For much of the nineteenth century, atoms were thought to be the smallest and most basic building blocks of all matter, but as that century drew to a close, there was increasing evidence that atoms were in fact made up of smaller particles. Scientists began to experiment with anode and cathode rays – these are positively and negatively charged rays produced by gas discharge tubes.
Therefore, in the first hypothesis of the structure of atoms, negatively charged electrons were scattered in an amorphous distributed mass of positive charge. it was called plum pudding patternWith electrons being analogous to plums embedded in the dough.
british physicist Ernest Rutherford I doubt this model. Between 1909 and 1911, under Rutherford’s tutelage at the University of Manchester, Hans Geiger and Ernest Marsden fired alpha particles—what we know today as helium nuclei—at a sheet of gold foil. In the plum pudding model, the alpha particles should have passed directly through the gold atoms, or deviated slightly.
Instead, Geiger and Marsden found in their experiment that alpha particles were sometimes deflected by large angles or even bounced straight off. This can only happen if the electric charge is lumped in the center of the atom, rather than spread out like in the plum pudding model. This convinced Rutherford that atoms were in fact composed of a tiny nucleus. and is tightly surrounded by empty space with electrons orbiting the nucleus at a distance.
This model, although simplified because it does not incorporate the quantum mechanical behavior of electrons, later became known as the Bohr model. niels bohrwho, along with Rutherford, put all the pieces together.
In the gold leaf experiment, the diffracted alpha particles were detected from this nucleus. But what was the core made of?
Various experiments, including some of Rutherford’s, showed that the hydrogen nucleus could arise from other elements, and by 1920 Rutherford had calculated that the hydrogen nucleus must be the basic building block of all atomic nuclei, because hydrogen is the lightest substance. He called the hydrogen nucleus a proton, which means “first” in Greek because Rutherford saw it as the first building block for all atoms. Today we know that protons (and neutrons) are made of even smaller particles, quarks, and that the nucleus of an atom is made of protons and neutrons. (Except for the elemental form of hydrogen, which has no neutrons).
A proton has what is called an “initial charge” (e), it is the basic unit of charge against which all other charges are measured. Only quarks have a small charge, one-third or two-thirds of the elementary charge.
Since hydrogen is by far the most common element (or molecule) in the universe, and since hydrogen nuclei are just individual protons, it suffices to say that proton science can tell us a lot about the distribution of matter and the violent mechanisms that produce it. can teach it.
Today we know that protons (and neutrons) are made of even smaller particles, quarks, and that the nucleus of an atom is made of protons and neutrons.
Davide Castelvecchi et al. How big is a proton? Particle-size puzzle leaps closer to resolution. nature 2019, DOI: 10.1038/d41586-019-03432-4