Chem 1 Day 47
Chapter 5: Chart Trends
Periodic Law: Chemical and physical properties of the elements are periodic functions of their
increasing atomic number.
The original law used atomic mass(weight) as the arrangement factor. Moseley changed that term
to atomic number as the factor for position on the chart. A few atoms were out of place when
atomic mass was used so Moseley’s change placed the atoms in correct position.
Periodic functions or periodic properties are any properties of the elements that repeat themselves
at regular intervals-the interval varies.
Look at periodic trends. All relate to atom size.
The smaller the atom, the more attraction an atom has for the electrons.
Trend in atomic radius: atomic radius decreases across a series. Group 13 is a flaw to this orders2p1 configuration causes the atom to get slightly larger. Greater nuclear charge pulls electrons
closer to the nucleus.
Atomic radius increases down a group because an extra level of electrons makes the atom larger.
Discuss size of cations and anions as compared to atoms.
Cations are smaller than the atom because electron(s) have been lost
Anions are larger than the atom because electron(s) have been added
Discuss the ability of atoms to lose or gain more than one e
Ionization Potential or Ionization Energy: Energy added to an atom when removing an electron.
: increases across the chart (smaller atom), decreases down the chart ( larger atom)
GF: A + IE = A+ + eNa +
J = Na+ + eThe energy value comes from the text or periodic chart.
Electron Affinity: Energy released when an e is added to an atom, forms an anion
A + e- = A- + EA energy
EA: Increases across the chart (smaller atom) decreases down the chart ( larger atom)
Cl + e- = Cl- +
J
energy from table in text book.
Noble gases are assigned zero. Some other elements do not want to gain e so are also zero
EN: increases across the chart (smaller atom) decreases down the chart (larger atom)
Density, mp and bp also have trends but tend to vary in the pattern
Review in text the E needed to remove more than one electron and where it becomes a problem.
Ion formation
Some atoms can lose more than one electron but more energy is needed in the IP
Na—1st e = 496 kJ, 2nd electron = 4562kJ (why such an increase?)
Mg—1st e = 738 kJ, 2nd electron = 1451 kJ, 3rd e = 7733 kJ
Even F with its desire to added one e, can have an electron removed to become a + ion
F + 1681 kJ = F+ + e-