Atomic Structure Electron Configuration, Valence Electrons, and Ions

Quick Review Energy shells hold electrons around nucleus _ _ _ _ _ _ _ 1st Shell can hold 2 electrons 2nd Shell can hold 8 electrons 3rd Shell can hold 18 electrons* *We only ever put 8 electrons in the 3rd _ _ _ _ _ _ _ _ _ Nucleus _ _ _ _ _ _ _ _ _

What Atoms Want to Do VALENCE ELECTRONS: electrons in the outermost energy shell Atoms want their outermost shell filled with as many valence electrons it can hold: 2 valence e- in the 1st shell 8 valence e- in the 2nd shell 8 valence e- in the 3rd shell Atoms will take, give, or share electrons to have the outermost shell filled 3 protons (3+) How many valence electrons? ________ 4 neutrons (0) 2 8 protons (8+) 8 neutrons (0) How many valence electrons? ________ 6

Valence Electrons Rules Rules to determine if an atom will gain or lose valence electrons If atom has 8 valence electrons... No gain or loss Is neutral (this includes helium with 2) If atom has 1-3 valence electrons… Loses them Becomes a positive (+) ion= Cation If atom has 5-7 valence electrons… Gains however many it needs to have 8 Becomes a negative (-) ion = Anion Don’t worry about atoms with exactly 4 valence electrons

Making Ions Atoms will either gain or lose valence electrons to make sure the outermost shell is full Losing or gaining valence electrons makes the atom an ion and gives it a (+) or (–) charge ION: A positively or negatively charged atom (the atom has lost or gained an electron 2 Ways to Determine the Charge... Protons – Electrons 11 protons – 10 electrons = 1+ charge 15 protons – 18 electrons = 3- charge # of valence electrons lost or gained Lost 2 valence electrons = 2+ charge Gained 1 valence electron = 1- charge

Li Li 3 7 3 7 Atom vs. Positive Ion + Neutral Lithium Atom Protons = 3 Neutrons = 4 Electrons = 3 Valence Electrons = 1 Charge = 0 3+ protons and 3- electrons Positive Lithium Ion Electrons = 2 Valence Electrons = 2 Charge = 1+ 3+ protons and 2- electrons 3 Li 3 protons (3+) 4 neutrons (0) 7 Lithium wants to get rid of its 1 valence electron so that its outermost shell is full Getting rid of a negative electron makes the atom positively charged. 3 Li + 3 protons (3+) 7 4 neutrons (0)

O O 8 16 8 16 Atom vs. Negative Ion 2- Neutral Oxygen Atom Protons = 8 Neutrons = 8 Electrons = 8 Valence Electrons = 6 Charge = 0 8+ protons and 8- electrons Negative Oxygen Ion Electrons = 10 Valence Electrons = 8 Charge = 2- 8+ protons and 10- electrons 8 O 8 protons (8+) 8 neutrons (0) 16 Oxygen wants to 2 more valence electron so that its outermost shell is full. Gaining 2 negative electrons makes the atom negatively charged. 8 O 2- 16 8 protons (8+) 8 neutrons (0)

An atom has a mass number (A) of 35. Practice Problem #1 An atom has a mass number (A) of 35. If it has 17 protons, how many neutrons does it have? 35 – 17 = 18 neutrons What is the atomic number (Z)? 17 What element would it be? Chlorine If it has 17 electrons, what would the charge on the atom be? 17 protons – 17 electrons = 0 (it is a neutral atom)

An atom has a mass number (A) of 24. Practice Problem #2 An atom has a mass number (A) of 24. If it has 12 protons, how many neutrons does it have? 24 – 12 = 12 neutrons What is the atomic number (Z)? 12 What element would it be? Magnesium If it has 10 electrons, what would the charge on the atom be? 12 protons – 10 electrons = 2+ (it is an ion)

An atom has a mass number (A) of 14. Practice Problem #3 An atom has a mass number (A) of 14. If it has 7 protons, how many neutrons does it have? 14 – 7 = 7 neutrons What is the atomic number (Z) 7 What element would it be? Nitrogen If it has 10 electrons, what would the charge on the atom be? 7 protons – 10 electrons = 3- (it is an ion)