1. Atomic structure
Mrs. Meadows

2. What is the Atomic Theory?
states that matter is composed of discrete units called atoms.

3. What is an atom?
The smallest particle of an element that retains the properties of that element

4. Who took part in the atomic theory?
Democritus
Dalton
Thompson
Rutherford
Bohr

5. When did the atomic theory start?
460 B.C.

6. Who is Democritus?
Was the first scientist to suggest the existence of atoms

7. What did he discover? Democritus believed that
Everything is composed of atoms
Atoms are hard small particles
Thought matter was made of tiny particles that could not be divided (indivisible)

8. Who is Dalton?
In 1808 Dalton continued Democritus work He believed that -All matter is composed of atoms -atoms are indivisible (atoms are the smallest) -All atoms of an element are identical

9. What was wrong with Democritus and Daltons theory?
Atoms can be subdivided into protons/Neutrons/ electrons

10. Who was the next guy?
JJ Thompson ( )

11. What did Thompson propose?
Discovered the electrons by the cathode ray experiment
Came up with the Plum Pudding Model
(Electrons are in a soup
of positive charge)

12. What was wrong with Thompsons theory?
Electrons and protons are not evenly disturbed through out the atom

13. Who was the next guy?
Rutherford (1910)

14. What did Rutherford propose?
-Nucleus theory
Gold Foil Experiment
Atoms have a large center mass that is composed of a positive charge
-Atoms are mostly empty space
-Electrons orbit randomly around
nucleus

15. What is a nucleus?
Central part of atom containing protons and neutrons

16. What was wrong with Rutherford's theory?
Electrons do not orbit randomly around the nucleus

17. Who was the next guy?
Neils Bohr ( )

18. What did Bohr propose? Planetary model (1913)
Nucleus surrounded by orbiting electrons at different energy levels
Electrons do not randomly orbit
Electrons orbit like the solar system are the sun

19. Atomic Stucture

20. What are Subatomic Particles?
Particles smaller than an atom
Protons, neutrons, electrons

21. What are Protons? Positively charged subatomic particle
Located in the nucleus

22. What are electrons? Negatively charged subatomic particle
Located outside of nucleus

23. What are neutrons? Subatomic particle with no charge
Located inside the nucleus

25. What Charge does atoms have?
All atoms have the same number of protons and electrons
Atoms want to be neutral
Positive charge proton = negative charge electron

26. What subatomic particle determines the element?
The proton!
Build elements
atom/latest/build-an-atom_en.html

27. What are Neutral atoms?
Elements that are neutral have the same number or protons, electrons, and neutrons.
The number of protons = number of electrons
Protons (+) charge and electrons (-) charge
4 protons and 4 electrons = 0 net charge

28. What is Bohrs Models?

29. What are electron shells?
Each element has the same number of orbirts around the nucleus.
Those orbits are called electron shells

30. How do we make a bohr model?
1) Determine the number of protons in nucleus
Draw them in inner circle
2) Determine the number of electrons
Place in orbits around the nucleus
1st orbit – 2e max
2nd orbit – 8e max
3rd orbit – 8e max

31. What are Valence Electrons?
Valence electrons are electrons in the outer shell of an atom

32. Draw bohrs model for Boron
5 electron
2 in 1st shell and 3 in outershell

33. What is the atomic number?
Is the number of protons in the atom.
Number of protons = number of neutrons

34. What is the mass number
Is the number of protons AND neutrons in the nucleus

35. Does every atom of the same element have the same # of neutrons?
No, some atoms of the same element have different number of neutrons
They are called isotopes
Will result in a different mass number

36. What is an exmple of an isotope
Carbon 12 and carbon 15
We put the mass number after the name of the element
So carbon 12 has 6 protons and 6 neutrons
So carbon 15 has 6 protons and 9 neutrons

37. How do we find the number of neutrons in an isoptope?
N = neutrons
N = atomic mass – atomic number
N = (# of protons and neutrons) – ( # of protons)

38. Calculating average atomic mass given isotopes
The element nitrogen has two isotopes with masses of 14(99.5%) and 15(0.5%). Calculate the average atomic mass of nitrogen

39. Your Turn
The element chlorine has two isotopes with masses of 35 (75.5%) and 37 (24.5%). Calculate the average atomic mass of chlorine