Unit 4 Chapter 6.3 Chemical PeriodicityPrt 2

6.1 – Classification of the Elements History of the Periodic Table (A Review) Mendeleev- arranged elements in order of increasing atomic mass Moseley- arranged elements in order of increasing atomic number Periodic Law- When the elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Periodic Trends The arrangement of the Periodic Table also provides scientists with a general idea of periodic trends. We will now examine those trends.

Effective Nuclear Charge (Zeff) The pull the nucleus exerts on the electrons. The larger the Zeff, the tighter the electrons are pulled and the smaller the atom. Trend: Zeff is highest near the top right of the periodic table

Which elements in the following pairs would have the highest Zeff? Question Which elements in the following pairs would have the highest Zeff? Mg or Cl Rb or Sr Al or At

14.2 – Periodic Trends Atomic radius – one-half the distance between the nuclei of two like atoms in a diatomic molecule (ex: Cl2) The more energy levels present, the larger the atom. When comparing atoms that all have similar energy levels, the atoms with the largest nuclei (and thus greatest number of protons) will have the smallest radii. Trend: atomic radius increases from right to left and from top to bottom.

Atomic Radius Increasing Atomic Radius Increasing Atomic Radius SMALLEST Increasing Atomic Radius BIGGEST Increasing Atomic Radius

Question Place the following elements in order of increasing atomic radius. Ca, C, Ra, Br

Periodic Trends: Ionization Energy Ionization energy - energy required to overcome the attraction of the nuclear charge and remove one electron from a gaseous atom to form an ion. 1st ionization energy: the energy required to remove the first electron 2nd ionization energy: the energy required to remove the second electron 3rd ionization energy: the energy required removing the second electron Trend: ionization energy increases from left to right and bottom to top.

Ionization Energy Increasing Ionization Energy

Question What electron do you think would be easiest to remove, the first, second, or third? Why?

Periodic Trends: Ion Size Anions, or atoms that have gained electrons, are larger than the atoms from which they were formed. The negative charge means more electrons are present causing the size of the ion to be larger. Cations, which are atoms that have lost electrons, are smaller than the atoms from which they were formed. The positive charge means fewer electrons are surrounding the nucleus, thus pulling the existing electrons closer and causing the ion to be smaller. Trend: ionic radius increases from right to left and from top to bottom. Please add this trend to your flipbook.

Ionic Radius Increasing Ionic Radius Increasing Ionic Radius

Question What is larger; an atom of nitrogen or its anion? Why?

Periodic Trends: Electronegativity Electronegativity – the tendency for the atoms of the element to attract electrons when they are chemically combined with atoms of another element Note: Nobel gases don’t have any electronegativity because their orbitals are filled so they don‘t bond with other elements. Trend: electronegativity increases from left to right and bottom to top.

Electronegativity Increasing Electronegativity HIGHEST Increasing Electronegativity Electronegativity

Question If hydrogen and fluorine made a bond, which atom would have more bonded electrons near its nucleus?