| A | B |
|---|
| atom | nucleus surrounded by a cloud with moving electrons |
| nucleus | center of the atom |
| Protons | positive particles inside the nucleus |
| atomic number | the number of protons in the nucleus of an atom |
| neutrons | a particle in the nucleus of an atom with no charge |
| isotopes | atoms that have the same number of protons in the nucleus but have a different mass |
| relative mass | mass of the atom expressed in terms of the mass of the standard atom |
| atomic mass unit (amu) | standard unit for measuring the mass of an atom |
| mass number | sum of its protons and neutrons |
| atomic mass of an element | average of the mass numbers of its atoms |
| stable electron arrangement | atom with all of its electrons in the lowest possible energy levels |
| Energy levels of an atom | k shell 2 electrons, L shell 8, M shell 18, N shell 32 |
| Atoms reacting with other atoms | when their outer energy levels are unfilled. They exchange or share electrons with each other |
| Excited electrons | electrons that have absorbed energy and have moved farther from the nucleus |
| Electrons gain energy and lose energy | gain they move to a higher energy level, lose they fall to a lowest level but never collapse |
| Periodic table | arrangement of elements in rows (periods) and columns (groups or families) |
| In periodic table three types of elements that are grouped by color | metals, nonmetals, and metalloids |
| metals-group 1 | alkali metals, shiny, softer, less dense, chemically active |
| metals-group 2 | alkaline earth metals, harder, denser, high melting points, chemically active |
| transition elements | rows 4-7 under groups 3-12, hard high melting points, compounds are colorful, silver, gold mercury |
| alloy | mixture of two or more elements having metal properties |
| nonmetals | not shiny, are brittle, not good conductors of electricity |
| nonmetals take the form of | solids, gases and liquid (bromine) |
| nonmetals react | with metals |
| halogens | cobine readily with metals to form salts, salt fluoride, bleach |
| Noble gases | do not react chemically with other gases, only combine under very specific conditions INERT |
| metalloids | properties between metals and nonmetals, solids look like metals, white or gray but not shiny, conduct electricity but not as well as metals |
| Boron | poor conductor of electricity at low temperatures, improves if heated which is opposite of metals (semiconductor) |
| semiconductors | are used in electrical devices that have to function at temperatures too high for metals |
| silicon | semiconductor found in great abundance in earth's crust. sand,glass, cement |
| chemical bond | force of attraction that holds atoms together, lose individual properties (water) |
| covalent bond | formed when two atoms share electrons. usually with nonmetals |
| valence electrons | outermost electrons in the atoms energy shell |
| covalent compounds | compounds whose atoms are joined by covalent bonds sugar methane, ammonia |
| ionic bond | formed by the transfer of electrons (metals and nonmetals) fill each others outer shell and are stable |
| ions | atoms with unequal number of protons and electrons (more protons pos charged, more electrons then neg charged) |
| ionic compounds examples | table salt(sodium chloride), drain cleaner(sodium hydroxide), salt substitute(potassium chloride) |
| composition reaction | two or more substances combine to form a compound (silver and sulfur yield silver dioxide) A+B-> AB |
| decomposition reaction | a compound breaks down into two or more simpler substances (water breaks down into hydrogen and oxygen) AB->A+B |
| single replacement reaction | free element replaces an element that is part of a complex (iron plus copper sulfate yields iron sulfate plus copper) A+BX->AX+B |
| double replacement reaction | parts of two compounds replace each other (sodium chloride plus mercury nitrate yeild sodium nitrate plus mercury chloride) AX+BY->AY+BX |
