1. Atomic Structure
Subatomic Particles

2. Henry Mosley
Mosley used the cathode ray tube in a slightly different way.
Substituted a denser material in place of the glass and was able to get even higher radiation 
X- Rays

3. He tried 30 different metal targets!

4. Atomic Number - 1913 Mosley tried 30 different elements as “STOPPERS.”
Found that the greater the atomic weight of the “stopper,” the shorter the wavelength of the x-rays.

5. What does any good scientist do?
PLOTS THE DATA!
Moseley tried plotting the wavelength of the x-ray vs. the atomic mass of the stopper. Not so nice…
Then he tried correlating the wavelength of the x-ray with an integer, n. Got a very pretty graph.

6. Mosley’s integer was the atomic number!

7. Atomic Number Size of nuclear charge.
Atomic number = # protons in nucleus.
Determines the identity of the element.
Used to order the periodic table.
For neutral atoms
atomic number (#p) = number of electrons.

8. Henry Mosley
Killed in WWI at the age of 28.

9. What we knew by 1932: Relative Charge Relative Mass Electron, 0e -1
amu
Or 0 amu
Proton, 1p or 1H +1
amu
Or 1 amu
Neutron, 1n
amu -1 1 1

10. What is an a.m.u.? Relative Mass atomic mass unit
Defined as 1/12th the mass of the C-12 atom
C-12 is used as the reference for atomic masses.
One atom of C-12 has a mass of exactly 12 amu
Relative Mass

11. Location of Subatomic Particles
Electrons located outside nucleus.
Protons & neutrons located inside nucleus.
Protons and neutrons combined are called:
nucleons

12. Mass Number Mass number = # protons + # neutrons
Always a whole number (no decimals)
Mass number can be estimated from the atomic mass by rounding to the nearest integer.
REMEMBER: Only the # neutrons can vary for any given element. The number of protons must remain the same – it identifies the element!

13. Isotopes
These are atoms of the same element with a different number of neutrons. The protons are the same!
So Dalton’s theory has been modified in a number of important ways.
The atom is divisible.
Atoms of the same element can be different.

14. Isotopic Notation 12C 6 The left superscript is the mass number.
The left subscript is the atomic number.
Sometimes both are given; sometimes only the mass number is given. (You can figure out the atomic number from the P.T.)

15. Notation 12C 6 How many neutrons in this atom?
12 = no. of protons + neutrons.
6 = no. of protons.
12C 6
How many neutrons in this atom?
12 – 6 = 6 neutrons

16. 17O
Mass number is ?
Atomic number is ?
# of neutrons is ?
# of electrons in atom is? 17 8 8
17 – 8 = 9 8

17. 15N
Mass number is ?
Atomic number is ?
# of neutrons is ?
# of electrons in atom is? 15 7 7
15 – 7 = 8 7

18. 19F
Mass number is ?
Atomic number is ?
# of neutrons is ?
# of electrons in atom is? 19 9
19 – 9 = 10 9

19. Hyphen Notation
Might also see C-12. The number following the symbol is the mass number!
You have to look up the atomic number.

20. What’s the difference between H-1, H-2, and H-3?
All H’s have 1 proton.
H-1: mass # = 1. Has 1 proton, 0 neutrons.
H-2: mass # = 2. Has 1 proton, so it must have 1 neutron.
H-3: mass # = 3. Has 1 proton, so it must have 2 neutrons.

21. Consider U-234, U-235, & U-238 What’s the atomic number of U?
How many protons in U?
How many neutrons in U-234?
How many neutrons in U-235?
How many neutrons in U-238?
How many electrons in U? 92 92
234 – 92 = 142
235 – 92 = 143
238 – 92 = 146 92

22. How many neutrons in Po-217?
What’s the atomic number?
How many protons?
So the neutrons are … 84 84
217 – 84 = 133 neutrons!

23. IONS
Charged Particles

24. IONS Atoms  electrically neutral # of electrons = # of protons
IONS are atoms that have gained or lost electrons.
The protons and electrons don’t balance out anymore, so ions carry a charge.

25. IONS Charge of ion = #protons - #electrons
(We subtract the electrons since they’re negative.)

26. IONS
If the atom loses electrons, it’s going to have more positive charge than negative. What kind of ion is it?
If the atom gains electrons, it’s going to have more negative charge than positive. What kind of ion is it?
Positive (cation)
Negative (anion)

27. Charge of Ions
If we want to specify an ion, we write the charge as a right superscript.
Cl-1 a chloride ion with a charge of -1.
Na+1 a sodium ion with a charge of +1.
O-2 an oxide ion with a charge of -2.
If there’s no right superscript, it’s understood to be zero and a neutral atom.

28. Putting it all together
How many protons, neutrons, & electrons in each of the following:
23Na+1
Got 1
Got 2
Lost 1
34S-2
19F-1 16 9 11
16 p, 18 n, 18 e
9 p, 10 n, 10 e
11 p, 12 n, 10 e
Got 3
Lost 2
Lost 2
64Zn+2
13N-3
25Mg+2 30 7 12
7 p, 6 n, 10 e
30 p, 34 n, 28 e
12 p, 13 n, 10 e