Trends of the Periodic Table

1. Trends of the Periodic Table Know group trends & period trends. Know why the trends exist.

2. The Periodic Table of Elements devised by Dmitri Mendeleev, “adjusted” by Glenn Seaborg has 18 groups going up and down, and 7 periods going left to right. All atoms are metals or non-metals. Most are metals, some have a sort of transitional set of properties, they’re the seven metalloids.

3. The metal groups have names, group 1 are the ALKALI METALS. Group 2 are the ALAKALINE EARTH METALS. These yellow groups at left are the TRANSITIONAL METALS, with the “INNER” TRANSITIONAL METALS in the bottom two rows (Alaska & Hawaii) Some group 13—16 metals are also transitional as well.

4. Two more groups with names are these, group 17 + group 18: Halogens & Noble Gases.

5. The Trends to think about: • Atomic Size, measured in picometers. Your reference table shows a column in Table S for atomic radius. An atom’s size is twice its radius. • Atomic Mass, measured in amu. Each atom’s mass is the nearest whole number of the average atomic mass (the total of neutrons plus protons). • Net Nuclear Charge, is always a positive number. Atoms are all neutral since proton number equals electron number. But the electrons are NOT in the nucleus. • Neutrons are neutral so they have no effect on this either. The Net Nuclear Charge is the total of positive charges (total of protons) in a nucleus, with a + sign. 4. 1st Ionization Energy is the amount of energy it takes to change one mole of atoms into one mole of +1 cations and one mole of electrons. It’s unit is kJ/mole. It’s on Table S. • 5. Electronegativity Values are the only column on Table S without a unit. This scale measures the relative tendency to gain an electron in a bonding situation. Fluorine has the highest EN value, the strongest attraction to gain an electron in a bond. Since all other elements are measured relative to fluorine, this is a relative scale. Since Linus Pauling said that value is 4.0, and not say, 10.0 or 100 or anything else, this scale is also “arbitrary” in that the numbers themselves do not have any real value outside of a ranking of the atoms. He could have picked any numbering scale.

6. Cation Size is measured only relative to each other cation, not in picometers. There probably is a picometer measurement of each cation, but we do not have access to it. Since we do have atom sizes, and we know that cations lose electrons AND whole orbitals when they form, we can compare the numbers of orbitals to rank their sizes. Cations are always much smaller than their atoms since they lose a whole orbital when they form from the atoms. • Anion Size is also measured only relative to each other. We do not have access to anion sizes in picometers. We can compare them relative to their atom sizes. When anions form, they gain 1, 2, or 3 electrons into the existing orbitals they have. Therefore, anions are all slightly larger than their atoms, as these extra electrons, all of negative charge, all push a little harder against each other, stretching out the valence orbital. • Atomic Number is the whole plan to the table. Atomic number means how many protons, which is equal to the number of electrons. The whole table follows in numeric order for atomic number. • Metallic Properties is just an understanding of the metallic properties, if ranked, would show us that francium is the element with the most metallic nature, and that when compared, metals closer to francium are more metallic than those further away (on the table). • Non-metallic Properties work the same way as above, but proximity to Helium, the most non-metallic of the non-metals on the table is the standard element.

7. Group trends mean the pattern you find among the elements going from the top to the bottom of a group. Period trends mean the pattern you find among the elements going from the left to the right side of the periodic table.

8. The 10 Group Trends first… • Atomic Size • Atomic Mass • Net Nuclear Charge • 1st Ionization Energy • Electronegativity Values • Cation Size • Anion Size • Atomic Number • Metallic Properties • Non-metallic Properties

9. The group trend for atomic size is increasing because each time you go down a box on the periodic table, you have atoms with more and more orbitals. Atom sizes is based upon the number of orbitals they have. The group trend for atomic mass is increasing too. Each time you go down a box on this table you find much bigger atoms, containing many more protons and neutrons. You get more electrons too, but in our class their mass is insignificant. The atomic masses get bigger too: look how the average atomic masses change on the periodic tables on your reference tables.

