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The exam is the most extensive of the GCSE science boards; made up of nine papers and three practical exams. For each of biology, chemistry and physics there are three papers and one practical exam: Paper 1 is one hour long, Paper 2 is one hour and fifteen minutes, Paper 3 is a practical skills paper and is thirty minutes long, and the ...
A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 Da), but this number will not be exactly an integer except (by definition) in the case of carbon-12. [67] The heaviest stable atom is lead-208, [59] with a mass of 207.976 6521 Da. [68]
In late 1998, Polish physicist Robert Smolańczuk published calculations on the fusion of atomic nuclei towards the synthesis of superheavy atoms, including elements 118 and 116. [54] His calculations suggested that it might be possible to make these two elements by fusing lead with krypton under carefully controlled conditions.
In chemistry and atomic physics, an electron shell may be thought of as an orbit that electrons follow around an atom's nucleus.The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and further from the nucleus.
Thomson's model marks the moment when the development of atomic theory passed from chemists to physicists. While atomic theory was widely accepted by chemists by the end of the 19th century, physicists remained skeptical because the atomic model lacked any properties which concerned their field, such as electric charge, magnetic moment, volume, or absolute mass.
In a May 1911 paper, [8] Rutherford presented his own physical model for subatomic structure, as an interpretation for the unexpected experimental results. [3] In it, the atom is made up of a central charge (this is the modern atomic nucleus, though Rutherford did not use the term "nucleus" in his paper). Rutherford only committed himself to a ...
The liquid drop model is one of the first models of nuclear structure, proposed by Carl Friedrich von Weizsäcker in 1935. [5] It describes the nucleus as a semiclassical fluid made up of neutrons and protons , with an internal repulsive electrostatic force proportional to the number of protons.
Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal . Because of its high chemical reactivity , barium is never found in nature as a free element.