Chapter 19Chapter 19

Chemical BondsChemical Bonds

Lesson 1Lesson 1

Chemical BondChemical Bond

• Strong attractive force between atoms or ions in a molecule or compound.

• Formed by:– transferring e- (losing or gaining)

– sharing e-

PropertiesProperties

• Compounds formed – Properties aren’t anything

like those of the individual elements.

• Sodium chloride – a compound made from the

elements sodium and chlorine.

Chemical FormulasChemical Formulas

• chemical formula – elements that make up a compound and the

exact number of atoms of each element in a unit of the compound

• H2O

– contains the symbols H for the element hydrogen and O for the element oxygen.

FormulasFormulas

• Subscript – means “written

below”– tells how many

atoms of that element are in a unit of the compound.

– no subscript the unit contains only one atom of that element

Atomic StabilityAtomic Stability

• electric forces– oppositely charged electrons and

protons hold atoms and molecules together

– the forces that cause compounds to form.

• noble gases – unusually stable.– Compounds rarely form

– they are almost always less stable than the original atoms.

StabilityStability

• Octet Rule– most atoms form bonds in order to have

8 valence e- (This is important)

– full outer energy level– like the Noble Gases!

• Stability is the driving force behind bond formation!

Ne

The Unique Noble The Unique Noble GasesGases

• Electron dot diagrams– show only the

electrons in the outer energy level of an atom.

– Notice that eight dots surround Kr, Ne, Xe, Ar, and Rn, and two dots surround He

Energy Levels and Other Energy Levels and Other ElementsElements

• Hydrogen – contains one electron in its lone

energy level.

– has a single dot next to its symbol.

– outer energy level is not full.

• It is more stable when it is part of a compound.

Energy Levels and Other Energy Levels and Other ElementsElements

• Helium– outer energy level contains two

electrons.– already has a full outer energy level by

itself and is chemically stable.– rarely forms compounds but, by itself,

the element is a commonly used gas.

Energy Levels and Other Energy Levels and Other ElementsElements

• Groups 13 through 17, – Each falls short of having a stable

energy level.

Energy Levels and Other Energy Levels and Other ElementsElements

• Each group contains too few electrons for a stable level of eight electrons.

Outer Levels —Getting Their Outer Levels —Getting Their FillFill

• How does hydrogen, or any other element, trying to become stable, gain or lose its outer electrons? – combining with other atoms that also

have partially complete outer energy levels.

– As a result, each achieves stability.

Stability

• Transferring e-

• Sharing e-

Outer Levels —Getting Their Outer Levels —Getting Their FillFill

• electron dot diagram– chlorine now has a

stable outer energy level.

– Sodium had only one electron in its outer energy level

– lost to combine with chlorine in sodium chloride.

Stability Is ReachedStability Is Reached

• Look back to the next, outermost energy level of sodium.

Stability Is ReachedStability Is Reached

• atoms – gain, lose, or share electron

– an attraction forms between the atoms, pulling them together to form a compound.

• chemical bond – is the force that holds atoms together in

a compound..

Lesson Check

• How many hydrogen atoms are present in one molecule of ammonium acetate,

NH C H O 7• An ion is a positively or negatively

charged atom; an ionic bond occurs when oppositely charged ions attract each other and an equal exchange of electrons takes place.

4 2 3 2