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עמוד:30
Summary Atoms are the most basic building blocks of all materials . Elements are basic substances consisting of only one kind of atoms . In the atom negatively charged electrons form a "cloud" . At the center of the atom is a tiny area known as a nucleus , consisting of positively charged protons and neutrons that have no electrical charge . Electrical forces of attraction are active between the positive nucleus and the negative electrons . The number of protons in the atom’s nucleus distinguishes one element from another , and this is known as the element’s atomic number . In a neutral atom , the number of protons equals the number of electrons . In an electrically charged atom , an ion , the number of electrons does not equal the number of protons . The periodic table is a table in which all the known elements are organized in ascending order of their atomic numbers . The table columns are also called chemical families , or groups , since they include elements with similar properties . For example : the alkali metals group , the halogens group and the noble gases group . Metals group is the largest group of elements , and it is located at the center and on the left side of the periodic table . Metals are good conductors of electricity and heat , they are shiny and they can be worked . Most of them are solid . The non-metals elements are located on the right side of the periodic table . These elements are poor conductors of electricity and of heat , they do not shine and they cannot be hammered into shape .
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