Ch. 20 Chemical BondsCh. 20 Chemical Bonds

Stability in BondingStability in Bonding

Ch. 20 Section 1Ch. 20 Section 1

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are now on Chapter 20, Section 1 (page 602 in your book). Please get started on are now on Chapter 20, Section 1 (page 602 in your book). Please get started on the Bell Work quietly.the Bell Work quietly.

1). Explain why some elements are stable on their own while others are 1). Explain why some elements are stable on their own while others are more stable in compounds?more stable in compounds?

2). Describe why chemical bonding occurs. Give two examples of how 2). Describe why chemical bonding occurs. Give two examples of how bonds can form.bonds can form.

3). Compare and contrast the properties of the individuals elements that 3). Compare and contrast the properties of the individuals elements that combine to make salt with the compound salt. (NaCl)combine to make salt with the compound salt. (NaCl)

AnswersAnswers

1). If an element has eight electrons in its outer electron 1). If an element has eight electrons in its outer electron energy level, it has a tendency not to react.energy level, it has a tendency not to react.

2). Electrons are either gained, lost, or shared between 2). Electrons are either gained, lost, or shared between atoms.atoms.

3). Sodium, as an elements, is a solid metal. Chlorine is 3). Sodium, as an elements, is a solid metal. Chlorine is a gas. When the two combine to form sodium chloride, a gas. When the two combine to form sodium chloride, they form a solid compound.they form a solid compound.

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Sodium is in group one of the periodic Sodium is in group one of the periodic table. A sodium atom has one table. A sodium atom has one valence valence electronelectron. Atoms with one electron in their . Atoms with one electron in their outer energy levels will bond easily with outer energy levels will bond easily with atoms having 7 valence electrons. Name atoms having 7 valence electrons. Name one element sodium could give its one one element sodium could give its one extra electron to.extra electron to.

Combining ElementsCombining Elements

Many elements exist around you in their Many elements exist around you in their uncombined forms, but elements can unite uncombined forms, but elements can unite chemically to form compounds when chemically to form compounds when conditions are rightconditions are right

Combining ElementsCombining Elements

CompoundsCompounds often often have properties have properties unlikeunlike the properties of their the properties of their individual elementsindividual elements

Combining ElementsCombining Elements

A A Chemical FormulaChemical Formula tells what elements a tells what elements a compound contains compound contains and the exact number and the exact number of atoms of atoms of each of each element in a unit of element in a unit of the compoundthe compound

Combining ElementsCombining Elements

A A subscriptsubscript is written is written after and below after and below the the elementelement’’s symbols symbol

Subscripts Subscripts tell how many atoms tell how many atoms are in are in each unit of a compoundeach unit of a compound

NH3

Atomic StabilityAtomic Stability

An atom is chemically An atom is chemically stablestable when its outer energy level is when its outer energy level is completecomplete (like the Noble (like the Noble Gases)Gases)

Other elements are more Other elements are more stable when they can complete stable when they can complete their outer energy levels by their outer energy levels by becoming part of a compoundbecoming part of a compound

Atomic StabilityAtomic StabilityThe The Octet RuleOctet Rule says that atoms tend to says that atoms tend to

combine so they have 8 electrons in their combine so they have 8 electrons in their outer energy levelouter energy level

Atoms can gain, lose, or share Atoms can gain, lose, or share electrons to complete their outer electrons to complete their outer energy levels and become stableenergy levels and become stable

Gaining, losing, and Gaining, losing, and sharing electrons sharing electrons forms an forms an attractionattraction between atomsbetween atoms

Atomic StabilityAtomic Stability

The attraction is called The attraction is called a a Chemical BondChemical Bond, , and atoms are pulled and atoms are pulled together, forming a together, forming a compoundcompound

Atomic StabilityAtomic Stability Generally, ionic bonds Generally, ionic bonds

are formed between a are formed between a metal and a nonmetal, metal and a nonmetal, and covalent bonds and covalent bonds are formed between are formed between two or more two or more nonmetalsnonmetals

Electronegativity is the ability Electronegativity is the ability of atoms to attract electrons of atoms to attract electrons within a bond – this within a bond – this determines the bond typedetermines the bond type