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  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)

Electron Affinity Energy given off when a neutral atom gains an electron to form a negative ion Why do we see peaks and valleys in the electron affinity of different elements?

Electron Affinity Trend Generally increases Why does electron affinity increase as we move left to right across a period? Why is electron affinity higher as we move up a group?

Let’s Practice  Between the elements Sn, As and P, which has the highest electron affinity? PP  Between the elements Ba, Sr and K, which has the lowest electron affinity?  Ba

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?

Let’s Practice Between the elements As, Sn and Sb, which is the most electronegative? 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? 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. SiN 2.CaAl 3.PbBiSn 4.OSFCl 5.GeSiPAsS Which elements are excluded from electronegativity? Why?

Reactivity Trend Nonmetals increase Metals increase Why is the trend in reactivity different for metal and nonmetals?

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?

Let’s Practice 1st2nd3rd4th5th6th 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. __________________________

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

Atomic Radius Half the distance between adjacent nuclei of identical atoms

Atomic Radius Generally increases 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?

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O  In the group below, which is the largest and which is the smallest? Mg 2+ Br -1 KB 3+ P 3-  Largest = K, Smallest=B 3+

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 Cu 2+  (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 Generally increases Shielding is constant across the period Why is shielding constant moving across the period?