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46

Atomic Radius of Elements

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Atomic radius is the measure of the distance from the centre of the nucleus to the outer electron.

Refresher:  Atoms consist of a nucleus with positively charged protons and neutral neutrons surrounded by shells of electrons. Elements in the periodic table are organized into periods and groups. Periods run across the table horizontally, while groups are the vertical groupings. Elements in the same period have the same number of electron shells, while elements in the same group have the same number of valence electrons. 


FAQs

How do you find the atomic radius?

The atomic radius is calculated by measuring the distance between the nuclei of two identical atoms bonded together. Half this distance is the atomic radius.  

Why does the atomic radius increase as you progress down a group? 

As we progress down a group in the periodic table, the number of electrons increases, and so does the number of shells that those electrons are organized into.  This increases the atomic radius as the electrons in the outermost shell are further away from the nucleus. 

Why does the atomic radius decrease across a period?

Across a period, the number of electron shells remains the same, while the number of electrons increases. Thus, as the nuclear charge increases across a period, the protons in the nucleus can attract the higher number of electrons more closely due to the attraction of the positive protons to the negative electrons. This means the electrons are pulled more closely to the nucleus, reducing the size of the atomic radius. 


Which element has the smallest atomic radius?

Helium has the smallest atomic radius at 31 picometers. Helium is in the top period and the farthest right group, which follows the patterns of atomic radius on the periodic table.


Measuring Atomic Radius

The atomic radius of a particular element is an important characteristic as it helps us to understand many properties of atoms and how they react. Atomic radius is the distance from the atom’s nucleus to the outermost electron orbital, and a lot of trends in the periodic table rely on this property due to its relationship to other atomic properties such as nuclear charge and shielding. Because the boundaries where the electron shells end on an atom can be a bit unclear, the actual definition of atomic radius is one-half the distance between the nuclei of two identical bonded atoms.  The atomic radius is measured in picometers, which is one trillionth of a meter or 1x10-12. 

Atomic Radius Trends on the Periodic Table

As we progress down a group in the periodic table, the number of electrons increases, and so does the number of shells that those electrons are organized into.  This increases the atomic radius as the electrons in the outermost shell are further away from the nucleus. The size of the nucleus also increases as you move down the group. Thus, as you move down the periodic table, both the size of the nucleus and the number of shells grows, increasing the total radius.

For example the atomic radius of Lithium is 152 picometers, but if we progress down to caesium, its atomic radius is 262 picometers. This is because caesium not only has a greater number of protons, but also 6 electron shells  Due to the large nucleus and the large number of shells, the outer valence electron is much further away, meaning it’s atomic radius is larger.

‍Things are a little different when you look across the periods, though. While the number of protons and the nuclear size still does increase across a period, the atomic radius actually decreases. This has to do with the number of electron shells.  Across a period, the number of electron shells remains the same, while the number of electrons increases. Thus, as the nuclear charge increases across a period, the protons in the nucleus can attract the higher number of electrons more closely due to the attraction of the positive protons to the negative electrons. This means the electrons are pulled more closely to the nucleus, reducing the size of the atomic radius. 

 For example, Sodium in period 3 has an atomic radius of 186 picometers and chlorine in the same period has an atomic radius of 99 picometers. This is because Chlorine has a larger number of protons and a higher nuclear charge, with no additional shells to put the electrons further away. This increased nuclear charge  attracts the electrons more strongly to the nucleus, making the radius smaller.

Related Lessons 

The Atomic Structure in the Periodic Table

Groups and Periods in the Periodic Table

Electron Configuration and Structure

Nuclear Charge of Atoms


Terms in section
Corpuscularism

Corpuscularism was a theory proposed by Descartes that all matter was composed of tiny particles.

Rene Descartes

Rene Descartes was a famous mathematician and philosopher of the 16th century who hypothesised the theory of corpuscularism about the atom

Luster

Luster is a term for a reflective surface that reflects light giving a shiny appearance.

