What is Atoms: Definition and 878 Discussions

An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics—as if they were tennis balls, for example—is not possible due to quantum effects.
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions.
The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force. This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay.
The number of protons in the nucleus is the atomic number and it defines to which chemical element the atom belongs. For example, any atom that contains 29 protons is copper. The number of neutrons defines the isotope of the element. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature. Chemistry is the discipline that studies these changes.

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  1. S

    If all the empty space of atoms were removed, how big would this earth be?

    Hi everyone, first time poster. Considering some of the things discussed here, I apologize if my question sounds simplistic. If this Earth could be compressed so that all the empty space in atoms would disappear how big would this Earth be? My science teacher once told me that it would be...
  2. I

    Measuring Displacement in Hydrogen Atoms: Exploring d

    Homework Statement Part A) Assume you have a capacitor with H-atom gas with a separation of the plates of {10}^{-4}meter and a voltage of 20 volts across the capacitor. Calculate the distance "d" (the displacement of the charges in the atom), where the induced dipole of the hydrogen atom...
  3. M

    Where Do the Atoms for a Fetus Come From?

    hi all, i have a problem that has been puzzling me, when a child has been conceived where do the atoms come from that form the fetus and the baby, did the atoms that now are forming the baby exist before conception ,(leading me to think that maybe not everything is made from start dust if...
  4. F

    Distance between atoms based on density

    Homework Statement Iron has a mass of 7.87 g per cubic centimeter of volume, and the mass of an iron atom is 9.27 * 10^-26 kg. If you simplify and treat each atom as a cube, (a) what is the average volume (in cubic meters) required for each iron atom and (b) what is the distance (in meters)...
  5. PrincePhoenix

    Electromagnetic force and resistance to displacement of atoms.

    It is written over here http://www.particleadventure.org/electromagnetism.html that, "...the force that keeps you from falling through the floor is the electromagnetic force which causes the atoms making up the matter in your feet and the floor to resist being displaced." Can anyone explain...
  6. H

    Stripping Oxygen Atoms of Electrons and Exciting to 4th Energy Level

    How could the Oxygen atom be stripped of at least 4 electrons and excited at the least to it's 4th energy level? I came across a device which claims to do this with Solid State Lasers (LED's) and a high voltage oscillating field...Just wondering how it would work since LED's only go to...
  7. K

    Number of C-14 atoms in old piece of wood

    Homework Statement I'm working a homework problem that states: A very old specimen of wood contained 1012 atoms of 14C in 1986. • How many 14C atoms did it contain in the year 9474 B.C.? • How many 14C atoms did it contain in 1986 B.C.? Homework Equations N(t) =...
  8. I

    If a system is made of 3 atoms with no degeneracy with energy levels

    if a system is made of 3 atoms with no degeneracy with energy levels of fro example 0, e, 2e would it be safe to say that the system only has three microstate or will it be 2^3 microstates. if it is 2^3 can you please explain why?
  9. P

    How long would it take to count all the atoms in

    How long would it take to count all of the atoms in 12 grams of Carbon-12, If you could only count one atom per second?
  10. L

    Exploring the Compression of Atoms in Black Holes

    How compressed are the atoms black holes are made of? Is there a limit to how much you can compress matter? It seems to me, the most you can compress matter would be until the individual subatomic particles are side by side touching each other. Are black holes compressed more than that? Are...
  11. K

    Hybridized in order for it to bond to other atoms?

    Does an atom ALWAYS need to be hybridized in order for it to bond to other atoms? Why or why not? In what cases does it need to be hybridized in order to bond with other atoms?
  12. L

    Arragnement of atoms inside a steel

    How are atoms inside a steel arranged? Ussually we can get the data about the mass share of different elements of steel and the lattice type. But the lattice only tells us where an atom is situated, not the type of the atom. Can we tell anything about the type of the atom at a certain...
  13. T

    Heat and Photons: Understanding the Effects on Isolated Atoms"

    What does it mean to heat an isolated atom with photons, from a hypothetical 0deg, to 100deg? What is happening in the atom's electron shells, and how long can the atom retain the heat?
  14. L

    Solve de Broglie Wavelength of Atoms in eV: Urgent Help

    Homework Statement http://www.strings.ph.qmul.ac.uk/~russo/QP/r06QPHYEX.pdf Question 3. The Attempt at a Solution I can easily derive the equation I need, which is: lamda = h/p Which after some playing around with K.E =1/2mv^2 etc we obtain: lambda (de brogile) = h/SQRT(2mKE)...
  15. fluidistic

    Questions About Atoms: Protons & Neutrons

    How did we know that the more common isotope of iron has 26 protons and 30 neutrons? I'm asking a general question so the iron example is just a special case. How did we know that oxygen has 8 protons? (and 8 neutrons), and also that the 8 neutrons is the most stable isotope and that there...
  16. S

    Chemical potential-fictitious atoms

    Hello, I am sorry to ask a relatively unrelated question. I need to know if the chemical potential of fictitious atoms like hydrogen used to saturate the dangling bonds is different from the chemical potential of hydrogen in common chemical potential tables. Regards, Sarah
  17. C

