Protons Positively charged particles that

In the early part of the twentieth century, then, a simple model of atomic structure became accepted, now known as the Rutherford nuclear model of the atom, or, subsequently, the Bohr-Rutherford model. This supposed that most of the mass of the atom is concentrated in the nucleus, which consists of protons (positively charged particles) and neutrons (electrically neutral particles, of approximately the same mass). The number of protons in the nucleus is called the atomic number, which essentially defines the nature of... 

The positively charged particles that repelled the alpha particles in the gold foil experiments and that compose the nucleus of an atom are called protons. The charge of a proton was calculated to be exactly equal in magnitude but opposite in sign to the charge of an electron. Later experiments showed that the proton s mass is almost 2000 times the mass of an electron. 

The definition of an element became more precise at the dawn of the 20th century with the discovery of the proton. We now know that an atom has a small center called the nucleus. In the nucleus are one or more protons, positively charged particles, the number of which determine an atom s identity. The number of protons an atom has is referred to as its atomic number. Hydrogen, the lightest element, has an atomic number of 1, which means each of its atoms contains a single proton. The next element, helium, has an atomic number of 2, which means each of its atoms contain two protons. Lithium has an atomic number of 3, so its atoms have three protons, and so forth, all the way through the periodic table. Atomic nuclei also contain neutrons, but atoms of the same element can have different numbers of neutrons we call atoms of the same element with different number of neutrons isotopes. ... 

By the 1930s, however, it was clear that atoms were made up of even smaller particles—protons, neutrons, and electrons, then considered to be the fundamental particles of matter. (A proton is a positively charged particle that weighs about one atomic mass unit [1.0073 AMU] a neutron has about the same mass [1.0087 AMU] but no charge and an electron has a much smaller mass [0.0005 AMU] and a negative charge.) Protons and neutrons make up the tiny nucleus of an atom, while electrons exist outside the atomic nucleus in discrete energy levels within an electron cloud. ... 

Protons Positively charged particles, also found in the nucleus it s important to note that the number of protons an atom possesses is the sole factor that distinguishes one element from another. 

Nuclei that have too many protons relative to their number of neutrons correct this situation in either of two ways. They either capture one of their Is electrons or they emit a positron (a positively charged particle with the same mass as an electron). Either process effectively changes a proton to a neutron within the nucleus. 

When Rutherford allowed the radiation to pass between two electrically charged electrodes, he found that one type was attracted to the negatively charged electrode. He proposed that the radiation attracted to the negative electrode consists of positively charged particles, which he called a particles. From the charge and mass of the particles, he was able to identify them as helium atoms that had lost their two electrons. Once Rutherford had identified the atomic nucleus (in 1908, Section B), he realized that an a particle must be a helium nucleus, He2+. An a particle is denoted or simply a. We can think of it as a tightly bound cluster of two protons and two neutrons (Fig. 17.5). 

Neutrons readily induce nuclear reactions, but they always produce nuclides on the high neutron-proton side of the belt of stability. Protons must be added to the nucleus to produce an unstable nuclide with a low neutron-proton ratio. Because protons have positive charges, this means that the bombarding particle must have a positive charge. Nuclear reactions with positively charged particles require projectile particles that possess enough kinetic energy to overcome the electrical repulsion between two positive particles. 

Proton A nuclear particle that contains one unit of positive electrical charge. 

The exploration of atomic structure began in 1911, when Ernest Rutherford, a New Zealander who worked in Canada and England, discovered that atoms had a dense central nucleus that contained positively charged particles, which he named protons. (See Table 3-1.) it was soon established that each chemical element was characterized by a specific number of protons in each atom. A hydrogen atom has 1 proton, helium has 2, lithium has 3, and so forth through the periodic table. The atomic number is the number of protons for each element. 

Elements are fundamental substances that cannot be broken down into smaller chemical components. The smallest unit of an element is an atom, a term based on the Greek word atomos, meaning indivisible. But atoms are divisible—they consist of a nucleus containing positively charged particles called protons and electrically neutral particles called neutrons, surrounded by a swarm of electrically negative particles called electrons. In chemical reactions, atoms interact and combine to form a molecule of a compound. (Chemical reactions also occur when the atoms in molecules interact and combine to form even bigger com-... 

Nucleus Densely packed central region of an atom that consists of positively charged particles called protons and neutral particles called neutrons. 

This symbol provides a great deal of information about the composition of this particular atom. The atomic number, 2 in this case, tells the number of protons. The definition of an atom indicates that it is a neutral particle so the number of positively charged particles must be offset by the same number of negatively charged particles. Electrons are negatively charged, so the number of protons in an atom must be the same as the number of electrons in that atom. The mass number is defined as the number of protons plus the number of neutrons. Since the mass number of this example is 4, the sum of the number of protons and the number of neutrons is also 4. That means there are 2 neutrons in the nucleus. Hydrogen is the only element in with no neutrons since its nucleus has only one proton. 

Several years later, in 1919, the positively charged particle, the proton, was discovered that makes up the dense nucleus of an atom. It would be another thirteen years before James Chadwick discovered the neutrally charged neutron, the second component of the nucleus. 

Rutherford suggested that this nucleus at the center of the atom was composed of densely packed positively charged particles. Soon after, Henry Moseley, before his early death at Gallipoli in World War I, supplied experimental evidence for these particles, the protons. The other particles in the nucleus, the neutrons, proved a bit harder to pin down because they have no charge. But James Chadwick, taking Rutherford s advice, finally confirmed their existence in 1932. Chadwick measured the rebound of certain radiation from nitrogen and helium and found it corresponded to a neutral particle with about the same mass as a proton. ... 

So it is with this disclaimer in mind that we present the structure of the atom as it is currently understood. We first note the main features that are of common knowledge. The nucleus, or center of the atom, is composed of positively charged particles called protons and uncharged, neutral particles called neutrons. Electrons, as is customarily acknowledged, are the negatively charged particles that reside in orbits around the nucleus. 

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