O H CHAPTER 7 CHEMICAL FORMULAS AND BONDING Date _____________ H2O, CO2, NaCl makes “stuff” stick how many atoms or ions of each element are in a piece of the substance Before we can understand/predict the chemical formula, we need to understand how/why bonds form… …. before that, let’s consider just what is a bond between atoms? H O what is a bond made of?

e- e- what is a bond made of? electrons / connection of electrons always something about… i.e. made of something – that something is electrons somehow those somethings (electrons) would have to hold together 8O 1s22s22p4 e- 1H 1s1 e- the hook

e- e- there must be some kind of “wireless” connection what is a bond made of? electrons / connection of electrons i.e. made of something – that something is electrons somehow those somethings (electrons) would have to hold together 8O 1s22s22p4 e- 1H 1s1 doesn’t make sense 1. the hooks would have to be made of something… 2. have to decide “to hook or not to hook? (that is the question)” 3. electrons repel 4. electrons couldn’t move… so, we could know where they are e- the hook there must be some kind of “wireless” connection

how / why do bonds form? two (or more) atoms do not bond together by simply coming close to each other… the universe would be just a clump …. so…. why/how do atoms bond? and what is this “wireless” connection?

e- well, what holds a single atom together?.... made of p, n, and e- 8O 1s22s22p4 e- The forces present include… pull between p(+) and e- (e/m force) nuclear (strong) force between nucleons – p(+), n repulsion between e- and e- and between p(+) and p(+) (e/m force) the attractions and repulsions balance… … get an atom the electrons are held on without touching the nucleus… like planets orbiting the Sun

e- this does not help answer the question… why / how do atoms bond? on average, the electrons are evenly around the nucleus, so an atom is spherical 8 p(+) 8 e- e- atom is neutral (NOT sticky) to the outside world an atom looks like a neat little “happy” round package this does not help answer the question… why / how do atoms bond?

because I don’t have a FOS!! we must ask… what lies behind that happy face the atom presents to the world feelings of emptiness / incompleteness e- because I don’t have a FOS!! struggle angst feelings of bloatedness / too-full-nes turmoil

8O 1s22s22p4 e- e- e- e- e- e- e- 12Mg 1s22s22p63s2 e- e- e- e- e- e- I would be so happy if I had two more electrons oh… oh… oh… is there anyone with electrons to spare ? e- e- e- e- e- e- 12Mg 1s22s22p63s2 e- e- e- e- I do…. I do… I have two to spare ! e- e- e- e-

8O 1s22s22p4 8O2- 1s22s22p6 e- e- e- e- e- e- e- 12Mg 1s22s22p63s2 e- here you go! e- e-

-2 +2 8O2- 1s22s22p6 e- e- e- e- e- e- e- e- e- e- e- e- e- To each other, they look like uniform spheres, of mostly empty space -2 one with a +2 charge and one with a -2 charge e- e- e- e- attracted to each other via the e/m force nothing actually touches!! there are no “hooks” the bond is made of NOTHING physical e- +2 e- e- e- e- e- e- e- 12Mg2+ 1s22s22p6

what is a bond made of ? the chemical bond is an e/m force between two particles (atoms / ions) of elements acting through space why do bonds form ? the chemical bond forms as a consequence of “satisfying the needs” of atoms to get a FOS

Chemical Formulas and Bonding Start with Bonding enough atoms of each element bond by ________________ such that each atom gains _________________________________________ first, need to be able to determine what type of bond forms: do atoms share electrons to get their stable electron configurations ? OR do atoms gain / lose electrons to get their stable electron configurations ? other atoms simplest language a FOS

Type of bond You now know that metal atoms tend to ___________ electron(s) (Why? but only if there is an atom that is willing to _________ electron(s) You now know that nonmetal atoms tend to ___________ electron(s) When will electrons be shared between atoms ? ________________________________________________________ lose cations (+) ionic bonds opposites attract (bond) more gain anions (-) gain anions (-) opposites attract (bond) more lose cations (+) James Bond covalent bonds both atoms “want” to lose electrons (both with low IE) both atoms “want” to gain electrons (both with low EAE)

