Chapter 6.2 – Ionic and Covalent Bonding Objectives Why do atoms form bonds? How do ionic bonds form? What do atoms joined by covalent bonds share? What gives metals their distinctive properties? How are polyatomic ions similar to other ions?

Chapter 6.2 – Ionic and Covalent Bonding atoms bond when their valence electrons interact so that each atom has a full or stable electron configuration each atom wants to fill its outer s and p sublevels 2 basic kinds of compounds each type of compound has a different kind of bond

Chapter 6.2 – Ionic and Covalent Bonding ionic compounds formed from ions have ionic bonds – an attractive force between oppositely charged ions, which form when electrons are transferred from one to another one atom loses one or more electrons and another atom or atoms gains them the oppositely charged ions are then attracted to each other and form an ionic bond

Chapter 6.2 – Ionic and Covalent Bonding ionic compounds form strong networks because they do not form individual molecules, to write the chemical formulas use the smallest ratio of one ion to another, called the formula unit NaCl 1:1 Na2O 2:1 AlBr3 1:3 smallest ratio means they will not be divisible by each other and get a whole number will never have an ionic compound with a 2:2, 6:3, or 2:4 ratio

Chapter 6.2 – Ionic and Covalent Bonding ionic bonds are very strong therefore ionic compounds are solid at room temperature and have high melting and boiling points solid ionic compounds do not conduct electricity because their electrons are held tightly by the ions when melted or dissolved in water, the ions can move and will conduct electricity

Chapter 6.2 – Ionic and Covalent Bonding ionic compounds are neutral can tell from their formula units NaCl Na+ Cl- 1:1 ratio need 1 Na+ for every Cl- to be neutral MgF2 Mg2+ F- 1:2 ratio need 2 F- for every Mg2+ to be neutral Na2S Na+ S2- 2:1 ratio need 2 Na+ for every S2- to be neutral

Chapter 6.2 – Ionic and Covalent Bonding Covalent compounds – have covalent bonds – bonds formed when atoms share one or more pairs of electrons - electrons are shared so that both atoms have full outer energy levels also called molecules low melting and boiling points do no conduct electricity formed between nonmetals

Chapter 6.2 – Ionic and Covalent Bonding the lines in a structural formula show covalent bonds each line represents 2 electrons that are shared dots around atoms represent unshared electrons pairs of electrons stay together in structural formulas

Chapter 6.2 – Ionic and Covalent Bonding atoms can share multiple electrons when this happens the bonds are stronger when two pairs of electrons are shared it is called a double bond when three pairs of electrons are shared it is called a triple bond when only one pair of electrons are shared it is called a single bond

Chapter 6.2 – Ionic and Covalent Bonding atoms do not always share electrons equally when electrons are not shared equally the electrons spend more time near one atom than the other this gives the atoms small charges and the bond is called polar polar covalent bond – bond where electrons are shared unequally and the atoms have partial positive and negative charges ex. H2O, HF, NH3, HCl

Chapter 6.2 – Ionic and Covalent Bonding when atoms share electrons equally the bond is nonpolar nonpolar covalent bond – bond where electrons are shared equally and the atoms are not partially charged ex. H2, Cl2, N2, CH4, CO2

Chapter 6.2 – Ionic and Covalent Bonding Metals form metallic bonds – bonds between metal cations and the sea of electrons around them the nuclei form a closest packing structure the electrons flow around them and do not belong to any one atom there is a sea of freely moving electrons this allows metals to flex into sheets or wires without breaking very strong bonds high melting and boiling points conducts electricity well

Chapter 6.2 – Ionic and Covalent Bonding polyatomic ion – a group of covalently bonded atoms that have a charge form ionic bonds and ionic compounds with other atoms acts as a single ion in a compound polyatomic ions can be positive or negative polyatomic ions can combine with other ions or other polyatomic ions

Chapter 6.2 – Ionic and Covalent Bonding when more than one of a specific polyatomic ion appears in a compounds name put parentheses around (NH4)2S Al2(SO4)3 Fe3(PO4)2 the charge of a polyatomic ion applies to the whole ion many polyatomic ions have oxygen in them polyatomic ions with many oxygen atoms end with –ate polyatomic ions with few oxygen atoms end with -ite