Semi conductors

Semi conductors is a term to describe metalloids that are able to conduct a current when electrical energy is applied due to the movement of electrons but the conductivity measurements are not as high as metals due to fewer electrons to carry a charge or a less ordered structure.

Ionic compound

An ionic compound is a bond that forms between metals and non metals to form a large ionic lattice

Nuclear Fusion

Nuclear fusion is a process which occurs in. the sun. Hydrogen atoms under a lot of heat and pressure are forced together to make a larger atom of helium

Uncertainty Principle

Heisenberg’s uncertainty principle is used to describe the relationship between the momentum and position of an electron. Where by if the exact position of the electron is known the momentum will be uncertain.

Heisenberg

Werner Heisenberg was a German physicist who was a pioneer in the field of quantum mechanics. He devised the principle of uncertainty relating to the momentum and position of an electron.

Lobes

Lobes refers to the shape of electron waves and the area of highest probability of where that electron as a particle would be found.

Pauli Exclusion principle

The Pauli Exclusion refers to the theory that each electron can only have a unique set of the 4 quantum numbers and no two electrons can have the same quantum numbers

Quantum Numbers

Quantum numbers is a term used to describe the assigning of numbers to electrons as a mathematical function to describe their momentum and energy.

Bohr Model

The Bohr model refers to the treatment of electrons as particles that orbit the nucleus.

Quantum Mechanics

The term quantum mechanics refers to energy levels and the theoretical area of physics and chemistry where mathematics is used to explain the behaviour of subatomic particles.

Trough

A trough is the lowest point on a transverse wave.

Peak

A peak is the highest point on a transverse wave.

Vibrational Modes

Vibrational modes is a term used to describe the constant motion in a molecule. Usually these are vibrations, rotations and translations.

Erwin Schrodinger

Erwin Schrodinger was an Austrian physicist who used mathematical models to enhance the Bohr model of the electron and created an equation to predicted the likelihood of finding an electron in a given position.

Alkali Metal

The alkali metals, found in group 1 of the periodic table (formally known as group IA), are so reactive that they are generally found in nature combined with other elements. The alkali metals are shiny, soft, highly reactive metals at standard temperature and pressure.

Alkaline Earth Metals

Alkaline earth metals is the second most reactive group of elements in the periodic table. They are found in group 2 of the periodic table (formally known as group IIA).

Unknown Elements

Unknown elements (or transactinides) are the heaviest elements of the periodic table. These are meitnerium (Mt, atomic number 109), darmstadtium (Ds, atomic number 110), roentgenium (Rg, atomic number 111), nihonium (Nh, atomic number 113), moscovium (Mc, atomic number 115), livermorium (Lv, atomic number 116) and tennessine (Ts, atomic number 117).

Post-Transitional Metal

The post-transition metals are the ones found between the transition metals (to the left) and the metalloids (to the right). They include aluminium (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb) and bismuth (Bi).

Oganesson

Oganesson (Og) is a radioactive element that has the atomic number 118 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 18. It has the symbol Og.

Tennessine

Tennessine (Ts) is a radioactive element that has the atomic number 117 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 17. It has the symbol Ts.

Livermorium

Livermorium (Lv) is a radioactive element that has the atomic number 116 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 16. It has the symbol Lv.

Moscovium

Moscovium (Mc) is a radioactive metal that has the atomic number 115 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 15. It has the symbol Mc.

Flerovium

Flerovium (Fl) is a radioactive metal that has the atomic number 114 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 14. It has the symbol Fl.

Nihonium

Nihonium (Nh) is a radioactive metal that has the atomic number 112 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 13. It has the symbol Nh.

Copernicium

Copernicium (Cr) is a radioactive metal that has the atomic number 112 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 11. It has the symbol Rg.

Roentgenium

Roentgenium (Rg) is a radioactive metal that has the atomic number 111 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 11. It has the symbol Rg.