10. The group trend for NET NUCLEAR CHARGE is increasing. This is true in every group. At left is magnesium in diagram form. Note it has 12 protons and 12 neutrons (mass = 24 amu). It has 2 electrons in its first orbital, eight in the second orbital (purple), and then two more electrons in the blue valence orbital. That means that Mg has 12 protons and has a+12 net nuclear charge. At right is carbon in diagram form. Note it has 6 protons and 6 neutrons (mass = 12 amu). It has 2 electrons in its first orbital, four in the second valence orbital. That means that Mg has 6 protons and has a+6 net nuclear charge.

11. The group trend for 1st ionization energy is decreasing*. This is true in every group. This table at right uses old fashioned group numbering rather than the current 1-18, but is clearly shows the trend for first ionization energy. The amount of energy to change one mole of atoms into one mole of +1 cations plus one mole of electrons is called first ionization energy. It’s measured in kilojoules/mole, or kJ/mole. *It’s easier to snatch away that last electron when it’s further from the positive nucleus

12. Electronegativity The tendency to gain an electron in a bonding situation is measured relative to fluorine, which has the highest electronegativity value which is 4.0 Linus Pauling created this ranking system, he made the “RULES” about it too, his scale is relative (to F), and it’s arbitrary (4.0 could just as well have been 100 or 10 or any other number he might have liked better.) 2 Nobel Prizes on the left. No Nobel prizes onthe right. The other Linus.

13. Group Trend for Electronegativity… The general trend is closer to fluorine the higher the electronegativity. Going down any group shows that the group trend for electronegativity is decreasing. The number of protons “attracting” electrons increases, but the distance from the nucleus to the valence orbital is much further, hence a lessening of the overall attraction for these electrons. Metals do not have much tendency to gain electrons, they tend to make cations by losing electrons. It’s the nonmetals that tend to gain electrons when bonding ionically with metals. When two or more nonmetals form a molecular compound, electronegativity shows the sharing of electrons as balanced (non-polar bond), or unbalanced (a polar bond). The greater the difference in electronegativity values, the more polar the bond. Bonds can be ranked in polarity when comparing their electronegativity differences.

14. Group Trend for Cation Size Cations lose electrons, and their valence orbitals. Cations are smaller than their atoms, but the group trend for cations is they increase in size going down any group.

15. Group Trend for Anion Size Nitrogen has the least number of protons pulling the orbital in, so it’s the biggest. Fluorine has the most protons, so it’s the smallest. The group trend for anion size is decreasing. All atoms in a period have the same number of orbitals, but they also have an increasing number of protons.

16. Group Trends for Atomic Number, Metallic Properties, & Non-Metallic Properties The whole periodic table is arranged by the Atomic Numbers, so the group trend for atomic numbers in (of course) increasing. Atomic number is the number of protons in an atom (and electrons), so since every atom has different numbers of protons, and they are arranged in increasing number of protons, this trend should be obvious. Metallic properties are governed by our “rule of thumb”, that when all metals are ranked compared to each other, for all the possible properties of metals, that the most metallic of all is FRANCIUM. Therefore, going down any group would put you in a box of an atom which is closer to Francium, so by definition, it would be more metallic. The group trend for metallic properties is increasing. Non-Metallic properties are governed by our other “rule of thumb”, that when all non-metals are ranked compared to each other, for all the possible properties of non-metals, that the most non-metallic of all is HELIUM. Therefore, going down any group would put you in a box of an atom which is further from Helium, so by definition, it would be less non-metallic. The group trend for non-metallic properties is decreasing.

17. If you ever forget a trend, what do you do? Write down 4 atoms in a group, or a period, and then write down the measure of the quality you’re looking at. Make a decisionare the numbers are increasing or decreasing? Don’t use just 2 or even 3 atoms, as you might be in the middle of an exception on the table, and you’ll be fooled by the “trend” you have located rather than the true, overall trend.

