 Valence electrons: Electrons in the highest energy level  These electrons are the ones that bond!!  The group A # matches how many valence electrons

Group ## of valence electrons 1 or 1A1 2 or 2A2 13 or 3A3 14 or 4A4 15 or 5A5 16 or 6A6 17 or 7A7 18 or 8A8 Group # of valence electrons equal to group number - 10

 Octet rule: atoms will gain or lose electrons to have a full energy level (8 electrons)  Period number responds to how many energy levels an atom has

 ION: an atom that lost or gained electrons  Cation: metal atom that loses e - ( + )  Anion: nonmetal atom that gain e - ( - )

(cation is positive: metals)

 There are 4 trends of the periodic table you will need to know  Ionic Size  Atomic Size  Electronegativity  Ionization Energy  Need to know how AND why they trend the way they do.

 Cations are smaller than their neutral atoms  Because they lost an electron and energy level  Anions are larger than their neutral atoms  Because they gain electrons (which repulse one another)

 Ex 1: Which is larger?  Mg or Mg 2+  Ans: Mg  Ex 2: Which is larger?  S or S 2-  Ans: S 2-

 The size of the atom

 Atomic size increases as you move:  from right to left in a period  from top to bottom in a group  Francium has the largest size Fr

 Going from Left to Right  Gets smaller because you add more protons to nucleus and then pull in the electrons  Going Down  Gets larger because you add energies

 Ex. 1: Arrange the following elements in order of their decreasing size.  P(15), Mg(12), S(16)  Ans: Mg,P, S

 Electronegativity is a measure of the ability of an atom to attract electrons from another atom

 Electronegativity increases as you move:  from left to right across a period  from bottom to top in a group  Fluorine (9) is the most electronegative element F

Electronegativity is opposite of atomic size, because the smaller the atom…the more electrons are attracted to the nucleus

Why are the noble gases not on here??!

 Arrange the following in order of their increasing electronegativity.  Rb(37), I(53), Sn(50)  Ans: Rb, Sn, I

 The ionization energy is the energy needed to remove an electron from a gaseous atom.  The higher ionization energy, the harder it is to pull off electrons

 Ionization energy increases as you move:  from left to right across a period  from bottom to top in a group  Helium (2) has the highest ionization energy He

 Reason: The smaller the atom, the closer electrons are to nucleus so higher the ionization energy

 Arrange the following in order of increasing ionization energy.  He(2), Xe(54), Ar(18)  Ans: Xe, Ar, He

 Metal reactivity increases as you move:  right to left across a period  top to bottom in a group  Francium (87) is the most reactive metal Fr

 Non-metal reactivity increases as you move:  left to right across a period  bottom to top in a group  Fluorine (9) is the most reactive non-metal F

 Ex. 1: Which is more reactive?  Fe(26) or Co(27)  Ans: Fe  Ex. 2: Which is less reactive?  Cl(17) or F(9)  Ans: Cl