Vocabulary: 1. valence shell 2. valence electrons 3. anion 4. cation 5. isoelectric 6. Lewis structure (Lewis dot diagram) Banksy, British, 2002

Pauling Electronegativities  Linus Pauling developed the concept of electronegativity and assigned values to atoms to quantify electronegativity.  Electronegativities have no units; they are comparative only.

chlorine 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 17 protons potassium 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 19 protons

chlorine 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 17 protons potassium 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 19 protons

chlorine 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 17 protons potassium 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 19 protons Only 2 more protons  But a whole new energy level 

chlorine 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 17 protons potassium 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 19 protons That means strong attraction for these valence electrons (large Z eff ). And weak attraction for this valence electron (low Z eff ).

chlorine 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 17 protons potassium 4s __ 4p ___ ___ ___ 3s ___3p ___ ___ ___ 2s ___2p ___ ___ ___ 1s ___ 19 protons That means easy to gain 1 more electron here (high electronegativity) And easy to lose an electron here (low ionization energy)

 Elements that have a nearly full valence shell, like chlorine, have high electronegativities and can gain electrons easily. chlorine 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ 17 protons and 17 electrons = 0 charge

 Elements that have a nearly full valence shell, like chlorine, have high electronegativities and can gain electrons easily. chlorine 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ 17 protons and 18 electrons = 1- charge

 Atoms that have gained one or more electrons are now negative ions and are called anions ( ˈ an-ī- ə n). chlorine 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ 17 protons and 18 electrons = 1- charge

potassium 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ 19 protons + 19 electrons = 0 charge  Elements that have a nearly empty valence shell, like potassium, have low electronegativities and can lose electrons easily.

potassium 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ 19 protons + 18 electrons = 1+ charge  Atoms that have lost one or more electrons are now positive ions and are called cations (kat-ī- ə n).

chlorine anion (1- charge) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ potassium cation (1+ charge) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ When each atom gained or lost electrons, the new outer shell (energy level) is full, like the noble gases.

Different atoms or ions that have the same electron configuration are called isoelectric. The Cl - ion is isoelectric with the K + ion. They are both isoelectric with neon. chlorine anion (1- charge) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ potassium cation (1+ charge) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___

Atoms lose or gain electrons in order to have a full valence shell (a noble gas configuration). This will typically result in 8 valence electrons and make the resulting ion isoelectric with the noble gas.

Rather than draw orbital diagrams, we can use Lewis Structures (Lewis Dot Diagrams) to show numbers of valence electrons. Cl 1. Write symbol of element. 2. Determine number of valence electrons by position on periodic table 3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.) 7 valence electrons because in group 17

Cl So when chlorine forms an ion, will it gain or lose electrons? How many? It needs one more to have an octet. What will its charge be now? 1-

K 1. Write symbol of element. 2. Determine number of valence electrons by position on periodic table 3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.) 1 valence electrons because in group 1

K So when potassium forms an ion, will it gain or lose electrons? How many? It will lose one electron to have a full valence What will its charge be now? 1+

N 1. Write symbol of element. 2. Determine number of valence electrons by position on periodic table 3. Use dots to represent electrons around symbol (one at a time on each side and then pair them up.) 5 valence electrons because in group 15

So when nitrogen forms an ion, will it gain or lose electrons? How many? It will gain three electrons to have a full valence What will its charge be now? 3- N

 Using periodic trends, we can predict the ion charge for the main group elements /