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 F Chemical 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 dots Fluorine = group 17 Group 7a

Lewis Symbols Transition Metals

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 atoms Interaction between valence electrons Ionic bonds Covalent bonds Metallic Bonds Don’t need to copy this slide

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 Don’t need to copy this slide

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. NaF Na + F-F- NaF Na + F-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  Mg 2+ –Oxygen wants to gain 2 electrons O  O 2- –What happens? Mg 2+ O 2- 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 Now each fluorine has eight electrons around it.

2 fluorine atoms

Example The shared electrons pair is a Covalent Bond Don’t need to copy this slide