Science With Mr. Milstid

We’ve learned so far that all matter is made of atoms. We’ve looked at the history of the science surrounding the atom. Now, we will look at the atom itself – its structure, variations of atoms and how they all fit together.

 


 
Atomic Structure
Atoms are composed of 3 main subatomic particles: Electrons, Protons and Neutrons. There are even smaller subatomic particles, such as quarks and gluons, but for the purposes of understanding the basic composition of matter, these 3 are sufficient.

The Nucleus
At the very center of an atom is the nucleus.
It is a small, dense, positively charged “core” that contains most of the atom’s mass, and is composed of the atom’s protons and neutrons.

Protons
Protons are tiny, positively charged particles found in the nucleus.
Their mass is only about 1.7 x 10^-24g, or 1 atomic mass unit (amu).
Protons are incredibly important to the identity of an atom/element – each elemental atom has a unique number of protons in its nucleus. Boron, for example has 5 protons, while Carbon has 6. Variations on atoms (which we will discuss later as isotopes and ions) always have the same number of protons.
The number of protons an atom has is called its atomic number.

Neutrons
Housed next to the protons are particles called neutrons.
These particles have no charge, and are considered to have about the same mass as a proton. In a general, model atom, neutrons exist in the same number as protons. That is, in a model atom with 5 protons, there will be 5 neutrons. 6 protons, 6 neutrons, and so on.

Electrons
Swirling outside the nucleus in clouds are extremely small, negatively charged particles called electrons.
Compared to protons and neutrons, electrons are very, very small in mass.
It takes more than 1,800 electrons to equal the mass of one proton – in fact, the mass is so small, that we typically describe electrons as having no mass whatsoever.
In a general, model atom, electrons exist in the same number as protons – their charges (negative and positive) work to cancel each other out and provide a net charge of zero (neutral) to the atom. So for instance, if there are 5 protons in a model atom, there will be 5 electrons.

 
In the real world, however, this is not always the case. Sometimes, atoms have an unequal number of electrons and protons, which creates a positively or negatively charged atom.
We call this type of atom an ion.

An atom that has fewer electrons than protons and thus an overall positive charge, is called a cation.
An atom with more electrons than protons and thus an overall negative charge, is called an anion.
Ions are particularly important in chemistry because they allow for the joining of multiple atoms together to form compounds.

 
Occasionally, an atom will have an abnormal amount of neutrons in its nucleus.
This type of atom is called an isotope.

An atom is still the same element if it is missing an electron. The same goes for isotopes – they are still the same element, they are just a little different from every other atom of the same element.
Isotopes are pretty common.
In fact, no elements in the world are made up of purely neutral, model atoms. They are made of a mixture of different isotopes of the same atom.
As such, the atomic mass (the recorded measurement of the mass of protons and neutrons in an atom combine) that appears in the periodic table is an average number. Not all isotopes’ masses will equal this. Some will be higher, some lower.

 
Because there are so many different forms of isotopes in the universe, they get unique isotope names, based on their atomic number, combined with the number of neutrons the atom has.
For example:
A normal, neutral Carbon atom has an atomic number of 6, indicating it would have 6 protons.
In a model atom, the neutrons and protons would be the same, adding up to a total of 12 protons and neutrons.
Its atomic name would be: Carbon-12.

We can use isotopes to calculate the average atomic mass of an element using the percent composition of an atom (which scientists have figured out over years of painstaking research).
The steps to do so are as follows:

1. Multiply the mass number of each isotope by the percentage it exists in an element.
2. Add those numbers together to get a final atomic mass for our isotope.

 
The simulation at this link allows you to build atoms and isotopes of each of the first 10 elements on the periodic table.

 
This simulation asks you to use your understanding of atomic number, mass and electron configuration to build isotopes of an element (but in an altogether different way than the one above).

Here’s a link to the big version.

Tags: Atomic Mass, Atomic Number, Atomic Structure, Ions, Isotopes
Posted in Atomic Structure, Matter & Properties of Matter, Physics & Physical Science