Atomic Number
69
Element 69
Thulium (Tm)
Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series.
Atomic Mass
168.93 u
Category
Lanthanide
Period
6
Group
Lanthanide series
Phase
solid
Density
9.32 g/cm3
Electron Shells
2, 8, 18, 31, 8, 2
Atomic Structure
Protons: 69. Electrons: 69. Neutrons: Varies by isotope.
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³
Why Thulium Matters
Thulium helps connect atomic number 69, lanthanide behavior, period 6 trends, and electron shell structure. Its solid phase, atomic mass of 168.93 u, and electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³ make it useful for comparing bonding patterns across the periodic table.
Discovery and Occurrence
Thulium was discovered 1879 by Per Teodor Cleve. Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series.
Safety and Handling Context
Thulium is presented here for learning and comparison. Pure elements and laboratory compounds can have hazards that depend on dose, form, and setting.
Related Elements
Frequently Asked Questions
- What is the atomic number of Thulium?
- Thulium has atomic number 69, which means a neutral atom has 69 protons and 69 electrons.
- What is the chemical symbol for Thulium?
- The chemical symbol for Thulium is Tm.
- What category is Thulium in?
- Thulium is classified as a lanthanide and sits in period 6 of the periodic table.
Explore Thulium in 3D
Use the interactive table above to rotate atomic models, compare periodic trends, and move from Thulium to neighboring elements without losing your place.