Thallium (Tl) – Periodic Table [Element Information & More]

thallium element periodic table

Thallium element (Tl) is in group 13 and period 6 of a periodic table. Thallium is in the p-block and it is classified as a post-transition element on the periodic table.

There is a lot more information related to thallium which is mentioned in the Information Table given below.

So let’s dive right into it!

Table of contents

Thallium Element (Information Table)

The important data related to thallium element is given in the table below.

Appearance of thalliumSilvery gray appearance
Atomic number of thallium81
Symbol of thalliumTl
Atomic mass of thallium204.38 u
Protons, Neutrons & Electrons in thalliumProtons: 81, Neutrons: 123, Electrons: 81
State of thallium (at STP)Solid
Group number of thallium in periodic table13
Period number of thallium in periodic table6
Block of thallium in periodic tablep-block
Category of thalliumPost transition element (boron group)
Bohr model or Electrons per shell or Electrons arrangement in thallium2, 8, 18, 32, 18, 3
Electron configuration of thallium[Xe] 4f14 5d10 6s2 6p1
Orbital diagram of thalliumorbital diagram of thallium
Valence electrons in thallium3
Electronegativity of thallium (on pauling scale)1.62
Atomic radius of thallium (van der Waals radius)196 picometers
Density of thallium11.85 g/cm3
1st ionization energy of thallium6.108 eV
Main isotope of thallium205Tl
Melting point of thallium577 K or 304 °C or 579 °F
Boiling point of thallium1746 K or 1473 °C or 2683 °F
Crystal structure of thalliumHexagonal Close Packed (HCP)
Discovery of thalliumBy William Crookes (in 1861)

Also see: Interactive Periodic Table (It has rotating bohr models as well as many other details of all the 118 elements in a single periodic table).

Thallium element in Periodic table

The Thallium element (Tl) has the atomic number 81 and is located in group 13 and period 6. Thallium is a metal and it is classified as a post-transition element.

H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La* Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac** Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
*Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
**Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Facts about thallium

Here are a few interesting facts about thallium.

  1. William Crookes discovered thallium in the year 1861.
  2. Thallium was given its name from the Greek word “thallos”, meaning green shoot.
  3. The earth’s crust contains around 850 parts per billion (by weight) of thallium.
  4. Around 70% of the total thallium is used in the electronics industries.
  5. Thallium is stored in mineral oil because of its reactivity.

Properties of thallium

Here is a list of some physical properties and chemical properties of thallium.

Physical properties of thallium

  • Thallium has a silvery gray appearance.
  • Thallium is soft metal and it can be cut with a knife too.
  • The density of thallium is 11.85 g/cm3 and its atomic mass is 204.38 amu.
  • The melting point and boiling point of thallium is 577 K and 1746 K respectively.
  • Thallium has HCP crystal structure.
  • Thallium has many isotopes, and the most abundant isotope is 205Tl.

Chemical properties of thallium

  • Thallium easily reacts with the atmospheric oxygen and tarnishes, if kept open in the air.
  • Thallium reacts with water and forms a thallium hydroxide.
  • Thallium has an electronegativity of 1.62 on the pauling scale.

Uses of thallium

Here are some uses of the thallium element.

  • Thallium oxide is used in making glasses that require a higher refractive index.
  • Thallium is also used in electronic industries (specially in the semiconductor material used for selenium rectifiers).
  • Thallium sulfide is a compound of thallium which is used in photocells.

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