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9Sci CH10
9th Science CH10 Atomic Structure and the Periodic Table
| Term | Definition |
|---|---|
| atomic number | the number of protons in an atom’s nucleus |
| average atomic mass | the average mass of an element is the average mass of the mixture of its isotopes |
| chemical symbol | a shorthand way to write the name of an element; for example C for carbon, Ag for silver |
| dot diagram | a diagram to represent electrons in the outer energy level of an atom; uses the element symbol and dots |
| electron | negatively charged particles that move around the nucleus of an atom |
| electron cloud | region where electrons most probably are found surrounding the nucleus of an atom |
| group | in the periodic table, each of the 18 vertical columns of elements; each group (family) is made up of elements with similar properties |
| isotope | atoms of the same element that have different numbers of neutrons; for example, boron-10 and boron-11 |
| mass number | sum of the number if protons and neutrons in an atom’s nucleus |
| metal | elements usually having these common properties: shiny, good conductors of heat and electricity; are solids at room temperature; in the periodic table, metals are found at the left of the stair-step line |
| metalloid | elements having properties of both metals and nonmetals; in the periodic table metalloids are found along the stair-step line that separates metals from nonmetals |
| neutron | atomic particle with no charge (neutral) that is part of an atom’s nucleus |
| nonmetal | elements that usually are gases or brittle solids at room temperature; most do not conduct heat or electricity well; in the periodic table, nonmetals are found at the right of the stair-step line |
| nucleus | the positively charged center of an atom that contains protons and neutrons |
| period | a horizontal row in the periodic table |
| periodic table | a table of the elements arranged according to repeated changes in properties |
| proton | atomic particle with a positive charge that is part of an atom’s nucleus |
| quark | very small particles of matter that make up protons and neutrons; presently six different types of quarks are known |