Periodic Properties of the Elements Chapter 8 Notes Periodic Properties of the Elements Sections 8.1 – 8.9

I. Nerve Signal Transmission Right now, tiny pumps in your cells are working hard to transport Na+ ions out of your cells and K+ ions into your cells. Your cells are able to differentiate between the ions due to their size: Na+ ions have a radius of 95 pm while K+ ions have a radius of 133 pm. The size of atoms and ions is a predictable property based on their location on the periodic table. a property that is predictable based on an element’s location on the periodic table Periodic Property:

II. The Development of the Periodic Table The modern periodic table is primarily credited to the Russian chemist Dmitri Mendeleev (1834-1907). What did Mendeleev arrange the elements on his periodic table according to? By increasing mass Mendeleev’s table did have predictive properties, but encountered problems as well. Henry Mosely (18887-1915) corrected these problems by organizing the periodic table according to this: By increasing atomic number

Electron Configurations: Valence Electrons and the Periodic Table We saw that Mendeleev arranged elements with similar periodic properties in the same column. Also, notice that as you move down a column, the number of electrons in the outermost principle energy level stays the same. The key connection between the macroscopic world (an element’s chemical properties) and the microscopic world (an atom’s electronic structure) lies in the outermost electrons.

For multielectron atoms, not all electrons experience the same attractive charge from the nucleus to the same degree. The force that each electron feels from the nucleus is called the effective nuclear charge (Zeff). The nucleus attracts electrons (because it’s positive) but other electrons repel one another (because they are negative). This negative effect is called shielding. The electrons furthest from the nucleus experience the weakest effective nuclear charge and are held least tightly within the atom; therefore, they are the easiest/ first electrons to be lost or shared

Valence electrons: Located in highest energy s & p orbitals The e− involved in bonding / ion formation Determine element’s chemical properties For elements in Groups 1 – 8: For transition metals: # valence e─ = group # count the highest energy s, p, and d e─ Core electrons: inner e─ ; exist in completely filled energy levels

Periodic Trends in the Size of Atoms and Effective Nuclear Charge Atomic radius: - used to represent the size of an atom, assuming it is roughly spherical - measured as half the distance between two nuclei of bonded atoms DOWN a column: radii INCREASE RIGHT across a row: radii DECREASE Trend:

Explaining the Trend: Down a column: e─ occupy larger orbitals further from nucleus so e─ are more spread out  radius increases Right across a row: e─ enter orbitals in the same energy level (equal distance from nucleus) ; nuclear charge also increases (an attractive force) so e─ are being pulled closer to the nucleus  radius decreases

VII. Ions: Electron Configurations, Magnetic Properties, Ionic Radii, and Ionization Energy Magnetic Properties Paramagnetic: an atom/ion that contains unpaired e─ and is attracted by a magnetic field Diamagnetic: an atom/ion that contains no unpaired e─ and is not attracted by a magnetic field Note that an element may be diamagnetic but an ion of that element may be paramagnetic. In order to determine if an atom/ion is paramagnetic or diamagnetic, we must look at its orbital diagram.

Ionic Radii Cations: positive ions are smaller than neutral atoms Ca2+ smaller than Ca WHY? Anions: negative ions are larger than neutral atoms F─ larger than F WHY?

Ionization Energy Ionization energy: energy required to remove an electron from an atom or ion in its gaseous state Ex. Na (g)  Na+ (g) + 1 e─ IE1 = 496 kJ/mol The e─ is a product (it was lost) DOWN a column: IE generally DECREASES RIGHT across a row: IE generally INCREASES Trend (1st Ionization Energy):

VIII. Ions: Electron Affinities and Metallic Character Electron Affinity: energy change associated with gaining an electron in the gaseous state Ex. Cl (g) + 1 e−  Cl − (g) EA = − 349 kJ/mol The e─ is a reactant (it was gained) EA’s are usually negative because energy is released when an atom or ion gains an electron * NO regular trend for columns / rows * In general, nonmetals tend to have larger negative EA’s (more readily accept e─) Trend:

Metallic Character: metals are good conductors of heat and electricity, are malleable (hammered into sheets) and ductile (drawn into wire), and readily LOSE e─. DOWN a column: M.C. INCREASES RIGHT across a row: M.C. DECREASES Trend: