Ch 5.3 Electron Configuration and Periodic Properties

Atomic Size } Radius Measure the Atomic Radius - this is half the distance between the two nuclei of a diatomic molecule.

#1. Atomic Size - Period Trends Going from left to right across a period, the size gets smaller. Electrons are in the same energy level. Outermost electrons are pulled closer. Na Mg Al Si P S Cl Ar

#1. Atomic Size - Group trends H As we increase the atomic number (or go down a group), each atom has another energy level. Valence electrons get further from the nucleus. So the atoms get bigger. Li Na K Rb

Trend in Atomic Radius

Ions An ion is an atom (or group of atoms) that has a positive or negative charge Atoms are neutral because the number of protons equals electrons Positive and negative ions are formed when electrons are lost or gained between atoms

#2: Ionic Group trends Li1+ Na1+ K1+ Rb1+ Cs1+ Ions therefore get bigger as you go down, because of the additional energy level. Na1+ K1+ Rb1+ Cs1+

Ionic Period Trends Across the period from left to right, they get smaller. N3- O2- F1- B3+ Li1+ Be2+ C4+

Trends in the Periodic Table Atomic Size vs. Ion Size

#3. Trends in Ionization Energy Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom). The energy required to remove 1 electron is called the first ionization energy.

Ionization Energy The second ionization energy is the energy required to remove the second electron. Always greater than first IE. The third IE is the energy required to remove a third electron. Greater than 1st or 2nd IE.

3. Trend in Ionization Potential The energy required to remove the valence electron.

Ionization Energy - Group trends As you go down a group, the first IE decreases because... The electron is further away from the attraction of the nucleus, and There is more shielding.

Ionization Energy - Period trends All the atoms in the same period have the same energy level. So IE generally increases from left to right.

He has a greater IE than H. Both elements have the same shielding since electrons are only in the first level But He has a greater nuclear charge H First Ionization energy Atomic number

These outweigh the greater nuclear charge Li has lower IE than H more shielding further away These outweigh the greater nuclear charge H First Ionization energy Li Atomic number

greater nuclear charge He Be has higher IE than Li same shielding greater nuclear charge First Ionization energy H Be Li Atomic number

greater nuclear charge He B has lower IE than Be same shielding greater nuclear charge By removing an electron we make s orbital half-filled First Ionization energy H Be B Li Atomic number

First Ionization energy He First Ionization energy H C Be B Li Atomic number

First Ionization energy He N First Ionization energy H C Be B Li Atomic number

He Oxygen breaks the pattern, because removing an electron leaves it with a 1/2 filled p orbital N First Ionization energy H C O Be B Li Atomic number

First Ionization energy He F N First Ionization energy H C O Be B Li Atomic number

Ne has a lower IE than He Both are full, Ne has more shielding Greater distance F N First Ionization energy H C O Be B Li Atomic number

Na has a lower IE than Li Both are s1 Na has more shielding He Ne Na has a lower IE than Li Both are s1 Na has more shielding Greater distance F N First Ionization energy H C O Be B Li Na Atomic number

First Ionization energy Atomic number

Electron Affinity The energy change that occurs when an electron is acquired by a neutral atom. Most atoms release energy when they gain an electron. (negative value) However, some must be forced to gain an electron which requires energy. (positive value) Halogens gain electrons most readily. The larger the negative value for electron affinity, the easier it is for that atom to gain an electron.

Metals tend to LOSE electrons, from their outer energy level Ions Metals tend to LOSE electrons, from their outer energy level Sodium loses one electron. There are now more protons (11) than electrons (10), and thus a positively charged particle is formed = “cation” The charge is written as a number followed by a plus sign: Na1+ Now named a “sodium ion” Lost an electron, so a decrease in size from atom to ion.

Nonmetals tend to GAIN one or more electrons Ions Nonmetals tend to GAIN one or more electrons Chlorine will gain one electron Protons (17) no longer equals the electrons (18), so a charge of -1 Cl1- is re-named a “chloride ion” Negative ions are called “anions” Gained an electron so increase in size from atom to ion.

Valence Electrons The electrons available to be lost, gained, or shared in the formation of chemical compounds. Main group elements: valence electrons are in the outermost s and p orbitals.

Electronegativity is the tendency for an atom to attract electrons. It decreases as it goes down a group because electrons get farther away from the nucleus.

Electronegativity Period Trend Metals (left side) They let their electrons go easily Low electronegativity Nonmetals (right side). They want more electrons. Try to take them away from others High electronegativity.

Summary of Trends Ionization Energy and Electronegativity Atomic and Ionic Radius

Additional Assessment Questions For each of the following pairs, predict which atom is larger. a. Mg, Sr d. Ge, Br b. Sr, Sn e. Cr, W c. Ge, Sn

Answers a. Mg, Sr Sr b. Sr, Sn Sr c. Ge, Sn Sn d. Ge, Br Ge e. Cr, W W Additional Assessment Questions Answers a. Mg, Sr Sr b. Sr, Sn Sr c. Ge, Sn Sn d. Ge, Br Ge e. Cr, W W

Additional Assessment Questions For each of the following pairs, predict which atom or ion is larger. a. Mg, Mg2+ d. Cl–, I– b. S, S2– e. Na+, Al3+ c. Ca2+, Ba2+

Answers a. Mg, Mg2+ Mg b. S, S2– S2– c. Ca2+, Ba2+ Ba2+ d. Cl–, I– I– Additional Assessment Questions Answers a. Mg, Mg2+ Mg b. S, S2– S2– c. Ca2+, Ba2+ Ba2+ d. Cl–, I– I– e. Na+, Al3+ Na+

Additional Assessment Questions For each of the following pairs, predict which atom has the higher first ionization energy. a. Mg, Na d. Cl, I b. S, O e. Na, Al c. Ca, Ba f. Se, Br

Answers a. Mg, Na Mg b. S, O O c. Ca, Ba Ca d. Cl, I Cl e. Na, Al Al Additional Assessment Questions Answers a. Mg, Na Mg b. S, O O c. Ca, Ba Ca d. Cl, I Cl e. Na, Al Al f. Se, Br Br