Everything in this world is composed of atoms. Ancient Greeks theorized that everything is composed of tiny and indivisible particles. As time passed, theories of what atoms are, how they behave, and the concepts about atomic structure developed further until today. We can now prove that the small stuff that makes up everything in the world is made up of much smaller stuff, too!
In this section, weโll dive into the basics of atomic structure to understand how to apply this concept to more complicated topics.
The Atomic Theory at a Glance
Greeks - Matter is made up of indivisible particles.
Dalton - Atoms of one element differ from another.
J.J Thomson - Electrons are spread around a positively charged space like plums (electrons) on a pudding (positively charged stuff).
Ernest Rutherford - Positively charged particles exist mostly in the center of the atom. He fired positively charged particles on a sheet of gold and realized that some passed through (most of the atom is just an empty space) and some deflected (positive particles hit positive particles, causing light to deflect).
Niels Bohr - Electrons move in orbits.
Erwin Schrodinger - Electrons move in positively charged clouds, called orbitals, where electrons are likely to be found.
You probably wonโt need to know everything here, but having insight into how these ideas came to life might help you understand more about the atom and how it works.
I. The Electron Cloud Atomic Model
Hereโs what you need to know:
- Protons have a positive charge.
- Electrons have a negative charge.
- Neutrons have no charge.
- The nucleus carries the neutron and the proton, the heaviest subatomic particles with almost the same mass.
- The โcloudโ is an area where electrons might be.
II. How elements differ
You might wonder what makes elements different from each other. What you need to know is that each elementโs atoms have different properties, and what makes these elements unique is their number of subatomic particles.
When you look at the periodic table of elements, youโll see how these elements differ. The atomic number is the whole number on the top left of an elementโs symbol. This refers to the number of protons in an atom. The number of protons is unique to an element. No two different elements can have the same atomic number.
Atomic mass is a quantity that shows the sum of protons and neutrons. Unlike the atomic number, the same elements can differ in atomic mass. There is a different way of calculating this quantity. Right now, all you have to know is that this number is the sum of the protons and neutrons of an atom. Elements with the same atomic number (number of protons) but differ in atomic masses (number of neutrons) are called isotopes.
Isotopes exist everywhere. Some isotopes are valuable in medicine, especially in diagnosing diseases through in-depth scans. Unstable isotopes will usually interact with cancer cells and undergo radioactive decay. When they do, specialized scanners like PET scans can detect the energy isotopes released to isolate the areas of the body where possible cancer cells lie.
These are usually denoted by their element name followed by their atomic mass. Carbon-14, for example, is an isotope used for carbon dating and can be denoted as C-14. You donโt have to study too hard about isotopes. However, itโs a good starting point in learning how these concepts relate to the medical field and why itโs crucial for you to understand them as well.
III. Summary
Everything is made up of atoms. Subatomic particles are smaller particles that make up the whole atom. The proton is a positively charged particle found at the atomic nucleus along with the neutronโa subatomic particle with no charge. Both the proton and the neutron are so heavy that they almost make up for the whole atomic mass. Electrons, on the other hand, are much lighter subatomic particles that travel around the nucleus in cloudy orbits. Electrons are negatively charged. The atomic number counts for the number of protons present in an element, whereas the atomic mass indicates the sum of the number of protons and neutrons present in an atom. Elements of the same kind will always have the same number of protons or atomic numbers. Isotopes have the same number of protons but different numbers of neutrons. The atom is composed of subatomic particles that play a vital role in the behavior of a specific element. These subatomic particles vary in charge, weight, and function.
IV. Key Terms
Atomic mass - Provides the sum of the number of protons and neutrons.
Atomic number - Shows how many protons are in an atom.
Electron - A negatively charged subatomic particle
Isotope - Elements of the same kind with a different number of neutrons.
Neutron - A neutral subatomic particle.
Nucleus - The core of the atom containing the proton and the neutron
Proton - A positively charged subatomic particle
Subatomic particle - A particle smaller than an atom.
V. Practice Questions
Sample Practice Question 1
Which of the following statements is TRUE?
A. The atomic weight determines the number of protons in an atom.
B. Isotopes have the same atomic mass.
C. The electron cloud model shows where electrons are at a specific time.
D. Isotopes have the same atomic number.
Ans. D
Isotopes have the same atomic number.
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