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Matter, elements, and atoms

AP.BIO:
ENE‑1 (EU)
,
ENE‑1.A (LO)
,
ENE‑1.A.2 (EK)
Learn about the structure of the atom, and how atoms make up matter. An atom is the smallest unit of matter that retains all of the chemical properties of an element. 

Introduction

What is your body made of? Your first thought might be that it is made up of different organs—such as your heart, lungs, and stomach—that work together to keep your body going. Or you might zoom in a level and say that your body is made up of many different types of cells. However, at the most basic level, your body—and, in fact, all of life, as well as the nonliving world—is made up of atoms, often organized into larger structures called molecules.
Atoms and molecules follow the rules of chemistry and physics, even when they're part of a complex, living, breathing being. If you learned in chemistry that some atoms tend to gain or lose electrons or form bonds with each other, those facts remain true even when the atoms or molecules are part of a living thing. In fact, simple interactions between atoms—played out many times and in many different combinations, in a single cell or a larger organism—are what make life possible. One could argue that everything you are, including your consciousness, is the byproduct of chemical and electrical interactions between a very, very large number of nonliving atoms!
So as an incredibly complex being made up of roughly 7,000,000,000,000,000,000,000,000,000 atoms, you'll probably want to know some basic chemistry as you begin to explore the world of biology, and the world in general.

Matter and elements

The term matter refers to anything that occupies space and has mass—in other words, the “stuff” that the universe is made of. All matter is made up of substances called elements, which have specific chemical and physical properties and cannot be broken down into other substances through ordinary chemical reactions. Gold, for instance, is an element, and so is carbon. There are 118 elements, but only 92 occur naturally. The remaining elements have only been made in laboratories and are unstable.
Each element is designated by its chemical symbol, which is a single capital letter or, when the first letter is already “taken” by another element, a combination of two letters. Some elements follow the English term for the element, such as C for carbon and Ca for calcium. Other elements’ chemical symbols come from their Latin names; for example, the symbol for sodium is Na, which is a short form of natrium, the Latin word for sodium.
The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), which together make up about 96% of the human body. In the nonliving world, elements are found in different proportions, and some elements common to living organisms are relatively rare on the earth as a whole. All elements and the chemical reactions between them obey the same chemical and physical laws, regardless of whether they are a part of the living or nonliving world.

The structure of the atom

An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, a gold coin is simply a very large number of gold atoms molded into the shape of a coin, with small amounts of other, contaminating elements. Gold atoms cannot be broken down into anything smaller while still retaining the properties of gold. A gold atom gets its properties from the tiny subatomic particles it's made up of.
An atom consists of two regions. The first is the tiny atomic nucleus, which is in the center of the atom and contains positively charged particles called protons and neutral, uncharged, particles called neutrons. The second, much larger, region of the atom is a “cloud” of electrons, negatively charged particles that orbit around the nucleus. The attraction between the positively charged protons and negatively charged electrons holds the atom together. Most atoms contain all three of these types of subatomic particles—protons, electrons, and neutrons. Hydrogen (H) is an exception because it typically has one proton and one electron, but no neutrons. The number of protons in the nucleus determines which element an atom is, while the number of electrons surrounding the nucleus determines which kind of reactions the atom will undergo. The three types of subatomic particles are illustrated below for an atom of helium—which, by definition, contains two protons.
Structure of an atom. The protons (positive charge) and neutrons (neutral charge) are found together in the tiny nucleus at the center of the atom. The electrons (negative charge) occupy a large, spherical cloud surrounding the nucleus. The atom shown in this particular image is helium, with two protons, two neutrons, and two electrons.
Image credit: modified from OpenStax CNX Biology
Protons and neutrons do not have the same charge, but they do have approximately the same mass, about 1, point, 67, ×, 10, start superscript, minus, 24, end superscript grams. Since grams are not a very convenient unit for measuring masses that tiny, scientists chose to define an alternative measure, the dalton or atomic mass unit (amu). A single neutron or proton has a weight very close to 1 amu. Electrons are much smaller in mass than protons, only about 1/1800 of an atomic mass unit, so they do not contribute much to an element’s overall atomic mass. On the other hand, electrons do greatly affect an atom’s charge, as each electron has a negative charge equal to the positive charge of a proton. In uncharged, neutral atoms, the number of electrons orbiting the nucleus is equal to the number of protons inside the nucleus. The positive and negative charges cancel out, leading to an atom with no net charge.
Protons, neutrons, and electrons are very small, and most of the volume of an atom—greater than 99 percent—is actually empty space. With all this empty space, you might ask why so-called solid objects don’t just pass through one another. The answer is that the negatively charged electron clouds of the atoms will repel each other if they get too close together, resulting in our perception of solidity.

Want to join the conversation?

