Chemical Bonds and Chemical Bonds and CompoundsCompounds

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Elements combine to form Elements combine to form compoundscompounds

Compounds have different properties Compounds have different properties from the elements that make themfrom the elements that make them

Atoms of different elements are held Atoms of different elements are held together by chemical bondstogether by chemical bonds

Bonds help to determine the Bonds help to determine the properties of a compoundproperties of a compound

Properties of CompoundsProperties of Compounds Depend on atoms Depend on atoms

in the compoundin the compound

Depend on how the Depend on how the atoms are atoms are arranged in the arranged in the compoundcompound

Example:Example:• C and H combine to C and H combine to

form natural gas, form natural gas, auto gas, waxes in auto gas, waxes in candle, plastics…candle, plastics…etc.etc.

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Properties of Compounds are different Properties of Compounds are different than the elements that make themthan the elements that make them

HH22O (water) O (water) • H and O are colorless gases H and O are colorless gases

at room temperatureat room temperature• Water is a liquid at room Water is a liquid at room

temperaturetemperature

NaCl (salt)NaCl (salt)• Na is a metallic solidNa is a metallic solid• Cl is a greenish-yellow gas Cl is a greenish-yellow gas

that is poisonousthat is poisonous• Table salt (NaCl) is used to Table salt (NaCl) is used to

flavor and preserve foodsflavor and preserve foods

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Atoms combine in predictable Atoms combine in predictable numbersnumbers

A given compound A given compound always contains atoms always contains atoms of elements in a specific of elements in a specific ratioratio

Ammonia NHAmmonia NH3 3 always always has a 1:3 ratio of has a 1:3 ratio of Nitrogen to HydrogenNitrogen to Hydrogen

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Chemical FormulaChemical Formula

Chemical Formula:Chemical Formula: uses the chemical uses the chemical symbols to represent symbols to represent the atoms of the the atoms of the elements and their elements and their ratios in the chemical ratios in the chemical compound. Hcompound. H22O 2:1 O 2:1 ratio of H to O ratio of H to O

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Chemical Bonds hold Compounds Chemical Bonds hold Compounds TogetherTogether

Chemical bonds Chemical bonds are the “glue” that are the “glue” that holds the atoms of holds the atoms of elements togetherelements together

Chemical bonds Chemical bonds form when the form when the electrons in the electrons in the electron clouds electron clouds interactinteract

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Atoms can transfer electronsAtoms can transfer electrons

Ions are formed when atoms gain or Ions are formed when atoms gain or lose electronslose electrons

Gaining electrons = negative charge Gaining electrons = negative charge

Losing electrons= positive chargeLosing electrons= positive charge

An elements location on the periodic An elements location on the periodic table gives a clue as to the type of ions table gives a clue as to the type of ions the atoms of that element will formthe atoms of that element will form

Group 1 metals (Li, Na, K…) usually lose Group 1 metals (Li, Na, K…) usually lose one electron to form positive ions.one electron to form positive ions.

Group 2 metals (Be, Mg, Ca…) usually Group 2 metals (Be, Mg, Ca…) usually lose two electrons to form positive ions.lose two electrons to form positive ions.

Group 17 nonmetals (F, Cl, Br…) gain one Group 17 nonmetals (F, Cl, Br…) gain one electron to form ions with a 1- charge. electron to form ions with a 1- charge.

Group 16 nonmetals (O, S, Se…) gain two Group 16 nonmetals (O, S, Se…) gain two electrons to form ions with a 2- charge. electrons to form ions with a 2- charge.

Group 1Group 1

Group 1 lose e-Group 1 lose e- Group 17 gains 1 e-Group 17 gains 1 e- Group 2 lose 2e-Group 2 lose 2e- Group 16 gains 2 e-Group 16 gains 2 e-

Ionic BondsIonic Bonds

The force of attraction between positive The force of attraction between positive and negative ions.and negative ions.

Particles with opposite electrical charges Particles with opposite electrical charges attract each otherattract each other

Atom from element group 1 (1+) Atom from element group 1 (1+) combines with an atom from element combines with an atom from element group 17 (1-) to form an ion.group 17 (1-) to form an ion.

Example Na combines with Cl Example Na combines with Cl • Na loses 1 electron and Cl gains the Na loses 1 electron and Cl gains the

electronelectron• Creating an ionic bondCreating an ionic bond

Ionic compoundsIonic compounds

Ionic bonds form between all nearby Ionic bonds form between all nearby ions of opposite charge.ions of opposite charge.

Ionic compounds are very stable and Ionic compounds are very stable and their crystals are very strong.their crystals are very strong.

