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Periodic Trends Periodic Law The statement that there is a periodic repetition of chemical and physical properties of elements when arranged by increasing atomic number Groups Elements in the same group have the same number of valence electrons. Group 1 have 1 valence electron Group 2 have 2 valence electrons Group 13 have 3 valence electrons Group 14 have 4 valence electrons Why? Problem Without looking at the periodic table, determine the group, period and block in which strontium is located. [Kr] 5s2 Group: superscript 2 = valence electrons Period: coefficient of 5, so 5th period Block: s-block Ion an atom or bonded group of atoms that has a positive or negative charge Ionization energy the energy required to remove an electron from a gaseous atom Octet Rule States that atoms tend to gain, lose or share electrons in order to acquire a full set of eight valence electrons Electronegativity Relative ability of atoms to attract electrons in a chemical bond Noble Gas An extremely unreactive group 18 element Valence Electron The electrons in an atom’s outermost orbitals Determine the chemical properties of an element Make squares Periodic Trend Atomic Radius Ionic Radius Ionization Energy Electronegativity Period Group Atomic Radius Atomic size is defined by how closely an atom lies to a neighboring atom. Decreases left to right across a period Atomic mass increases left to right Atomic mass increases as you go down Atomic mass increases as you go down Which has the largest atomic radius? Carbon, fluorine, beryllium, or lithium? All 4 elements are in period 2, so write in order across the period Li, Be, C, F Lithium is first, so it has the largest radius Ionic Radius Atom loses electron(s) becomes positive decreases in size Atom gains electron(s) becomes negative increases in size Why? Lose valence electrons gives empty outer shell Electrostatic repulsion among the remaining electrons decreases and they are pulled closer to the nucleus Add electrons, increases electrostatic repulsion, forcing electrons further apart Ionization Energy Trends Increases left to right across a period Decreases when you move down a group less energy to remove valence electrons bc they are farther from the nucleus Octet Rule Atoms want a full set of 8 valence electrons First period is the exception bc only have 1 or 2 electrons Predict What part of the periodic table has the greatest electronegativity. Upper right Squares Periodic Trend Period Group Atomic Radius Left to right down Ionic Radius Left to right down Ionization Left to right down Energy Electronegativity Left to right down Electron-dot Diagram Calcium Aluminum Arsenic Tellurium Xenon Resource http://www.docbrown.info/page03/3_34ptabl e.htm
