Elements, Symbols, and the Periodic Table

X represents the element symbol (from the periodic table), Z is the atomic number, the number of protons, and A is the mass number, the sum of the protons plus neutrons. Subtracting the atomic number from the mass number (A— Z) gives the number of neutrons present in this particular isotope. For example, iiNa would contain 11 protons, 11 electrons, and 12 neutrons (23-11). 

Symbols, introduced in Section 1.4, are used to represent the elements. The periodic table, introduced in Section 1.5, groups together elements with similar properties. Chemical symbols and the periodic table are both designed to decrease the effort required to learn a great deal of chemistry. Section 1.6 presents scientific laws, hypotheses, and theories that generalize and explain natural phenomena. 

The number of protons in an atom—which is also the number of electrons in an uncharged atom—is known as the element s atomic number. The atomic number can be found above each of the elements symbols on the periodic table. Because it displays the atomic numbers, the periodic table can be used to determine the number of protons and electrons in an uncharged atom of any element. For example, the atomic number of phosphorus is 15, so we know there are 15 protons and 15 electrons in each uncharged atom of phosphorus. 

This discussion and these exercises have shown that one mole of atoms of any element is simply the atomic weight in grams listed below the element symbol in the periodic table. This is the molar mass of the element (Figure 8.1). 

Atoms of elements have no electrical charge and so must contain identical numbers of positive protons and negative electrons. However, because neutrons have no electrical charge, their numbers in an atom do not have to be the same as the numbers of protons or electrons. The number of protons in the nucleus of an atom is given by the atomic number for the atom. Atomic numbers are represented by the symbol Z. All atoms of a specific element must have the same atomic number. The atomic numbers for each element are the numbers above the elemental symbols of the periodic table inside the front cover of this book. Remember, this is also the number of electrons in the atoms of each element. 

Figure 6-10 shows the electronegativity Vcdues of the various elements below each element symbol on the periodic table. Notice that with a few exceptions, the electronegativities increase from left to right in a period and decrease from top... 

The names of all the elements and their symbols are shown in the tables in the back of this book. Most of the symbols match up with the names H for hydrogen, 0 for oxygen, C for carbon. He for helium, Li for lithium. Symbols for the newer elements are easy to interpret, too. Element 101, for instance, has the symbol Md and the well-deserved name of Mendelevium. But a few of the symbols in the periodic table do not match the names of their elements. Sodium, for instance, does not have the symbol So. Instead, it is Na. Potassium isn t Po, but rather K. 

Information about an element s protons and neutrons is often summarized using the chemical notation shown in Figure 2.3. The letter X represents the atomic symbol for an element. (The atomic symbol is also called the element symbol.) Each element has a different atomic symbol. All chemists, throughout the world, use the same atomic symbols. Over the coming months, you will probably learn to recognize many of these symbols instantly. Appendix G, at the back of this book, lists the elements in alphabetical order, along with their symbols. You can also find the elements and their symbols in the periodic table on the inside back cover of this textbook, and in Appendix C. (You will review and extend your understanding of the periodic table, in section 2.2.)... 

Atomic numbers and atomic masses are usually included in the boxes with the chemical symbols in the periodic table. The atomic number is the integer. (The mass number, also an integer, is given in parentheses for the most stable isotope of the synthetic elements.)... 

The chemical symbols of the periodic table make it easy to write the formulas for chemical compounds. For example, table salt, which is called sodium chloride, is composed of one part sodium (Na) and one part chlorine (Cl), and its chemical formula is NaCl. Water is composed of two parts hydrogen (H) and one part oxygen (O), and its chemical formula is H2O. The subscript 2 indicates that two hydrogen elements combine with one oxygen element to form water. 

Each element box on the periodic table contains useful information. In the Elements Handbook, each element box has an element name, symbol, atomic number, and electron configuration. At the beginning of each section, each element box also identifies the state of matter at 25°C and 1 atm. A typical box from the handbook is shown below. 

