Science Writing: Chemistry

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.

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.

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.

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.

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.

Ionic Compounds are collections of atoms held together by opposite electric forces.  In these bonds, one atom gives up and electron, and another atom takes that electron.  Since every atom has an electric charge, all the atoms are held together very tightly.  They are usually solids at room temperature, but this also makes them brittle, and they easily dissolve in water.

Covalent Compounds share electrons.  Because of this, individual molecules may consist either of a very small number of atoms or a very large number of atoms, but the molecules themselves aren't bonded together.  Covalent compounds might or might not be soluble in water, and they can have high or low boiling points.  They normally aren't as brittle as ionic compounds, but this can vary.