Trends on the Periodic Table

1. Trends on the Periodic Table • You will be responsible for five trends. • 1. Atomic radius • 2. Metal reactivity • 3. Non-metal reactivity • 4. Ionization Energy • 5. Electronegativity

2. Atomic Radius • All trends on the periodic table relate to atomic radius! They all have to do with how easy it is to lose or gain electrons. • Atomic radius measures size of atoms • Defined by how closely an atom lies to a neighboring atom. • Trend for within a period and within a group….graph to find out!!

3. Trends for Atomic Radius • Atomic Radius INCREASES as you go down the P.T. because there are increasing number of energy levels (think of it as layers of fat…getting bigger). • Atomic Radius DECREASES across the P.T. because there is more of a positive pull on the electrons. More of an attraction pulls the electrons a bit closer. (think about having four people pull on a rope versus five. Five people are able to pull harder and will therefore bring the rope closer)

4. Hands on a clock: • A way to remember the trends is to relate them to hands on a clock. • You point an arrow in the direction where the trend INCREASES. • For atomic Radius, you would have a hand pointing down and a hand pointing left. • This looks like 9:30 on a clock.

6. Practice Problems: Which atomic radius is bigger? (Hint, write the symbols how they appear on the periodic table…which ever one the arrow points to is bigger) • Na or S • Ba or Ca • K or Ra • Cl or Au • As or P • Fr or Cs • Na • Ba • Ra (period matters more than group) • Au • As • Fr

7. Ion Radius • Atoms that lose electrons to become cations, always become smaller. (when you lose weight, you become smaller!) Since there are less electrons that are repelling each other, they can settle in a little closer to each other. • Atoms that gain electrons to become anions, always become larger. (when you gain weight, you become bigger). More electrons mean more repulsion. They have to spread out even further!

8. Ca atom or Ca ion (hint…what oxidation number does Ca form?) F atom or F ion Fe+2 or Fe+3 Ca+2 ion is smaller because it loses 2 e- F atom is smaller because the ion gains 1e- Fe+3 is smaller because it loses 3 e- compared to Fe+2 that loses 2 e- Practice Problems: Which is SMALLER! (pay attention to the questions)

9. Metal Reactivity • When Metals react, they lose electrons due to the fact they have a low amount of valence electrons. • Would it be easier for an electron to be lost if it was close to the nucleus or far away? • Electrons are lost easier when they are farther away from the nucleus since there is less of a positive pull on them. • Therefore, the greater the Atomic Radius, the more reactive the metal is. (easier to lose = more reactive)

10. Metal Reactivity Trendhttp://video.google.com/videoplay?docid=-2134266654801392897&q=brainiac&hl=enBlocked by Cobb County but you can watch this at home! • INCREASES DOWN a Group due to the fact that the electrons are further from the positive pull of the nucleus and they are easier to remove. • DECREASES ACROSS a period due to the fact that there is more of a positive pull holding onto the electrons and they are harder to remove.

12. Na or Cs Ni or Fe Au or Cu Ag or K Cs Fe Au K (group always matters more…alkali metals are more reactive than transition metals! Good thing or we wouldn’t be able to wear jewelry!!) Which metal is more reactive?

13. Non Metal Reactivity • When Non-metals react, they gain electrons due to the fact that they have a high number of valence electrons. • Would it be easier to gain electrons if they were closer to the nucleus or farther away? • Electrons are gained easier if they are closer to the nucleus due to the positive attraction. • The trend is exactly opposite of Metal Reactivity and Atomic Radius. • Noble Gases are excluded…they hardly ever react!

14. Non-Metal Reactivity Trend • DECREASES DOWN a group due to the fact that the atomic radius is getting larger and it is harder for the positive nucleus to attract electrons. • INCREASES ACROSS a period due to the fact that there is more of a positive pull and is easier to attract the electrons. • What time would this be on a clock?

16. F or Br S or Cl N or He F Cl N (remember Noble gases don’t react!) Which non-metals is more reactive?

17. Ionization Energy • Energy required to remove an electron from an atom. • Energy is needed to overcome the attraction between the positive charge in the nucleus and the negative charge of the electron. • What type of atoms want to lose electrons? • Metals…therefore, they have lower I.E.

18. 1st I.E. = Energy to remove the 1st electron • 2nd I.E. = Energy to remove the 2nd electron • 3rd I.E. = etc.

19. Trends for I.E. • I.E. DECREASES down a group. It becomes easier to remove an electron because there are more energy levels blocking the positive pull. • I.E. INCREASES across a period. There is more of a positive pull holding on to the electrons, therefore, it is harder to remove them. You are also approaching the Non-metals, which gain electrons!

21. When will you see a drastic increase in I.E.??? • After the element has lost its valence electrons. • Example: Potassium’s 1st I.E. is low. Its 2nd is very high. • Calcium’s 1st and 2nd I.E. is low. Its 3rd is high.

22. Ca or Br Cl or I Au or Cu Ag or Rb Mg or I Ca I Au Rb Mg (metals always have a lower I.E. than nonmetals….metals want to lose, nonmetals want to gain) Practice problems: Which atom has a lower 1st I.E.?

23. Electronegativity • The relative ability of its atoms to attract electrons in a chemical bond. • What type of elements want to ATTRACT electrons?? • Nonmetals! Therefore, nonmetals have a high E.N. value. • Numerical value from 0.0 (least) to 4.0 (most) • Unit is a Pauling • Noble Gases are excluded!!

24. Trends for E.N. • Down a group, E.N. DECREASES. More energy levels makes it harder to attract electrons • Across a period, E.N. INCREASES. More and more valence electrons, and less for the atoms to have a full octet. More positive pull also. Also, pointing towards the non-metals.

26. F or Be S or Po Sr or Br Kr or As F (highest E.N. value on P.T.) S Br (Nonmetals always higher than metals) As (Noble gases are are excluded) Which element is more electronegative?

27. Using E.N. values to calculate bond types: • Ionic Bond – electrostatic force holds oppositely charged particles together in an ionic compound. Formed by losing or gaining electrons. • Polar Covalent – Bond formed when electrons are not shared equally. • Non-polar Covalent – bond formed from the equal sharing of valence electrons.

28. Like Dissolves Like • Water is a polar covalent solvent (meaning one end of the molecule has a slight charge). • Only Ionic compounds and Polar compounds will dissolve in water because they also have a charge. • Non-polar covalent compounds will not dissolve in water because it does not have a charge.

29. E.N. differences • Subtract the lowest E.N. element in a compound from the highest E.N. element (the subscripts do not matter) • Difference greater than 1.70 = IONIC • Difference 0.5 to 1.70 = Polar • Difference less than .5 =Non-polar

30. SO2 BaCl2 H2S Ca2N3 As2O3 .94 = polar covalent 2.27 = ionic 0.3 = non-polar 2.04 = ionic 1.26 = polar covalent Use your book pg. 403 to find the E.N. values of each element. What kind of bond will the compounds likely have?