Unit 4 - Bonding Part 1 – Ionic Bonding & Metallic Bonding

Chemical Reactivity  Octet Rule – atoms tend to bond in order to have full valence shells of electrons  Noble gases  Least reactive elements  Already have 8 valence electrons  Alkali metals & halogens  Most reactive elements  Have 1 and 7 valence electrons respectively

Octet Rule  Most electrons follow this rule and strive for 8 electrons in their valence shell  Some Exceptions:  Helium (2 electrons) – full shell already  Hydrogen – share 2 electrons  Boron – share 6 electrons  Happy atoms have full shells!!!!

Valence Electrons  Representative Elements (Group 1,2, ) have predictable valence electrons  Atoms gain or lose valence electrons to form stable ions  These ions react together to form compounds

Ions  Ion – an atom or molecule that has gained or lost one or more electron and has a negative or positive charge  Cation – positive charged ion  Anion – negative charged ion

Ionic Bonding  Happens between anions and cations (opposite charges attract)  Salt – a electrically neutral ionic compound that are made of cations and anions held together in a tightly packed structure  Ionic bonds are very strong, which is reflected in their properties

Ionic compounds  Do NOT consist of molecules like you would see in water  Consist of formula units – lowest whole number ratio of atoms in crystal structure of an ionic compound  Most are crystalline solids – component ions arranged in orderly 3-D patterns  Are electrically neutral

Ionic compounds, continued  Most conduct electric current when melted or when dissolved in water  Salts are hard and brittle  Have high boiling points & high melting points  What causes these properties?

Metallic Bonding  Metallic bond – attraction of free-floating valence electrons for the positively charged metal ions.  Valence electrons of metal atoms can be thought of as a sea of electrons; these electrons are free to move anywhere in the metal  The positive metal ions are insulated from each other by the valence electrons (picture ball bearings in oil)

Metallic Properties  Properties of metals are explained by metallic bonding  Electrically conductive: electrons are free to move from one end of the metal to the other (electrons are electricity)  Malleability and ductility: explained by the valence electrons insulating the positive ions; the ions slide past each other allowing the shape to change; unlike in ionic crystal where the pressure would push like charges toward each other - shattering