Lead at a glance
- Atomic number
- 82
- Symbol
- Pb
- Atomic mass
- 207.2 u
- Category
- Post-transition metal
- Group / period
- 14 / 6
- Electron configuration
- [Xe] 4f 14 5d 10 6s 2 6p 2
- State at 25 °C
- Solid
- Melting point
- 327.5 °C
- Boiling point
- 1749 °C
- Density
- 11.34 g/cm³
- Electronegativity
- 2.33
- 1st ionization energy
- 716 kJ/mol
- Oxidation states
- +2, +4
- Discovered
- Antiquity
Atomic structure
A neutral lead atom has 82 protons and 82 electrons, and its most common isotope carries about 126 neutrons. One atom weighs about 3.44 × 10⁻²⁵ kg, so a mole of lead (6.022 × 10²³ atoms) weighs 207.2 g. That nucleus holds 1.54 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. Its symbol Pb comes from plumbum. The electrons fill 6 shells (K 2, L 8, M 18, N 32, O 18, P 4), which gives the configuration [Xe] 4f 14 5d 10 6s 2 6p 2. With 4 electrons in its outer shell, it usually shares electrons in covalent bonds. It has 4 stable isotopes: Pb-204, Pb-206, Pb-207 and Pb-208. No other element has a stable isotope with mass number 208, so Pb-208 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) lead is a solid. It melts at 327.5 °C and boils at 1749 °C, so it stays liquid across a 1421-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 11.34 g/cm³, 11.3 times as dense as water. Its atoms have a radius of about 180 pm (Thallium next door is 190 pm). In the solid, its atoms pack into a face-centred cubic lattice.
Chemical behaviour
Its electronegativity is 2.33 on the Pauling scale. Pulling off its outermost electron takes 716 kJ/mol, more than Tin above it (709 kJ/mol). A bond between lead and chlorine would be polar covalent, with an electronegativity difference of 0.83. It releases 35 kJ/mol when it gains an extra electron. Its common oxidation states are +2, +4, so in compounds you will usually meet it as Pb²⁺ and Pb⁴⁺. Group 14 also holds Carbon, Silicon, Germanium, Tin and Flerovium, which share its outer-shell pattern. Its Lewis symbol is Pb surrounded by 4 dots. Handle with care: as a pure element it is toxic.
Where it comes from
It makes up 14 mg/kg of Earth's crust, the 36th most abundant element there. In the human body it accounts for about 0.00017 % of body mass. It has been known since ancient times, one of only 11 elements people used before modern chemistry. When excited it glows at its own set of colours; its brightest visible lines are at 405.8 nm, 406.2 nm and 560.9 nm. In a flame test its compounds colour the flame pale grey-blue.