Darmstadtium

Darmstadtium (Ds) is a radioactive metal that has the atomic number 110 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 10. It has the symbol Ds

Meitnerium

Meitnerium (Mt) is a radioactive metal that has the atomic number 109 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 9. It has the symbol Mt.

Hassium

Hassium (Hs) is a radioactive metal that has the atomic number 108 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 8. It has the symbol Hs.

Bohrium

Bohrium (Bh) is a radioactive metal that has the atomic number 107 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 7. It has the symbol Bh.

Seaborgium

Seaborgium (Sg) is a radioactive metal that has the atomic number 106 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 6. It has the symbol Sg.

Dubnium

Dubnium (Db) is a radioactive metal that has the atomic number 105 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 5. It has the symbol Db.

Rutherfordium

Rutherfordium (Rf) is a radioactive metal that has the atomic number 104 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 4. It has the symbol Rf.

Lawrencium

Lawrencium (Lr) is a silvery-white colored radioactive metal that has the atomic number 103 in the periodic table. It is an Actinoid Metal with the symbol Lr.

Nobelium

Nobelium (No) is a radioactive metal that has the atomic number 102 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is an Actinoid Metal with the symbol No.

Mendelevium

Mendelevium (Md) is a radioactive metal that has the atomic number 101 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is an Actinoid Metal with the symbol Md.

Fermium

Fermium (Fm) is a silvery-white colored radioactive metal that has the atomic number 100 in the periodic table. It is an Actinoid Metal with the symbol Fm.

Einsteinium

Einsteinium (Es) is a silvery-white colored radioactive metal that has the atomic number 99 in the periodic table. It is an Actinoid Metal with the symbol Es.

Californium

Californium (Cf) is a silvery-white colored radioactive metal that has the atomic number 98 in the periodic table. It is an Actinoid Metal with the symbol Cf.

Berkelium

Berkelium (Bk) is a silvery colored radioactive metal that has the atomic number 97 in the periodic table. It is an Actinoid Metal with the symbol Bk.

Curium

Curium (Cm) is a silvery-white colored radioactive metal that has the atomic number 96 in the periodic table. It is an Actinoid Metal with the symbol Cm.

Americium

Americium (Am) is a silvery colored radioactive metal that has the atomic number 95 in the periodic table. It is an Actinoid Metal with the symbol Am.

Plutonium

Plutonium (Pu) is a silvery colored radioactive metal that has the atomic number 94 in the periodic table. It is an Actinoid Metal with the symbol Pu.

Neptunium

Neptunium (Np) is a silvery colored radioactive metal that has the atomic number 93 in the periodic table. It is an Actinoid Metal with the symbol Np.

Protactinium

Protactinium (Pa) is a shiny silver colored radioactive metal that has the atomic number 91 in the periodic table. It is an Actinoid Metal with the symbol Pa.

Thorium

Thorium (Th) is a silvery-white colored radioactive metal that has the atomic number 90 in the periodic table. It is an Actinoid Metal with the symbol Th.

Actinium

Actinium (Ac) is a silvery colored radioactive metal that has the atomic number 89 in the periodic table. It is an Actinoid Metal with the symbol Ac.

Radium

Radium (Ra) is a silvery-white colored metal that has the atomic number 88 in the periodic table. It is an Alkaline earth Metal with the symbol Ra and is located in Group 2 of the periodic table.

Francium

Francium (Fr) is thought to be a gray colored metal that has the atomic number 87 in the periodic table. It is an Alkali Metal with the symbol Fr and is located in Group 1 of the periodic table.

Radon

Radon (Rn) is a colourless, odourless, radioactive gas non-metal that has the atomic number 86 in the periodic table in Group 18. It has the symbol Rn.

Astatine

Astatine (At) is a radioactive non-metal that has the atomic number 85 in the periodic table in Group 17. It has the symbol At.

Polonium

Polonium (Po) is a silvery-gray metal that has the atomic number 84 in the periodic table in Group 16. It has the symbol Po.

