Atoms, how do we know they exist

Question

They say everything is made of atoms that also contain nentrons protons etc wizzing round each other,There are millions across the width of a human hair they say , How the h**l do we prove that if we can't see them even with an electron microscope

Answer 1

Chemical materials always react in integer ratios (you never get a reaction in which the ratio of reactants or products is not a rational number). From that we may conclude there are discrete units of matter for if they were not discrete then irrational ratios would be common place (there are many many more irrational ratios than rational). Passing a fixed amount of electrical charge into some solutions deposits fixed and directly proportional amounts of matter (again integer ratios). That's enough evidence from first principles. The dimensions of the atom can be calculated using scattering of x-rays and the dimensions of the atomic nucleus by the scattering of alpha particles. The electron density of atoms can be mapped using a scanning tunnelling electron microscope which gives a map, much like if you measured the altitude of mountains and plotted them in 3D would give a representaion of the land.

Answer 2

We can see them with help of a Scanning Tunneling Microscope. Not only we can see them, but we also can pick them up and place them around like Lego bricks.

http://www.youtube.com/watch?v=47UgMpXFV...

Answer 3

We can see them, oh yes we can. We are clever.

Answer 4

The word is Whizzing. If you don't know that, the mystery of the atom will be lost on you.

Answer 5

And the earth is flat.

Answer 6

they have used other techniques to prove their existance,such as neutron scattering. They fired neutrons as gold foil and small percentage scatter, depending on whether they hit the nucleus or not.

it has taken a while to build up a picture of how atoms work, not just by looking at them.

Answer 7

mainly through collisions, rutherford and bohr were fundamental pioneers in this regard.

Chadwick also was the main person behind discovering the neutron.

Einsteins photoelectric effect gave even further credence to this, as it showed the particle nature of light, and how it affects the energy of the electrons in atoms.

Answer 8

Go wiki "atomic theory" and you can learn how Dalton figured it out in the first place using evidence available in the 19th century.

http://en.wikipedia.org/wiki/Atomic_theo...

Today there is so much evidence that it would be a waste of time to go listing it.  But we can, in fact, now "see" atoms--that is, form an image of them using a scanning tunneling electron microscope.

Answer 9

they have scientific evidences....

Answer 10

This answer has been built using snippets of Wikipedia articles.

The atomic hypothesis was first proposed by John Dalton FRS (September 6, 1766 – July 27, 1844) in the first few years of the nineteenth century, and the five main points of Dalton's Atomic Theory were as follows: -

i. Elements are made of tiny particles called atoms.

ii. All atoms of a given element are identical.

iii. The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights.

iv. Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms.

v. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.

His atomic theory built upon the earlier work in gas laws of Joseph Louis g*y-Lussac and J.A.C. Charles's. It was the law of conservation of mass, formulated by Antoine Lavoisier in 1789, which states that the total mass in a chemical reaction remains constant, that suggested to Dalton that matter was indestructible. Dalton also measured and tabulated the atomic weights of six elements namely: - hydrogen, oxygen, nitrogen, carbon, sulphur, and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1.

In 1827, the British botanist Robert Brown observed that pollen particles floating in water constantly jiggled about for no apparent reason. In 1905, Albert Einstein theorized that this Brownian motion was caused by the water molecules continuously knocking the grains about, and developed a hypothetical mathematical model to describe it. This model was validated experimentally in 1908 by French physicist Jean Perrin, thus providing additional validation for particle theory (and by extension atomic theory).

The name "atom" (from the Greek word atomos, which means "indivisible") was attributed to the basic particle that constituted a chemical element, because the chemists of the era believed that these were the fundamental particles of matter. However, in 1897, J.J. Thomson (later Sir Joseph John “J.J.” Thomson, OM, FRS (18 December 1856 – 30 August 1940)) discovered the electron through his work on cathode rays. A Crookes tube is a sealed glass container in which two electrodes are separated by a vacuum. When a voltage is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube. Through experimentation, Thomson discovered that the rays could be deflected by an electric field (in addition to magnetic fields, which was already known). He concluded that these rays, rather than being waves, were composed of negatively charged particles he called "corpuscles" (they would later be renamed electrons by other scientists).

