Types of Chemical Bonds

Objectives•Explain why atoms join to form bonds.

•Explain why some atoms transfer their valence electrons to form ionic bonds, while other atoms share valence electrons to form different bonds.

•Differentiate between ionic, covalent, and metallic bonds.

•Compare the properties of substances withdifferent types of bonds.

Why do atoms bond??

• Atoms bond to be more stable!!

• Atoms join to form bonds so that each atom has a full outermost energy level.

• What is the number of electrons that atoms want to have in their outermost shell?

Ionic Bonds•Ionic bonds are

formed between oppositely charged ions.

Ionic bonds are formed by the transfer of electrons

•As shown at right, ionic compounds are in the form of networks, not molecules.

Conductivity of Ionic Substances

•Solid ionic compounds do not conduct electricity because the charged ions are locked in place.

•When melted or dissolved in water, the ions are then free to move, and will conduct electricity.

Covalent BondsCovalent bonds are formed by the

sharing of electrons between atoms

Conductivity of Covalent Bonds-Covalent bonds are poor conductors of

electricity

Types of Covalent Bonds

•Bonds in which atoms share electrons equally are called nonpolar covalent bonds, as shown below.

•Non-polar covalent bonds are formed between atoms of the same element

Types of Covalent Bonds•Atoms do not always share electrons equally.

•An unequal sharing of electrons forms a polar covalent bond.•Polar covalent bonds are formed between atoms of different elements

Can there be more than one bond (shared pair of electrons) between two atoms??

• Totally!! • When 2 atoms in a molecule share two pairs

of electrons, it is called a double bond• When 2 atoms in a molecule share three pairs

of electrons, it is called a triple bond

Metallic Bonds•A metallic bond is a bond formed by the

attraction between positively charged metal ions and the electrons around them.

•Electrons move freely between metal atoms.

•Because electrons can movefrom atom to atom, metals:• conduct electricity• conduct heat

Check it out!!

• https://www.youtube.com/watch?v=QIfTT-_-xLo

• https://www.youtube.com/watch?v=_M9khs87xQ8

Conductivity

• What type of bond, when dissolved in water, dissociates into ions and conducts electricity??

• In what situation will electricity be conducted? When charged particles are locked in place or when they are free to move?

• Let’s test it!

How does the structure of a substance affect its properties??

• Very strong bonds are harder to break and require a higher temperature to melt and to boil.

• Substances with weaker bonds between atoms are easier to break and so they require____________ (higher/lower) temperatures to melt and to boil.

Ionic substances and boiling point

• Ionic compounds are held together by very strong bonds (attractions) between ions

• Therefore, they require very __________ (high/low) temperatures to break these bonds and melt

Compared to ionic, molecular substances..

• Bonds between atoms of molecular (covalent) substances are much weaker so they require _____________ (more/less) heat to break bonds and melt, as compared to ionic substances

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How Does Structure of Atoms Affect Properties?•Compounds with network

structures are strong solids.

• Example: Quartz is made of silicon and oxygen atoms bonded in a strong, rigid structure:

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Copyright © by Holt, Rinehart and Winston. All rights reserved.

How Does Structure Affect Properties?•Compounds made of networks of bonded ions

have high melting points and boiling points.

• Example: Table salt—sodium chloride—is made of a tightly packed repeating network of positive sodium ions and negative chlorine ions.

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So, which substance is easier to melt??

• A molecular substance• An ionic substance

To answer this question, consider the structure of each and the strength of bonds between atoms