Bismuth

Bismuth (Bi) is a hard steel-gray metal that has the atomic number 83 in the periodic table in Group 15. It has the symbol Bi.

Lead

Lead (Pb) is a soft gray metal that has the atomic number 82 in the periodic table in Group 14. It has the symbol Pb.

Thallium

Thallium (Tl) is a soft gray metal that has the atomic number 81 in the periodic table in Group 13. It has the symbol Tl.

Mercury

Mercury (Hg) is a liquid silver coloured metal that has the atomic number 80 in the periodic table. It is a Transition metal in Group 12. It has the symbol Hg.

Gold

Gold (Au) is a soft gold coloured metal that has the atomic number 79 in the periodic table. It is a Transition metal in Group 11. It has the symbol Au.

Platinum

Platinum (Pt) is a heavy white metal that has the atomic number 78 in the periodic table. It is a Transition metal in Group 10. It has the symbol Pt.

Iridium

Iridium (Ir) is a heavy white metal that has the atomic number 77 in the periodic table. It is a Transition metal in Group 9. It has the symbol Ir.

Osmium

Osmium (Os) is a hard fine black powder or blue-white metal that has the atomic number 76 in the periodic table. It is a Transition metal in Group 8. It has the symbol Os.

Rhenium

Rhenium (Re) is a silvery-white coloured metal that has the atomic number 75 in the periodic table. It is a Transition metal in Group 7. It has the symbol Re.

Tungsten

Tungsten (W) is a steel-gray coloured metal that has the atomic number 74 in the periodic table. It is a Transition metal in Group 6. It has the symbol W.

Tantalum

Tantalum (Ta) is a gray coloured metal that has the atomic number 73 in the periodic table. It is a Transition metal in Group 5. It has the symbol Ta.

Hafnium

Hafnium (Hf) is a silvery coloured metal that has the atomic number 72 in the periodic table. It is a Transition metal in Group 4. It has the symbol Hf.

Lutetium

Lutetium (Lu) is a silvery-white coloured metal that has the atomic number 71 in the periodic table. It is a Lanthanide metal. It has the symbol Lu.

Ytterbium

Ytterbium (Yb) is a silvery coloured metal that has the atomic number 70 in the periodic table. It is a Lanthanide metal. It has the symbol Yb.

Thulium

Thulium (Tm) is a silvery coloured metal that has the atomic number 69 in the periodic table. It is a Lanthanide metal. It has the symbol Tm.

Erbium

Erbium (Er) is a silvery coloured metal that has the atomic number 68 in the periodic table. It is a Lanthanide metal. It has the symbol Er.

Holmium

Holmium (Ho) is a silvery coloured metal that has the atomic number 67 in the periodic table. It is a Lanthanide metal. It has the symbol Ho.

Dysprosium

Dysprosium (Dy) is a silvery coloured metal that has the atomic number 66 in the periodic table. It is a Lanthanide metal. It has the symbol Dy.

Terbium

Terbium (Tb) is a silvery-gray coloured metal that has the atomic number 65 in the periodic table. It is a Lanthanide metal. It has the symbol Tb.

Gadolinium

Gadolinium (Gd) is a silvery-white coloured metal that has the atomic number 64 in the periodic table. It is a Lanthanide metal. It has the symbol Gd.

Europium

Europium (Eu) is a silvery-white coloured metal that has the atomic number 63 in the periodic table. It is a Lanthanide metal. It has the symbol Eu.

Samarium

Samarium (Sm) is a silvery coloured metal that has the atomic number 62 in the periodic table. It is a Lanthanide metal. It has the symbol Sm.

Promethium

Promethium (Pm) is a rare metal that has the atomic number 61 in the periodic table. It is a Lanthanide metal. It has the symbol Pm.

Neodymium

Neodymium (Nd) is a silvery white coloured metal that has the atomic number 60 in the periodic table. It is a Lanthanide metal. It has the symbol Nd.

