Molecular Compounds

Objectives Distinguish between the melting points and boiling points of molecular compounds and ionic compounds Describe the information provided by a molecular formula

Important Vocabulary Covalent bond Molecule Diatomic molecule Molecular compound Molecular formula

Molecules Matter takes may forms in nature Noble gas elements exist as single atoms (monatomic) Some atoms of elements form salts that are crystalline solids with high melting points Many atoms form molecules, which are neutral groups of atoms joined together by covalent bonds A covalent bond is formed when two atoms share electrons

Sharing Electrons Takes place between neutral atoms within covalent compounds Attractive and repulsive forces must be equal for a bond to form The simplest example of this is found in diatomic molecules, which are molecules consisting of two atoms What seven elements are diatomic? HINT: HI BrONClF

Molecular Compounds Molecular compounds are composed of molecules The molecules of a given molecular compound are all the same For example: water (dihydrogen oxide) & carbon monoxide They are also known as covalent compounds because they form covalent bonds

Molecular Compound Properties Molecular compounds tend to have relatively lower melting and boiling points Most are liquids or gases at room temperature Most molecular compounds are composed of atoms of two or more nonmetals

Ionic Compounds vs. Covalent Compounds

Molecular Formulas A molecular formula is the chemical formula of a molecular compound A molecular formula shows how many atoms of each element a molecule contains For example: A water molecule consists of 2 hydrogen atoms and 1 oxygen atoms, so its molecular formula is H2O What doesn’t a molecular formula tell us?

Practice How many atoms of each? C2H6 CO2 CCl4