Science Writing: Chemistry
Unit 3: Electron Structures and the Periodic Table
See also Chemistry: Atoms First 2e, Chapter 3
Although the identity of each atom is determined by the number of protons, the chemical reactivity is determined by the activities of the electrons.
Electromagnetic Energy
Electromagnetic Waves
Electromagnetic energy is all around us, from the light of the sun to the microwave frequencies used to heat our food to the radio frequencies you pick up in your car.
Frequency of electromagnetic waves indicates the oscillations per second.
Wavelength describes the length of each individual wave.
Wave-Particle Duality
Light travels in waves...but also as particles. This is also true for particles such as electrons — every object oscillates at a specific frequency, but the frequency changes depending upon the mass.
For a large object like a baseball, the waves are so small compared to the ball that you can't detect them. But for an electron, the wavelenght is larger than the electron, which means you can't actually "see" an electron unless you happen to hit it with a photon of light.
Photons are the specific particles of light. Each frequency of light as a specific quantum energy — that's the lowest possible amount of energy you can produce in that frequency.
Perimeter Institute | "Wave Particle Duality Explained"
Electron Orbitals
The Bohr Model
In the early models of the atom, we thought the electrons orbited the nucleus like the planets orbit the sun. Although this isn't accurate, it's a helpful way to understand the different energy levels the electrons can occupy.
Crash Chemistry Academy | "Louis de Broglie's explanation of Bohr's atomic model"
Quantum Theory
Quantum Mechanics is how we describe the statistical locations of electrons. It has two main components:
Quantum simply means that energy comes in little packets. If you hit an electron with a specific frequency of light, the electron will absorb a set amount of energy depending upon that frequency.
Mechanics refers to motion. So quantum mechanics just means we're studying how electrons move in relation to wavelength.
Arvin Ash | "The Quantum Mechanical model of an atom"
Electron Configurations
Electron orbitals define the behaviors of specific electrons in the atom — the level of the orbit and the number of protons in the nucleus will determine how likely it is the electron will leave the atom.
Remember, however, that each electron's energy corresponds with a specific frequency wave. These waves can't overlap — electrons are all negatively charged, so they repel each other. Because of this, the number of electron orbitals are limited, and the shapes of these orbitals change to prevent electrons from hitting each other.
Minute Physics - "A Better Way To Picture Atoms"
The Periodic Table
Periodic Variation: Repeating Patterns of Properties
Because electrons fill the orbitals in quantum patterns, you can predict the specific orbitals in each element based on the number of electrons — and the number of electrons is determined by the number of protons.
As you add more protons, each new proton allows you to add another electron in a steady pattern of orbitals. But as you add more protons, the atomic properties seem to "reset" every so often. This happens when all the orbitals in a single energy shell get filled up, and then the next shell starts to fill.
The Periodic Table: A Chart of Recurring Properties
To help us keep track of atomic properties, the periodic table lists atoms based on their electron orbitals:
Periods are the seven horizontal rows of the table.
Groups are the eighteen vertical columns.
The location of an element in the table can indicate whether it's a metal, nonmetal, or metalloid.
Different symbols and colors provide the atomic number, symbol, average atomic mass, physical state at room temperature, and material type.
Professor Dave Explains | "The Periodic Table: Atomic Radius, Ionization Energy, and Electronegativity"