Type of bond You now know that metal atoms tend to ___________ electron(s) (Why? but only if there is an atom that is willing to _________ electron(s) You now know that nonmetal atoms tend to ___________ electron(s) When will electrons be shared between atoms ? ________________________________________________________ lose cations (+) ionic bonds opposites attract (bond) more gain anions (-) gain anions (-) opposites attract (bond) more lose cations (+) covalent bonds both atoms “want” to lose electrons (both with low IE) both atoms “want” to gain electrons (both with low EAE) NOTE: you cannot tell what kind of bond an atom will form until you know what the other type of atom is that it is bonding to

so now….. how low does the IE have to be for one atom and how low does the EAE have to be for the other atom OR how close do the IE have to be for two atoms how close do the EAE have to be for two atoms would be “nice” to have a single measure OR quantity that would allow us to predict whether two atoms will form a bond by sharing electrons _____________________ or by transferring (gaining/losing) electrons __________________________ called _____________________ ________________________________________ desire to lose so that electron(s) will actually come off of one atom and go onto the other desire to gain TheLoseItGainIt_Series desire to lose so that electron(s) will be shared by the two atoms desire to gain covalent bond ionic bond THERE IS !!! electronegativity measure of the relative tendency of an atom to attract electrons when bonded to another atom

called ___________________________ ________________________________________ for which atoms will electronegativity (EN) be high ? easy / hard to gain electrons ? easy / hard to lose electrons ? for which atoms will electronegativity (EN) be low ? easy / hard to lose electrons ? easy / hard to gain electrons ? electronegativity measure of the relative tendency of an atom to attract electrons when bonded to another atom NONMETALS low EAE high IE METALS low IE high EAE

4.0 0.8

Let’s make a compound! with one atom of Fluorine (9F)and one atom of Cesium (55Cs) EN = _____ EN = ______ shell diagrams electron dot diagrams (aka Lewis dot structures) 4.0 0.8 on the board

Let’s make a compound! with one atom of Fluorine (9F)and one atom of Cesium (55Cs) EN = _____ EN = ______ shell diagrams electron dot diagrams (aka Lewis dot structures) 4.0 0.8 fluorine has such a greater tendency to attract electrons that the fluorine atom pulls the electron off of the cesium atom ions ionic bond “off” = no probability of the electron on cesium

what happens when there are two atoms of Chlorine (17Cl) both atoms have the same EN ______ shell diagrams electron dot (Lewis dot structures) 3.0 inner shell (core) electrons +17 10e- e- now draw this one……… +17 10e- e- don’t draw this one yet! e- e- e- 10e- e- +17 e- outer shell electrons Cl Cl e- e- each atom “wants” _______________________ to have a _________________ “get” by _________________ an electron with the other atom (_____________ bond) each atom now “thinks” it has another electron each atom now has the equivalent of a full outer shell one more electron full outer shell sharing covalent example of ___________________________ since each atom “wants” the electron equally (EN values are equal), the electrons are shared _____________________________ pure covalent bond equal probability of the shared electrons being on either atom equally

1s22s22p4 1s1 H O H covalent or ionic ? electrons shared or electrons transferred ? how close do the electronegativity values have to be for the electrons to be shared between atoms ? how different do the electronegativity values have to be for the electrons to be transferred between atoms ? use water as an example to introduce the answer H2O 8O ____________________ 1H ___________ “wants” ________ has ______ EN(O) ______ EN(H) _______ 1s22s22p4 1s1 electron dot (Lewis dot structure) 2e- 1e- H O H 3.5 2.1

H O H use water as an example to introduce the answer H2O EN(O) ______ EN(H) _______ electron dot (Lewis dot structure) H O H 3.5 2.1 are the electrons pulled “off” of ______________ and onto _____________ to form _______________ ____________________ probability of electron on H = __________ OR are the electrons shared between atoms __________________ there is probability of the shared electrons being on both the H and O atoms H (hydrogen) O (oxygen) H+ and O2- ionic bonds 0 (zero) covalent bonds

electrons transferred… to answer whether the electrons are “pulled off” (transferred) or shared we will use the following general rules when the EN < 1.7, electrons will be shared between atoms now, more general EN will be large when elements are ___________________on the PT like __________________ and ____________________ EN will be small when elements are __________________ on the PT back to water….. we’ll use this general rule for predicting the type of bond electrons transferred… ionic bond far apart metals nonmetals close metals electrons shared… covalent bond metals nonmetals nonmetals metalloids metalloids

- + H O O H H H O it’s my birthday and I get more than you do…. YES electron dot (Lewis dot structure) H ________________ O ________________ electrons shared ?__________ equally ? __________ _________ gets a bigger share nonmetal nonmetal polar covalent bond - + NO O H O H greater probability of the shared electrons being “on” oxygen H O electrons are shared but not shared equally the atom with the higher electronegativity gets a bigger “share” of the electrons since electrons are negative, the atom with the bigger “share” will end up with a “bit” of a negative charge the atom with the lesser “share” will end up with a “bit of a positive charge