Arrangement of Electrons in Atoms CHEM1.PS4:1 Using a model, explain why elements emit and absorb characteristic frequencies of light and how this information is used.

The Development of a New Atomic Model Rutherford’s model did not explain how electrons are distributed in space surrounding the positive nucleus. Bohr discovered the hydrogen-atom spectrum which lead him to propose a new atomic model. In the new model, electrons circle the nucleus only in allowed paths called orbits. Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. Some examples of electromagnetic radiation are: Visible (or white) light Infrared (IR) Ultraviolet (UV) light Gamma (γ) ray X-ray Radio waves

The Development of a New Atomic Model All forms of electromagnetic radiation move at a constant speed: c (speed of light) = 3.00 X 108 m/s (meters per second)

The Development of a New Atomic Model Wavelength is the distance between corresponding points on adjacent waves. Frequency is the number of waves that pass a given point in a specific time, usually 1 second. Units of measurement for wavelength can be _________, _________ or ________ and measures distance. Frequency is expressed in waves/second and one wave/second is called a ________. Frequency and wavelength are wave properties of electromagnetic radiation. But EM radiation (light) also behaves as particles.

The Development of a New Atomic Model Wavelength (λ), frequency (ν) and the speed of light (c ) are mathematically related as such: c = λν meaning that wavelength and frequency are inversely proportional to one another.

The Development of a New Atomic Model A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom. Energy and frequency are related according to the following equation: E = hν where h is called “Planck’s constant” named after German physicist Max Planck. h = 6.626 X 10-34Js A photon is a particle of EM radiation that has zero mass and carries a quantum of energy. The lowest energy state of an atom is its ground state. A state in which an atom has a higher potential energy than it has in its ground state is an excited state.

The Development of a New Atomic Model Whenever a hydrogen atom (or any atom) falls to a ground state from an excited state, it emits a photon of radiation. This process is called emission. Energy must be added to an atom in order to move an electron from a lower energy state to a higher one – this process is called absorption.

The Quantum Model of the Atom The Heisenberg uncertainty principle states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle. Quantum theory describes mathematically the wave properties of electrons and other very small particles. An orbital is a three dimensional region around a nucleus that indicates the probable location of an electron. Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. principal quantum number, n angular momentum,l magnetic quantum number, m spin number, +1/2, -1/2

The Quantum Model of the Atom

The Quantum Model of the Atom

Electron Configurations The quantum model of the atom improves on the Bohr model because it describes the arrangements of electrons in atoms other than hydrogen. The arrangement of electrons in an atom is known as the atom’s ________ ______________. The Aufbau principle states that an electron occupies the lowest- energy orbital that can receive it. (shows the order in which electrons occupy orbitals) The Pauli exclusion principle states that for two electrons to occupy the same orbital, they must have opposite spin states. Hund’s rule states that orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state.

Electron Configurations Youtube.electronconfiguration.tutorial.com https://youtu.be/K-jNgq16jEY

Electron Configurations PRACTICE: The electron configuration of nitrogen is 1s22s22p2. How many electrons are present in an N atom? How many protons? Write the orbital notation for nitrogen. The electron configuration of fluorine is 1s22s22p5. How many of its p orbitals are filled?

Electron Configurations To simplify sodium’s notation, the symbol for neon, enclosed in square brackets, is used to represent the complete neon configuration: [Ne]3s1. This is called noble-gas notation. How many electron-containing orbitals are in an atom of iodine? 27 How many of these orbitals are filled? 26 How many unpaired electrons are there in an atom of iodine? 1 Write the noble gas notation for tin, Sn. [Kr]5s24d105p2 How many unpaired electrons are there in an atom of tin? 2

Electron Configurations POPQUIZ! Write the complete electron configuration notation for a rubidium atom. Write the noble-gas notation for a rubidium atom. Identify the element having the following electron configuration: 1s22s22p63s23p3 [Ar]4s1 How many unpaired electrons are there in an atom of iodine?