Trends of the Periodic Table

Atomic radius - one half the distance between the nuclei of identical atoms that are bonded together

Atomic Radius Trend: 1. Down a group – atomic radii increases This happens because of the increased number of energy levels The energy levels shield the electrons from the attraction of protons in the nucleus 2. Across a period – atomic radii decreases This happens because as more electrons are added to the same energy level Those electrons are pulled closer due to the increased number of protons in the nucleus

Largest atomic radii – 87 francium Smallest atomic radii – 9 fluorine

Valence electrons - the electrons found in the outermost energy level These are the electrons available to be gained, lost, or shared All atoms want 8 valence electrons or a full outer energy level Valence electrons determine the chemical properties of the atom The group number is the number of valence electrons

Atoms are neutral because there are equal numbers of both protons and electrons Sometimes atoms can gain or lose electrons to form ions An ion is an atom or group of atoms that has a positive or negative charge Losing electrons results in a positive ion called a cation Gaining electrons results in a negative ion called an anion

Cations Metals (left side of the table) form cations Cations are smaller than their atom counterparts because they are losing an electron (and sometimes an energy level) More positive charges have a greater pull on less negative charges

Cation formation

Anions Nonmetals (right side of the table) form anions Anions are larger than their atom counterparts because they are gaining an electron Less positive charges cannot pull in the greater number of negative charges

Anion formation

Ionization Energy Ionization energy is the energy required to remove an electron from an atom a low IE means it is easier to remove the electron Atoms can lose an electron, to form an ion They do this to achieve noble gas electron configuration (or 8 valence electrons) When an atom easily loses electrons, it is said to be active Metals tend to lose electrons

Ionization Energy Trend: 1. Down a group – ionization energy decreases As the valence electrons are farther from the nucleus, the atom gives them up with less energy 2. Across a period – ionization energy increase As the number of valence electrons increases in the same energy level, the atom is more resistant to giving up an electron (more energy) Greatest IE – fluorine Least IE - francium

Electron affinity Electron affinity is the energy change required to gain an electron (released energy is a negative value) When an atom releases a lot of energy it is said to be active Nonmetals tend to gain electrons (large energy change)

Electron Affinity Trend 1. Down a group – electron affinity decreases (slightly) Distance from the positive nucleus decreases the pull on the electrons 2. Across a period – electron affinity increases As the number of valence electrons added to the same energy level increases, the atom easily accepts another electron (to reach 8) Greatest EA – fluorine Least EA – francium

Electronegativity Electronegativity is the measure of the ability of an atom in a chemical compound to attract electrons All values are based on fluorine Fluorine is most electronegative atom The trend decreases in either direction from fluorine