(The Dalton (Da) and the unified atomic mass unit (u) are alternative units that are equivalent to the amu.) The fundamental unit of charge (also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 × × 10 −19 C.Ī proton has a mass of 1.0073 amu and a charge of 1+. (This isotope is known as “carbon-12” as will be discussed later in this module.) Thus, one amu is exactly 1 12 1 12 of the mass of one carbon-12 atom: 1 amu = 1.6605 × × 10 −24 g. Since 1961, it has been defined with regard to the most abundant isotope of carbon, atoms of which are assigned masses of exactly 12 amu. The amu was originally defined based on hydrogen, the lightest element, then later in terms of oxygen. When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu) and the fundamental unit of charge (e). For example, a carbon atom weighs less than 2 × × 10 −23 g, and an electron has a charge of less than 2 × × 10 −19 C (coulomb). (credit middle: modification of work by “babyknight”/Wikimedia Commons credit right: modification of work by Paxson Woelber)Ītoms-and the protons, neutrons, and electrons that compose them-are extremely small. For a perspective about their relative sizes, consider this: If the nucleus were the size of a blueberry, the atom would be about the size of a football stadium ( Figure 2.11).įigure 2.11 If an atom could be expanded to the size of a football stadium, the nucleus would be the size of a single blueberry. The diameter of an atom is on the order of 10 −10 m, whereas the diameter of the nucleus is roughly 10 −15 m-about 100,000 times smaller. The nucleus contains the majority of an atom’s mass because protons and neutrons are much heavier than electrons, whereas electrons occupy almost all of an atom’s volume. It was learned that an atom contains a very small nucleus composed of positively charged protons and uncharged neutrons, surrounded by a much larger volume of space containing negatively charged electrons. The development of modern atomic theory revealed much about the inner structure of atoms. Calculate average atomic mass and isotopic abundance.Define the atomic mass unit and average atomic mass.Write and interpret symbols that depict the atomic number, mass number, and charge of an atom or ion.Explain the long form of the periodic table.By the end of this section, you will be able to:.Which one of the following elements found a place in the periodic table later?GermaniumChlorineOxygenSilicon In Mendeleev’s periodic table, gaps were left for the elements to be discovered later.How does the number of valence electrons vary on moving from left to right:(i) In the first period of the periodic table? (ii) In the second period of the periodic table?.Consider the following elements:Na, Ca, Al, K, Mg, Li (a) Which of these elements belong to the same period of the periodic table? (b) Which of these elements belong to the same group of the periodic table?.(a) What is the main characteristic of the last elements in the periods of the periodic table? What is the general name of such elements?(b) What is the number of elements in: (a) 1st period, and (b) 3rd period, of the modern periodic table?.Define the Periodic Table with elements name.Atomic number of a few elements are given below 10, 20, 7, 14(a) Identify the elements(b) Identify the Group number of these elements in the Periodic Table(c) Identify the Periods of these elements in the Periodic Table(d) What would be the electronic configuration for each of these elements?(e) Determine the valency of these elements.(a) What is the usual number of valence electrons and valency of group 18 elements of the periodic table?(b) What happens to the number of valence electrons in the atoms of elements as we go down in a group of the periodic table?.(a) How does the electropositive character of elements change on going down in a group of the periodic table?(b) State how the valency of elements varies (i) in a group, and (ii) in a period, of the periodic table.In the modern periodic table, which are the metals among the first ten elements?.Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.What is the major characteristic of the first elements in the periods of the periodic table? What is the general name of such elements?.Name of 118 elements in the periodic table. ![]() How does the valency of elements change on moving from left to right in the third period of the periodic table?. ![]() ![]()
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