chapter 19 chemical bonds lesson 1. chemical bond strong attractive force between atoms or ions in a...
TRANSCRIPT
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