Compounds

Ionic Compounds

• made by combination of metal and nonmetal

• metal loses electrons – forms cation• nonmetal gains electrons – forms

anion• consider Na and S

– Na+ and S2- ions formed– pack together to make compound Na2S

Ionic Compounds

• can contain polyatomic ions• like (NH4)+

• consider (NH4) + and S2- ions formed– pack together to make compound

(NH4)2 S

+

NaCl Crystal Lattice

Properties of Ionic Compounds

• high melting point• hard but brittle• cleave with flat edges• when dissolve in water, dissolves

as ions• Conductors when melted or

dissolved in water

Cleave1.mov

Covalent (Molecular) Compounds

• made by combination of nonmetals only

• made by “sharing” electrons• make molecules…fundamental

particle of compound

Example of a Molecule - Water

If have water, have water molecules

Pure and Polar Covalent Bonds

are electrons shared equally?

H – H and F - F

H - Cl

pure covalent bond

polar covalent bond

Electronegativity: A Measure of Polarity

Electronegativity and Bonds

• Using electronegativities, arrange the following bonds in order of increasing polarity and identify the shift of the electrons: C – N, O – H, and H – Cl.

Bond EN EN

C - N C 2.5 N 3.0

O – H O 3.5 H 2.1

H - Cl H 2.1 Cl 3.0

Electronegativity and Bonds

• Without using the numbers in the electronegativity scale, determine which would be more ionic LiF or BF3?