Chemical Bonds

Quick review: Lewis (electron)Dot

A) What is a Lewis dot diagram• A way to represent the potential reactivity of

an atom without drawing the entire electron arrangement

• A diagram showing the number of valence electrons for an element’s atom

FChemical Symbol

Each dot represents a valence electron

B) How do you know how many valence electrons?

• Look at the group number• Groups 1 and 2, use their number• Groups 13-18, subtract 10 from their number

F 7 dotsFluorine = group 17 Group 7a

Lewis Symbols

TransitionMetals

Bonding Notes

• Why bond?– Want to fill their outer energy level (octet rule)

– Want to be like the noble gases (they have full energy levels!!)

What are Chemical Bonds

Attraction between two or more atomsInteraction between valence electronsIonic bondsCovalent bondsMetallic Bonds

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Ionic Bonds

• Definition: bond formed between a metal and a non-metal

– If an atom gains or loses an electron it becomes an ion

• An Ion is an atom with a charge (+ or -)• Metals have a tendency to LOSE electrons

(become positively charged).

Why?• Why would an atom want to lose or gain

electrons?– Want to have full outer energy levels– If an atom only has 1 electron in its outer level,

then by losing that electron, its “new” outer level will be full

– If an atom only needs 1 electron to be full then it will gain 1 electron

Li Li

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Examples• Sodium only has 1 electron in its outer

energy level– by losing this electron its “new” energy level

will be full– By losing an electron it loses a negative

charge, thus becoming slightly positive

Examples

• Fluorine only has 7 electrons in its outer energy level– by gaining an electron its “new” energy level

will be full– By gaining an electron it becomes slightly

negative

Examples

• What is Sodium gave it’s electron to Flourine?

• They would make an Ionic bond.

Na F Na+

F-Na F Na+

F-

Losing or Gaining more than 1?

• Elements can gain or lose as many electrons as needed to make their outer energy level full– Magnesium wants to lose 2 electrons

• Mg Mg2+

– Oxygen wants to gain 2 electrons• O O2-

– What happens?• Mg2+O2- making MgO

A general rule

• Groups 1, 2, and 13 like to lose electrons

• Groups 15, 16, and 17 like to gain electrons

Covalent Bonds

• Some atoms are unlikely to gain or lose electrons– Carbon has 4 electrons in its outer energy

level, it would either need to gain 4 or lose 4, how could it ever decide?

– Atoms that don’t gain or lose electrons become more stable by sharing electrons

• A covalent bond is a bond formed between a nonmetal and another nonmetal.

Example

:..

..F:

..

..F: :

..

..F

..

..F:

Now each fluorine has eight electrons around it.

2 fluorine atoms

Example

H:H H H

The shared electrons pair is a

Covalent Bond

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