1 Chemistry Chapter 11 Electron Configuration and the Periodic Table World of Chemistry Zumdahl Last revision Fall 2008

2 We left off at Rutherford’s atom… Rutherford had told us about the nucleus but he said nothing about the electrons moving in the electron cloud. Neils Bohr decided to study the electron cloud by looking at how light interacts with matter

3 Light and Energy Light is a form of Electromagnetic energy This energy is the interaction between electricity and magnetism.

4 Parts of a wave Crest: The highest point of the wave Trough: the lowest point of the wave Wavelength ( ): The distance between two crests or two trough Amplitude: How far the wave is from the origin

5 Terms to describe waves: Cycle: The motion from beginning to end before it begins repeating. Period (T): The time it takes to complete one cycle. Metric SI Unit: (s) seconds Frequency (f): The number of cycles that occurs in a second. Metric SI Unit: (Hz) Hertz or (s -1 ) inverse seconds Amplitude: How big the wave is or how far away from its origin it is. Unit depends on the kind of wave. Decibels for sound, Candela for light.

6 The duel nature of light It was found that if you shine light through a slit you can make a pattern that implies a particle nature to light. That particle is called a photon

7 Energy of light The amount of energy a light wave carries corresponds to its frequency and wavelength. The longer (higher) the wavelength, the lower the energy. Inverse relationship The higher the frequency, the higher the energy. Direct relationship

8 Neils Bohr noticed that atoms will emit a specific color of light when energy is added to the atom, like in a flame.

9 Bohr concluded that the electron must be transitioning to different levels in the atom each with it’s own specific amount of energy Energy is absorbed from the flame and electrons get excited. When the electrons get excited they transition or jump up orbits to a higher energy level. They will not stay excited for long and when the electron drops down to the original ground state orbit the energy will be released in the form of light

10 Think of the energy levels in an atom like a ladder. You can only stand on the rungs. Not in between Just like electrons can only be in one energy level Electrons jumping between energy levels will absorb and release only a specific amount of energy. The energy released corresponds to a specific wavelength of light

11 Bohr Models A specific amount of energy is called a quanta Bohr’s energy levels are called quantized orbits. Each orbit or energy level is symbolized with the letter n, this is called its principle quantum number. n= 1 n= 2 n= 3

12 The problem was Bohr’s model only worked for a hydrogen atom and a new way of looking at the electrons needed to be discovered. Even though the electron is a particle it could propagate through space as an energy wave just like light. To understand the atom, one must understand the behavior of electromagnetic waves Louis deBroglie Erwin Schrödinger and Louis deBroglie worked on the problem of the electrons.

13 Erwin Schrödinger used calculus and quantum mechanics to analyze the electrons energy and make a density plot of where the electron will probably be based on their wave energy. This gave us a fuzzy view of the atom based on where the electron probably is but the equation worked for all atoms. Quantum Mechanical Model

14 Schrödinger’s Quantum Mechanical Model Schrödinger's model gave various shapes for the location of electrons. These shapes are called orbitals. There are 4 orbital shapes denoted with letters: s, p, d, and f

15 d orbitals s orbitals p orbitals

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17 Electron Configurations can give you the position of the electrons in the atom. This shows the distribution of all electrons in an atom. Each component consists of  A number denoting the energy level; the principle quantum number  A letter denoting the type of orbital,  A superscript denoting the number of electrons in those orbitals.

18 Orbital Diagrams Each box in the diagram represents one orbital. Aufbau’s rule: Electrons will fill the lowest energy orbital before filling higher energy orbitals

19 Hund’s Rule: Electrons will fill an orbital individually before pairing up Pauli’s Exclusion Principle : an orbital can hold two electrons and those electrons have opposite spins

20 Bohr Models Bohr’s model was not entirely useless. It can give a simplified look at an atom and its electrons

21 Each row of the Periodic table is called a Period. This is the 1 st PeriodThis is the 2 nd PeriodThis is the 3 rd PeriodThis is the 4 th PeriodThis is the 5 th Period

22 Bohr Models – Energy Levels The period in which the element is found in tells us the number of energy levels the atom will have. Ex. Carbon is in period 2, and therefore has 2 energy levels. The particles in the nucleus are written in a center circle. 6P + 6N 0

23 Each column has a number at the top between 1 and 8

24 This is the Valence Number The electrons in an atom that are involved in the formation of chemical bonds. These are in the outer energy level.

25 Valence Shells and Groups Valence shell – This is the outermost energy level that contains valence electrons. Groups – columns of elements that act similarly are called groups. Those with the same valence electrons are in the same group.

26 The energy levels have a maximum number of electrons they can hold. Maximum number of electrons n1 = 2 n2 = 8 n3 = 18 n4 = 32 n5 = increasing amounts Energy Levels

27 If we construct a Bohr model of Carbon, what information should it contain? 1- The number of protons and neutrons in the nucleus. 2- The energy levels present 3- The total number of electrons in the electron cloud Carbon Bohr Model

28 How to make a Bohr Model Drawing Bohr Models: 1) Draw the nucleus 2) Determine energy levels by period 3) Fill outer energy level first by the column (valence) number 4) Fill from inside out until you reach the outer level. This should use all of the electrons.

29 Follow the steps to draw a carbon Bohr model: Step 1 Step 2 Step 3 Step 4 Carbon

30 Remember: Column number tells us the Valence electrons. We diagram the valence electrons with Lewis Dot diagrams Lewis Dot diagrams – dots around the symbol represent valence electrons around the nucleus. 1. Place two electrons together if there are more than four, otherwise spread them out around the symbol. 2. Spread the rest out before pairing.

31 Practice drawing Lewis Dots HMgCO F Ar N B