Praseodymium

Praseodymium (Pr) is a silvery white coloured metal that has the atomic number 59 in the periodic table. It is a Lanthanide metal. It has the symbol Pr.

Cerium

Cerium (Ce) is a iron-gray coloured metal that has the atomic number 58 in the periodic table. It is a Lanthanide metal. It has the symbol Ce.

Lanthanum

Lanthanum (La) is a soft silvery white coloured metal that has the atomic number 57 in the periodic table. It is a Lanthanide metal. It has the symbol La.

Barium

Barium (Ba) is a soft silvery white coloured metal that has the atomic number 56 in the periodic table. It is an Alkaline earth metal and is located in Group 2 of the periodic table. it has the symbol Ba.

Caesium

Caesium (Cs) is a soft gray coloured metal that has the atomic number 55 in the periodic table. It is an Alkali Metal and is located in Group 1 of the periodic table. it has the symbol Cs.

Xenon

Xenon (Xe) exists as a colourless, odourless gas and is chemically inert. It has the atomic number 54 in the periodic table and belongs in Group 18, the Noble Gases. It is a non metal with the symbol Xe.

Iodine

Iodine (I) is a purple grey solid non metal. It has the atomic number 53 in the periodic table. It is located in Group 17, the Halogens. It has the symbol I.

Tellurium

Tellurium (Te) is a silver-white semi metal that has the atomic number 52 in the periodic table. It is located in Group 16 of the periodic table. It has the symbol Te.

Antimony

Antimony (Sb) is a hard brittle silver-white semi metal that has the atomic number 51 in the periodic table. It is located in Group 15 of the periodic table. It has the symbol Sb.

Tin

Tin (Sn) is a silver-white metal that has the atomic number 50 in the periodic table. It is located in Group 14 of the periodic table. It has the symbol Sn.

Indium

Indium (In) is a silver-white metal that has the atomic number 49 in the periodic table. It is located in Group 13 of the periodic table. It has the symbol In.

Cadmium

Cadmium (Cd) is a blue-white metal that has the atomic number 48 in the periodic table. It is a Transition metal and located in Group 12 of the periodic table. It has the symbol Cd.

Silver

Silver (Ag) is a silver metal that has the atomic number 47 in the periodic table. It is a Transition metal and located in Group 11 of the periodic table. It has the symbol Ag.

Palladium

Palladium (Pd) is a silver-white metal that has the atomic number 46 in the periodic table. It is a Transition metal and located in Group 10 of the periodic table. It has the symbol Pd.

Rhodium

Rhodium (Rh) is a brittle silver-white metal that has the atomic number 45 in the periodic table. It is a Transition metal and located in Group 9 of the periodic table. It has the symbol Rh.

Ruthenium

Ruthenium (Ru) is a brittle silver-gray metal that has the atomic number 44 in the periodic table. It is a Transition metal and located in Group 8 of the periodic table. It has the symbol Ru.

Technetium

Technetium (Tc) is a silvery-gray metal that has the atomic number 43 in the periodic table. It is a Transition metal and located in Group 7 of the periodic table. It has the symbol Tc.

Molybdenum

Molybdenum (Mo) is a silvery-white metal that has the atomic number 42 in the periodic table. It is a Transition metal and located in Group 6 of the periodic table. It has the symbol Mb.

Niobium

Niobium (Nb) is a shiny white metal that has the atomic number 41 in the periodic table. It is a Transition metal and located in Group 5 of the periodic table. It has the symbol Nb.

Zirconium

Zirconium (Zr) is a gray white metal that has the atomic number 40 in the periodic table. It is a Transition metal and located in Group 4 of the periodic table. It has the symbol Zr.

Yttrium

Yttrium (Y) is a silvery metal that has the atomic number 39 in the periodic table. It is a Transition metal and located in Group 3 of the periodic table. It has the symbol Y.

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