The shape of the crystals formed The shape of the crystals formed depends on the ratio of positive to depends on the ratio of positive to negative ions and the sizes of the negative ions and the sizes of the ionsions

Names of Ionic CompoundsNames of Ionic Compounds

First, take the name of the positive metal First, take the name of the positive metal elementelement

Second, take the name of the negative, Second, take the name of the negative, nonmetal element and give it an –ide nonmetal element and give it an –ide endingending

Third, combine the two namesThird, combine the two names Example: BaIExample: BaI22 1: barium1: barium 2: Iodine…add ide…Iodide2: Iodine…add ide…Iodide 3: barium iodide3: barium iodide

Covalent BondsCovalent Bonds

A pair of A pair of sharedshared electrons between electrons between atoms.(prefix atoms.(prefix co-co- means partner) means partner)

Neither atom gains or loses an electronNeither atom gains or loses an electron The shared electrons are attracted to both The shared electrons are attracted to both

positively charged nuclei. (nucleus has a positively charged nuclei. (nucleus has a positive charge because of protons)positive charge because of protons)

A covalent bond is represented by a line A covalent bond is represented by a line between the two atomsbetween the two atoms

II22

I-II-I

Covalent BondCovalent Bond

The number of covalent bonds that The number of covalent bonds that an atom can form depends on the an atom can form depends on the number of electrons that it has number of electrons that it has available for sharing.available for sharing.• Atoms of Group 16 (O,S…)can form two Atoms of Group 16 (O,S…)can form two

covalent bonds. covalent bonds. • Atoms of group 15 (N,P…) can form Atoms of group 15 (N,P…) can form

three bondsthree bonds• Atoms of group 14 (C, Si…)can form four Atoms of group 14 (C, Si…)can form four

bondsbonds

Valence ElectronsValence Electrons Valence electrons: are the electrons in the Valence electrons: are the electrons in the

outer electron cloud. outer electron cloud. Electrons orbit in shells: 2, 8, 18, 32, 50Electrons orbit in shells: 2, 8, 18, 32, 50

(Inner shell is 2, next shell has 8 (Inner shell is 2, next shell has 8 electrons…)electrons…)

A quick way to determine the number of A quick way to determine the number of valence electrons for a representative valence electrons for a representative element is to look at which group it is in.  element is to look at which group it is in. 

Elements in group 1 have 1 valence Elements in group 1 have 1 valence electron.  electron. 

Elements in group 2 have 2 valenceElements in group 2 have 2 valence

Finding Valence ElectronsFinding Valence Electrons For example:For example: Sodium has an Atomic Number of Sodium has an Atomic Number of

11 11 This means an atom of Sodium has This means an atom of Sodium has

11 Protons 11 Protons and therefore 11 electrons. and therefore 11 electrons.

The electrons are arranged as: The electrons are arranged as: • First Shell = 2, First Shell = 2, • Second Shell = 8, Second Shell = 8, • Third Shell = 1 Third Shell = 1 • (Giving a total of 11.) (Giving a total of 11.)

(2+8+1=11)(2+8+1=11)

Na has 1 valence electron and is in Na has 1 valence electron and is in group 1group 1

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Chemical Bonds Give all Materials Chemical Bonds Give all Materials their Structuretheir Structure

Ionic Compounds (losing/gaining e-)Ionic Compounds (losing/gaining e-)• Most have a crystal structureMost have a crystal structure• Solid at room temperatureSolid at room temperature• High melting and boiling points (takes a High melting and boiling points (takes a

lot of energy to break the bond)lot of energy to break the bond)• Hard, brittle, good conductors of Hard, brittle, good conductors of

electricity once the ions are separatedelectricity once the ions are separated• Dissolve easily in waterDissolve easily in water

Chemical Bonds Give all Materials Chemical Bonds Give all Materials their Structuretheir Structure

Covalent Compounds (sharing valence e-)Covalent Compounds (sharing valence e-)• Exist as individual moleculesExist as individual molecules• Chemical bonds give each molecule a specific Chemical bonds give each molecule a specific

three-dimensional shapethree-dimensional shape• Molecular shape can affect properties of the Molecular shape can affect properties of the

compounds compounds • Melt and boil at lower temperatures (takes less Melt and boil at lower temperatures (takes less

energy to break up because atoms are energy to break up because atoms are organized as individual molecules)organized as individual molecules)

Metals have unique Metals have unique bondsbonds

Metallic bondMetallic bond: the equal sharing of electrons in all : the equal sharing of electrons in all directions so electrons move easily among the directions so electrons move easily among the atoms of the metalatoms of the metal

Atoms can slide past one another in metallic bonds Atoms can slide past one another in metallic bonds which allows for easy shapingwhich allows for easy shaping

Properties of metals depend on bondsProperties of metals depend on bonds• Good conductors of electric currentGood conductors of electric current• High melting pointHigh melting point• Solid at room temperature (except Hg)Solid at room temperature (except Hg)• Easily shaped and poundedEasily shaped and pounded

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