Elements above lead (atomic numbers 83 and above) on the Periodic Table are radioactive (see Figure 9.2). Other elements may have one or more radioactive isotopes. Some elements occur naturally, while others are manmade. Each symbol on the Periodic Table represents one atom of that element. An atom is made up of a nucleus with varying numbers of electrons in orbits circling around the nucleus (see Figure 9.3). Located inside the nucleus are protons and neutrons. Protons in the nucleus of an atom represent the atomic number of that element. Neutron numbers may vary within the same type of element or from one element to another, but the number of protons must stay the same. The atom is the smallest part of an element that normally exists so any particle of an element that is smaller than an atom is commonly referred to as a subatomic particle. 

As shown in Figure 3-1, chemists use the placeholder to represent the chemical symbol. You can find an element s chemical symbol on the periodic table or a list of elements (see Table 3-2 for a list of elements). The placeholder Z represents the atomic number — the number of protons in the nucleus. And A represents the mass number, the sum of the number of protons plus neutrons. The mass number (also called the atomic weight is listed in amu. 

If you wish to look up the element in the Periodic Table, refer to Table 2.1-5, where the element symbol and the atomic number will be found. Then use Table 2.1-2 or Table 2.1-3 to find the numbers of the pages where the properties of the element of interest are tabulated. 

Write the symbol and name for the elements located in the periodic table as follows ... 

Next, reverse the process with part (a) still covered. Look at the alphabetical list in the caption. For each name, mentally write —in other words, think—the symbol. Glance up to the periodic table and find the element. Again, use part (a) as a temporary help only if necessary. Repeat the procedure several times, taking the elements in random order. Move in both directions, from name to symbol in the periodic table and from symbol to name. 

Using the periodic tabie and some oharaoteristics of an atom, you can determine the composition of subatomic particles in a neutral atom. Complete the table indicating the element symbol, and the number of protons, neutrons, and electrons in each atom. 

The atomic mass of each elanent is directly beneath the element s symbol in the periodic table and represents the average mass of the isotopes that compose that element, weighted according to the natural abundance of each isotope. For example, the periodic table lists the atomic mass of chlorine as 35.45 amn. Naturally occurring chlorine consists of 75.77% chloiine-35 atoms (mass 34.97 amn) and 24.23% chlorine-37 atoms (mass 36.97 amu). We can calcnlate its atomic mass ... 

Figure 21.1 Nonmetals and the periodic table. The location of all non-metals in the periodic table is shown in yellow. Symbols are given for the nonmetallic elements discussed in this chapter.

Chapter 4, Atoms and Elements, introduces elements and atoms and the periodic table. The names and symbols of element 114, Herovium, FI, and 116, Livermorium, Lv, have been added to update the periodic table. Atomic numbers and mass number are determined for isotopes. Atomic mass is calculated using the masses of the naturally occurring isotopes and their abundances. Trends in the properties of elements are discussed, including atomic size, electron-dot symbols, ionization energy, and metallic character. 

Matter is made up of very tiny units called atoms. Each different type of atom is the building block of a different chemical element. Presently, the International Union of Pure and Applied Chemistry (lUPAC) recognizes 118 elements, but four do not yet have names or symbols. The known elements range from common substances, such as carbon, iron, and silver, to uncommon ones, such as lutetium and thulium. About 90 of the elements can be obtained from natural sources. The remainder do not occur naturally and have been created only in laboratories. On the inside front cover you will find a complete listing of the elements and also a special tabular arrangement of the elements known as the periodic table. The periodic table is the chemist s directory of the elements. We will describe it in Chapter 2 and use it throughout most of the text. 

As indicated in Figure 4, the early transactinide elements find their place back in the main body of the Periodic Table. The discoverers of the currendy known transactinide elements, suggested names and symbols, and dates of discovery are Hsted in Table 10 (19). Because there are competing claims for the discovery of these elements, the two groups of discoverers in each case have suggested names for elements 104 and 105. In the case of elements 106—109, names for the elements have not been suggested in order to avoid another dupHcation. 

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