1. Periodic Trends

3. Atomic Size Trends often determined by one half the distance between the nuclei of two atoms of the same element when joined Atomic radius (r)

4. often measured in picometers (10 -12 m) in general, atomic size: –increases from top to bottom within a group the atom has more levels –these additional levels shield the electrons(-) in outer levels from the protons’(+) attractive force –decreases from left to right across a period more positive charged protons pulls electrons in closer see Figure 6.14 in text

5. Atomic radii flash animation

7. Ionization Energy (IE) Trends the energy required to remove an electron –energy to remove the first electron is called the first ionization energy –energy to remove the second…. –energy to remove the third….

8. in general, ionization energy: –decreases from top to bottom within a group as the atom’s size increases (more levels and therefore shielding effect), it is harder for the nucleus to “hang on” to the electrons –increases from left to right across a period more positively charged protons holds the electrons tighter but no new levels to shield electrons

13. Electronegativity Trends ability of an element to attract more electrons based on a scale from 0.7 (Cesium) to 4.0 (Fluorine) in general: –decrease from top to bottom with a group the electrons are further away from the nucleus and better shielded from the nuclear charge and thus not as attracted to the nucleus –increase from left to right across a period as # protons increases, so will the attraction that the atom has for electrons in its outermost energy level

17. Practice Problems 1.Organize the following elements in decreasing atomic size: Fr…Na…Rb…K…H…Cs…Li Fr…Cs…Rb…K…Na…Li…H 2.Organize the following elements based on increasing first ionization energy: Li…O…F…Ne…N…C…Be…B Li…Be…B…C…N…O…F…Ne 3.Organize the following elements according to decreasing electronegativity: K…Br…Zn…Sc…Kr…Ca…As…Se Br…Se…As…Zn…Sc…Ca…K…Kr