    Limits of Perturbation theory for hydrogenic atoms

    Homework Statement Why can't we use perturbation theory to calculate the effect of the spin orbit interaction in hydrogen like uranium? Homework Equations The Attempt at a Solution Is it something to do with the fact that the perturbation must be small compared to the rest of the...
  18. H

    Calculate Spacing b/w Atoms of Ideal Gas@273K,1atm

    Homework Statement Hi, I've got the following problem: Calculate the spacing between atoms of an ideal gas at a temperature of 273K and a pressure of 1atm. Homework Equations Mean free path equation: ʎ = 1 / 4(pi)(n)(σ²) The Attempt at a Solution I first used the ideal...
  19. D

    Number of atoms reacting with a gas

    Homework Statement 4Al + 3O2 = 2Al2O3 What number of O-atoms will react if 45dm3 of the gas reacts with an excess of Al? The answer is apparently: 4 atoms Homework Equations The Attempt at a Solution Using the formula n=V/Vn (or the law stating that any gas occupies 22.4dm3 at...
  20. C

    Are space and time definable without atoms?

    Atoms are remarkable little creatures. Not only are they generally very stable, but they fit together to make molecules, in which the distances and angles between nuclei are fixed quite precisely (subject to quantum fluctuation). So you can make measuring-rods out of them, among other things...
  21. N

    Charge analysis by projecting the density of states on orbitals of atoms

    Dear all, I really need help. My question: How do i project the density of states onto orbitals of atoms? this is to do a charge analysis. Can anyone provide me with an eqn or refer me to any relevant text or paper. Greatly apprieciate your help. Thanks nisha
  22. C

    Finding the number of atoms in 0.500 mol of Argon

    Question: How many atoms are there in 0.500 mol of Argon? No relevant equations do you take atomic molar mass (39.95) divided by 0.500 mol?
  23. A

    Atomic Physics: Investigating Electron Hull of Atoms

    Atomic physics studies the electron hull of atoms. This branch of physics is distinct from nuclear physics, despite their association in the public consciousness. Atomic physics is not concerned with the intra-nuclear processes studied in nuclear physics, although properties of the nucleus can...
  24. W

    About the spin-orbit coupling in atoms

    i am now reading the book by woodgate: elementary atomic strucure, 2nd edition. on page 62, he discusses the spin-orbit coupling in hydrogen atom, and calculates the first order shift of the energy due to this effect. I have some doubt about his procedure from eq.4.25 to eq.4.27 the...
  25. G

    Is there a definite number of atoms in the universe?

    This may be a silly question but it just popped into my head yesterday. Are there a definite number of atoms in the universe? Because if the universe is expanding, then does that mean that there are more atoms in the universe or is everything just being pulled farther apart? (however, that logic...
  26. H

    Elastic Collision problem with atoms.

    Homework Statement A neutron in a nuclear reactor makes an elastic head-on collision with the nucleus of a carbon atom initially at rest. (a) What fraction of the neutron's kinetic energy is transferred to the carbon nucleus? (The mass of the carbon nucleus is about 12 times the mass of...
  27. H

    Can Atoms Produce Photons Through Electron Excitation?

    I know that 'When electrons get excited, they release photons to "un-excite".' So how can a atom 'produce' photons?
  28. M

    Electron Configuration of Large Atoms

    I've read a good few different explanations and learned about electron configurations in school but I still don't understand how to write the electron configuration for a big atom like Copper. Heres how I would write it 1S2,2S2,2P6,3S2,3P6,3D... First off he told me 3D didn't even belong...
  29. K

    Are Atoms Real? Investigating the Existence of Subatomic Particles

    I've studied enough of physics and chemistry to find out this question has not yet been answered. All theories derive mathematical formulas that deal with point particles. But how are scienstists convinced that nature is made of point particles.
  30. F

    Looking for Layman's Physical Explanation for the lowest energy level in atoms

    I'm looking for a simple physical explanation of the lowest energy level in atoms, so I can provide a brief explanation to interested laypeople (not to mention just to help myself understand better). Does anybody want to take a crack at it? Or am I asking for the impossible? Since electron...
  31. F

    Looking for Layman's Physical Explanation for energy level in atoms

    I'm looking for a simple physical explanation of the discrete energy level in atoms, so I can provide a brief explanation to interested laypeople (not to mention just to help myself understand better). Does anybody want to take a crack at it? Or am I asking for the impossible?
  32. B

    More atoms in a cup of water, than cups in an ocean?

    I've heard this before, and am just wondering if you guys think it's true. The saying is "There are more atoms in a cup of water than there are cups of water in the oceans of the world." I am pretty sure I heard this on some Science Channel show about atoms. I know it would depend on the...
  33. A

    Energy and Orbit Radius for Multielectron Atoms: Lithium's N=1 Electrons

    Homework Statement Treat one of lithium's n=1 electrons as a single electron in a one-electron atoms of z=3. a) Find the energy and orbit radius. b) The other n=1 electron, being in the same spatial state, must have the same energy and radius, but we must account for the repulsion...
  34. T

    What Is the Packing Fraction in a Simple Cubic Crystal Structure?

