What is Atom? - All about that tiny little thing
Topics covered: Definition of atom and matter, atomic structure, and subatomic particles (protons, neutrons, and electrons)
Imagine you cut an apple to a half. Imagine you cut the half again. And then you cut it again. You repeatedly cut an apple over and over, and smash it until it becomes a tiny powder. Sounds pretty tiny, right? Well, an atom is much, much tinier than that. In fact, a row of 108 atoms (100,000,000 atoms) would make up only the size of your fingernail!
The word atom means “indivisible” in Greek*. An atom is a fundamental piece of matter. What is matter? Matter is any substance that has mass and volume. Everything in the universe (except energy) is made up of matter; this means everything in the universe is made up of atoms! But even an atom itself is made up of three tiny subatomic particles: protons, neutrons, and electrons.
Before we talk about these particles, let’s first talk about the different parts of an atom. Atom is made up of a nucleus and an electron cloud. Nucleus is the small dense center of an atom that consists of protons and neutrons. The nucleus takes up a small volume of an atom, but most of the atom’s mass! Electron cloud is the region around the nucleus of an atom, where electrons are located. In contrast to the nucleus, the electron cloud takes up the most volume, but the least of an atom’s mass (most of the electron cloud is an empty space!).
Now let’s move on to protons. The protons are located in the nucleus of an atom and have the mass of 1 amu (atomic mass unit)**. They are positively charged (think of p = positive) and determine the identity of the atom. You’ll learn what this means as we learn more about the atoms.
Neutrons are similar to the protons for the most part. Like protons, they are located in the nucleus and have the mass of 1 amu. However, the main difference between protons and neutrons is that the neutrons have no charge; they are neutrally charged (think of n = neutral). What does this mean? Well, this means the nucleus of an atom will always have a positive charge, because the protons are positive and the neutrons are neutral.
Finally, let’s take a look at electrons. Electrons are much tinier than the protons and neutrons; in fact, they are more than 1,800 times smaller than other subatomic particles and have the mass of almost zero. Electrons are negatively charged and are located outside of the nucleus (on electron clouds).
*Atoms were once considered “indivisible” because ancient Greeks thought that atoms were the smallest things in the universe that couldn’t be divided! However, we now know that atoms are NOT the smallest unit of matter- there are things smaller than the atoms, such as subatomic particles!
** AMU, which stands for atomic mass unit, is the unit that expresses the mass of an atom. 1 amu is approximately equal to 1.67 x 10-24 grams. This number is extremely small, and scientists don’t like to work with small numbers. That’s why they created this new unit (amu) to represent the atomic mass.
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Now it's time to check your comprehension.......
ATOMIC STRUCTURE QUIZ
1. What are the three subatomic particles of an atom?
2. What is the charge of the nucleus? Why?
3. Where are electrons located in an atom?
4. What is the mass of a neutron (in amu)?
5. Nucleus / Electron cloud (choose one) is a part of an atom that has high mass but low volume.
Answers: 1. Protons, neutrons, and electrons. 2. Positive, because protons (that have positive charge) and neutrons (that have neutral charge) are located inside of the nucleus. 3. Outside the nucleus (on electron clouds). 4. 1 amu. 5. Nucleus. (Electron cloud is the opposite: it has high volume but low mass).
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