Group I

Group I Trends

As we move down the first group of the periodic table, elements become larger, with valence electrons further from the nuclear attraction and more heavily shielded by a larger number of core electrons. This causes each successive element to have a lower electronegativity, lower ionization energy, and greater reactivity than the element above it in the group. Magnetic susceptibility also generally increases as we move down the group.

HYDROGEN (1H)
Hydrogen has only one electron encapsulating one proton. This makes it quite intent upon keeping that electron, and gives it a much higher ionization energy (1,312 kJ/mol) than the other Group I elements. Hydrogen is really unlike the other Group I elements. It is a non-metal and they are metals. What they have in common is that they all have one valence electron and can therefore make a 1+ ion. As the smallest Group I element, hydrogen also has the highest electronegativity.

LITHIUM (3Li)
With only one 2s-electron, lithium is much more willing to lose its single valence electron since it would then have a full shell — a stable 1s2 di-electron. This shows that a full electron shell is more stable than a neutral charge. Since lithium is small, its nuclear attraction is rather strong. Lithium is therefore mildly reactive, bubbling as it gives off hydrogen gas when placed in water. As the first metal on the periodic table, it has a much lower electronegativity and ionization energy (520 kJ/mol) than the non-metal hydrogen (1H) atom above it. Lithium is paramagnetic (χm=+14.2), which means that it is attracted to a magnetic field because its unpaired outer electron can align with an external magnetic field.

SODIUM (11Na)
Sodium is significantly larger than lithium. Its 3s1 electron occupies more space than a 2s2 di-electron and is further away and more shielded from the attraction of the nuclear charge. This makes sodium much more willing to lose its valence electron in search of a full shell configuration. This results in sodium having a lower electronegativity, a lower ionization energy (496 kJ/mol), and a much higher reactivity than lithium. When placed in water, sodium spontaneously ignites the hydrogen gas that is given off when it reacts with the water. Sodium is only slightly more paramagnetic (χm=+16) than lithium, given the similarity of their electron configurations.

POTASSIUM (19K)
Potassium is larger than sodium. Its 4s1 electron occupies more space than a 3s shell. It is further away and more shielded from the attraction of the nuclear charge, and also has a full 3rd shell within, increasing the electron shielding. This makes potassium much more willing to lose its valence electron in search of a full shell configuration. This results in a lower electronegativity, a lower ionization energy (419 kJ/mol), and a higher reactivity than sodium. Potassium explodes when placed in water as the heat of its reaction ignites the hydrogen gas that is given off when it is placed in water. Potassium is only slightly more paramagnetic (χm=+20.8) than sodium and lithium, given the similarity of their electron configurations.

RUBIDIUM (37Rb)
Rubidium is larger than potassium. Its 5s1 electron occupies more space than a 4s shell. It is further away and more shielded from the attraction of the nuclear charge, and also has a full 4th shell within, now featuring a full d-orbital as well. This increases the electron shielding, making rubidium even more willing to lose its valence electron in search of a full shell configuration. This results in a lower electronegativity, a lower ionization energy (403 kJ/mol), and a higher reactivity than potassium. Rubidium self-ignites in air as it eagerly donates its valence electron to oxygen atoms in the air. It also has a similar paramagnetic strength (χm=+17) to potassium, sodium, and lithium, given the similarity of their electron configurations.

CESIUM (55Cs)
Cesium is larger than rubidium. Its 6s1 electron occupies more space than a 5s shell. It is further away and more shielded from the attraction of the nuclear charge, and also has a full 5th shell within, now featuring two full d-orbitals as well. This increases the electron shielding, making cesium even more willing to lose its valence electron in search of a full shell configuration. This results in a lower electronegativity, a lower ionization energy (376 kJ/mol), and a higher reactivity than rubidium. Cesium self-ignites in air even more readily than rubidium, as it eagerly donates its valence electron to oxygen atoms in the air. Cesium has a slightly higher paramagnetic strength (χm=+29) than rubidium and potassium, probably due to its larger size and the great core electron symmetry it has beneath its valence shell.

PERIODIC TRENDS: GROUP I, GROUP II

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