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Periodic Trends. Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends.

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Presentation on theme: "Periodic Trends. Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends."— Presentation transcript:

1 Periodic Trends

2 Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends using above factors. Include: atomic / ionic radii, ionization energy, electronegativity.

3 Atomic properties are set by valence electrons. Valence electrons are affected by these 3 factors: 1.Nuclear charge - more protons, increased attractive force on valence electrons. 2.Distance – the further away from the nucleus, the less attractive force. This is based on Coulomb's Law 3. Shielding Effect - inner electrons shield and decrease the attractive force for outer electrons.

4 1.Atomic Radius Decrease Across same quantum (n) level (same distance) increase proton number (more charge) Increase Down new quantum level (more distance) more shielding (less force) Nuclear charge has the biggest impact moving across, but distance has the biggest impact moving down

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

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

7 Same basic trend as atomic radius: Decreases across…Increases down Gets larger at the jump to Anions….then decreases again

8 Cl Na +- Cations – smaller radii Anions – larger radii

9 Energy required to remove an electron from an atom forming an ion 3. Ionization Energy Subsequent electrons takes more ionization energy Atom + energy → Ion + + e 1 − Ion + + energy → Ion +2 + e 2 − The amount of energy required depends on the force on the electron – distance, shielding, nuclear charge

10 Increases Across increase proton number (more charge) same quantum (n) level (same distance) Decreases Down new quantum level (more distance) more shielding (less force) Ionization energy requirements are connected to atomic radius…

11 Cl Na + Chlorine: nuclear charge is great enough to attract valence electrons – higher IE

12 Na Cs Cesium: distance is too great for its nuclear charge to attract – lower IE

13 The largest jumps in IE requirements occur when valence electrons are exhausted and electrons are then removed from closer quantum levels. “Subsequent electrons takes more ionization energy” 1 valence e - 3 valence e - 6 valence e -

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

15 Cl: Na: Lower ionization energy Lower Electronegativity HIGHER ionization energy HIGHER Electronegativity WEAKER nuclear charge Large radius STRONGER nuclear charge Small radius

16 EN DifferenceBond TypePercent Ionic less than 0.4non-polar covalent0% − 5% 0.4 − 1.9polar covalent5% − 60% greater than 1.9ionic> 60% These numbers vary slightly depending on the source…

17 Large enough EN difference – create ionic bonds + - ClH polar covalent CH non-polar covalent 2.1 2.5 3.0 2.1 0.9 3.0 Greater EN differences create more polar the bonds

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

19 CAN YOU / HAVE YOU? Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends using above factors. Include: atomic / ionic radii, ionization energy, electronegativity.


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