- the trend to smaller atoms across a period is caused by the increasingly positive charge of the nucleus
- as electrons add to the s and p sublevels in the same energy levels, they get pulled closer the nucleus, thus making the atomic radii shorter
- the atomic radii of the main group elements increase down a group
Ion- is an atom or group of bonded atoms that has a positive or negative charge
Ionization- any process that results in the formation of an atom
Ionization Enegry (IE)- the energy required to move one electron from a neutral atom of an element
- ionization energy is expressed in kilojules per moles
- Ionization energies if the main group elements increase across each period
- this is caused by increasing nuclear charge
- higher charges strongly attract electrons in the same energy level
- higher nuclear charges are responsible for increasing ionization energy and decreasing radii across the periods
- Ionization energy decreases down the groups
- electrons removed from atoms of each succeeding element in a group are in higher energy levels, farther from the nucleus
- this means they can move easier
- as atomic number increases going down a group, more electrons lie between the nucleus and the electrons in the highest occupied energy levels
Removing Electrons from Positive Ions
- energies for removal of additional electrons from an atom are second ionization energy, third ionization energy and so on
- each successive electron removed from an ion feels an increasingly stronger effective nuclear charge
Electron Affinity- energy that occurs when an electron is acquired by a neutral atom
- electrons add to the same p sublevel of atoms with increasing nuclear charge, electron affinities become more negative across the p block
- electrons add with greater difficulty down a group
- this pattern is a result of a slight increase in effective nuclear charge down a group, which increases electron affinities and in increase in atomic radius down a group, which decreases electron affinities
Cation- positive ion
Anion- negative ion
- the metals at the left tend to form cations and the nonmetals at the upper right tend to form annions
- outer electrons in both cations and anions are in higher energy levels as one reads down a group
- this means there is a gradual increase of atomic radii down a group, there is also a gradual increase of ionic radii
Valence Electrons- electrons available to be lost, gained, or shared in the formation of chemical compounds.
- Valence Electrons hold atoms together in chemical compounds. In most compounds the negative charge of the valence electrons is concentrated closer to one atom than to another.
- Linus Pauling, a famous American chemist, created a scale of numerical values reflecting the tendency of an atom to attract electrons.
Electronegativity- measure of the ability of an atom in chemical compound to attract electrons from another atom in the compound.
- The most electronegative element is fluorine.
-the alkali and alkaline-earth metals are the least electronegative elements. Their atoms have low attraction for electrons. Nitrogen, oxygen, and the halogens are the most electronegative elements, and their atoms attract electrons strongly in compounds.
-Electronegativities tend to either decrease down a group or remain about the same size.
-Some of the noble gases do not form compounds and then cannot be assigned electronegativities. But when a noble gas forms a compound its electronegativity is high, similar to the halogens.
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch7/graphics/ch7_15.gif - electron affinity picture
Davis, R., Frey, R., Sarquis, M., & Sarquis, J. (2009). Modern chemistry. Orlando, FL: Holt, Rinehart, and Winsten. - book