#Atom theory series#

For example, if we were to draw a hydrogen atom to scale and used a 1-cm proton (about the size of this picture - ), the atom's electron would spin at a distance of ~0.5 km from the nucleus. Most of the space taken up by an atom is actually empty because the electron spins at a very far distance from the nucleus. To put that in perspective, it would take almost 20 million hydrogen atoms to make a line as long as this dash. One hydrogen atom (the smallest atom known) is approximately 5 x 10 -8 mm in diameter. Correct! Size, number, and weight of atomsĪtoms are extremely small. Interactive Animation: Atomic and ionic structure of the first 12 elementsī. The illustration linked below compares the two simplest atoms, hydrogen and helium. However, neutrons do not have any electrical charge they are electrically neutral.Ītoms are electrically neutral because the number of protons (+ charges) is equal to the number of electrons (- charges) and thus the two cancel out. As the atom gets larger, the number of protons increases, and so does the number of electrons (in the neutral state of the atom). Neutrons always reside in the nucleus of atoms and they are about the same size as protons. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help stabilize the protons in the atom's nucleus. In 1932, James Chadwick discovered a third type of subatomic particle, which he named the neutron. Rutherford's atom resembled a tiny solar system with the positively charged nucleus always at the center and the electrons revolving around the nucleus.ī. The nucleus was so dense that the alpha particles would bounce off of it, but the electrons were so tiny, and spread out at such great distances, that the alpha particles would pass right through this area of the atom. Suggested that the atom consisted of a small, dense core of positivelyĬharged particles in the center (or nucleus) of the atom, surrounded by a swirling ring of electrons. In 1911, Rutherford proposed a revolutionary view of the atom. Rutherford's experiments suggested that gold foil, and matter in general, had holes in it! These holes allowed most of the alpha particles to pass directly through, while a small number ricocheted off or bounced straight back because they hit a solid object.

While it was unclear at the time what the alpha particle was, it was known to be very tiny. Rutherford fired tiny alpha particles at solid objects such as gold foil. He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle (as if they had bumped up against something) and some bounced straight back like a tennis ball hitting a wall.

#Atom theory series#

Rutherford performed a series of experiments with radioactive alpha particles. Rutherford proposes a planetary model of an atom In 1908, Ernest Rutherford, a former student of Thomson's, proved Thomson's raisin bread structure incorrect.

These particles were later named electrons.Īfter Eugen Goldstein's 1886 discovery that atoms had positive charges, Thomson imagined that atoms looked like pieces of raisin bread, a structure in which clumps of small, negatively charged electrons (the 'raisins') were scattered inside a smear of positive charges. Thomson theorized, and was later proven correct, that the stream was in fact made up of small particles, pieces of atoms that carried a negative charge. Thomson found that the mysterious glowing stream would bend toward a positively charged electric plate. For years scientists had known that if an electric current was passed through a vacuum tube, a stream of glowing material could be seen however, no one could explain why. Thomson's notion of the electron came from his work with a nineteenth century scientific curiosity: the cathode ray tube. Was not an 'indivisible' particle as John Dalton had suggested but a jigsaw puzzle made of smaller pieces.

Thomson dramatically changed the modern view of the atom with hisĭiscovery of the electron. Until the final years of the nineteenth century, the accepted model of the atom resembled that of a billiard ball – a small, solid sphere. An updated version of the Atomic Theory I module is available.