1. Atomic Structure
BASIC INFORMATION

3. About Atoms….. atomic number = # protons atoms are made up of:
protons (+ charge)
neutrons (no charge)
electrons (- charge)
atomic number = # protons
Lithium’s atomic # is 3
atomic mass = # protons + # neutrons
Lithium’s atomic mass is 6.94 (round to 7)
in a neutral atom: # protons = # electrons
Lithium has 3 electrons
the # neutrons = atomic mass - # protons
Lithium has 4 neutrons (7 – 3 = 4)

4. ELECTRONS ARE ARRANGED IN “SHELLS” AROUND THE NUCLEUS
The first electron shell can hold up to 2 electrons
The second electron shell can hold up to 8 electrons
The third electron shell can hold up to 8 electrons
In biology, we usually don’t have to deal with elements having more than three electron shells!
Element: Boron Mass =
Symbol: B # P =
# Neutrons = # e =
# Valence Electrons =

5. Which of an atom’s electrons are involved in bonding with other atoms?
Only the electrons in its outermost shell!
These electrons are called the valence electrons!
Hydrogen atoms have
1 valence electron
Helium atoms have
2 valence electrons

6. First shell  2 electrons Second shell  8 electrons
Element: Boron Mass # =
Symbol: B # P =
# Neutrons = # e =
# Valence Electrons =
First shell  2 electrons
Second shell  8 electrons
Third shell  8 electrons
Fourth shell  16 electrons

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8. About Atoms….. atomic number = # protons atoms are made up of:
protons (+ charge)
neutrons (no charge)
electrons (- charge)
atomic number = # protons
Lithium’s atomic # is _____
atomic mass = # protons + # neutrons
Lithium’s atomic mass is _____
in a neutral atom: # protons = # electrons
Lithium has _____ electrons
the # neutrons = atomic mass - # protons
Lithium has _____ neutrons

9. ELECTRONS ARE ARRANGED IN “SHELLS” AROUND THE NUCLEUS
The first electron shell can hold up to _____ electrons
The second electron shell can hold up to _____ electrons
The third electron shell can hold up to _____ electrons
In biology, we usually don’t have to deal with elements having more than three electron shells!
Element: Boron Mass =
Symbol: B # P =
# Neutrons = # e =
# Valence Electrons =

10. Which of an atom’s electrons are involved in bonding with other atoms?
Only the electrons in its ____________ shell!
These electrons are called the ________________!

11. Element: Boron Mass # =
Symbol: # P =
# Neutrons = # e =
# Valence Electrons =