Atomic Structure and Periodic Table

Isotopes

Isotopes are atoms with the same number of protons, but different number of neutrons.

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Relative isotopic mass

Relative isotopic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.

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Mass Spectrometer

The mass spectrometer can be used to determine all the isotopes present in a sample of an element and to therefore identify elements,

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Ionisation

A vaporised sample is injected at low pressure. An electron gun fires high energy electrons at the sample. this knocks out an electron forming positive ions with different charges.

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Acceleration

A negative electric field accelerated the positive ions and makes them into a beam.

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Deflection

The beam of positive ions is deflected by a strong magnetic field. The degree of deflection depends on the mass-to-charge ratio, m/z. The smaller this ratio the larger the deflection.

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Detection

The ions reach the detector and generate a small current, which is fed to a computer for analysis. The current is produced by electrons transferring from the detector to the positive ions.

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First ionisation energy

The first ionisation energy is the energy required when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge.

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Factor that affect ionisation energy

1.- The attraction of the nucleus (the more protons in the nucleus the grater the attraction) 2.- The distance of the electrons from the nucleus. 3.- Shielding of the attraction of the nucleus.

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Atomic Radius

Atomic radii decrease as you move from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are the in the same shell with similar shielding.

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1st ionisation energy in period 3

Small drop between Mg and Al because Mg has its outer electrons in the 3s sub shell, whereas Al starts to fill the p sub shell. P electrons are higher in energy so easier to remove.

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1st ionisation energy in period 3

There's a small drop between P and S. Sulphur's outer electron is being paired up with another electron in the same 3p orbital. There's a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.

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Melting and boiling points across period 3

Na, Mg, Al, have metallic bonding. This bonding gets stronger the more electrons there are in the outer shell that are released to the sea of electrons. A smaller positive centre also makes the bonding stronger.

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Melting and boiling points across period 3

Si is macromolecular: many strong covalent bonds between atoms high energy needed to break the covalent bonds.

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Melting and boiling points across period 3

P, S, Cl are simple molecular: weak london forces between molecules, so little energy is needed to break them. S has a stronger melting point than P because it has more electrons so has stronger london forces.

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Melting and boiling points across period 3

Ar is monoatomic: weak london forces between atoms.

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Atomic Structure and Periodic Table

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