Electron Structure

Electron Structure

1. Ionisation Energy

   • The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. Units are KJmol-1.
   • Sodium 1st 1.E. Na(g) --> Na+(g) + e-
   • Magnesium Mg(g) --> Mg+(g) + e-
   • Oxygen O(g) --> O+(g) + e-

2. Factors affecting the I.E.

   • Negative electrons are held in shells by their mutual attraction for the positive protons in the nucleus. In order to form a positive ion energy is needed to overcome this attraction.
   • Electrons in the outer shells are removed first since they have a weaker attractions therefore lower I.E.
   • Atomic Radius; The distance from the nucleus to the outer electrons. The greater the atomic radius the smaller the nuclear attraction by the outer electrons the easier it is to remove the electron from the outer shell.
   • Nuclear Charge; The number of protons in the nucleus. The greater the nuclear charge the greater the attractive force on the outer electrons.
   • Electron shielding; is the repulsion between the electrons in different shells. Shielding reduces the attractive force from the positive nucleus on the outer shell electrons.

3. Successive I.E.

   • Is a measure of the energy required to remove each electron in turn.
   • Each successive I.E. is greater than the last as each electron is removed the atomic radius decrease and the nuclear attraction increases.
   • 1st; Li(g) --> Li+(g) + e- 2nd; Li+(g) --> Li2+(g) + e- 3rd; Li2+(g) --> Li3+(g) + e-

4. Shells, sub shells and orbitals

   • Na 1s2 2s2 2p6 3s1
   • A region within an atom that can hold up to two electrons in turn with opposite spins.
   • Shell 1; sub shell s; e- 2; orbitals 1
   • Shell 2; Sub shell s - 2e- - 1 orbital; Sub shell p - 6 e- - 3 orbitals
   • Shell 3; Sub shell s - 2e- - 1 orbital; Sub shell p - 6e- - 3 orbitals; Sub shell d - 10 e- - 5 orbitals.

5. Electron spin

   • One arrow up one arrow down to show two electrons in an orbital with opposite spins.
   • The 4s orbital has a lower energy than 3d ans as such the 4s fills before the 3d.
   • Krypton; 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

6. Shapes of Atomic Orbitals

   • sub shell s orbital has a spherical shape on x & y axis.
   • sub shell p orbitals has a dumbbell shape, there are 3 of these on the x, y and z axis.
   • 5 d orbitals do not need to know the shape.