Title: North West England
Content:  Sir Ernest Marsden (of Blackburn) and Hans Geiger conducted the Geiger–Marsden experiment at the University of Manchester in 1909, where the Geiger counter was invented, which demonstrated the existence of the atomic nucleus. Sir J. J. Thomson of Cheetham Hill discovered the electron (given its name in 1891 by George Johnstone Stoney) in April 1897 and received the Nobel Prize for Physics in 1906; his son George Paget Thomson would win the Nobel Prize for Physics 1937 for discovering electron diffraction (at the University of Aberdeen). John Dalton, from Cumbria and moved to Manchester, developed atomic theory. William Sturgeon of Lancashire invented the electromagnet in 1825. Sydney Chapman, a mathematician from Eccles, in 1930 explained the ozone–oxygen cycle in the 
Title: Atomic physics
Content:  One of the earliest steps towards atomic physics was the recognition that matter was composed of atoms. It forms a part of the texts written in 6th century BC to 2nd century BC such as those of Democritus or Vaisheshika Sutra written by Kanad. This theory was later developed in the modern sense of the basic unit of a chemical element by the British chemist and physicist John Dalton in the 18th century. At this stage, it wasn't clear what atoms were although they could be described and classified by their properties (in bulk). The invention of the periodic system of elements by Mendeleev was another great step forward. The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably 
Title: Chemistry
Content:  elements in the 1860s by Dmitri Mendeleev and independently by several other scientists including Julius Lothar Meyer. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. In 1897, J.J. Thomson of Cambridge University discovered the electron and soon after the French scientist Becquerel as well 
Title: Atomic nucleus
Content:  The nucleus was discovered in 1911, as a result of Ernest Rutherford's efforts to test Thomson's "plum pudding model" of the atom. The electron had already been discovered by J.J. Thomson. Knowing that atoms are electrically neutral, J.J.Thomson postulated that there must be a positive charge as well. In his plum pudding model, Thomson suggested that an atom consisted of negative electrons randomly scattered within a sphere of positive charge. Ernest Rutherford later devised an experiment with his research partner Hans Geiger and with help of Ernest Marsden, that involved the deflection of alpha particles (helium nuclei) directed at a thin sheet of metal foil. He reasoned that if J.J Thomson's model were correct, the positively charged alpha particles would easily pass through the foil with very little deviation in their paths, as the foil 
Title: Discovery of the neutron
Content:  At the start of the 20th century, the vigorous debate as to the existence of atoms had not yet been resolved. Philosophers such as Ernst Mach and Wilhelm Ostwald denied that atoms were real, viewing them as a convenient mathematical construct, while scientists such as Arnold Sommerfeld and Ludwig Boltzmann saw that physical theories required the existence of atoms. Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working with phosphorescent materials. In 1898, Ernest Rutherford at Cavendish Laboratory distinguished two types of radioactivity, alpha rays and beta rays, which differed in their ability to penetrate, or travel into, ordinary objects or gases. Two years 
Title: History of subatomic physics
Content:  However, near the end of 19th century, physicists discovered that Dalton's atoms are not, in fact, the fundamental particles of nature, but conglomerates of even smaller particles. The electron was discovered between 1879 and 1897 in works of William Crookes, Arthur Schuster, J. J. Thomson, and other physicists; its charge was carefully measured by Robert Andrews Millikan and Harvey Fletcher in their oil drop experiment of 1909. Physicists theorized that negatively charged electrons are constituent part of "atoms", along with some (yet unknown) positively charged substance, and it was later confirmed. Electron became the first elementary, truly fundamental particle discovered. Studies of the "radioactivity", that soon revealed the phenomenon of radioactive decay, provided another argument against considering chemical elements as fundamental nature's elements. Despite these discoveries, the term atom stuck to Dalton's (chemical) atoms and now denotes the smallest particle of a chemical element, not something really indivisible.
Title: Atomic Age
Content: 1896 – Henri Becquerel notices that uranium gives off an unknown radiation which fogs photographic film. ; 1898 – Marie Curie discovers thorium gives off a similar radiation. She calls it radioactivity. ; 1903 – Ernest Rutherford begins to speak of the possibility of atomic energy. ; 1905 – Albert Einstein formulates the special theory of relativity which explains the phenomenon of radioactivity as mass–energy equivalence. ; 1911 – Ernest Rutherford formulates a theory about the structure of the atomic nucleus based on his experiments with alpha particles. ; 1930 – Otto Hahn writes an article with his prophecy "The Atom – the source of power of the future?" in the newspaper Deutsche Allgemeine Zeitung. ; 1932 – James Chadwick discovers the neutron. ; 
Title: History of physics
Content:  In the 19th century, experimenters began to detect unexpected forms of radiation: Wilhelm Röntgen caused a sensation with his discovery of X-rays in 1895; in 1896 Henri Becquerel discovered that certain kinds of matter emit radiation on their own accord. In 1897, J. J. Thomson discovered the electron, and new radioactive elements found by Marie and Pierre Curie raised questions about the supposedly indestructible atom and the nature of matter. Marie and Pierre coined the term "radioactivity" to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel's forms of radiation with electrons and the element helium. Rutherford identified and named two types of radioactivity and in 1911 interpreted experimental evidence as showing that the atom consists 
Title: Discovery of the neutron
Content:   The discovery of the neutron and its properties was central to the extraordinary developments in atomic physics in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model of the atom, based on the gold foil experiment of Hans Geiger and Ernest Marsden. In this model, atoms had their mass and positive electric charge concentrated in a very small nucleus. By 1920 chemical isotopes had been discovered, the atomic masses had been determined to be (approximately) integer multiples of the mass of the hydrogen atom, and the atomic number had been identified as the charge on the nucleus. Throughout the 1920s, the nucleus was viewed as composed of combinations of protons and electrons, the two elementary particles known at the time, 
Title: Timeline of chemistry
Content:  1894–1898: William Ramsay discovers the noble gases, which fill a large and unexpected gap in the periodic table and led to models of chemical bonding. 1897:J. J. Thomson discovers the electron using the cathode ray tube. 1898:Wilhelm Wien demonstrates that canal rays (streams of positive ions) can be deflected by magnetic fields, and that the amount of deflection is proportional to the mass-to-charge ratio. This discovery would lead to the analytical technique known as mass spectrometry. 1898:Maria Sklodowska-Curie and Pierre Curie isolate radium and polonium from pitchblende. c. 1900: Ernest Rutherford discovers the source of radioactivity as decaying atoms; coins terms for various types of radiation.                                         

Question: who discovered the atom and in what year?
Answer: early 1800s.
John Dalton.