Chapter 4: Arrangement of Electrons in Atoms by Chris Baldwin, Kayla Cooper, Melissa Thomas, and Taylor Washington

Section 1: The Development of a New Atomic Model by Chris Baldwin

The Wave Description of Light ---- Visible light is a type of electromagnetic radiation, a form of energy that exhibits wavelike behavior as it travels through space ---- Other examples of electromagnetic radiation would be ultraviolet or infrared light, microwaves, radio waves, and X rays ---- All forms of electromagnetic radiation travel at a constant speed of about 3.0 * 10^8 meters per second

The Wave Description of Light ---- The motion of waves is very repetitive, which means that waves can be categorized by measureable properties ---- One of these properties is wavelength, (λ) the distance between corresponding points on adjacent waves ---- Another property is frequency, (v) the number of waves that pass a given point in a specific time, usually one second, measured in waves per second, which is called a hertz

The Wave Description of Light ---- Frequency and wavelength are mathematically related to each other ---- The relationship between frequency and wavelength is c=λv, with c being the speed of light, λ being wavelength, and v being frequency ----The product of λv is always a constant. λis inversely proportional to v. As wavelength decreases, frequency rises, and vice versa

The Photoelectric Effect ---- The photoelectric effect is the emission of electrons from a metal when light shines on the metal ---- The photoelectric effect was a phenomenon because for a given metal, no electrons were released if the frequency of the light was below a certain measurement

The Particle Description of Light ---- German scientist Max Planck suggested that objects emit energy in small, specific amounts, called quanta. A quantum is the minimum quantity of energy that can be lost or gained by an atom ---- Planck also came up with a relationship between a quantum of energy and the frequency of radiation, represented by E=hv, E being the energy in joules of a quantum of radiation, v the frequency of the radiation, and h, Planck’s constant, which is about * 10^-34 J*s ---- Einstein expanded on Planck’s ideas by introducing an idea that light could be thought of as a stream of particles and each particle carries a quantum of energy ---- These particles were named photons, particles of electromagnetic radiation having zero mass and carrying a quantum of energy

The Hydrogen-Atom Line-Emission Spectrum ---- The lowest energy state of an atom is its ground state ---- A state where an atom has a higher potential energy than it has in its ground state is an excited state ----When an excited atom goes back down to its ground state, energy is given off in the form of electromagnetic radiation ----Scientists conducted an experiment where an electric current was passed through hydrogen, which resulted in the emission of a pinkish glow ----The line-emission spectrum is when narrow beams of emitted light are shined through a prism, separating it into specific frequencies of visible light

Bohr Model of the Hydrogen Atom ---- Scientists were puzzled by the fact that excited hydrogen atoms gave off only specific frequencies of light ---- Niels Bohr solved the dilemma by creating a model of the hydrogen atom

Section Questions Q:What is the difference between wavelength and frequency? Q:What is the definition of a quantum? A:Wavelength is the distance between adjacent waves, while frequency is the number of waves that pass in a specific amount of time. A:A quantum is the minimum quantity of energy that can be lost or gained by an atom

Section 2: The Quantum Model of the Atom by Kayla Cooper

Electrons As Waves ---- Scientists contradicted Bohr’s model of atoms ---- They believed that electrons could move on an direction and weren’t confined to an orbital ---- Louis de Broglie suggested that electrons could act like waves ---- Experiments confirmed that electrons could be bent or diffracted and can interfere when two beams of electrons overlap

The Heisenberg Uncertainty Principle ---- Werner Heisenberg experimented on the movement of electrons ---- Discovered the Heisenberg uncertainty principle which stated that it is impossible to know the location and velocity of an electron at the same time because they are always moving ---- This principle was proven to be one of the most fundamental ways of understanding the concepts of light and matter

The Schrodinger Wave Equation ---- Erwin Schrodinger believed electrons acted as waves ---- Schrodinger’s wave equation and the Heisenberg uncertainty principle led to the discovery of the quantum theory ---- The quantum theory describes mathematically the wave properties of electrons and other very small particles ----Electrons move in orbitals which are three-dimensional regions around the nucleus that indicate the probable location of an electron

