Periodic Trends Notes in packet

Octet Rule and Ions Octet Rule – atoms ability to gain, lose or share electrons to acquire a full set of 8 valence electrons

Octet Rule and Ions What will determine if an atom will gain or lose electrons? Metals have 1, 2, or 3 valence electrons – they will lose electrons (cations) Nonmetals have 5, 6, or 7 valence electrons – they will gain electrons (anions)

Effective Nuclear Charge Charge felt by a particular electron Inner electron shields outer electrons from the nuclear charge More energy levels, higher shielding effect for outer electrons

Effective Nuclear Charge

Trend: Effective Nuclear Charge Exceptions There are some areas of the periodic table that do not follow the general trend. Due to electron pair repulsion Due to s shielding p Due to electron pair repulsion in doubly occupied orbitals

Coulombic Attraction Force between positive and negative charges Directly proportional to charge size As charge increases, attraction increases Inversely proportional to distance As distance increases, attraction decreases

Electronegativity Indicates the relative ability of its atoms to attract electrons in a chemical bond

Electronegativity Trend Generally increases Why would we see higher electro-negativities in the nonmetals than we do in the metals? Horizontal trend takes precedence over vertical trend!!! Generally increases

Let’s Practice Between the elements As, Sn and Sb, which is the most electronegative? As Between the elements Sr, Ba and Ra, which is the most electronegative? Sr

More Practice Circle the element with the largest electronegativity and underline the smallest electronegativity: 1. Si N 2. Ca Al 3. Pb Bi Sn 4. O S F Cl 5. Ge Si P As S Which elements are excluded from electronegativity? Why?

Reactivity Trend Nonmetals increase Why is the trend in reactivity different for metal and nonmetals? Nonmetals increase Metals increase Metals react because of the fact that they lose electrons. Fr has the lowest electronegativity meaning it’s the metal that loses electrons the easiest. Nonmetals react because of the fact that they gain electrons. F has the highest electronegativity meaning that it gain electrons easily. Metals increase

Practice Questions As you go from left to right across the periodic table, what happens to reactivity of the elements? Why?  As you go from top to bottom down the periodic table, what happens to reactivity of the elements? Why?  How are reactivity and the valence electrons related?

First Ionization Energy Energy required to remove an electron from an atom A measure of how strongly a nucleus hangs onto its valence electrons High ionization energy = atoms less likely to form positive ions Low ionization energy = an atom loses an outer electron easily

First Ionization Energy Trend Generally increases Why do we see the same trend in electro-negativity as we do first ionization energy? Why do metals have low first ionization energies? Horizontal trend takes precedence over vertical trend!!! Generally increases

Second Ionization Energy The energy required to remove 2nd (or more) electrons from the atom

Let’s Practice Consider the table of ionization energies for element X shown below. Ionization Energy in kJ/mol (a) In which group will X be found? Explain. __________________________________ (b) Predict the formula of X’s bromide. __________________________ 1st 2nd 3rd 4th 5th 6th 737 1450 7732 10540 13360 17995

Atomic Radius Half the distance between adjacent nuclei of identical atoms

Vertical trend takes precedence over horizontal trend!!! Atomic Radius Vertical trend takes precedence over horizontal trend!!! Why does atomic radius increase as we move down a group? Why does atomic radius increase as we move right to left across a period? Generally increases Across a period, we are not adding any additional energy levels but we are adding protons which increase nuclear charge. Since the additional electrons are in the same energy level, they are not shielded from increased nuclear charge which brings the energy level in closer to the nucleus. Generally increases

Let’s Practice Between the elements Po, Te, I, which one has the largest atomic radius? Po Between the elements Sc, Rb and Cr, which one has the smallest atomic radius? Cr

Ionic Radius The size of the atom once it has formed an ion Positive ions form smaller atoms Negative ions form larger atoms

Ionic Radius Trend Nonmetals increase Metals increase

Let’s Practice Between the elements N, O and P, which will form the smallest ion? O In the group below, which is the largest and which is the smallest? Mg2+ Br-1 K B3+ P3- Largest = K, Smallest=B3+

More Practice 1. Which diagram best represents the relationship between the diameter of a sodium atom and the diameter of a positive sodium ion? a. b. c.   1. In each of the following pairs, pick the larger species. Explain you answer in each case. (a) Cu and Cu2+  (b) F and F- 

Shielding Effect Shielding of outer electrons by inner electrons Shields the outer electrons from the positive pull of the nucleus

Shielding Effect Trend Why is shielding constant moving across the period? Generally increases We are not adding any additional energy levels so not putting anything else between valence electrons and the nucleus. Shielding is constant across the period