2.14 A–C), although some are not, like copper (Cu, Fig. Metals are usually malleable, they can be bent or molded without breaking, and lustrous, or shiny. Metals are elements that conduct heat and electricity. These two groups are arranged in rows rather than columns. The elements in each of these rows behave similarly, so are considered groups. The two long rows that are at the bottom of the periodic table are exceptions. Although technically a nonmetal, hydrogen has properties of both metals and nonmetals and is often placed in Group 1. Groups 1–12 contain only metals, Groups 13–16 contain both metals and nonmetals, and Groups 17 and 18 contain only nonmetals. The group number is found at the top of the column. Third, the periodic table is arranged in columns of elements that react similarly. For example, in Figure 2.13, the atomic number of hydrogen is 1, found over the H. The atomic number corresponds to the number of protons and is found above the elements’ symbol. Second, all of the elements are listed sequentially according to their atomic numbers. Table 2.2 shows the atomic number, atomic symbol, atomic structure, and number of protons, neutrons, and electrons for the first three elements. The element Actium (Ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom. This means a neutral oxygen atom has eight protons and eight electrons. An oxygen atom (O) has an atomic number of eight (8). If a hydrogen atom is neutral, it must also have one electron. This means a hydrogen atom has one proton. For example, hydrogen (H) has an atomic number of one (1). On the periodic table, the atomic number is usually given as the whole number above the symbol for the element (see Fig. The atomic number is equal to the number of protons in an element. When the number of protons and electrons in an atom are same, the charges cancel out, or counteract each other.Įvery atom of a particular element has the same number of protons. An uncharged atom is electrically neutral because electrons and protons have opposite charges of equal sizes. A single uncharged atom has an equal number of protons (+) and electrons (–). Some atoms exist naturally as neutral, or uncharged, atoms. The subatomic particles in an atom determine the properties of the atom. This means that it would take one hundred trillion (100,000,000,000,000) electrons put side-by-side to equal a centimeter! Electrons are about one-thousandth (1/1000) the diameter of a proton or neutron. This means it would take about one hundred billion (100,000,000,000) protons or neutrons put side-by-side to equal a centimeter. Protons and neutrons are both about one-thousandth (1/1000) the diameter of a hydrogen atom. One hundred million (100,000,000) hydrogen atoms put side-by-side equals about a centimeter. Chemical properties include the specific ways that atoms and molecules react and the energy that they release or use in these reactions. The number of electrons and protons in an atom determines its chemical properties. This force got its name because it is strong enough to overcome the force of the positively charged protons repelling each other. The strong force holds neutrons and protons together in the nucleus. The attraction between negatively charged electrons and positively charged protons in an atom give the atom its structure. Electrostatic forces also hold electrons and protons together in the atom. 2.11).Įlectrostatic forces hold atoms together in molecules-like the two hydrogen atoms held together in H2 gas. Electrons exist in regions called shells outside of the atom’s nucleus (Fig. Protons and neutrons occupy the nucleus, or center, of the atom.
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