Atomic Orbitals & Quantum Numbers ---- Quantum numbers are used to describe different orbitals ---- Quantum numbers specify the properties of the orbitals and the properties of the electrons inside of them ---- The principal, angular momentum, magnetic, and spin are the four quantum numbers

Atomic Orbitals & Quantum Numbers ---- The principal quantum number which is symbolized by n, indicated the main energy level occupied by the electron ---- n is the number of energy levels and n squared is the number of orbitals in each energy level ---- As n increases, the energy of the electron and its average distance from nucleus heighten

Atomic Orbitals & Quantum Numbers ---- The angular momentum quantum number, symbolized by l, indicates the shape, or sublevel, of the orbital ---- These orbitals can be either s, p, d, or f ---- The number of orbital shapes possible is equal to the principal quantum number: if n=1, s is the only orbital present l, if n=2, it can hold both s and p orbitals, and so on

Atomic Orbitals & Quantum Numbers ---- The magnetic quantum number, m, states the orientation of orbitals around the nucleus ----The s orbital only has one possible orientation, since it’s a sphere p has 3, and d has 5

Atomic Orbitals & Quantum Numbers ---- The spin quantum number, has 2 possible values, (-1/2 and +1/2), since there are only 2 ways an electron can spin ----An orbital can only hold a maximum of 2 electrons, which have to have the opposite spin

Section Questions Q:How did Louis de Broglie change the way that we think about electrons? Q:What is a quantum number? State the 4 quantum numbers with a brief description of each. A:de Broglie was the scientist who suggested that electrons act like waves. A:A quantum number specifies the properties of orbitals and or the properties of the electrons inside of them. The principal quantum number states the energy level, the angular momentum quantum number indicates the sublevel, the magnetic quantum number shows the orientation of orbitals, and the spin quantum number tells the direction electrons are spinning.

Section 3: Electron Configurations

Part 1: Rules and Representation of Electron Configuration by Taylor Washington

Rules Governing Electron Configurations ---- Electron configuration is the arrangement of electrons in an atom ----Electrons are added to orbitals according to three basic rules ---- The first rule is the order in which electrons occupy orbitals, the Aufbau principle says that an electron occupies the lowest- energy orbital that can receive it ---- Beginning with the third energy level, sublevels begin to overlap

Rules Governing Electron Configurations ----The second rule is the Pauli exclusion principle, which says that no two electrons in the same atom can have the same set of four quantum numbers ---- The final rule is known as Hund’s rule, or the “empty bus seat” rule. This 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

Orbital and Electron Configuration Examples of elements in both electron and orbital notation.

Part 2: Rules for Periods on the Periodic Table by Melissa Thomas

Elements of the Second Period ----The highest occupied energy level in the second period is n= The highest occupied energy level is the electron-containing main energy level with the highest principal quantum number ---- Inner shell electrons are electrons at an energy level below the highest occupied energy level

Noble Gas Notation ---- Group 18 elements are known as the noble gases ---- Each noble gas, with the exception of helium (He), has an electron octet in its highest energy level ---- Noble-gas configuration is an outer main energy level fully occupied, in most cases, by eight electrons

Elements of the Fourth Period ----The 4s orbital if filled first, followed by 3d, and then 4p ---- The 3d sublevel is lower in energy than the 4p sublevel

Elements of the Fifth Period ----The 5s sublevel is filled before the 4d sublevel, which is followed by 5p ---- The reason for this is the same reason as elements of the fourth period

Elements of the Sixth and Seventh Periods ----The sixth period has 32 elements ---- Electrons are first added to the 6s orbital in Cesium and Barium, next the 4f, then 5d, then 6p ---- The 13 elements after Cerium fill the 4f sublevels ----The 4f and 5d sublevels are close in energy levels, so there are many fluctuations in the order they are written for varying elements ----The seventh period is incomplete with synthetic elements

In order to further understand how the elements in each period are written in electron-configuration form, you should study the chart in the textbook on page 105.

Section Questions Q:What are the three rules that determine how electrons are added to orbitals and what do they state? Q:What happens to some of the sublevels after period 3? A: The Aufbau principle: an electron occupies the lowest-energy orbital that can receive it. The Pauli exclusion principle: no two electrons can have the same 4 quantum numbers. Hund’s Rule: 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. A:Some of the sublevels begin to overlap, for example, 3d comes before 4s.

The End!