1. Chapter 4
Atomic Structure

2. 4.1 Atoms Democritus (460 BC – 370 BC)
first suggested the idea of atoms
Indivisible and indestructible

3. Atoms The first model of the atoms was Dalton’s
“All mater is made up of individual particles , which are indivisible”

4. Dalton’s Atomic Theory
1. All matter is made of atoms. Atoms are indivisible and indestructible.

5. Dalton’s Atomic Theory
2. All atoms of a given element are identical in mass and properties

6. Dalton’s Atomic Theory
3. Compounds are formed by a combination of two or more different kinds of atoms.

7. Dalton’s Atomic Theory
4. A chemical reaction is a rearrangement of atoms

8. Thomson’s Model Discovered electrons
Often called the “Plum-Pudding” Model
No mention of amount of electrons or their arrangement around the nucleus
Revised Dalton’s theory to account for subatomic particles

9. Rutherford Model Discovered nucleus
All of an atom’s positive charge is concentrated in its nucleus
Electrons surround a dense nucleus
Rest of the atom is empty space

10. Rutherford Model Known as the nuclear model
The protons are located in the nucleus
The electrons are around the nucleus
The electrons occupy most of the volume of the nucleus

11. The Atom
The smallest part of an element
VERY SMALL

12. Atomic Structure Atoms can be broken down Protons Neutrons Electrons
Every Element is different based on the number of each (individual personality)

13. Protons (p+)
Positively Charged
Each has a “+1” charge

14. Electrons (e-)
Negatively charged
Each has a “-1” charge

15. Neutrons (n0)
No charge or “neutral”
Mass = mass of proton

16. The Atomic Nucleus Most of the mass, little volume
The central core of an atom
Made of p+ and n0
Most of the mass, little volume
Nucleus has a positive charge

17. The Atomic Nucleus
Electrons orbit around nucleus like planets in the solar system
Called the “electron cloud”
Very little mass, lots of volume

18. How do we know the number of each elements p+ , e- , n0
Periodic Table is arranged by the element’s numbers

19. Hydrogen Name of Element
Atomic Number
Mass Number (round to the nearest whole number)
H Nuclear Symbol
Hydrogen Name of Element

20. Atomic Number Amount of protons from one element to the next
Ex: Oxygen
atomic number = 8 because it has 8 protons

21. Atomic Number Since all elements start off as neutral ….
The number of protons = number of electrons!

22. Mass Number
Mass Number = protons + neutrons

23. Composition of an Element
Use atomic number and mass number to determine composition
# p+ = atomic #
# e- = atomic #
# n0 = mass # – atomic #

24. What can change in an atom
Protons: can never change
Electrons: if the number changes, then an ion is formed
Neutrons: If the number changes, then an isotope is formed

25. IF the proton number changes…
Then you have an entirely different atom

26. If the neutron number changes…
Called an Isotope
Mass number changes

27. If an atom gains electrons, then…
The atom becomes negatively charged
If an atom loses an electron, then…
It becomes positively charged

28. Isotopes of Elements
Protons never change, but the number of neutrons may vary

29. Isotopes Isotopes of the same element are the same except for # of n0
# of n0 vary so mass number changes

30. Isotopes Carbon-12, Carbon-14, Carbon-16
How many protons in each version of carbon?
How many neutrons in each version of carbon?

31. Hydrogen Hydrogen has three known isotopes
Hydrogen-1 (one proton, no neutrons)
Hydrogen-2 (one proton, 1 neutron)
Hydrogen-3 (one proton, 2 neutron)

32. 4.3 Bohr’s Model Electrons arranged in circular paths around nucleus
Orbit like planets
n = energy level
Only a certain amount of electrons can fit in each energy level

33. Bohr’s Model
Electrons are located in energy levels with a fixed amount of energy

34. Energy Levels Each energy level can only hold 2 electrons
Each energy level has “X” number of orbitals that can hold 2 electrons each
Pauli Exclusion Principle
Each orbital holds 2 electrons that spin in opposite directions

35. Maximum number of Electrons
Energy Levels
How many electrons fit in the 1st, 2nd, 3rd and 4th energy levels?
Energy Level
Number of Orbitals
Maximum number of Electrons 1 2 4 8 3 9 18 16 32

36. Hund’s Rule
When electrons occupy orbitals, one electron enters each orbital until all orbitals contain their max amount

37. Hund’s Rule
Partially filled orbitals are much more stable than empty orbitals
Example:
Carbon has 6e-
has 2e- in first orbital
has 4e- in second orbital

38. Orbitals simplified
Each energy level can hold 8 electrons except the first which holds 2
Fill in each level until