![]() The lanthanide and actinide groups are actually a subset of the transition metals. The groups are the alkali metals, alkaline earth metals, transition metals, basic metals, metalloids, nonmetals, halogens, and noble gases. Probably the names arose because of the different numbering systems for the groups. While the periods of the periodic table just have numbers corresponding to their rows, the periodic table groups have both numbers and names. Forming chemical bonds gives the halogens this stability. This group is right next to the noble gases, so why is it so reactive? The reason is that they are only one electron away from having a stable configuration. The halogens (fluorine, chlorine, iodine, etc.) are as reactive as the noble gases are stable. In other words, the noble gas atoms become less stable if they lose or gain electrons. The reason is that atoms of elements of this group have stable valence electron shells. While the noble gases sometimes do participate in chemical reactions, they are mostly unreactive and are exceptions to periodic table trends. For the most part, using atomic weight instead of atomic number produces the same table. But, he made the table before protons were discovered. ![]() So, Mendeleev is considered the “ inventor of the periodic table.” His 1869 table differed from the modern table in that it ordered elements by increasing atomic weight instead of atomic number. While lots of scientists have made periodic tables over the years, the one that most closely resembles the table we use today was formulated by Dmitri Mendeleev. There are other also other trends, such as ionic radius, covalent radius, and metallicity. It increases moving across a period and decreases moving down a group. Ionization energy is the energy required to remove an electron from an atom.It increases moving across a period, but does not always decrease moving down a group. It is the energy change that occurs when a neutral atom accepts an electron. Electron affinity is related to electronegativity.It increases moving left to right (except for the noble gases) and mostly decreases moving down a group. Electronegativity is a measure of how easily an atom attracts electrons that can form a chemical bond. ![]() It decreases moving from left to right across a period (row) because adding protons (increasing atomic number) attracts and draws the electrons in more tightly. In increases moving down a group (column) because the atom gains a new electron shell.
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