7.1: Development of the Periodic Table

Mendeleev and Meyer recognized predictable patterns in elements as atomic weight increased

Moseley developed atomic numbers

7.2: Effective Nuclear Charge

Properties of the atom depend on electron configuration and how the attraction between electrons and the nucleus

Electron- electron repulsion-- same charge

• Cancel some of the electron nucleus attraction

• More electrons= more repulsion= less attraction between nucleus and electron

• Effective nuclear charge- net attraction

  • Less than the actual nuclear charge

  • increases right to left across a periodic table

    • Number of core electrons stays the same; the number of protons increases

  • increases slightly as we go down a column

7.3: Sizes of Atoms and Ions

bonding atomic radius: shortest distance between the two nuclei during an atomic collision divided by 2

bonding radius< non bonding radius

Atomic radius increases as you go down a column

• Increasing n (energy levels) therefore greater probability of electrons being farther from the nucleus

Atomic radius decreases left to right

• Effective nuclear charge decreases (less shielding ) and therefore increasing atomic radius

Cations are smaller than parent atoms

• electron - electron repulsion is reduced

Anions are greater than parent atoms

• electrons are added therefore electron- electron repulsion is increased, increasing radius

Isoelectronic series have the same number of electrons

• When listed in increasing atomic number, nuclear charge increases ; electron number stays the same, but protons increase; stronger attraction of electrons to the nucleus; ionic radius decreases.

7.4: Ionization Energy

Ionization energy is the minimum energy needed to remove an electron from the ground state of an atom

• Greater ionization energy = more difficulty removing electrons

• first ionization energy is the smallest and increases with each successive ionization

• Sharp increase in the ionization energy occurs when inner shell is removed

• Always positive- energy must be absorbed to remove electrons

Ionization energy increases as we move across a period

• Increase in effective nuclear charge and decrease in atomic radius

Ionization energy decreases are we move down a period

• atomic radius increases

7.5: Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a gaseous atom

• Energy is released--- answer is in negatives

  • Greater attraction between atom and added electron the more negative the answer

• Energy change when atom gains and electron

7.6: Metals, Non-metals and Metalloids

Metals:

• Low ionization energy

• Loose electrons

Non Metals:

• Gain electrons

Metalloids: in between the two

7.7: Trends for Group 1A and Group 2A Metal

Group 1A-- alkali metals

• Low densities and melting points

• Increasing atomic radius, decreasing ionization energy

• Very reactive

Group 2A -- alkaline earth metals

• Denser, higher melting points

• Less reactive

7.8: Trends for Selected Nonmetals

Hydrogen is the most reactive

Oxygen is polar

7A is halogens

8A is noble gases-- not reactive

• High first ioniization energy