![]() The subscript indicating the atomic number is actually redundant because the atomic symbol already uniquely specifies Z. The isotope of carbon that has 6 neutrons is therefore 12 6C. An isotope of any element can be uniquely represented as A ZX, where X is the atomic symbol of the element, A is the mass number and Z is the atomic number. In a typical sample of carbon-containing material, 98.89% of the carbon atoms also contain 6 neutrons, so each has a mass number of 12. The element carbon (C) has an atomic number of 6, which means that all neutral carbon atoms contain 6 protons and 6 electrons. Mass Number(A) = Number of Protons + Number of Neutrons Because different isotopes of the same element haves different number of neutrons, each of these isotopes will have a different mass number(A), which is the sum of the number of protons and the number of neutrons in the nucleus of an atom. All isotopes of an element have the same number of protons and electrons, which means they exhibit the same chemistry. Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. ![]() Unlike protons, the number of neutrons is not absolutely fixed for most elements. Recall that the nuclei of most atoms contain neutrons as well as protons. Hence, the atomic number defines the element in question. If you change the atomic number to 12, you are no longer dealing with sodium atoms, but magnesium atoms. That means that all sodium atoms have 11 protons. For example, the atomic number (z) for sodium (Na) is 11. The symbol for the atomic number is designated with the letter Z. This number is known as the atomic number, which identifies the number of protons in the nucleus of ALL atoms in a given element. When you study the periodic table, the first thing that you may notice is the number that lies above the symbol. Lead's toxicity was first documented by ancient Greek and Roman writers, who noted some of the symptoms of lead poisoning, but became widely recognized in Europe in the late 19th century.\) It damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders ranging from behavioral problems to brain damage, and also affects general health, cardiovascular, and renal systems. Lead is a devastating and persistent neurotoxin that accumulates in soft tissues and bones. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, plumbing, batteries, bullets and shot, weights, solders, pewters, fusible alloys, white paints, leaded gasoline, and radiation shielding. Lead's high density, low melting point, ductility and relative inertness to oxidation make it useful. In 2014, the annual global production of lead was about ten million tonnes, over half of which was from recycling. Lead played a crucial role in the development of the printing press, as movable type could be relatively easily cast from lead alloys. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. Interest in silver helped initiate widespread extraction and use of lead in ancient Rome. Galena is a principal ore of lead which often bears silver. Since lead is easily extracted from its ores, prehistoric people in the Near East were aware of it. Like the lighter members of the group, lead tends to bond with itself it can form chains and polyhedral structures. Exceptions are mostly limited to organolead compounds. Compounds of lead are usually found in the +2 oxidation state rather than the +4 state common with lighter members of the carbon group. Its weak metallic character is illustrated by its amphoteric nature lead and lead oxides react with acids and bases, and it tends to form covalent bonds. Lead is a relatively unreactive post-transition metal.
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