chapter 1 -ionisation energy

what is a period?

• a row in the periodic table

• elements in the same period have their valence electrons in the same shell

what is a group?

• a column in the periodic table

• elements in the same group have their electrons in similar orbitals

• they often have similar properties

what is the s block?

• the 2 leftmost columns make up the s block

• this is called the s block because elements in it have all their valence electrons in s orbitals

  • helium is also an s block element

what is the p block?

• the 6 rightmost columns make up the p block

• this is called the p block because elements in this block have a partially filled p sub-shell

what is the d block?

• the d block lies between the s block and p block

• elements in the d block have a partially filled sub-shell

• elements in this block are often called transition metals

what is the f block?

• this block is detached along the bottom of the periodic table

• elements in the f block have a partially filled f sub-shell

• these elements are referred to as the lanthanides and the actinides (top row and bottom row respectively)

what is ionisation energy?

• a specific amount of energy needed to remove an electron from an atom or ion

what is the first ionisation energy?

• energy required to remove an electron from every atom in a mole of atomic gas, to produce a mole of uni-positive gaseous ions

second ionisation energy?

• energy required to remove an electron from every ion in a mole of uni-positive gaseous ions, to produce a mole of di-positive gaseous ions

third ionisation energy?

• energy required to remove an electron from every ion in a mole of di-positive gaseous ions, to produce a mole of tri-positive gaseous ions

nth ionisation energy?

• overall we can form an equation for each successive ionisation energy

  • where the value for n, is the value of the charge on the ion in the products

factors affecting ionisation energies?

• nuclear charge

• distance from the nucleus

• shielding

nuclear charge?

• the greater the number of protons in the nucleus, the greater the attraction of the electron to the nucleus

• a greater attraction of electron means more energy is needed to remove the electron

• this means the ionisation energy is greater

distance from the nucleus?

• electrostatic attraction decreases sharply with distance

• this means that less energy is needed to remove the electrons which are further away

• so, as distance increases, ionisation energy decreases

shielding?

• the greater the number of electrons between the nucleus and the outer electrons, the lower the effective nuclear charge

• this is because the positive charge felt by the electron is reduced by the electrons in between

• therefore, the greater number of electrons, the lower the ionisation energy

why does first ionisation increase across a period?

• because the atomic radius decreases as the proton number increases across a period, so electrons are more attracted to the nucleus

  • the electron is closer to the nucleus, and so experiences a greater attraction

why does first ionisation energy decrease down a group?

• because the atomic radius increases because the electron is further from the nucleus, and so experiences a lower attraction

• there are also more electrons between the nucleus and outer electrons, due to greater shielding