1. ATOMIC STRUCTURE
CHAPTER 17

2. OUTSIDE NUCLEUS IN ENERGY SHELLS
What’s in an atom?
Sub-atomic
Particle
Mass of
Charge of
Location in
Atom
PROTON
1 AMU +1
IN NUCLEUS
NEUTRON
NONE
ELECTRON
0 AMU -1
OUTSIDE NUCLEUS IN ENERGY SHELLS
PROTONS & NEUTRONS ARE CALLED NUCLEONS

3. How Many Protons Does an Atom Have?
The number of protons is unique to each element.
The number of protons is equal to the ATOMIC NUMBER.
Each proton contributes 1 AMU to the atomic mass of the atom.

4. How Many Neutrons Does an Atom Have?
The number of protons + neutrons= atomic mass
ISOTOPES are atoms of the same element that have a different number of neutrons, therefore, a different mass.
Each neutron contributes 1 AMU to the atomic mass of the atom.

5. How Many Electrons Does an Atom Have?
For neutrally charged atoms:
The number of protons will be equal to the number of electrons.
For IONS (atoms that are charged due to the loss or gaining of electrons):
#electrons = # protons – (charge of ion)
IONS form to create full outer or valence shells (8 electrons)

6. How Can You Use the Periodic Table to Find the Number of Subatomic Particles?
The periodic table shows the atomic number and mass number:
# Protons= 3
# Neutrons= 4
# Electrons= 3

7. INFORMATION ON THE SYMBOL
Mass Number
Atomic charge +2
207 Pb 82
Atomic number

8. How About for an Isotope?
Isotopes are written with the elemental symbol and the mass of the isotope:
C-12
C-14
# Protons= 6
# Protons= 6
# Neutrons= 6
# Neutrons= 8
# Electrons= 6
# Electrons= 6

9. How About for an Ion?
Ions are written with a charge as a superscript following the elemental symbol:
Mg +2
P -3
# Protons= 12
# Protons= 15
# Neutrons= 12
# Neutrons= 16
# Electrons= 10
# Electrons= 18

10. How are Electrons Arranged in the Atom?
Electrons are arranged in energy levels surrounding the nucleus.
The period that the element resides in is equal to the number of energy levels that the atom has.
The number of elements in a period is equal to the number of electrons in the corresponding energy level

11. How are Electrons Arranged in the Atom?
Period/Energy Level
# of electrons it can hold 1 2 8 3 4 18 5 6 32 7

12. What Element is This?
Bohr Model of an Atom
NITROGEN