5Boron

Boron is a metalloid in group 13, period 2. At 25 °C it is a solid.

Shells: 2, 3. A simple picture: electrons do not move in circles.

Symbol: B
Atomic number: 5 protons in the nucleus
Standard atomic weight: 10.81 ± 0.02Commercial samples can have a changed isotope mix, because material has been processed or isotopes removed (for example lithium sold after its lithium-6 was taken out).
Electron configuration: [He] 2s² 2p¹
Electrons in each shell: 2, 3
Group, period, block: 13, 2, p
Family: Metalloids
State at 25 °C: solid
Electronegativity: 2.04 (Pauling scale)
First ionisation energy: 800.6 kJ/mol (8.298019 eV)

Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.