  • aqualine ultimate style avatar for user Sean Collin
    The first sentence of the section "The structure of an atom" reads: "An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, one gold atom has all of the properties of gold and is still a solid metal at room temperature."

    My question is, how can just one atom be a liquid or sold or gas, etc? won't it still look and act the exact same no matter what state it's in? It still has electrons and a nucleus. What would the change look like on the atomic level in these different states?
    (2 votes)
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    • leafers tree style avatar for user emilyabrash
      Thanks very much to everyone who noticed this problem and upvoted or commented on it. You're absolutely right that there is no meaningful way to classify an individual atom as a solid, liquid, or gas, as these terms are based on interactions between atoms or molecules.

      I've corrected that paragraph to reflect that the gold atom is still considered gold because it has the same chemical properties as a larger quantity of gold (thanks to having the set of subatomic particles, specifically protons, that define gold at the atomic level). The correction should be live on the site later today.

      If that section is still unclear, or if you have any other comments or suggestions, please don't hesitate to ask here (or to report issues with the "Report a mistake" button).

      Thanks again for noticing this!
      (65 votes)
  • aqualine sapling style avatar for user Lim Ern You
    The last paragraph said that the electrons will repel each other if they get too close and resulting in our perception of solidity...what does that mean..can someone explain to me thx a lot
    (2 votes)
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  • piceratops ultimate style avatar for user Tabrez Doulat
    in the first paragraph in The Structure of an Atom it says that Gold atoms cannot be broken down into anything smaller while still retaining the properties of gold. So what would happen if the gold atom was split? What kinds of properties would it have?
    (4 votes)
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    • male robot johnny style avatar for user A@ry@D13
      You can't split atom because atom derives from the latin word atomos, which means indivisible. But if you could split gold, it would most likely keep its properties. Gold will always be gold, it can never be oxygen. You can have liquid gold but the number of protons, neutron, and electrons will be the same as solid gold. I might be wrong, but I hope I answered your question
      (1 vote)
  • piceratops tree style avatar for user lilajane2000
    The only thing that has always confused me about atoms, is, how can nonliving atoms make up living things? If you look at the world at the subatomic viewpoint, does that mean nothing is alive? I mean, I get how living things are living and the defining properties of a living organism make sense to me, but if you talk about atoms, doesn't that mean we are living, but only to a point?
    (7 votes)
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    • piceratops ultimate style avatar for user Just Keith
      How can atoms form a computer or an Egyptian pyramid or a novel? These are examples of what is known as an emergent property -- a property possessed by a group that is not present in any individual making up that group. Life is an emergent property.
      (7 votes)
  • mr pink red style avatar for user cheryl ferrero
    So water is a main element in our body right?
    (5 votes)
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    • old spice man green style avatar for user Matt B
      Water is not an element but a molecule but it is the most common molecule in our bodies.
      Oxygen is the most common element by mass (43% of all weight; carbon is 16% and hydrogen is 10%) in the body. The most common element by number is hydrogen (62% of all atoms; water is only 24% and carbon is 12%).
      (7 votes)
  • aqualine ultimate style avatar for user Isabel  Poinsette
    So I was watching the video in the next section and at the very beginning it said that atoms were still a completely philosophical idea, or "mental abstraction," I believe he said. Does that mean that no one has actually ever seen an atom yet and that their existence is simply a guess?
    (4 votes)
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  • female robot amelia style avatar for user Max Hinkle
    I'm very interested in the whole idea of our perception of solidity (last sentence). Does this mean that the reason I cannot punch through a wall is because the atoms making up the elements of matter in the wall are repelling the atoms making up my body (more specifically my fist)?
    (4 votes)
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  • primosaur sapling style avatar for user Goldleaf
    How are scientists able to tell if an element was created when they make them in laboratories (paragraph 4) if they are so unstable? Don't the elements immediately break apart or something? Or do they look at the evidence left behind?
    (3 votes)
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  • piceratops tree style avatar for user Sendhil Kumar
    What happens when an electron orbiting just stops dead on its tracks?
    (2 votes)
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  • piceratops seedling style avatar for user Orian Stephens
    If more than 99% of the atom is empty space, how do we have such high weight to the point that normal weight is triple digits? Being as atoms have very minuscule weight already, how does this work?
    (3 votes)
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    • male robot hal style avatar for user Charles LaCour
      The idea that atoms are 99% empty space is a misleading idea. This idea is basically applying macroscopic concepts to things at an atomic level where they don't really apply.

      What is meant by two things touching? When you talk about every day macroscopic things this is simple to define. When you are dealing with fundamental particles that are basically points that do not have any volume the way you define touching is not so simple. Electrons and quarks interact through fields and it is based on these interactions that determines the size of protons, neutrons and atoms. What we define as touching at the macroscopic level is basically when the attractive van Der Waals forces are offset by the repulsive Pauli exclusion forces on the electrons, there is no physical touching like we normally think of it.
      (2 votes)