Ions & Lewis Dot

Structures

Electrons

� Valence electrons – electrons in the highest occupied energy level of an element’s atoms

� Outermost energy level

� Only the electrons in the s & p orbitals

� Remember Bohr Diagrams?

Valence Electrons� Lithium: 1s22s1

� 2 electrons in 1st energy level

� 1 electron in 2nd energy level – Highest energy level

� 1 valence electron

� Fluorine: 1s22s22p5

� 2 electrons in 1st energy level

� 7 electrons in 2nd energy level

� 7 valence electrons

� Aluminum: 1s22s22p63s23p1

� 2 electrons in 1st energy level

� 8 electrons in 2nd energy level

� 3 electrons in 3rd energy level

� 3 valence electrons

Valence Electrons

�We can also use the group number as a shortcut to determine the number of valence electrons:

� Lithium: Group 1: 1 valence electron

� Fluorine: Group 17: 7 valence electrons

� Aluminum: Group 13: 3 valence electrons

� Valence electrons are the only electrons involved in creating chemical bonds.

� Lewis Dot Structures show just the valence electrons.

Lewis Dot Structures

� Element symbol is drawn with dots surrounding it representing valence electrons.

�Move clockwise around the atom adding a dot for each electron

Lewis Dot Structures

� All elements within a group have the same valence electrons, therefore the same electron dot structure.

Octet Rule

�Octet rule - When forming compounds all elements want to achieve the electron configuration of a noble gas.

�Everyone wants 8 electrons!!!! (except H, He, Li, Be and B - they only need 2)

�During reactions:

�Metal atoms tend to LOSE electrons

�Nonmetal atoms tend to GAIN electrons.

Cation

�When a metal loses an electron, it forms a cation.

� Cation - positively charged ion

� Na· � Na+ + e- Sodium Ion

� 11 protons (+)

� 10 electrons (-)

� · Mg· � Mg2+ + 2e- Magnesium Ion

� 12 protons (+)

� 10 electrons (-)

+1

+2

Anion

� When a nonmetal gains an electron, it forms an anion.

� Anion - negatively charged ion

� + e-�

� 17 protons (+)

� 18 electrons (-)

� + 2e- �

� 8 protons (+)

� 10 electrons (-)

-1

-2

Isoelectronic

� Isoelectronic – two atoms/ions that have the same electron configuration

� Cl-1 – 1s22s22p63s23p6

� Ar - 1s22s22p63s23p6

� Ca2+ - 1s22s22p63s23p6

� F-1 – 1s22s22p6

� Ne - 1s22s22p6

� Na+1 - 1s22s22p6