Energy Level of the Atom

1. Energy Level of the Atom Based on the Bohr & The Wave Mechanical Model

2. The Bohr Model of the Atom Neils Bohr described an atom with quantized energy levels. These are discrete energy levels. Since we cannot tell both location and momentum of an electron at the same time (Heisenberg Principle), this model serves to predict the probabilities of where the electrons in an atom are located.

3. The Wave Mechanical Model • Is used today to describe all atom models. It was developed by Broglie & Schrodinger in the 1920’s and replaced the Bohr Model. • This model describes light as having both wave and particle properties. This model was developed based upon the study of Quantum Physics.

4. Quantum Theory • Describes mathematically the properties of electrons and small particles. • This field of study is also known as Quantum Mechanics.

5. A Quantum of Energy • Is the minimum amount of energy that can be gained or lost by an atom. • When an electron loses or gains energy, it is always in quantum amounts. These are always discrete amounts.

6. Quantum Numbers • Are numbers that specify the properties of atomic orbitals and the properties of electrons in those orbitals. • There are a total of FOUR QUANTUM NUMBERS.

7. Principal Quantum Number • Is the first quantum number and is symbolized by the letter n. • It indicates the main energy level occupied by the electron. • There are seven prinicipal quantum numbers. • n= 1 through n = 7 • The lowest energy level occupied by an atom is n = 1. • This quantum number describes the amount of energy the electron possesses.

8. Ground State & Excited Stateof an Atom The lowest energy level of an electron, n =1, is also known as the atom’s ground state. The state of an electron that has a higher potential energy than the ground state is called an excited state. The atom has said to gain one or more quantums of energy.

9. Angular Momentum Quantum Number • The second quantum number is symbolized by the letter l and indicates the shape of the orbital path the electrons create. • Depending on the shape, it is assigned a letter, s,p, d and f. • It describes as best as possible the movement of the electron around the atom.

10. Shapes of Orbitals • The s orbitals have a spherical shape left by the electrons energy signatures. • The p orbitals have a figure eight shape left by the electrons energy signatures. • The d orbitals have a clover shape left by the electrons energy signatures. • The f orbitals have ? shape left by the electrons energy signatures.

12. Magnetic Quantum Number • The third quantum number is symbolized by the letter m and indicates the orientation of an orbital around the nucleus. • It describes the direction the electron is traveling in 3-dimensional space. • It takes on an x,y and z vector much like the direction of N, S, E, and W in 2-dimensional space.

13. Spin Quantum Number • The fourth quantum number has no letter to represent it, but instead has two possible values. • It has a +1/2 or -1/2 spin value and indicates the fundamental spin states of an electron on its own axis within an orbital. • Much like the Earth spins on its own axis to give us night and day while revolving around the sun to give us our four seasons, the electron in every atom spins on its own axis, one to the right, the other to the left in the same orbital as the pair revolve around the nucleus of an atom.

14. Orbitals • Are places in an atom where there is a high likelihood of finding an electron. (Heisenberg Priniple) • No more than two electrons can be in any orbital. The is called the Pauli Exclusion Principle. • There are three possibilities for electrons in an orbital. The orbitals have 0,1, or 2 electons contained in them. • This is due to the nature of how an atom fills its orbitals which will be discussed later.

15. The Bohr Model of the Atom • Describes a very tiny dense nucleus (compact) with a very large diameter where the electrons are thought to reside (exist) in the various every levels (distances the electrons exist around the nucleus based on the amount of energy they contain). • How the electrons are arranged in these energy levels dictate the atom’s physical and chemical properties. *****************************

16. Electron Configuration • Is a description of the occupied orbitals in an atom. Electrons occupy the orbitals in a certain manner. • In regular electron configurations, atoms fill their orbitals with electrons from the lower to higher energy levels. • These types of configurations are true of the main group elements. • In each energy level, there certain types of orbitals.

17. Example of how Atoms fill their Orbitals • In the first main energy level, n =1, there is only one type of orbital that exists. • It is an s orbital with a spherical shape that holds a maximum of 2 electrons designated 1s2. • The one stands for the Principle Quantum Number, The s stands for the shape of the orbital and the 2 signifies the number of electrons in the orbital. • A perfect example of a 1s2 configuration is HELIUM.

18. Continued…………. • In the second Principle Energy Level, n =2, there are two types of orbitals, an s and p orbital. • The s orbital has a maximum of 2 electrons. • There are 3p orbitals, each with a maximum of 2 electrons in each, making a total of 6 electrons. • For example Neon, which has a total of 10 electrons has configuration of 1s22s22p6. • It has 2 electrons in the s orbital of the first energy level and 8 electrons in the second energy level, 2 in the s orbital and 2 in each of the 3p orbitals.

19. Continued…………… • Fluorine has a total of 9 electrons with 2 electrons in the first energy level and 7 electrons in the second energy level. • Its configuration would look like this: • 1s22s22p5. • In order to learn how to figure the configurations for the other atoms, we will learn the Wave Mechanical Model and practice writing the configurations.

20. Number of Orbitals • In each energy level, there are that many sublevels, otherwise known as orbitals with a total of the following electrons. • n=1 1s 2e 2e • n=2 1s,3p 2e, 6e 8e • n=3 1s,3p,5d 2e, 6e, 10e 18e n=4 1s,3p,5d, 7f 2e,6e,10e,14e 32e

21. Wave Mechanical Model We use the Wave Mechanical Model below to figure the electron configurations of each atom.