18. Period Trendsgoing across - left to right The easier period trends, quick and out. The period trend for… 1. Atomic Size is decreasing, because in any period with the SAME number of orbitals, there are always an increasing number of protons, and a tighter attraction by the electrons towards the nucleus. Noble Gases are the smallest atoms in any period. Group 1 atoms are the largest. Size of atoms in measured in atomic radius, in picometers, on the reference table. 2. Atomic mass is increasing as well. Atoms in every period gain one proton box to box, and one or more neutrons as well. Mass increases, but there are some exceptions (Ni to Co). It’s a trend, not a rule or law on the table. 3. Net Nuclear Charge, is the charge of the nucleus. It’s always positive because there are only protons (+ charge) and neutrons (no charge) in the nucleus. So, the more protons, the more positive charge. The atomic number is the number of protons, the period trend for net nuclear charge is obviously increasing. 4. Atomic Number, clearly is nearly the same thing as net nuclear charge (same numbers but without the charges). The period trend for atomic number is increasing as well.

19. Period Trends continued… The Period Trend for… Electronegativity is increasing (just check your table S). Nonmetals tend to gain electrons when bonding with metals in an ionic bond. When 2 nonmetals bond in a covalent bond (sharing electrons), they don’t always share the electrons evenly. This scale allows us to rank how well two atoms share electrons or not. The greater the difference in electronegativity values, the more unfairly shared the electrons are. That makes a POLAR bond. Zero difference in electronegativity means a NON-POLAR bond. In this model of hydrogen (H2), the atoms each desire to fill the orbital with another electron. But since they both have the same electronegativity value (2.1), neither will have an advantage over the other and “gain” the electron more than the partner atom. This bond has no difference in electronegativity, hence it’s NON-POLAR.

20. A hydrogen atom and a chlorine atom find each other and decide to bond (written like a poet!) When they bond, they will share electrons. Hydrogen needs to fill its orbital so it wants to gain this electron from chlorine. Chlorine also needs to fill it’s outer orbital, borrowing the electron from hydrogen. This sharing is not going to be fair, since the electronegativity values are different. Hydrogen’s demand for this electron is a 2.1 on the scale, while chlorine wants this electron at a 3.2 level. Chlorine will win this tug of war (most of the time they are bonded together), making the bond uneven, or this is a POLAR BOND, chlorine becomes negatively charged most of the time by the gain of the electron most of the time. A little polar bear represents a mildly polar bond.

21. Same situation here, but with hydrogen and fluorine bonded together. Both atoms want to fill their outer orbitals in this bond, so they “share” the valence electrons. Hydrogen “wants” that electron at a 2.1 level on the electronegativity scale. Fluorine wants it at a 4.0 level! This has a very large difference in electronegativity, so the bond is very polar. Fluorine “gets” the electron most of the time, so the F side of this bond is more negative most of the time, hydrogen is more positive, most of the time. This big jumping polar bear symbolizes a greater difference in electronegativity, and a MORE POLAR BOND than with H and Cl from the slide previous.

22. PERIOD trend for cation size The period trend for cation size is decreasing size, since the cations get smaller going across the period.

23. PERIOD trend for Anion size The period trend for anion size is decreasing size, since the anions get smaller going across the period.

24. Period Trends for atomic number, metallic properties, & non-metallic properties Three quick and easy to see trends. The period trend for atomic number is clearly increasing. The whole table is arranged by increasing atomic number. The period trend for metallic properties is decreasing. Since we accept Fr as the most metallic element, moving away from francium means moving away from metallic properties. The period trend for non-metallic properties is increasing. Since we accept He as the most non-metallic element, when going left to right on the table, in any period, you are clearly moving towards He, moving towards the most non-metallic properties. You can be like Sam and learn this, or you can be like Dixie and skip this power point. How you feel for the whole vacation depends upon how hard you push your brains to decipher the periodic table.