1. 4.2 -Atomic Structure Theory

2. The Atom
Atoms – the smallest part of an element that cannot be broken down by chemical reaction.
- The basic unit of all matter

3. Actual Mass
The Atomic Mass Unit (amu) is a standardized unit to measure atomic mass. Carbon -12 is used as the standard. 1/12th of a Carbon-12 atom is 1 amu.
Proton – amu
Neutron – amu
Electron amu

4. Subatomic Particles
Neutron (n0) – neutrally charged particle making up the nucleus of the atom. Mass = 1 atomic mass unit (amu)
Proton (p+) – positively charged particles making up the nucleus of the atom. Mass = 1 atomic mass unit (amu)
Electron (e-) – Negatively charged particle found in energy levels outside the nucleus. Mass is negligible – not significant

5. Chart Particles Charge Mass Location Protons Positive 1 amu In Nucleus
Neutron
Neutral
Electrons
Negative
Negligible
Out of Nucleus

7. Atomic Number - number of protons in an atom.
All atoms of the same element have the same atomic number
All neutral atoms have equal protons and electrons
The number of neutrons = mass number – atomic number

8. Mass Number
Mass Number – the total number of protons and neutrons in an isotope of an atom.
Mass number = number of protons + number of neutrons
Ex. U-238
Isotopes – are atoms of the same element with a different mass number
Ex. Pb – 210 vs. Pb – 206

9. Isotopes Example Three types of Hydrogen
Protium – 1 proton, 0 neutrons
Deutrium – 1 proton, 1 neutron
Tritium – 1 proton, 2 neutron (radioactive)

10. Isotopes Mass = P + N C 12 12 = 6p + 6n C 14 14 = 6p + 8n
U p + __________n
U ___p + __________n
U ___p + __________n

11. Atomic Mass
Atomic Mass – the atomic mass of an element is the average mass of the isotopes of that element in a natural sample. Ex. Carbon = amu
Boron 11 – 80.0%
Boron 10 – 20.0%
Calculate Atomic Mass:

12. Atomic Mass of Boron – 10.8amu

13. B.5 Counting Subatomic Particles
Element Name
Element Symbol
Atomic Number
Mass
Number
Number of protons
Number of Neutrons
Number of Electrons a.
Hydrogen b.
Sodium 12 c.
Boron 5 d. B 6 e.
115 77 f. Pa
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