Chapter 1-Atomic Structure

AS CHEMISTRY AQA CHAPTER 1 REVISION CARDS

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Chapter 1-Atomic Structure

Proton +1 Neutron 0 Electron -1

Protons and neutrons are held together in the nucleus by a strong nuclear force. This is much STRONGER than the electrostatic forces that hold ELECTRONS and PROTONS.

Did you know?

Early models of atomic structure predicted that atoms and ions with noble gas electrons should be stable.

READ OVER SCIENTISTS UNDERSTANDINGS pg 6

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1.3 mass number, atomic number and isotopes

Number of protons = ATOMIC number or PROTON number (Z)

Number of protons+neutrons = MASS number (A) 


ISOTOPES

  • Atoms with same number of protons but different number of neutrons.
  • DIFFERENT isotopes of the same element react chemically in exactly the same way.
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The mass spectrometer

masspec.GIF.gif  

Isotopes- CARBON 12 ISOTOPE IS EXACTLY 12

Chlorine's RAM is 35.5. Not 35 or 37.

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What happens in the mass spectrometer

The mass spectrometer gives accurate information about relative isotope mass and about relative abundance of isotope.

  • It is kept under high vacuum so that the ions do not collide with the air particles, which might stop them from reaching the detector.
  • The sample must be in gaseous state. If it is solid than it is vaporised first by heating.

Ionisation- beam of electrons from 'electron gun' knocks out electrons from atoms or molecules so they form positive ions.

Acceleration- positive ions are attracted to the negatively charged plates and are accelerated to a high speed- the lighter the ion the faster it goes.

Deflection- The magnetic field deflects the beam of ions to form a curve. Heavier ions are deflected less than the lighter ones. The stronger the field the greater the deflection.

Detection- Ions strike the detector, accept electrons, lose their charge and create a current which is proportional to their abundance. 

A computer works out the value- mass/charge ratio. Mass spectrum is produced.

Mass spectrometry can be used to identify elements (planetary space probes). It can also be used to determine relative molecular mass.


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1.5 Electron arrangement

Energy levels= they are divide into sub-levels, s, p, d.

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d

Each atomic orbital holds 2 electrons- fill up singularly before pairing. 

Sometimes it can be written with a noble gas symbol.

IONISATION ENERGY

IS THE ENERGY REQUIRED TO REMOVE A MOLE OF ELECTRONS FROM A MOLE OF ATOMS IN THE GASEOUS STATE AND IS MEASURED IN KJ/MOLE.

  • Going across the period in the periodic table IE generally increases because the nuclear charge is increasing and makes it more difficult to remove an electron. 
  • Going down a group in the periodic table IE generally increases,the nuclear charge increases and makes it easier to remove an electron because of the inner electrons shielding the nuclear charge.
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