Periodic Trends

OUTCOME QUESTION(S): C12-2-07 PERIODIC TRENDS Vocabulary & Concepts Identify factors and account for periodic trends among the properties of elements, and relate to electron configurations. Include: atomic / ionic radii, ionization energy, and electronegativity. Construct Lewis dot diagrams for various compounds and use VSEPR to predict bond shape from the electron arrangement. Vocabulary & Concepts  Pauli Exclusion Principle Hund Rule Aufbau Principle

Valence electrons are affected by these 3 factors: *Atomic properties are controlled by valence electrons * Valence electrons are affected by these 3 factors: Nuclear charge - more protons, increased attractive force on valence electrons. Distance – the further away from the nucleus, the less attractive force. This is based on Coulomb's Law Notice less force on the outer electron 3. Shielding Effect - inner electrons shield and decrease the attractive force for outer electrons.

Atomic Radius Decreases Across same quantum (n) level (same distance) increase proton number (more attraction) Increases Down new quantum level (more distance) more shielding (less attraction) FACT: Nuclear charge has the biggest impact moving across, but distance has the biggest impact moving down

Na: 11 p+ 11 e- Cl: 17 e- 17 p+ The increased nuclear charge attracting the same quantum level (n=3) pulls valence electrons inward

Note: cations and anions have different factors 2. Ionic Radius Ion size differs from atom size Note: cations and anions have different factors Cations (lost electrons) – smaller radii increased nuclear attraction (same protons, less electrons) possible lost quantum (n) level (less distance) Anions (gained electrons) – larger radii decreased attraction (same protons, more electrons) repulsion of extra electrons causes expansion

+ - Na Cl Cations – smaller radii Anions – larger radii - increased nuclear attraction - decreased nuclear attraction - possible lost quantum (n) level - repulsion of extra electrons causes expansion

Gets larger at the jump to Anions….then decreases again Notice: it is the same basic trend as atomic radius: Size decreases across…size increases down Gets larger at the jump to Anions….then decreases again

3. Ionization Energy Energy required to remove an electron from an atom forming an ion Removing next electron takes more energy (IE2) Atom + energy1 → Ion+ + e1− Ion+ + energy2 → Ion+2 + e2− The amount of energy required depends on the force on the electron – distance, shielding, nuclear charge

increase proton number (more attraction) Increases Across increase proton number (more attraction) same quantum (n) level (same distance) Decreases Down new quantum level (more distance) more shielding (less attraction) Think about how/why charge, distance and shielding would affect energy needed to remove an electron

Na: nuclear charge is too weak to hold its valence electron – lower IE + Na Cl Comparing in a Period: Na: nuclear charge is too weak to hold its valence electron – lower IE Cl: nuclear charge is great enough to hold its valence electrons – higher IE

Na: distance is small enough to hold its valence electron – higher IE Comparing in a Column: Na: distance is small enough to hold its valence electron – higher IE Cs: distance is too great to hold tight to its valence electrons – lower IE Na Cs

1 valence e- 3 valence e- 6 valence e- Notice: significantly larger energy needed after the valence shell is emptied “Subsequent electrons takes more ionization energy” The largest jumps in IE requirements occur when valence electrons are exhausted and electrons are then removed from closer quantum levels.

4. Electronegativity Value (from 0 – 4.0) representing attraction an atom has for bonding electrons bigger the number, “greedier” they are for electrons Increases Across increase charge Increases attractive force Decreases Down increase distance Decreases attractive force

Stronger: able to attract your own…and grab after others WEAKER nuclear charge STRONGER nuclear charge Na: Cl: Lower ionization energy Lower Electronegativity HIGHER ionization energy (yours) HIGHER Electronegativity (others) Stronger: able to attract your own…and grab after others

These numbers vary slightly depending on the source… Bond type is less concrete than just ionic, polar and non-polar. It is a spectrum… These numbers vary slightly depending on the source… EN Difference Bond Type Percent Ionic less than 0.4 non-polar covalent 0% − 5% 0.4 − 1.9 polar covalent 5% − 60% greater than 1.9 ionic > 60%

- + Large enough EN difference – create ionic bonds polar covalent 2.1 2.5 H C Cl H 2.1 polar covalent non-polar covalent 3.0 Greater the EN difference - more polar the bonds Large enough EN difference – create ionic bonds - + 0.9 3.0

Instead of trying to memorize this, understand how the 3 factors relate so you can figure all of this out

CAN YOU / HAVE YOU? C12-2-07 PERIODIC TRENDS Vocabulary & Concepts Identify factors and account for periodic trends among the properties of elements, and relate to electron configurations. Include: atomic / ionic radii, ionization energy, and electronegativity. Construct Lewis dot diagrams for various compounds and use VSEPR to predict bond shape from the electron arrangement. Vocabulary & Concepts  Pauli Exclusion Principle Hund Rule Aufbau Principle