Atoms Are Made Up Of

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Initially this was a huge mass of quarks and electrons and photons, and in the very earliest instant the universe was so hot and dense that they couldn’t clump together to make atoms: any time. A substance made up of atoms of two or more different elements joined by chemical bonds. Atoms are extremely small and are made up of a few even smaller particles. The basic particles that make up an atom are electrons, protons, and neutrons. Atoms fit together with other atoms to make up matter. It takes a lot of atoms to make up anything. There are so many atoms in a single human body we won't even try to write the number here.

Background: Atoms and Light Energy

Atoms and Light Energy

What Is An Atom

The study of atoms and their characteristics overlap several differentsciences. Chemists, Physicists, and Astronomers all must understand themicroscopic scale at which much of the Universe functions in order to seethe 'bigger picture'.

Inside the Atom

Atoms Are Made Up OfJust like bricks are the building blocks of a home, atoms are the building blocks of matter. Matter is anything that has massand takes up space (volume). All matter is made up of atoms. Theatom has a nucleus, which contains particles of positive charge(protons) and particles of neutral charge (neutrons). Surrounding thenucleus of an atom are shells of electrons - small negatively chargedparticles. These shells are actually different energy levels andwithin the energy levels, the electrons orbit the nucleus of the atom.
The ground state of an electron, the energy level itnormally occupies, is the state of lowest energy for that electron.
There is also a maximum energy that each electron canhave and still be part of its atom. Beyond that energy, the electronis no longer bound to the nucleus of the atom and it is considered tobe ionized.
When an electron temporarily occupies an energy state greater than itsground state, it is in an excited state.An electron can become excited if it is given extra energy, such as if itabsorbs a photon, or packet of light, or collides with a nearby atom or particle.

Light Energy

Each orbital has a specific energy associated with it. For an electronto be boosted to an orbital with a higher energy, it must overcome thedifference in energy between the orbital it is in, andthe orbital to which it is going. This means that it must absorb a photonthat contains precisely that amount of energy, or take exactly that amountof energy from another particle in a collision.

The illustrations on this page are simplified versions of real atoms,of course. Real atoms, even a relatively simple ones like hydrogen,have many different orbitals, and so there are many possible energieswith different initial and final states. When an atom is in an excitedstate, the electron can drop all the way to the ground state in one go,or stop on the way in an intermediate level.

Electrons do not stay in excited states for very long - they soonreturn to their ground states, emitting a photon with the sameenergy as the one that was absorbed.

Identifying Individual Types of Atoms

Transitions among the various orbitals are unique for each element because theenergy levels are uniquely determined by the protons and neutrons in thenucleus. We know that different elements have different numbers ofprotons and neutrons in their nuclei. Whenthe electrons of a certain atom return to lower orbitalsfrom excited states, the photons they emit have energies that arecharacteristic of that kind of atom. This gives eachelement a unique fingerprint, making it possible to identify the elementspresent in a container of gas, or even a star.

We can use tools like the periodic table of elements to figure out exactlyhow many protons, and thus electrons, an atom has. First of all, we knowthat for an atom to have a neutral charge, it must have the same number ofprotons and electrons. If an atom loses or gains electrons, it becomesionized, or charged. The periodic table will give us the atomic number ofan element. The atomic number tells us how many protons an atomhas. For example, hydrogen has an atomic number of one - which means it hasone proton, and thus one electron - and actually has no neutrons.

For the Student

Based on the previous description of the atom, draw amodel of the hydrogen atom. The 'standard' model of an atom is knownas the Bohr model.

Different forms of the same chemical element that differ only by the numberof neutrons in their nucleus are called isotopes. Most elements havemore than one naturally occurring isotope. Many more isotopes have beenproduced in nuclear reactors and scientific laboratories. Isotopes usuallyaren't very stable, and they tend to undergo radioactive decay untilsomething that is more stable is formed. You may be familiar with the elementuranium - it has several unstable isotopes, U-235 being one of the mostcommonly known. The 235 means that this form of uranium has 235 neutronsand protons combined. If we looked up uranium's atomic number, and substractedthat from 235, we could calculate the number of neutrons that isotope has.

Atoms Are Made Up Of Elements

Here's another example - carbon usually occurs in the form of C-12 (carbon-12), that is, 6 protons and 6 neutrons, though one isotope is C-13, with 6protons and 7 neutrons.

For the Student

Use the periodic table and the names of the elements given below to figure out how many protons, neutrons and electrons they have.Draw a model of an atom of the following element: silicon-28,magnesium-24, sulphur-32, oxygen-16, and helium-4.

For the Student

Using the text, define the following terms: energy levels, absorption, emission, excited state, ground state, ionization,atom, element, atomic mass, atomic number, isotope.

Atoms Are Made Up Of Mostly

A Optional Note on the Quantum Mechanical Nature of Atoms

While the Bohr atom described above is a nice wayto learn about the structure of atoms, it is not the most accurate way tomodel them.

Although each orbital does have a precise energy, theelectron is now envisioned as being smeared out in an 'electron cloud'surrounding the nucleus. It is common to speak of the mean distance to thecloud as the radius of the electron's orbit.So just remember, we'll keep the words 'orbit' and 'orbital', though we arenow using them to describe not a flat orbital plane, but aregion where an electron has a probability of being.

Electrons are kept near thenucleus by the electric attraction between the nucleus and the electrons.Kept there in the same way that the nine planets stay near the Sun instead ofroaming the galaxy. Unlike the solar system, where all the planets' orbitsare on the same plane, electrons orbits are more three-dimensional. Eachenergy level on an atom has a different shape. There are mathematicalequations which will tell you the probability of the electron's locationwithin that orbit.