Thomson believed that the corpuscles emerged from the very atoms of the electrode. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea or cloud of positive charge; this was the plum pudding model.

Thomson's plum pudding model was disproved in 1909 by one of his students, Ernest Rutherford (later Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937) ), who discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very centre.

In the gold foil experiment, Hans Geiger and Ernest Marsden (colleagues of Rutherford working at his behest) shot alpha particles through a thin sheet of gold, striking a fluorescent screen that surrounded the sheet. Given the very small mass of the electrons, the high momentum of the alpha particles and the un-concentrated distribution of positive charge of the plum pudding model, the experimenters expected all the alpha particles to either pass through without significant deflection or be absorbed. To their astonishment, a small fraction of the alpha particles experienced heavy deflection. This led Rutherford to propose the planetary model of the atom in which point like electrons orbited in the space around a massive, compact nucleus—like planets orbiting the Sun.

While experimenting with the products of radioactive decay, in 1913 radio chemist Frederick Soddy (2 September 1877 – 22 September 1956)  discovered that there appeared to be more than one element at each position on the atomic table. The term isotope was coined by Margaret Todd as a suitable name for these elements.

That same year, J.J. Thomson conducted an experiment in which he channelled a stream of neon ions through magnetic and electric fields, striking a photographic plate at the other end. He observed two glowing patches on the plate, which suggested two different deflection trajectories. Thomson concluded this was because some of the neon ions had a different mass. The nature of this differing mass would later be explained by the discovery of neutrons in 1932.

In 1918, Rutherford bombarded nitrogen gas with alpha particles and observed hydrogen nuclei being emitted from the gas. Rutherford concluded that the hydrogen nuclei emerged from the nuclei of the nitrogen atoms themselves (in effect, he split the atom). He later found that the positive charge of any atom could always be equated to that of an integer number of hydrogen nuclei. This, coupled with the facts that hydrogen was the lightest element known and that the atomic mass of every other element was roughly equivalent to a whole multiple of hydrogen's atomic mass, led him to conclude hydrogen nuclei were singular particles and a basic constituent of all atomic nuclei: the proton. Further experimentation by Rutherford found that the nuclear mass of most atoms exceeded that of the protons it possessed; he speculated that this surplus mass was composed of hitherto unknown neutrally charged particles, which were tentatively dubbed "neutrons".

In 1928, Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles. It was later discovered that this radiation could knock hydrogen atoms out of paraffin wax. Initially it was thought to be high-energy gamma radiation, since gamma radiation had a similar effect on electrons in metals, but James Chadwick (later Sir James Chadwick, CH (20 October 1891 – 24 July 1974) )found that the ionisation effect was too strong for it to be due to electromagnetic radiation. In 1932, he exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles with a mass similar to that of a proton. For his discovery of the neutron, Chadwick received the Nobel Prize in 1935.

Finally, the experimental evidence for atoms may be obtained from - Bragg's law, which is the result of experiments into the diffraction of X-rays or neutrons off crystal surfaces at certain angles, derived by physicist Sir William Lawrence Bragg CH, FRS, (31 March 1890 – 1 July 1971) in 1912 and first presented on 11th November 1912 to the Cambridge Philosophical Society. Although simple, Bragg's law confirmed the existence of real particles at the atomic scale, as well as providing a powerful new tool for studying crystals in the form of X-ray and neutron diffraction. William Lawrence Bragg and his father, Sir William Henry Bragg, were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS, and diamond.

When X-rays hit an atom, they make the electronic cloud move as does any electromagnetic wave. The movement of these charges re-radiates waves with the same frequency (blurred slightly due to a variety of effects); this phenomenon is known as the Rayleigh scattering (or elastic scattering). The scattered waves can themselves be scattered but this secondary scattering is assumed to be negligible. A similar process occurs upon scattering neutron waves from the nuclei or by a coherent spin interaction with an unpaired electron. These re-emitted wave fields interfere with each other either constructively or destructively (overlapping waves either add together to produce stronger peaks or subtract from each other to some degree), producing a diffraction pattern on a detector or film. The resulting wave interference pattern is the basis of diffraction analysis. Both neutron and X-ray wavelengths are comparable with inter-atomic distances (~150 pm) and thus are an excellent probe for this length scale.

I hope this partial history and somewhat long-winded answer is of some use!