Notes

Hi. Today we're gonna talk about trends in a periodic table. The periodic table is arranged by periods (which are the rows) and groups (which are the columns). All elements within a period have the same number of electron shells. As we move left to right, the number of protons, neutrons and electrons increases for each next element. Conversely, within a group, all elements have the same number of electrons on their outermost shells, but the number of shells increases as we go downward. Because of this arrangement, we can observe a number of trends. The first trend has to do with atomic radius. Simply put, this is the size of the atom from its nucleus to the outermost shell. As we move left to right within a period, the number of protons increases. The more positively charged protons in a nucleus, the harder they pull on the negatively charged electrons, so the atomic radius becomes smaller. Conversely, as we move downward within a group, each next element will have a greater number of shells, so the atomic radius will increase. Another trend in the periodic table has to do with the ionization energy. This is the energy that needs to be applied to an atom in the gaseous state to remove one of its electrons. When going left to right within a period, the increasing number of protons pulls stronger on the electrons, so it gets harder to remove an electron. Going downward within a group, the electrons' attraction to the nucleus decreases, so it becomes easier to pull one of them away. The next trend has to do with electron affinity. Electron affinity is the energy that is released when an isolated gaseous atom gains an electron. So it reflects an atom's ability to receive additional electrons. Electron affinity generally increases going left to right because the incoming electron experiences a greater pull of the nucleus. In every period, the element with the highest electron affinity will be the *idontunderstand*, since it is only one electron away from a complete outer shell. Going downward within a group, electron affinity tends to decrease since the incoming electron ends up farther away from the nucleus. One final trend in the periodic table has to do with electronegativity. This is an atom's ability to attract electrons when bonding with other atoms. It increases going left to right since the atoms with smaller atomic radii are able to observe(?) a stronger pull on the electrons. Going top to bottom, however, the nuclear pull on the electrons decreases, so electronegativity tends to decrease as well. Thank you for watching, and for more information, please visit about.com