Bonding

Chapter 5BondingBondingWhen atoms combine they form a chemical bondThe force of attraction between two or more atoms.

Valence ElectronsAre the outer most electrons of an atom.They play a huge role in how an atom bonds.

Lewis StructureIs a diagram of atoms that only shows the valance electronsEx:

ClNaH ArThe Octet RuleThe octet rule says that atoms tend to gain, lose or share electrons so they can have eight electrons in their outer shell. They do this because they are more stable with a complete outer shell.There are some situations where it does not apply. For example, hydrogen wants to take one on to complete its outer shell with 2 electrons.

Oxidation NumbersOxidation numbers represent the charges that an ion has when it gains or loses its valence electrons.They are listed as a + or above each column on the periodic table.

IonAn ion is an atom which has lost or gained one or more electrons, making it positively or negatively charged.A negatively-charged ion, gains an electrons so it has more electrons then it has protons. A positively-charged ion, looses electrons so it has more protons then electrons.A polyatomic ion is an ion that is made up of more than one atom.Poly= ManyAtomic= AtomsEx: NH4+ is the chemical formula for an ammonium ion. It contains two elements nitrogen and hydrogen and has a positive charge.

Ionic BondsBonds that form as a result of the attraction between positive and negative ions. The atoms are attracted to each other because of their opposite chargesWe call the compound that results from the bond an Ionic Compound.Usually form between a metal and a nonmetal

In an IONIC bond,electrons are lost or gained,resulting in the formation of IONSin ionic compounds.FK9FK10FK11FK12FK13FK14FK+_The compound potassium fluorideconsists of potassium (K+) ionsand fluoride (F-) ions15FK+_The ionic bond is the attractionbetween the positive K+ ionand the negative F- ion16

FormulasReminder: A chemical formula is the combination of symbols that show the elements in the compound. i.e. MgCl2If a molecule contains more than one atom of a particular element, you indicate it by using a subscript after the chemical symbol (ex: the 2 in MgCl2).It tells you the ratio of atoms in the compound (MgCl2 has a 1:2 ratio).If no subscript is written the number 1 is understood( NaCl there is a 1:1ratio).A coefficient acts as a multiplier for all of the atoms in the entire compound, it is found in front of the chemical formulaEx: the 5 in 5 MgCl2

Example MgCl2Here we have one molecule of magnesium chloride. The subscript 2 in the formula aboveonly pertains to the chlorine in the compound. The total number of atoms in the compound is 3.

Now let us put a coefficient in front of the molecule and see how that changes things.5 MgCl2The coefficient 5 refers to the entire molecule. It shows that there are 5 compounds ofmagnesium chloride.Since each molecule is made up of 3 atoms, the total number of atoms is now 15. There are5 magnesium atoms and 10 chlorine atoms.

How many atoms are in the following bond 3Na2SSodium(Na)____Sulfur(S)____Sodium Sulfide(3Na2S) ____ = total atoms

639

19Naming Ionic CompoundsThe name of the positive ion comes first, followed by the name of the negative ion.The metal will be the positive because it gives away electrons and the nonmetal will be the negative because it gains electrons.If the negative ion is a single element the end of its name changes to ide.Ex: NaCl- Sodium Chloride MgO- Magnesium OxideIf the negative ion is polyatomic, its name usually ends in ate or ite.Ex: NH4NO3- Ammonium nitrate

What is the name of the ionic compound with the formula K2S? ______________

Potassium Sulfide20

Properties of Ionic CompoundsHardBrittleCrystalsHigh melting points- NaCl melts at 801C= 1473.8 FWhen dissolved in water they are electrolytes.An electrolyte solution is one that can conduct electricity.Ionic bonds in solid from are poor conductors.Covalent BondsThe chemical bond formed when two atoms share electrons.Usually form between nonmetals.We call the neutral group of atoms joined by a covalent bond a molecule.

In covalent bonding,atoms still want to follow the octet rule and have a complete valance shell 23But rather than losing or gainingelectrons, atoms now share an electron pair.In covalent bonding,atoms still want to follow the octet rule and have a complete valance shell 24The shared electron pairis called a bonding pairBut rather than losing or gainingelectrons, atoms now share an electron pair.In covalent bonding,atoms still want to follow the octet rule and have a complete valance shell 25Cl2Chlorineformsacovalentbondwithitself26ClClHowwilltwochlorineatomsreact?27ClClEach chlorine atom wants to gain one electron to achieve a full outer shell.28Neither atom will give up an electron.Whats the solution what can theydo to achieve an octet?ClCl29ClCl30ClClClCl31ClCl32ClCl33ClClcomplete34ClClcomplete35ClClThe complete outer shell is achieved byeach atom sharing theelectron pair in the middle36ClClThe complete outer shell is achieved byeach atom sharing theelectron pair in the middle37ClClThis is the bonding pair38ClClIt is called a SINGLE BOND39ClClSingle bonds are abbreviatedwith a dash40ClClThis is the chlorine molecule,Cl241O2Oxygen is also one of the diatomic molecules42How will two oxygen atoms bond?OO43OOEach atom has two unpaired electrons44Oxygen atoms want to gain two electrons.OO45OOBoth electron pairs are shared.466 valence electronsplus 2 shared electrons= full valance shellOO476 valence electronsplus 2 shared electrons= full valance shellOO48two bonding pairs,OOmaking a double bond49OO=For convenience, the double bond can be shown as two dashes. OO50OO=This is the oxygen molecule,O251Molecular CompoundsA compound that is composed of molecules.Ex: CH4- Methane H2O- WaterProperties:Low melting and boiling points.Poor conductors

Polar BondsA covalent bond in which electrons are shared unequally is called a polar bond. ex: water molecules

One atom pulls more strongly on a shared electron causing a slight charge.Polar molecules tend to pull close together because the negative end of each molecule is attracted to the positive end of other molecules.

Nonpolar BondsIf the electrons are shared equally it is called a nonpolar bond.

A molecule may contain a polar bond and still be nonpolar overall. In order for this to happen the molecule must bond in a straight line with opposite pulling. Ex: carbon dioxideThere is little attraction between non polar molecules

Why Doesnt Oil & Water Mix?The molecule in vegetable oil are nonpolar and have little attraction to other molecule.Water molecules are polar and are strongly attracted to one another.SO, the water stays with the water which leave the oil by itself.Adding soap allows them to mix easily because the soap molecule contains one end that is an ionic bond and the other end is a nonpolar covalent bond.The nonpolar end mixes with the oil and the charge on the ionic end attracts the waterMetallic BondsAn attraction between a positive metal ion and the electrons surrounding it. In other words: Many electrons are shared by many atoms.A metal consists of positively charged metal ions embedded in a sea of valence electrons.

Metallic PropertiesThe sea of electrons model of solid metals explains their properties:Heat/electrical conductivityThe free moving valance electrons make it easier for the particles to move faster.Changes in shapeDuctileMalleableThis happens because the ions in the metal are not attracted to each other, instead they are attracted to the loose electrons all around them.LusterA metals luster is due to its valance electrons. They absorb and then reflect the light which we see has shiny.