1. Periodic Trends Chapter 14 Notes, part II

2. Atomic Size Atomic size increases down a group.Atomic size increases down a group. Atomic size decreases from left to right across a period.Atomic size decreases from left to right across a period. Arrows show direction of increases

3. Why increasing down a group? The increasing trend occurs because as you go down a group more energy levels cause the atom to be larger.The increasing trend occurs because as you go down a group more energy levels cause the atom to be larger. Shielding also affects the size; the electrons in lower energy levels cause less pull to those electrons outside of it.Shielding also affects the size; the electrons in lower energy levels cause less pull to those electrons outside of it. Atomic size increases down a group.Atomic size increases down a group. Atomic size decreases from left to right across a period.Atomic size decreases from left to right across a period.

4. Why decreasing across a period? Across a period no new energy levels are added, but more protons are. The added positive charge gives more pull to the nucleus, so it can pull electrons towards the center.Across a period no new energy levels are added, but more protons are. The added positive charge gives more pull to the nucleus, so it can pull electrons towards the center. Atomic size increases down a group.Atomic size increases down a group. Atomic size decreases from left to right across a period.Atomic size decreases from left to right across a period.

5. Which is bigger? Li or Na?Li or Na? Se or As?Se or As? N or Si?N or Si? What is the biggest element?What is the biggest element? What is the smallest element?What is the smallest element? Atomic size increases down a group.Atomic size increases down a group. Atomic size decreases from left to right across a period.Atomic size decreases from left to right across a period.

6. Valence Electrons Valence electrons increase from left to right across a period.Valence electrons increase from left to right across a period. Valence electrons are the same in a group.Valence electrons are the same in a group. Arrows show direction of increases

7. Before we go on... An ion is an atom that loses or gains electrons to have a full outside energy level.An ion is an atom that loses or gains electrons to have a full outside energy level. In doing so, it becomes charged--ceasing to be electrically neutral.In doing so, it becomes charged--ceasing to be electrically neutral. A positively charged ion is called a cation, a negatively charged ion is called an anion.A positively charged ion is called a cation, a negatively charged ion is called an anion. We will look at trends in:We will look at trends in: –Ion size –Ionization energy

8. Oxidation Number Oxidation number is the charge that an element has after it becomes an ion. +1+2+3±4±4-3-20 Varies

9. Ion Size Essentially the same trend as atomic size, except anions are always bigger than cations.Essentially the same trend as atomic size, except anions are always bigger than cations. Arrows show direction of increases

10. Why are anions bigger? Anions have more electrons than the atom it is made from, so there will be more repulsion between them, causing increase in radius.Anions have more electrons than the atom it is made from, so there will be more repulsion between them, causing increase in radius. Cations have less electrons, so they will have one less energy level than the element made from.Cations have less electrons, so they will have one less energy level than the element made from. Essentially the same trend as atomic size, except anions are always bigger than cations.Essentially the same trend as atomic size, except anions are always bigger than cations.

11. Which is bigger? Cations or anions?Cations or anions? N 3- or F - ?N 3- or F - ? Ga 3+ or As 3- ?Ga 3+ or As 3- ? C 4+ or C 4- ?C 4+ or C 4- ? Essentially the same trend as atomic size, except anions are always bigger than cations.Essentially the same trend as atomic size, except anions are always bigger than cations.

12. Ionization energy Ionization energy is the amount of energy it takes to pull an electron from the outside shell of an atom.Ionization energy is the amount of energy it takes to pull an electron from the outside shell of an atom. 1 st Ionization energy is the amount of energy to pull the first electron away, the 2 nd ionization energy is the amount of energy to pull away a second electron, etc.1 st Ionization energy is the amount of energy to pull the first electron away, the 2 nd ionization energy is the amount of energy to pull away a second electron, etc. We will look at the trend in 1 st and 2 nd ionization energies.We will look at the trend in 1 st and 2 nd ionization energies.

13. 1 st Ionization Energy Ionization energy increases up a group.Ionization energy increases up a group. Ionization energy increases left to right across a period.Ionization energy increases left to right across a period. Arrows show direction of increases

14. Why decreasing down a group? As you go down a group, the valence electrons are farther away from the nucleus, and so it takes less energy to pull them away from the atom.As you go down a group, the valence electrons are farther away from the nucleus, and so it takes less energy to pull them away from the atom. Ionization energy increases up a group.Ionization energy increases up a group. Ionization energy increases left to right across a period.Ionization energy increases left to right across a period.

15. Why increasing across a period? The more electrons in the outside energy level, the less eager an atom will be to lose an electron.The more electrons in the outside energy level, the less eager an atom will be to lose an electron. This is because nuclear charge increases while shielding remains constant.This is because nuclear charge increases while shielding remains constant. Ionization energy increases up a group.Ionization energy increases up a group. Ionization energy increases left to right across a period.Ionization energy increases left to right across a period.

16. Which has a higher I.E.? K or Ca? Mg or Ba? Br or Sb? I or Rb? Ionization energy increases up a group.Ionization energy increases up a group. Ionization energy increases left to right across a period.Ionization energy increases left to right across a period.

17. 2 nd Ionization Energy The second ionization energy follows the same general trend as the first, except that all the elements in the first group have the highest IE.The second ionization energy follows the same general trend as the first, except that all the elements in the first group have the highest IE. This is because after the first row loses one electron it has a full valence, making as stable as possible. It takes much more energy to take away a second electron.This is because after the first row loses one electron it has a full valence, making as stable as possible. It takes much more energy to take away a second electron. Ionization energy increases up a group.Ionization energy increases up a group. Ionization energy increases left to right across a period.Ionization energy increases left to right across a period.

18. Electronegativity The electronegativity of an element is the tendency for the atoms of the element to attract an electron when combining with other elements.The electronegativity of an element is the tendency for the atoms of the element to attract an electron when combining with other elements. The scale is based on several factors, including the ionization energy of the element. It can be used to predict the type of bonds.The scale is based on several factors, including the ionization energy of the element. It can be used to predict the type of bonds.

19. Electronegativity Electronegativity increases up a group.Electronegativity increases up a group. Electronegativity increases from left to right across a period.Electronegativity increases from left to right across a period. Arrows show direction of increases

20. Electronegativity The exception to the general trend for electronegativity is that the noble gases have a value of zero!The exception to the general trend for electronegativity is that the noble gases have a value of zero! This is because they do not attract electrons, since they already have a full outside shell.This is because they do not attract electrons, since they already have a full outside shell. Electronegativity increases up a group.Electronegativity increases up a group. Electronegativity increases from left to right across a period.Electronegativity increases from left to right across a period.

21. Which has a higher electronegativity? S or P?S or P? Al or Ga?Al or Ga? Cl or Ar?Cl or Ar? C or Mg?C or Mg? Cs or He?Cs or He? Electronegativity increases up a group.Electronegativity increases up a group. Electronegativity increases from left to right across a period.Electronegativity increases from left to right across a period.