Yellow. Strontium red white. green. yellow violet. green. red. Chapter 4. Arrangement of Electrons in Atoms. Table of Contents

Transcription

1 Chapter 4 Arrangement of Electrons in Atoms Table of Contents Section 1 Section 2 Section 3 The Development of a New Atomic Model The Quantum Model of the Atom Electron Configurations Sodium Yellow Strontium red Al white Barium green Na yellow Rb violet Sr red Ba green 1

2 Li red 4.1 Objectives Explain the mathematical relationship among the speed, wavelength, and frequency of electromagnetic radiation. K lavender Cu.. blue green Discuss the dual wave-particle nature of light. Discuss the significance of the photoelectric effect and the lineemission spectrum of hydrogen to the development of the atomic model. Properties of Light The Wave Description of Light Electromagnetic Spectrum Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. Together, all the forms of electromagnetic radiation form the electromagnetic spectrum. v = λν 2

3 Wavelength (λ) is the distance between corresponding points on adjacent waves. Frequency (ν) is defined as the number of waves that pass a given point in a specific time, usually one second. v = λν or c = λν All waves have 3 characteristics: Speed, Wavelength & Frequency In a vacuum: 3 x 10 8 m/s m (γ) to 10 5 m (radio) Less than 1000 Hz to Hz Given: v = λν Speed of wave = x 10 8 m/s wavelength = 7.6 x 10-7 m Find: frequency Frequency = v x 10 8 m/s λν λν = λν ν Frequency = v = 7.6 x 10-7 m speed λ = 3.9 x /s divided λ by = 3.9 x Hz wavelength The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom. 3

4 German physicist Max Planck proposed the following relationship between a quantum of energy and the frequency of radiation: E = hv E = hv E is the energy, in joules, of a quantum of radiation, ν is the frequency, in s 1, of the radiation emitted, and h is a fundamental physical constant now known as Planck s constant; h = J s. When investigators passed electric current through a vacuum tube containing hydrogen gas at low pressure, they observed the emission of a characteristic pinkish glow. When a narrow beam of the emitted light was shined through a prism, it was separated into specific colors of the visible spectrum. The bands of light were part of what is known as hydrogen s line-emission spectrum. Current passed through glass tube containing Hydrogen at low pressure Pinky glow is given off 4

5 + + 5

6 + Niels Bohr proposed a hydrogen-atom model that linked the atom s electron to photon emission. + According to the model, the electron can circle the nucleus only in allowed paths, or orbits. Hyperlink to electron behavior Write down your address using the format of number street name, and ZIP Code. THS: 315 E. 11 th These items describe the location of your residence. 6

7 How many students have the same ZIP Code? How many live on the same street? How many have the same house number? No two houses have the same address, no two electrons in an atom have the same set of four quantum numbers. The quantum-number code to describe the properties of electrons in atoms Hyperlink to quantum theory Electrons as Waves French scientist Louis de Broglie suggested that electrons be considered waves confined to the space around an atomic nucleus. It followed that the electron waves could exist only at specific frequencies. According to the relationship E = hv, these frequencies corresponded to specific energies the quantized energies of Bohr s orbits. Electrons, like light waves, can be bent, or diffracted. Diffraction refers to the bending of a wave as it passes by the edge of an object or through a small opening. Electron beams, like waves, can interfere with each other. Interference occurs when waves overlap. 7

8 The Heisenberg uncertainty principle states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle. The Schrödinger Wave Equation Electrons do not travel around the nucleus in neat orbits, as Bohr had postulated. Instead, they exist in certain regions called orbitals. An orbital is a 3-D region around the nucleus that indicates the probable location of an electron. Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. The principal quantum number, symbolized by n, indicates the main energy level occupied by the electron. The angular momentum quantum number, symbolized by l, indicates the shape of the orbital. 8

9 The magnetic quantum number, symbolized by m, indicates the orientation of an orbital around the nucleus. The spin quantum number has only two possible values (+1/2, 1/2) which indicate the two fundamental spin states of an electron in an orbital. 1 1s 2s 2 2p 3s 3 3p 3d 4s 4p 4 4d 4f Spherical shape.. 1 shape holds 2 e - Dumbbell shape.. 3 shape holds 2 e - each.. A total of 6 e - 9

10 5 shape holds 2 e - each.. A total of 10 e - 7 shape holds 2 e - each.. a total of 14 e - No 2 electrons can have the same 4 quantum numbers Each orbital can hold 2 electrons one spinning clockwise and one spinning counterclockwise on their axis +1 2 Clockwise -1 2 Counterclockwise Electrons in an atom will occupy the lowest energy orbitals available. 10

11 The most stable arrangement of electrons is that with the maximum number of unpaired electrons, all with the same spin 7s 7p Fill up first seats, but don t share unless you 3s 3p 3d have to. 2s 2p 6s 5s 6p 5p 6d 5d 5f 4s 4p 4d 4f 1s 11