3 18-1 - Stability in Bonding Combined ElementsElements combine to form compoundsCompounds have properties very different from original elementsCompounds have chemical formulas to show the atoms and ratios that make them up.
4 18-1 - Stability in Bonding Chemical Formula Practice
5 18-1 - Stability in Bonding Unfilled & filled energy shellsFilling Outer energy shellsValence electronsGain/lose electronsShare electronsForming chemical bonds
6 An Atomic Model is Needed to Understand How Atoms Bond Review shell model of atom (Ch 16)Valence electrons –Electron Dot Diagrams –Tells valence electronsHow many (ve) are paired
8 18-2 - Types of Bonds Atoms are electrically neutral Why?Ions are not electrically neutralIon –Can be negative or positiveAtoms tend to lose or gain electrons so they end up with an outermost occupied shell that is filled to capacityThe Periodic table can be used to determine the type of ion that an atom tends to form
9 Types of BondsPositive Ion (cation)Negative Ion (anion)
10 Ionic Bonds Result from an Transfer of Valence Electrons Result of transfer of electrons forms a positive ion and a negative ionIonic Bond –Ionic Compounds –Characteristics of Ionic Bonds –
12 Ionic Bonds: One big greedy thief dog Ionic Bonds: One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone. If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged. The two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.
16 Covalent Bonds: Dogs of equal strength Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones. Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly. Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs. The molecule is not "polar" meaning one side does not have more charge than the other.
17 Polar Covalent Bonds Result from an Uneven Sharing or Electrons Dipole –Electronegativity –Difference in electronegativityNonpolar Bond –Polar Bond -
19 Polar Covalent Bonds: Unevenly matched but willing to share Polar Covalent Bonds: Unevenly matched but willing to share. These bonds can be thought of as two or more dogs that have different desire for bones. The bigger dog has more strength to possess a larger portion of the bones. Sharing still takes place but is an uneven sharing. In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.
21 Molecular Polarity Results from an Uneven Distribution of Electrons Polar and nonpolar are easy when 2 atoms, more complex when more than 2 atoms are bondedEnd result may be a even distribution or an uneven distributionCan make the dipole strongerExplains why water is “sticky”May explain other macroscopic properties
22 This molecular polarity causes water to be a powerful solvent and is responsible for its strong surface tension. The molecular arrangement taken by ice (the solid form of the water molecule) leads to an increase in volume and a decrease in density. Expansion of the water molecule at freezing allows ice to float on top of liquid water.