The atomic number is the number of protons in a nucleus. Boron has an atomic number of five. The English chemist and physicist John Dalton expanded Proust`s work and transformed the atomic philosophy of the Greeks into a scientific theory between 1803 and 1808. His book A New System of Chemical Philosophy (Part I, 1808; Part II, 1810) was the first application of atomic theory to chemistry. He provided a physical picture of how elements combine to form compounds, and a phenomenological reason to assume atoms exist. His work, along with that of Joseph-Louis Gay-Lussac de France and Amedeo Avogadro of Italy, provided the experimental basis for atomic chemistry. Mendeleev skipped hydrogen because it is anomalous and classified the 63 elements known at the time into six groups according to valence. Valence, which is the combining force of an element, determines the proportions of the elements in a compound. For example, H2O combines oxygen with a valence of 2 and hydrogen with a valence of 1.
Mendeleev realized that chemical qualities gradually change as atomic weight increases, and predicted that a new element must exist wherever there is a difference in atomic weight between neighboring elements. His system was therefore a research tool and not just a classification system. Mendeleev`s periodic table, however, raised an important question for future atomic theory: where does the model of atomic weights come from? There is an easy way to represent isotopes with atomic symbols. We use construction experiments with gases, which first became possible at the turn of the nineteenth century, led John Dalton in 1803 to propose a modern theory of the atom based on the following assumptions. When we refer to an atom, we simply use the name of the element: the term sodium refers to both the element and a sodium atom. But it can be difficult to use item names all the time. Instead, chemistry defines a symbol for each element. Atomic symbolA one- or two-letter representation of the name of an element.
is an abbreviation of the element`s name consisting of one or two letters. By convention, the first letter of an element`s symbol is always uppercase, while the second letter (if any) is lowercase. Thus, the symbol for hydrogen is H, the symbol for sodium is Na, and the symbol for nickel is Ni. Most symbols come from the English name of the element, although some symbols come from the Latin name of an element. (The symbol for sodium, Na, comes from its Latin name, sodium.) Table 3.2 “Names and symbols of common elements” lists some common elements and their symbols. You need to remember the symbols in Table 3.2 “Names and Symbols of Common Elements” because in this way we will represent the elements throughout chemistry. where X is the symbol for the element, A is the mass number, and Z is the atomic number. For the isotope of carbon, which has 6 protons and 6 neutrons, the symbol Based on the law of definite proportions, Dalton derived the law of multiple proportions, which states that if two elements form more than one compound by combining in more than one weight fraction, the weight of an element in one of the compounds is unique, an integer ratio to its weights in the other compounds. For example, Dalton knew that oxygen and carbon can combine to form two different compounds, and that carbon dioxide (CO2) contains twice as much oxygen by weight as carbon monoxide (CO).
In this case, the ratio of oxygen in one compound to the amount of oxygen in the other is the simple integer ratio 2:1. Although Dalton called his theory “modern” to distinguish it from the philosophy of Democritus, he retained the Greek term atom to honor the ancients. What are the charges for each of the three subatomic particles? The concept that atoms play a fundamental role in chemistry is formalized by modern atomic theory, the concept that atoms play a fundamental role in chemistry was first formulated in 1808 by John Dalton, an English scientist. It consists of three parts: List the three statements that make up modern atomic theory. To solve such problems of chemical notation, the Sicilian chemist Stanislao Cannizzaro revived Avogadro`s ideas in 1858 and explained them at the first International Congress of Chemistry, which met in Karlsruhe in 1860. Lothar Meyer, a well-known German chemistry professor, later wrote, listening to Avogadro`s theory at the congress: “It was as if scales fell from my eyes, doubts disappeared and were replaced by a sense of peaceful certainty.” Within a few years, Avogadro`s hypotheses were widely accepted in the world of chemistry. Because early chemists didn`t know how many atoms there were in a molecule, their chemical notation systems were in a state of chaos in the mid-19th century. Berzelius and his followers, for example, used the general MO formula for the major metal oxides, while others mapped the M2O formula used today. A single formula represented different substances according to the chemist: H2O2 was water or hydrogen peroxide; C2H4 was methane or ethylene. Proponents of the system used today based their chemical notation on an empirical law formulated in 1819 by French scientists Pierre-Louis Dulong and Alexis-Thérèse Petit on the specific heat of elements. According to Dulong-Petit`s law, the specific heat of all elements per atom is the same.
However, this law had many exceptions and was not fully understood until the development of quantum theory in the 20th century. Modern atomic theory states that the atoms of an element are the same, while the atoms of different elements are different. What distinguishes atoms from different elements? The fundamental characteristic that all atoms of the same element have in common is the number of protons. All hydrogen atoms have one and only one proton in the nucleus; All iron atoms have 26 protons in their nucleus. This number of protons is so important for the identity of an atom that it is called the atomic number, the number of protons in an atom. of the element. Thus, hydrogen has an atomic number of 1, while iron has an atomic number of 26. Each element has its own characteristic atomic number. The elements, when arranged according to their atomic weight, show a pronounced periodicity of their properties. Elements that have similarities in their chemical behavior have atomic weights that are approximately the same (as in the case of Pt, Ir, Os) or they have atomic weights that increase uniformly (as in the case of K, Rb, Cs). The elements are grouped in a special table called periodic tableA table of all elements.
A simple periodic table is presented in Figure 3.2 “A simple periodic table”, while a more detailed table is presented in Chapter 17 “Appendix: Periodic table of elements”. The elements of the periodic table are listed in order of ascending atomic number. The periodic table has a particular shape that becomes important for us when we consider the organization of electrons in atoms (see Chapter 8 “Electronic structure”). The direct use of the periodic table helps us identify metals and nonmetals. The nonmetals are located in the upper right corner of the periodic table, on one side of the heavy line that divides the right-hand side of the graph. All other elements are metals. Set the ordinal number. What is the atomic number of a boratom? where C is the symbol of the element, 6 is the atomic number, and 12 is the mass number.
Until the early 1860s, however, chemists` adherence to another concept, championed by the eminent Swedish chemist Jöns Jacob Berzelius, blocked acceptance of Avogadro`s ideas. (Berzelius was influential among chemists because he had determined the atomic weights of many elements with extreme precision.) Berzelius falsely claimed that all atoms of a similar element repel each other because they have the same electric charge. He believed that only atoms with opposite charges could combine to form molecules. The number of protons in the nucleus of a tin atom is 50, while the number of neutrons in the nucleus is 68. What are the atomic and mass numbers of this isotope? As more and more elements were discovered in the 19th century, scientists began to wonder how the physical properties of elements were related to their atomic weight. In the 1860s, several plans were proposed. The Russian chemist Dmitri Ivanovich Mendeleev based his system on the atomic weights of the elements determined by Avogadro`s theory of diatomic molecules. In his 1869 paper introducing the periodic law, he credits Cannizzaro with using “unshakable and indisputable” methods to determine atomic weights. Gay-Lussac quickly took the relationship between chemical masses, which involved Dalton`s atomic theory, and extended it to the volumetric relationships of gases.