Electronic Structure of the Atom Chemistry Chapter 5

The electronic structure is the arrangement of an atom’s electrons around the nucleus. Ease with which an atom gains or loses electrons determines it’s chemical properties. Electronic Structure

The energy of an atom is governed by how the electrons are arranged around the nucleus. Different amounts of energy are associated with different arrangements of electrons. A change in electron arrangement will change the energy of an atom. Energy of an Atom

The energy state of an atom is the sum of the energies of the electrons in the atom. The lowest energy state of the electrons in an atom is called the ground state. All energy states with more energy than the ground state are called excited states. Energy States

Changes in Energy States All things in nature tend toward the minimum energy state. Atoms in their ground state are considered stable because they have already reached their minimum energy state. Atoms that are in an excited state are considered unstable because they are not at their minimum energy state. Changes in Energy States

Minimum Energy in an Atom Electrons in an atom prefer to be arranged in a condition (or state) of minimum energy and hence maximum stability. Therefore, excited electrons seek to give up energy to return to their ground state. Minimum Energy in an Atom

Electrostatics deals with interactions between charged particles. Electrostatics tells us that opposite charges attract and like charges repel each other. Electrons in an atom must meet two conditions: Be close to the nucleus, but Avoid other electrons Electrostatics

Bohr’s model of the atom required that the electron could only have certain definite energies. Therefore, Electrons could only have certain orbits. Orbits would occur at specific distances from the nucleus. Orbits would be characterized by a specific energy. Bohr’s Model

Bohr was able to calculate the energy of the orbital and the amount of energy needed to change from one orbital to the next. Ground state occurred when an electron was in orbit 1, the one closest to the nucleus. Excited electrons would occur in orbitals further from the nucleus beyond orbital 1. Electrons could not exist between energy states. Bohr’s Model

Orbitals are used to describe the volume of space an electron is likely to be found in. Each can hold no more than two electrons. Each has a specific energy associated with it. Different energy levels have a specific number of orbitals possible. Orbitals

Orbitals have different shapes as indicated by the letter that represents them. S is spherical P is shaped like a dumbbell. D orbitals have five distinct shapes. Orbital Shapes

Shapes of Orbitals

Aufbau’s principle (# e-/energy level) 1st Energy Level = 1s 2nd Energy Level = 2s, 2p(x), 2p(y), 2p(z) 3rd Energy Level = 3s, 3-3p’s, 5-3d’s In general the formula 2n2 gives the total number of electrons that can occupy an energy level. Where n = the energy level (1, 2, 3, etc). This is Aufbau’s Principle. Aufbau’s principle (# e-/energy level)

Spin: A property of Electrons Pauli Exclusion Principle states that two electrons residing in the same orbital must have opposite spins. Electrons are believed to be spinning either clockwise or counterclockwise. The spin of the electrons produces a magnetic field with a charge either positive or negative. Spin: A property of Electrons

Electrons are identified by a series of four quantum numbers. Principle energy level Energy sublevel Orbital Spin of the electron Video on quantum numbers, orbital shapes and the principle. Quantum Numbers

When an electron is excited to a higher energy level it will emit energy in the form of visible light as it returns to the lower energy level. The color of the light is related to the amount of energy given off. Each element emits characteristic colors which can be used to identify the element. Spectroscopy

Wave properties: Amplitude: height of the wave (its intensity) Wavelength: distance between crests (its energy) Frequency: # of cycles per unit time (hertz) c = lambda (frequency) or c = ʎ v/f Nature of Light: Wave

Electromagnetic Radiation All forms of light, visible and invisible, make up the EM spectrum Electromagnetic Radiation

Nature of Light: Particle/Photon Max Planck showed that energy is emitted in globs or discrete units (called quanta so we say light is quantized) by hot objects (blackbody radiation), rather than gradually increasing levels. His equation is that energy is directly proportional to the frequency of the radiation times his constant (6.626 x 10-34 Js). Nature of Light: Particle/Photon

Atomic Emissions Atomic Emission Animation Spectroscopy by eye Photoelectric Effect Einstein identified and explained the photoelectric effect, which indicates that light behaves as if it has a particle nature (he called the particles or packets of energy photons) Atomic Emissions