Topic 2

Atomic Theory

SL+HL

Topic 2.1 The atom

Position Charge Relative Mass

Proton; p+ Nucleus 1+ 1

Neutron; n Nucleus 0 1

Electron; e- Cloud/orbitals 1- 5*10-4

around the ~ 0nucleus

Subatomic particles

• An atom has no net charge.• Atomic ions have lost or gained electrons and

have a charge

• The number of Protons in an atom • The Element • Atomic number • Z • Number of Electrons

Isotopes• Atoms with same number of Protons but different number of

Neutrons are isotopes

• They are the same element = same Atomic number = Z

• Isotopes have different mass numbers

• Mass number = A = no. of protons + no. of neutrons

• The chemical properties is the same

• The physical properties can differ a little

The Symbol for Isotopes/Atoms

+ -

Nucleus

ElectronH1

Atomic number

1

Mass number

Isotopes of hydrogen

Natural abundance 99,99 %

+-

ElectronH1

2

Isotopes of hydrogen- Deuterium

NucleusMass number

Atomic number

Heavy water- D2O natural abundance 0,01 %

http://www.webelements.com/

+-

ElectronH1

3

Isotopes of hydrogen- Tritium

NucleusMass number

Atomic number

Radioactive

-

Alpha radiation

+ +

Beta radiation

Gamma radiation

He24 2+

b- e-

g

Radioactivity

HalflifeRadiation intensity

t ½ = 1600 år

Ra88

226 Rn84

222g

Radium-226 Radon-222 alfaparticle gammaradiation

He24

RadioisotopesNot stable isotopes

14Carbon 14

• 14C less than 0.001% of carbon, half life 5730 years. 14C 14N + e-

• 14N + cosmic radiation 14C . Since the cosmic radiation is the same over time,

the concentration of 14C as Carbon dioxide will be the same in the air over time. There will be a fixed ratio between 12C and 14C.

• The plants take up CO2 with the ratio. But when the plant die the ratio will be

changed when the amount of 14C decreases due to radioactive decay.

• By looking at the ratio and knowing the half-life is it possible to determine the age of an object. It accurate to about 60 000 year old material.

60Co

• Penetrating power to treat cancerous cells• Gamma (g) radiation emitter• Been used more than 50 years for different

cancer forms.• Also to stop the immune system to attack

transplanted organs.

131I

• Half-life of 8 days• Beta (b) and Gamma (g) emitter• Thyroid cancer• Diagnose if thyroid gland functions normally

125I

• Half-life of 60 days• Prostate cancer and brain tumour

Topic 2.2 The mass spectrometerHow to measure atomic masses.

1. The sample is Vaporised in vacuum.

2. The sample is Ionised in an electron beam.A + e- A+ + 2e-.

3. The ions are Accelerated in an electric field into a long tube.

4. The ions are Deflected (= change of flight way) in a magnetic field.

5. Depending of the ions mass and the magnetic field some ion will deflect into a Detector. The number of ion that hit the detector is proportional to the signal from the detector.

By changing the power of the magnetic field different ions can be detected.

A mass spectrometer can be used to determine the natural abundance of isotopes.

The mass spectrum of Magnesium

The most abundant isotope is set to be 100. The other ones as in proportion to this.

Calculating the natural abundance:100+12.8+14.4 = 127.224Mg =100/127.2 = 78.6% 25Mg = 12.8/127.2 = 10.0%26Mg = 14.4/127.2 = 11.3%

24*0.786 + 25*0.10 + 26*0.113 = 24.3 (g/mol)

Topic 2.3 Electron arrangement Electromagnetic spectrum

• Electromagnetic radiation has been very important in the studies of the atom

• There are different types of electromagnetic radiation: Gamma rays, X-rays, UV, Visible light, IR, Microwaves, Radio waves. They differ in Wavelength. From 10-12 m to 104m

• The relation between Wavelength, L(m)and Frequency, n (s-

1,Hertz)Ln = c c =speed of light, 3*108 m/s

• Shorter wavelength => Higher frequency =>more energy.

Continuous spectrum

Line spectrum.

+ +

Atomíc nucleus

K L M

Electron shells

• Absorptions spectra: energy needed to move an electron to a higher shell.

• Emission spectra: energy released when the electron falls back to the lower shell.

• The color of the light show the energy difference between the two shells

The line spectrum of the hydrogen atom- Balmer series

Named after Johann Balmer, who discovered the Balmer formula, an empirical equation to predict the Balmer series, in 1885. Balmer lines are historically referred to as "H-alpha", "H-beta", "H-gamma" and so on, where H is the element hydrogen. Four of the Balmer lines are in the technically "visible" part of the spectrum, with wavelengths longer than 400 nm. Parts of the Balmer series can be seen in the solar spectrum. H-alpha is an important line used in astronomy to detect the presence of hydrogen.

The longest jump between two neighboring shells is K L (n=1 n=2)Line converge in the higher frequency end due to many similar energy transitions, and ionisation of the electron

Electron arrangement of atoms in terms of main energy levels (Shells)

Main Energy level Max Number of e- If valence e-

K 1 2 2L 2 8 8M 3 18 8

Valence electrons: The electron in the highest main energy level

+ -Electron

Hydrogen atom, H

1 p+

K-shell

+-

Helium atom, He

2 p+

+-

2 e-

+ -

Litiumatom, Li

3 p+

+-

3 e-

K-shellL-shell+

-

+ -

Berylliumatom, Be

4 p+

+-

4 e-

+

-

+

-

+ -

B

5 p+

+-

5 e-

K-shell

L-shell+

-

+

-

+

-

+ -

Carbon, C

6 p+

+-

6 e-

+

-

+

-

+

-

+ -+ -

Nitrogen, N

7 p+

+-

7 e-

+

-

+

-

+

-

+-

-

+ -

Oxygen, O

8 p+

+-

8 e-

+

-

+

-

+

-

+-

-

-

+ -

Fluor, F

9 p+

+-

9 e-

+

-

+

-

+

-

+

-

-

+ -

Neon, Ne

10 p+

+-

10 e-

+

-

+

-

+

-

+

-

-

-

Element Atomic number K L M NH 1 1

He 2 2

Li 3 2 1

Be 4 2 2

B 5 2 3

C 6 2 4

N 7 2 5

O 8 2 6

Electron arrangement for elements 1-8

Electron arrangement for elements 9-20

Element Atomic number K L M N

F 9 2 7

Ne 10 2 8

Na 11 2 8 1

Mg 12 2 8 2

Al 13 2 8 3

Si 14 2 8 4

P 15 2 8 5

S 16 2 8 6

Cl 17 2 8 7

Ar 18 2 8 8

K 19 2 8 8 1

Ca 20 2 8 8 2