Elemental Properties and Patterns Periodic Trends Elemental Properties and Patterns

The Periodic Law Dimitri Mendeleev (1869/1871) was the first scientist to publish an organized periodic table of the known elements. He was taking a chemistry course in Russia and tried to find a way to organize the periodic table.

The Periodic Law Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements. He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.

The Periodic Law Mendeleev understood the ‘Periodic Law’ which states: When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

Periodic Trends There are several important atomic characteristics that show predictable trends that you should know. Atomic properties— Deal with only single atoms

Atomic Radius Enables us to gain information on atom’s size Outer electrons hard to locate Radius is the distance from the center of the nucleus to the “edge” of the electron cloud. Measurement of distance between nuclei of 2 atoms Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.

1. Covalent Radius Half the distance between the nuclei of 2 bonded atoms. Radius of nonmetallic atoms Ex. Br 2.86 Å 1.43 Å

2. Metallic Radius Half the distance between nuclei of adjacent atoms in a metal Radius of metallic atoms

Atomic Radius Trend Decreases Increases

Atomic Radius The effect is that the more positive nucleus has a greater pull on the electron cloud. The nucleus is more positive and the electron cloud is more negative. The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

Identify the atom with the largest radii 1) Ca, F 2) Cl, O 3) N, P

Ionization Energy If an electron is given enough energy (in the form of a photon) to overcome the electrical forces holding it, the electron can be removed from the atom completely. Amount of energy needed to remove ONE electron from a neutral atom Removal from ground state in neutral atom of gaseous state to form positive ion

Ionization Energy (cont.) The energy required to remove an electron from an atom is ionization energy. The larger the atom is, the easier its electrons are to remove. Ionization energy and atomic radius are inversely proportional.

Ionization Energy (cont.) 1st ionization energy Energy required to remove 1st electron from atom Taken from highest energy level Easiest to remove Energy increases as more electrons are removed

Ionization Energy Trend Increases Decreases

Ionization Energy

Identify the highest ionization energy F, Mg Na, Rb P, O

Classwork: Ionization Energy Circle the atom with the highest first ionization energy. Al, B 5) Fr, Li 9) Se, Cl Mg, Na 6) Mg, Al 10) Rb, Mg P, As 7) C, F I, At 8) K, Sc

Homework Read pp. 150-156 p. 152 #1-3 atomic radii problems Ionization Energy problems Study for Nuclear Chemistry Quiz Start Periodic Trends Chart

What does affinity mean?

Electron Affinity energy change that occurs when electrons are added to a neutral atom Some atoms will release energy, others will absorb energy to “force” electron into atom Ex. Hot Potato Greater value with smaller atoms Energy released when electron added Exothermic, negative value An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! ! Metals—decrease electron affinity. Nonmetals—increase electron affinity, more reactive Stable atoms—full octet

Electron Affinity Trend Increases Decreases

Electron Shielding Repulsive forces exist between electrons. Electrons are found at various distances from the nucleus Electrons closer to the nucleus (at lower energy levels) can “screen/shield” outer electrons Outer electrons do not feel the attractive force from the nucleus as a result Affects periodic trends such as ionization energy Explains why ionization decreases down a column

Electronegativity increases decreases trait or characteristic of an atom Ability of an atom to pull electrons toward it, how tightly an atom wants to hold onto its electrons Atom’s ability to attract electrons from another atom Periodic Trend: increases decreases

Practice: Which atom is more electronegative? Lithium or fluorine Chlorine or iodine Magnesium or oxygen Calcium or barium Rubidium or Strontium F Cl O Ca Sr

Metallic Character This is simply a relative measure of how easily atoms lose or give up electrons. Tendency to LOSE electrons Related to atomic radius/ionization energy, how easy to remove electrons

Metallic Character Atoms with a tendency to LOSE electrons Decreases Increases

Nonmetallic Character Atoms with a tendency to GAIN electrons Increases Decreases

October 9th Homework Finish Periodic Trends Chart Finish Periodic Trends Worksheet