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An introduction to the concept of the atom as the smallest unit of matter that retains the properties of an element.
If you took a piece of pure gold and kept cutting it in half forever, would you eventually hit a piece so small that it could never be cut again? The answer is yes—and that tiny 'uncuttable' piece is what makes up everything you see, touch, and breathe.
In the world of chemistry, an atom is the smallest possible piece of an element that still behaves like that element. Imagine you have a bar of pure silver. If you could zoom in millions of times, you would eventually find individual silver atoms. If you were to split one of those atoms, it would no longer be silver! The word 'atom' comes from the Greek word atomos, which means 'indivisible.' While we now know atoms are made of even smaller parts (protons, neutrons, and electrons), the atom remains the fundamental building block of all matter in the universe.
Quick Check
If you divide a sample of the element Copper until you reach the smallest particle that still acts like Copper, what is that particle called?
Answer
An atom.
Atoms are unimaginably small. They are so tiny that they cannot be seen with the naked eye or even the most powerful light microscopes used in school. This is because atoms are smaller than the wavelength of visible light itself! To give you an idea of the scale, a single human hair is about carbon atoms wide. Scientists must use special tools called Scanning Tunneling Microscopes (STMs) which use electricity rather than light to 'feel' and map the surfaces of atoms.
To understand how small an atom is, follow this mental model: 1. Imagine a single grapefruit. 2. If you inflated that grapefruit to the size of the Earth, how big would the atoms inside be? 3. Each atom would be roughly the size of a blueberry. 4. This shows that there are more atoms in a single glass of water than there are glasses of water in all the Earth's oceans!
Quick Check
Why can't we see atoms using a regular microscope in a science lab?
Answer
Atoms are smaller than the wavelength of visible light, so light passes right over them.
It is easy to confuse the terms atom and element, but they describe different things. An element is a pure substance that consists entirely of one type of atom. Think of an element as a 'flavor' of matter. For example, 'Oxygen' is an element. If you have a tank of pure oxygen, it is filled with billions of individual oxygen atoms. You can think of the element as the 'category' and the atom as the 'individual unit.' If you have a pile of LEGO bricks that are all the same red block, the 'element' is Red , and the 'atom' is one single brick.
Consider a 24-karat gold ring: 1. The Element is Gold (). It is a pure substance. 2. The Atoms are the trillions of identical gold particles packed together to form the ring. 3. If you replaced just one atom with a Silver atom (), that specific spot would no longer be the element Gold.
Quick Check
True or False: A piece of pure Iron is made up of many different types of atoms.
Answer
False. A pure element is made of only one type of atom.
Atoms often bond together to form molecules. Let's look at Water (): 1. A single molecule of water contains atoms of the element Hydrogen (). 2. It also contains atom of the element Oxygen (). 3. Total atoms in one molecule: atoms. 4. Even though they are joined, each atom still represents its specific element.
Which of the following is the best definition of an atom?
If a human hair is carbon atoms wide, what does this tell us about atoms?
An element is a substance that contains two or more different types of atoms.
Review Tomorrow
In 24 hours, try to explain to a friend why you can't see the atoms in a piece of paper even though the paper is made of them.
Practice Activity
Look at a Periodic Table. Each name you see (like Helium or Carbon) is an element. Try to find three elements you interact with every day and remember that each is made of its own unique type of atom.