What is a Chemical What is a Chemical Bond?Bond?

A chemical bond is a force holding A chemical bond is a force holding two or more atoms together to form two or more atoms together to form a molecule.a molecule.

Why do atoms form Why do atoms form chemical bonds?chemical bonds?Atoms tend to form chemical bonds to Atoms tend to form chemical bonds to satisfy the “octet rule”satisfy the “octet rule”

Atoms share or transfer their valence Atoms share or transfer their valence electrons to fill their outermost electrons to fill their outermost energy level; either 2 (for hydrogen) energy level; either 2 (for hydrogen) or 8 electrons.or 8 electrons.

There are three types There are three types of chemical bonds we of chemical bonds we will studywill study

Ionic bondsIonic bonds

Covalent bondsCovalent bonds

Hydrogen bondsHydrogen bonds

Ionic Bonds: Ionic Bonds: Give & TakeGive & TakeIonic bonds form when atoms transfer (lose Ionic bonds form when atoms transfer (lose or gain) electrons with other atoms. or gain) electrons with other atoms.

Atoms with 5, 6,or 7 valence electrons Atoms with 5, 6,or 7 valence electrons tend to gain electrons to fill their outer tend to gain electrons to fill their outer shells . Gaining electrons makes the atom shells . Gaining electrons makes the atom a negative ion .a negative ion .

Atoms with 1, 2 or 3 valence electrons Atoms with 1, 2 or 3 valence electrons tend to lose electrons . Losing electrons tend to lose electrons . Losing electrons makes the atom a positive ion. makes the atom a positive ion.

Examples of Ionic Examples of Ionic BondsBondsIonic bonds form easily between the Ionic bonds form easily between the group 1 metals and the group 17 non-group 1 metals and the group 17 non-metalsmetals

These new ionic compounds are known as These new ionic compounds are known as metallic salts.metallic salts.

Sodium Chloride is a good example of an Sodium Chloride is a good example of an Ionic CompoundIonic Compound

Sodium Chloride is an Ionic Sodium Chloride is an Ionic CompoundCompound

Sodium (Na) has 1 valence electron in its Sodium (Na) has 1 valence electron in its third energy orbitalthird energy orbital

Chlorine (Cl) has 7 valence electrons in its Chlorine (Cl) has 7 valence electrons in its third energy level third energy level

They form an ionic compound when Sodium’s They form an ionic compound when Sodium’s electron is transferred to Chlorineelectron is transferred to Chlorine

Now Sodium is a 1+ ion and Chlorine is a 1- Now Sodium is a 1+ ion and Chlorine is a 1- ion. Their opposite charges keep them ion. Their opposite charges keep them attracted to each otherattracted to each other

Overall, the compound is electricallyOverall, the compound is electrically neutral.neutral.

Other examples of Ionic Compounds include Other examples of Ionic Compounds include rust, baking soda and limestonerust, baking soda and limestone

Properties of Ionic Properties of Ionic CompoundsCompounds

Crystal Shaped SolidsCrystal Shaped Solids

High Melting PointsHigh Melting Points

Electrical ConductivityElectrical Conductivity

Covalent Bonds: Covalent Bonds: Good at SharingGood at Sharing

Covalent bonds are Covalent bonds are formed when 2 or more formed when 2 or more atoms SHARE their atoms SHARE their valence electronsvalence electrons

Usually formed between Usually formed between two non-metals: oxygen, two non-metals: oxygen, carbon and nitrogen like carbon and nitrogen like to form covalent bondsto form covalent bonds

Atoms with exactly half Atoms with exactly half ( 1 or 4 electrons) of ( 1 or 4 electrons) of their valence electrons their valence electrons like to form covalent like to form covalent bonds.bonds.

Drawing a covalent Drawing a covalent bondbondDraw a molecule of Draw a molecule of methane. methane.

Start with 1 Start with 1 carbon atom (in carbon atom (in middle)middle)

Add the correct Add the correct number of hydrogen number of hydrogen atoms needed to atoms needed to form covalent form covalent bonds that satisfy bonds that satisfy the octet rule.the octet rule.

Properties of Covalently Properties of Covalently Bonded MoleculesBonded Molecules

• Low melting pointLow melting point

• PPoor Conductors of oor Conductors of electricityelectricity

• Typically form Typically form “organic” compounds “organic” compounds like fats, proteins like fats, proteins & carbohydrates& carbohydrates

Polar vs Non-polar Polar vs Non-polar Covalent Bonds:Covalent Bonds:Oil & Water don’t mixOil & Water don’t mixSome atoms tend to pull harder on the Some atoms tend to pull harder on the shared electrons in a covalently shared electrons in a covalently bonded molecule.bonded molecule.

This creates a positive side and a This creates a positive side and a negative side of the molecule.negative side of the molecule.

We call these kinds of molecules We call these kinds of molecules “polar”, because the electrons are “polar”, because the electrons are shared unequally, creating a molecule shared unequally, creating a molecule with positively charged pole and a with positively charged pole and a negatively charged polenegatively charged pole

Water is a good example of a polar Water is a good example of a polar molecule. Many molecules important to molecule. Many molecules important to living things are polar and dissolve living things are polar and dissolve easily in water.easily in water. ++

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Hydrogen Bonds: Hydrogen Bonds: “Opposites attract”“Opposites attract”Hydrogen bonds form Hydrogen bonds form betweenbetween two nearby water moleculestwo nearby water molecules

The negatively charged The negatively charged oxygen end of one water oxygen end of one water molecule is attracted to molecule is attracted to the positively charged the positively charged hydrogen end of another.hydrogen end of another.

Hydrogen bonds cause many Hydrogen bonds cause many unique properties of water: unique properties of water: it’s “stickiness” to it’s “stickiness” to itself, its ability to itself, its ability to dissolve all other polar dissolve all other polar substances easily, its substances easily, its ability to remain a liquid ability to remain a liquid at a wide range of at a wide range of temperatures.temperatures.

Non-polar moleculesNon-polar moleculesMolecules which Molecules which share their share their electrons equally electrons equally are non-polar.are non-polar.

Oils and fats are Oils and fats are non-polar. Their non-polar. Their molecules don’t have molecules don’t have an overall “charge”.an overall “charge”.

That’s why oil & That’s why oil & water don’t mix. water don’t mix. They’re not They’re not attracted to each attracted to each other.other.

So: How does soap So: How does soap clean?clean?Soap has a polar “head” and a Soap has a polar “head” and a

non-polar “tail”non-polar “tail”

The polar head is attracted to The polar head is attracted to water & the non-polar tail is water & the non-polar tail is

attracted to dirty oilsattracted to dirty oils

Each oil molecule is surrounded Each oil molecule is surrounded by a ring of soap moleculesby a ring of soap molecules

WWhen the water is washed away, ithen the water is washed away, it carries an oil molecule with it carries an oil molecule with it