Atomic Structure

1
Atomic Structure

• Subatomic Particles

2
Henry Mosley - 1913

• 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
Mosleys 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 .0005486 amu Or 0 amu
Proton, 1p or 1H 1 1.0073 amu Or 1 amu
Neutron, 1n 0 1.0087 amu Or 1 amu
-1
1
1
0
10
What is an a.m.u.?

• 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 Daltons 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.)

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Notation
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.

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Whats the difference between H-1, H-2, and H-3?

• All Hs 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

• Whats 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?

• Whats the atomic number?
• How many protons?
• So the neutrons are

84
84
217 84 133 neutrons!
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IONS

• Charged Particles

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IONS

• Atoms ? electrically neutral
• of electrons of protons
• IONS are atoms that have gained or lost
  electrons.
• The protons and electrons dont balance out
  anymore, so ions carry a charge.

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IONS

• Charge of ion
• protons - electrons
• (We subtract the electrons since theyre
  negative.)

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IONS

• If the atom loses electrons, its going to have
  more positive charge than negative. What kind of
  ion is it?
• If the atom gains electrons, its going to have
  more negative charge than positive. What kind of
  ion is it?

Positive (cation)
Negative (anion)
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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.
• Na1 a sodium ion with a charge of 1.
• O-2 an oxide ion with a charge of -2.
• If theres no right superscript, its understood
  to be zero and a neutral atom.

28
Putting it all together

• How many protons, neutrons, electrons in each
  of the following
• 23Na1

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
13N-3
64Zn2
25Mg2
30
7
12
7 p, 6 n, 10 e
30 p, 34 n, 28 e
12 p, 13 n, 10 e