantized energies.

Number of electrons in Shells and Subshells

Shell    Electrons          Subshell     Electrons

n = 1             2                     1s                 2

n=2              8                 2s/2p            2/6

n=3              18              3s/3p/3d     2/6/10

n=4              32        4s/4p/4d/df         2/6/10/14

Energy diagrams are ordered as follows, from low to high: 1s 2s 2p 3s 3p 4s 3d 4p…

Review

Noble gases: He, Ne, Ar, Kr, Xe, Rd

Types of bonding: ionic >1.7, polar covalent between, non polar <0.5

PV = nRT

METT TC mission enemy troops terrain time civilians

SALUTE size activity location unit time equipment

2s 6p 10d 14p

KE electron = E photon – Ionization Energy

Tissue: epithelial, connective, nervous, muscular

Epithelial: simple/stratified/pseudostratified    cuboidal/columnar/squamous

  • single covalent bond – 1 shared pair
  • double covalent bond – 2 shared pairs
  • triple covalent bond – 3 shared pairs

Bond energy: single < double < triple

Bond length: single < double < triple

pKa’s:

Alkanes (50)

CH4/CH3-

Alkene (44)

Alkyne (25

HF +3.2

HCl -7

HBr  -9

HI -10 NH3 38 L

RCOOH (4-5)

HF (3.2)

NH4+ (9.26)

H2O (15.7)

ROH (17)

RSH (11)

H30+  (-1.7)

pKa = – log Ka

Spectroscopy: emission/absorption

A = e l c

IGL: point source, random motion, elastic collisions, high temp, low pressure

6 strong acids:

  • HCl
  • H2SO4
  • HNO3
  • HClO4
  • HBr
  • HI

The stronger the acid, the higher the Ka, the weaker the conjugate base.

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