The Properties of a Group: The Alkali Metals
Representative elements within the same group exhibit similar chemical properties that change in a regular pattern. This is explained by the fact that these elements have similar valence-shell electron configuration. It is the electron configuration of the valence shell that primarily determines the chemical properties of an atom.
The alkali metals (Group 1A: Li, Na, K, Rb, Cs, and Fr) represent the most reactive group of metals. As a group, they have the largest atomic sizes and lowest ionization energies. The large shielding effect by “core” (inner-shell) electrons results in weak effective nuclear charge experienced by the valence electrons. This results in their relatively low ionization energy and consequently, their high reactivity. The alkali metals have relatively low melting points and they are generally soft. This is because they have weak metallic bonds that result from the single valence electrons per atom. Their melting points decrease going down the group. The density of the alkali metals increases going down the group. This is because atomic masses increase more rapidly than atomic sizes.
As atomic size increases down the group, ionization energy decreases and reactivity increases – the lower the ionization energy, the more easily the atoms lose the single valence-shell electrons. Thus, francium would be the most reactive metal and lithium the least reactive in that group. Alkali metals are strong reducing agents. The expected reducing trend for these metals is Li < Na < K < Rb < Cs.
Alkali metals react with the halogens to form alkali halides with the general formula MX. Only lithium reacts with oxygen to form the expected simple oxide with a formula Li2O. Sodium and potassium react with oxygen to form sodium peroxide (Na2O2) and potassium superoxide (KO2), respectively. Their reactions with water is very vigorous and exothermic, producing hydrogen gas and hydroxide solutions: 2M(s) + 2H2O(l) à 2MOH(aq) + H2(g).
Periodic Trends – Notebook
Cut out and paste Model 1 on page 55 of notebook, title: Periodic Trends. Highlight Atomic radius, 1st ionization energy and electronegativity data each in a different color. Title page 56 Atomic Radius and cut and paste a blue periodic table below the title. Using your knowledge of the trend, add 3 arrows; vertical, horizontal and diagonal to show the progression of atom size smallest largest. Obtain blue atomic radius graph and paste. Explain why atoms get smaller as you move from left to right, bottom to top in the periodic table. Your explanation should include references to coulumbic attraction.
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Title page 57 Ionization Energy then cut and paste a blue periodic table below the title. Using your knowledge of the trend, add 3 arrows; vertical, horizontal and diagonal to show change in ionization energy from lowest highest. Obtain the yellow ionization energy graph and paste. Define ionization energy using the POGIL. Explain why ionization energy increases from left to right, bottom to top in the periodic table. Your explanation should include references to coulumbic attraction.
Title page 58 Electronegativity then cut and paste a blue periodic table below the title. Using your knowledge of the trend, add 3 arrows; vertical, horizontal and diagonal to show change in electronegativity from lowest highest. Obtain the green electronegativity graph and paste. Define electronegativity using the POGIL. Explain why electronegativity increases from left to right, bottom to top in the periodic table. Your explanation should include references to coulumbic attraction.
Title page 59 Electron Affinity then cut and paste a blue periodic table.
Due Wednesday January 6 by the start of class! Pg 55- 59 will be check for completion during warmup! Points will be added to notebook check grade!
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