    Problem: A) In a simple cubic arrangement the atoms sit at the corners of imaginary cubes with their curved surfaces just touching. Show that the ratio of filled space to empty space between the atoms is pi/6 or about 0.5. This "packing fraction" is related to the density of the material. The...
  35. D

    Force constant between 2 atoms

    Homework Statement The atomic mass of tellurium is 2.12×10-25 kg, and the frequency, 7.53×1012 Hz. What is the effective force constant that connects the two atoms? Homework Equations Have no idea The Attempt at a Solution I am lost with this problem, we havn't learned it in...
  36. M

    Distance between copper atoms in cubic crystal lattice

    Homework Statement The atomic mass number of copper is A = 64. Assume that atoms in solid copper form a cubic crystal lattice. To envision this, imagine that you place atoms at the centers of tiny sugar cubes, then stack the little sugar cubes to form a big cube. If you dissolve the sugar, the...
  37. L

    Kinetic Enegry and Hydrogen atoms

    Homework Statement a) What is the minimum kinetic energy in electron volts that an electron must have to be able to ionize a hydrogen atom (that is, remove the electron from being bound to the proton)? I got the answer here which is 13.6 ev b) If electrons of energy 12.8 eV are incident...
  38. C

    Why do heavier atoms experience relavistic effects(contraction)?

    It is said that the electrons in heavier atoms have speed close to that of light and therefore undergo relativistic effects? May I ask why is this so? What is it in heavier elements that caused such a change to the speed of the electron? Is it related to the energy-mass equivalence formula?
  39. K

    Chemistry Chem Mole: Molecules to Atoms?

    Homework Statement What is the total number of atoms in the molecules? NH3 - 2.5 mole Homework Equations Would you multiply the number of atoms in NH3 by Avogadro constant to find the number of atoms? (4 atoms)(6.02*10^23) =answer Or would you multiply the number of moles by Avogadro...
  40. N

    Calculating the Center of Mass for a CO Molecule

    The distance between a carbon atom (m = 12.0u) and an oxygen atom (m = 16.0u) in the CO molecule is 1.13×10-10 m. How far from the carbon atom is the center of mass of the molecule? I know i have to found out the CM, but the center of mas is cm= (r1m1 + r2m2)/(m1+m2) and i don't have...
  41. N

    Distance CO Molecule: Center of Mass From Carbon Atom

    The distance between a carbon atom (m = 12.0u) and an oxygen atom (m = 16.0u) in the CO molecule is 1.13×10-10 m. How far from the carbon atom is the center of mass of the molecule?
  42. R

    Atoms, molecule, electron spin and magnetic media

    I read much about atoms, molecules and electrons but still i am not able to get answers for my study towards magnetic media. Please help me with the following questions in anyway you can, i would be really really grateful as it is going to help me a lot with my study towards magnetic media...
  43. X

    One atom v.s. atoms? (solved by schrodinger equation.)

    The intense laser-atom physics becomes hot today. There is a famous interesting phenomenon: High-order harmonic generation (HHG). Lots of works are on the single atom response in the strong field approximation. Some of them obtain the spectrum by solving the Schrödinger equation. Then they say...
  44. J

    Atoms of the highlighted elements

    Homework Statement I am an amateur researching elementary particles; on tabulating atoms the elements, atoms of the highlighted elements in the diagram below formed one group (of two possible groups); I should like to know if there is anything unique to the highlighted elements...
  45. S

    Chemistry Atoms, Moles, Grams Conversion

    Homework Statement A microscopic scientist is assembling sugar molecules (C6H12O6) from C, H, and O atoms. If he has 6.022x10^23 atoms of each type, how many grams of sugar molecules can he assemble? Which type of atom does he run out of first? Homework Equations 1 mol = 6.02x10^23 atoms 1...
  46. N

    Extra neutrons in heavy atoms and Gravity

    Question: The postulate that mass attracts mass is present in both the classical description of gravity and GR. My question is related to the extra nuetrons in heavy atoms, if there is experimental evidence that these extra neutrons are also part of the equation. I wish to read about...
  47. K

    Mixed States of Silver Atoms in a Stern-Gerlach Experiment

    Homework Statement In an experiment, we've isolated silver atoms that are in a purely |\uparrow \rangle state with respect to the z-axis, and feed these into a Stern-Gerlach apparatus oriented at an angle of \frac{\pi}{4} between the x and z axes, which measures an observable we will call...
  48. C

    Atomic Separation: Is It Possible?

    is it possible to separate an atom into its smaller subatomic particles like electrons and the quarks that make up protons and neutrons and keep those particles contained or do they always have to form an atom.
  49. D

    Molecules back to singular atoms.

    Do the atoms in molecules separate quicker if they are moved more vigourously in their lifetime and therefoe cause death of the living organism they makes up sooner? For example: A giant tortoise is slower than a cheatah during its life and lives longer. A tree is slower than a tortoise and...
  50. M

    The Number and Volume of Copper Atoms in a Grain

    How many copper atoms are there per grain? What is the volume of a grain of metal containing 1020 copper atoms?
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