Electrons and Ions Unit 3

Electron Energy Levels  What are electrons and where are they located?  Small negatively charged particles  Located in the orbitals  Energy level determines electrons energy  Can move from one energy level to another  Absorb energy = jump to higher level  Give off energy = jump to lower level

What are Valence Electrons?  Definition:  Electrons found in the outer energy level of an atom  Can participate in interactions with other atoms  Determine properties of atoms  Atoms are most stable when outermost energy level is full  Which atom pictured below would be most stable?

How do you determine valence electrons?  Valence electrons increase across periods from left to right  All elements in the same group have the same number of valence electrons

How can you represent valence electrons?  Electron dot diagrams are used to represent valence electrons  An elements chemical symbol is surrounded by dots that represent valence electrons  Elements have a maximum of 8 valence electrons

How do valence electrons determine reactivity?  Elements in groups 1, 2, 6 and 7 are highly reactive  Elements in group 1 and 2 want to give up their valence electrons to become stable  Elements in groups 6 and 7 want to gain valence electrons to become stable  Elements in group 8 (noble gases) have full outer shell of electrons and are very stable/non-reactive

What are ions?  Why are atoms electrically neutral?  Equal numbers of protons and electrons  When atoms gain or lose valence electrons they become charged  Definition:  Ions are atoms that have positive or negative charge due to unequal numbers of protons and electrons

How can you tell the charge of an ion?  Ions charge is identified by their group (column) number

Ions  When atoms lose valence electrons they become positively charged  Have more protons than electrons  Called “Cations”  When atoms gain valence electrons they become negatively charged  Have more electrons than protons  Called “Anions”