M OLECULAR AND I ONIC C OMPOUNDS Pgs

C HEMICAL C OMPOUNDS Compound: made of elements that are chemically combined in specific proportions 2 types: Molecular compounds Ionic compounds

M OLECULAR C OMPOUNDS Definition: a compound formed of atoms of two or more elements that share electrons Atoms of non-metals join together as molecules Properties: Most boil and melt at relatively low temperatures Although the bonds that hold the atoms together are strong, the bonds that attract the molecules together are relatively weak Most are relatively soft Relatively poor conductors of electricity and heat

M OLECULES Definition: particle formed by two or more atoms joined by covalent bonds Smallest independent unit of a molecular compound

E LECTRONS Elements give or share electrons from their electron shells (they will give/share their valence electrons) Electron shells: 1 st shell: 2 electrons 2 nd shell: 8 electrons 3 rd shell: 8 electrons

C OVALENT B ONDS Form when atoms share electrons Think tug-of-war

C OVALENT B ONDS H 2 O - water HCl - hydrogen chloride CO 2 - carbon dioxide

I ONIC C OMPOUNDS Definition: a compound composed of oppositely charged ions held together with ionic bonds What is an ion? An atom or group of atoms with a positive or negative charge A positive charged ion is called a cation A negative charged ion is called an anion

I ONIC B ONDS Properties Very strong bonds (due to the lattice structure of the ion) Have very high melting and boiling points Do not conduct electricity in a solid state Ions are held rigidly in place not allowing for this However when dissolved in liquid or melted they conduct electricity (as ions are free to move around)

I ONIC B ONDS Ionic compounds of 2 elements form when atoms of one element lose 1+ electrons to atoms of the second element. When an atom loses an electron it becomes positive (why?) When an atom gains an electron it becomes negative.

I ONIC B ONDS NaBr - sodium bromide KI - potassium iodide CaCl 2 - calcium chloride