Let's consider thehydrogen atom, which we already drew a Bohr model of. Genarts sapphire for mac.


Probable locations of the electron in theground state
of the Hydrogen atom.		 What you're looking at in these pictures are graphsof the probability of the electron's location. The nucleus is at thecenter of each of these graphs, and where the graph is lightest iswhere the electron is most likely to lie. What you see here is sort of across section. That is, you have to imagine the picture rotated aroundthe vertical axis. So the region inhabited bythis electron looks like a disk, but it should actually bea sphere. This graph is for an electron in its lowest possibleenergy state, or 'ground state.'

To the right is an excited state of hydrogen. Notice that at the center, where the nucleus is, the pictureis dark, indicating that the electron is unlikely to be there. The two lightregions, where the electron is most likely to be found, are really just one region. Remember, you have tomentally rotate this around a vertical axis, so that in three dimensionsthe light region is really doughnut shaped.
Probable locations of the electron in anexcited state
of Hydrogen.

The text and images in this section were adapted from Dave Slaven's page onThe Atom (see References below).

Reference URLs:

The Atom
http://webs.morningside.edu/slaven/Physics/atom/

Spectra
http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/quantumzone/

The Periodic Table
http://www.webelements.com/

Back to the Main Spectra Unit Menu

Atoms Are Made Up Of Small Particles


Jimmy -
Whoa! This is actually a way more complicated question than you probably expected. But I'll give it a shot anyways. The human (and other mammals) the skin has two layers, the dermis and the epidermis. The dermis is the layer on the inside and contains blood vessels, nerves, hair follicles, small muscles, sweat glands, and all sorts of other things. The chemical make-up of these things is very complicated.
The epidermis is the outside layer and is made up of the skin cells that you're used to thinking about. These are some of the simplest cells in the body, but they're still pretty complicated. Since it would take me a /really/ long time to talk about all of the different atoms and molecules in the dermis, I'll just talk about the regular skin cells (even though all of those other things are technically still part of the 'skin'). The most common molecule the human body (and the skin) is water (H2O). Water makes up about 50-70% of the body's total weight.
Other than water, there are 4 types of molecules that scientists call organic molecules. This is what almost all of the human body is made up of. (But there are some inorganic molecules in the body, too.)
The first of these types of molecules is the carbohydrates. Carbohydrates are molecules that are made up of Hydrogen, Carbon, and Oxygen atoms only. These are sugars and are used by the cells as a source of energy. The most common carbohydrate in the body is glucose (C6H12O6), and the cells use this to make a special molecule called ATP (adenosine triphosphate), which also contains phosphorus atoms. (ATP is the molecule that actually provides energy inside the cell.) Some other examples of carbohydrates are glycogen, sucrose, and fructose.
The next type of molecule is called a lipid. Lipids are also made of Hydrogen, Carbon, and Oxygen atoms, but they also sometimes contain Phosphorus and/or Nitrogen.) These are fats and are used by cells for a number of different things. Most of the skin cells on the very outside of your skin are actually dead, so the most important thing that these molecules do is to hold them together. This may sound wierd, but if you've ever mixed oil (a lipid) with water, you know that they don't mix at all. So these molecules are used to make the 'membrane' of the cell, which is the part that goes around the outside of the cell. This 'phospholipid bilayer' holds the water inside the cell. (It's called a 'bilayer' because there's actually two layers of it, and it's 'phospholipid' because it's actually a somewhat more complicated molecule than just a lipid.)
The next type of molecule is proteins. Proteins contain Hydrogen, Carbon, Oxygen, Nitrogen, and usually Sulfur atoms. Most of the things in cells that 'do stuff' are proteins. These are things like hormones and enzymes and all sorts of other things. One common protein in skin cells is called keratin. Keratin is a large, complicated molecule that makes cells stronger. This is important for skin cells, because they rub up against things a lot.
The last major type of organic molecule is nucleic acids. These contain Hydrogen, Carbon, Oxygen, Nitrogen, and Phosphorus atoms. These are the molecules that make up DNA (deoxyribonucleic acid). (They also make up RNA.) DNA is the most important part of any cell, because it contains the information that determines what your body is. For example, your DNA determines whether you'll have blue eyes or brown eyes and whether you'll be tall or short. It also tells your body to have two arms, two legs, etc. The four nucleic acids that make up DNA are called cytosine, guanine, thymine, and adenine. The DNA molecule also contains the sugar deoxyribose (a carbohydrate), which holds it all together.
These are only a few of the different molecules that make up the skin. In fact, there's more different molecules in just the skin than I can count! (And there's a whole lot of them that we don't even know about yet!)
This is a list that I found of the most common elements (atoms) in the human body and how much of them there are (I couldn't find a list for just the skin):
Element % of human body % of human body
Name (by weight) (by number of atoms)
------------------------------------------------------
Hydrogen 9.5% 63.0%
Carbon 18.5% 9.5%
Nitrogen 3.3% 1.4%
Oxygen 65.0% 25.5%
Sodium 0.2% 0.3%
Phosphorus 1.0% 0.22%
Sulfur 0.3% 0.05%
Chlorine 0.2% 0.03%
Potassium 0.4% 0.06%
Calcium 1.5% 0.31%
Iron trace trace
Iodine trace trace
(from 'Essentials of Anatomy and Physiology, 3rd Edition,' Seeley et. al., copyright 1999, Mc-Graw Hill Companies, Inc.)
-Tamara

An Atom Is Composed Of


What Are Atoms Made Of

(published on 10/22/2007) Mac os for vmware player.