Chapters 6 & 7 Chemistry 1L Cypress Creek High School Unit 7: Periodic Table Chapters 6 & 7 Chemistry 1L Cypress Creek High School 1

Part 4: Periodic Trends 2

Periodic Table Trends Patterns on the periodic table Atomic Radius Ionic Radius Electronegativity Ionization Energy

Periodic Trends Depend upon 4 important factors… Energy levels – the horizontal rows; ranked from 1-7 based on energy and distance from the nucleus Valence electrons – number of electrons in outermost energy level Shielding effect – the decrease in the attraction between the outer electrons and the nucleus due to the presence of other electrons between them Nuclear charge – depends on the number of protons – the more protons in the nucleus, the greater pull they have on their surrounding electrons

Atomic Radius Atomic radius is half the distance between the centers of two atoms that are just touching each other Influenced by 2 factors The number of energy levels The nuclear charge (pull of the positively charged nucleus on its electrons) The more energy levels, the ________ the atomic radius. (larger/smaller) The more protons in the nucleus, the ________ the atomic radius. larger smaller

Atomic Radius Trend Atomic radius increases as you move down a group Atomic radius decreases as you move from left to right in a period

Ionic Radius Metals lose electrons to form cations Li Li+ Atomic radius decreases - energy level is lost or “shed” (think of peeling an onion) Nonmetals gain electrons to form anions Make ions visibly smaller F F- Atomic radius increases - energy level expands because it is more “crowded” and electrons exert greater repulsive forces on each other (think of 7 people vs. 8 people holding hands in a circle)

Ionic Radius Trend Ionic radius increases as you move down a group Ionic radius decreases as you from left to right in a period BUT… Energy levels change between cations and anions Note: metals make smaller ions, nonmetals make larger ions decreasing ionic radius

Atomic & Ionic Radius Trends 9

Electronegativity Electronegativity is a measure of how easily an atom attracts the valence electrons of another atom Numbers are assigned to each element to rate the electronegativity (from 0.7 to 4.0) Low electronegativity = does not want to attract valence electrons (metals) High electronegativity = really wants to attract valence electrons (nonmetals) Influenced by 2 factors: Valence electrons Shielding 10

Electronegativity Trend Electronegativity decreases as you move down a group Electronegativity increases as you from left to right in a period 11

Ionization Energy Ionization Energy – the energy needed to remove the outermost electron in an atom Influenced by 2 factors: Nuclear charge – more protons pulling on the electrons, making it harder to remove them Shielding – Radius is larger; outer electrons are farther from the nucleus; more difficult to gain electrons

Ionization Energy First ionization energy is that energy required to remove the first electron Ex: Easiest to remove Na’s first electron, hardest to remove Ar’s first electron Second ionization energy is that energy required to remove the second electron Ex: Easiest to remove Mg’s second electron, hardest to remove Na’s second electron Third ionization energy is that energy required to remove the third electron Ex: Easiest to remove Al’s third electron, hardest to remove Mg’s third electron Fourth, fifth, sixth etc… the ionization energy patterns continues This graph shows first ionization energy only!

Ionization Energy Trends Ionization energy decreases as you move down a group Ionization energy increases as you from left to right in a period Increasing ionization energy Decreasing ionization energy

Summary of Periodic Trends