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Trends in Group 1 (Group IA or Alkali Metal) Elements

Properties of Group 1 (IA) Elements

Period Name
(Symbol)
Atomic Number (Z) Simple Electronic Configuration Atomic Radius
(picometres)
First
Ionization Energy(kJ/mol)
Second
Ionization Energy(kJ/mol)
Melting point (oC) Density (g/cm3) Electro-
negativity
(Pauling)
2 Lithium
(Li)
3 2,1 152 526 7296 180 0.54 0.98

3 Sodium
(Na)
11 2,8,1 186 504 4563 98 0.97 0.93

4 Potassium
(K)
19 2,8,8,1 231 425 3069 64 0.86 0.82

5 Rubidium
(Rb)
37 2,8,18,8,1 244 410 2650 39 1.5 0.82

6 Ceasium
(Cs)
55 2,8,18,18,8,1 262 380 2420 29 1.9 0.79

7 Francium
(Fr)
87 2,8,18,32,18,8,1   370 2170 27   0.7

Trends in Properties of Group 1 (IA) Elements

  • All Group 1 (IA) metals have 1 valence electron (1 electron in the highest energy level).

  • Atomic radius increases down the Group as successive 'electron shells' (energy levels) are filled.

  • Down the Group, first ionization energy (the energy required to remove 1 electron from the gaseous atom) decreases. As the atomic radius increases and the negatively charged electron is further from the positively charged nucleus it is less attracted to the nucleus (electron is said to be 'shielded').

  • Down the Group, second ionization energy (the energy required to remove an electron from the gaseous positive ion) decreases. As successive electron 'shells' (energy levels) are filled, the negatively charged electron is further from the positively charged nucleus and is therefore less attracted to the nucleus.

  • second ionization energy is much greater than the first ionization energy for each element. Once an electron has been removed from the gaseous atom, it forms an ion of charge 1+, this ion then has the electron configuration of a Noble Gas which is extremely stable, and it is therefore VERY difficult to remove an electron from this arrangement of electrons.

  • In general, electronegativities decrease down the Group as successive energy levels (electron shells) are filled resulting in the positive nucleus exerting less of a force of attraction on electrons.

  • Melting point decreases down the Group as the elements become less metallic in nature.

  • Densities increase down the Group.


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