Chemical Bonding Chapter 19

Why Driving force behind the formation of chemical compounds is the attainment of a lower energy state (more stable) Octet Rule -for most atoms this means the attainment of an octet (8 valence e- in their outer shell) 1A elements have 1 valence e- (s1 outer shell), 2A elements have 2 valence e- (s2 outer shell) 3A elements have 3 valence e- (s2p1 outer shell) 7A elements have 7 valence e- (s2p5 outer shell) 8A elements have 8 valence e- (s2p6 outer shell –full shell)

How –two types 1. Covalent Bonding means two atoms share a valence electron between them. -occurs between non-metals and non-metals 2. Ionic Bonding means one atom gives up an electron and the other gains it, transfers the electron to the other atom -occurs between metals and non-metals

Examples of ionic bonding Ionic bonding periods(horizontal rows on periodic table) Na 1s22s22p63s1 1 valence e- Cl 1s22s22p63s23p5 7 valence e- Na could gain 7 or give up 1 Na Lewis Dot formula Cl could gain 1 or give up 7 Cl Lewis Dot formula Metals tend to lose e- and nonmetals tend to gain e-

Na = 11 protons and 11 electrons, so neutral since protons are positive and electrons are negative. 11+ and 11- = 0 charge, so neutral, but still would like either a full outer shell or give up the extra e- in its outer shell Na is a metal, so it gives up the 1 valence e- so now it has 11 protons and 10 electrons It is now more positive = Na+ and called a cation Na minus e- = Na+

Cl has 17 protons and 17 electrons Cl is a non-metal and tends to gain electrons so now it would have 17 protons and 18 electrons It is now more negative = Cl- and is called an anion Cl plus electron = Cl - Na+ Cl - = Na+1 and Cl-1

Comparing ions A cation is smaller than the original atom (gave up an electron) An anion is larger than the original atom (gained an electron) When they combine, they are electronically neutral, but don’t totally pair together, instead they form a crystal lattus and are held together by the attraction of their opposite charges (unlikes attract, negative and a positive charge) NaCl is the compound’s ionic formula and is considered an ionic compound Sodium Chloride –table salt

Extra stuff to help Group # identifies the e- in the outer shell (column #) Metals = group # = charge group 1 = a charge of 1 Non-metals = group # = charge group 8 = a charge of 8, group 7 = a charge of 7 and wants one more to make 8 Transition metals usually have a charge of 3+ or 2+, but could be more or less. That is why we are not worrying about them. We will use group 1,2, 7, and 8 to form compounds. Lewis Dot –electrons like to stay away from each other, so fill them apart as long as you can because they have like negative charges and likes repel each other

You try two metal -Mg (magnesium) and non-metal -Br Bromide *Remember it wants to be neutral. Hint –you can put more than one of a same atom in an ionic formula Mg Br2 metal –Al and non-metal S 1.find the amount of valence electrons by filling s and p levels of each atom(look at periodic table and which vertical group they are in), 2. use Lewis Dot formula to show how many valence e-, 3. name which loses and which gains electrons plus identify how many, and finally 4. name the cation and anion,5. write the ionic formula, plus 6. name the new ionic compound

Mg Br

Al S

ok Try Ca and Br

Examples of Covalent Bonding H = 1s1 H shares to get 1s2 = a full s orbital H H = H H = single covalent bond Molecule H2 = molecular formula, Both s orbitals overlap during the sharing. They don’t have both e- all the time, they share

Types of overlap orbitals Sigma = 1 or more s orbitals or 2 p orbitals overlapping head on Pi = 2 p orbitals overlapping side-to-side H to H is 1s to 1s so it is sigma F shares with F = F2 2s22p5 p orbital shares with other p orbital head to head = sigma F F

HCl = H shares 1 Cl needs one, so they share H 1s1 Cl 3s23p5 Hydrochloric acid H Cl Sigma s orbital shares with a p orbital Anything with an H in front is usually an acid

Extra stuff Sometimes the e- is shared unevenly because one of the atoms attracts the e- more strongly Scale 0-4 = 0 weak attraction, 4 strong attraction Down a group, an atom decreases its attractive force to the e- being shared Across a period, an atom increased its attractive force to the e- being shared

You try S O Hint –Lewis Dot –fill around the O atoms first, then top and bottom of S. When you have 2 left, put them between the S and an O. That is a double bond. Sulfur dioxide

You try Carbon Dioxide C O Hint, it has 2 double bonds