2.5: The Periodic Table (2023)

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    Learning Objectives
    • To become familiar with the organization of the periodic table.

    Rutherford’s nuclear model of the atom helped explain why atoms of different elements exhibit different chemical behavior. The identity of an element is defined by its atomic number (Z), the number of protons in the nucleus of an atom of the element. The atomic number is therefore different for each element. The known elements are arranged in order of increasing Z in the periodic table (Figure \(\PageIndex{1}\)). The rationale for the peculiar format of the periodic table is explained later. Each element is assigned a unique one-, two-, or three-letter symbol. The names of the elements are listed in the periodic table, along with their symbols, atomic numbers, and atomic masses. The chemistry of each element is determined by its number of protons and electrons. In a neutral atom, the number of electrons equals the number of protons.

    2.5: The Periodic Table (1)

    The elements are arranged in a periodic table, which is probably the single most important learning aid in chemistry. It summarizes huge amounts of information about the elements in a way that facilitates the prediction of many of their properties and chemical reactions. The elements are arranged in seven horizontal rows, in order of increasing atomic number from left to right and top to bottom. The rows are called periods, and they are numbered from 1 to 7. The elements are stacked in such a way that elements with similar chemical properties form vertical columns, called groups, numbered from 1 to 18 (older periodic tables use a system based on roman numerals). Groups 1, 2, and 13–18 are the main group elements, listed as A in older tables. Groups 3–12 are in the middle of the periodic table and are the transition elements, listed as B in older tables. The two rows of 14 elements at the bottom of the periodic table are the lanthanides and the actinides, whose positions in the periodic table are indicated in group 3.

    Metals, Nonmetals, and Semimetals

    The heavy orange zigzag line running diagonally from the upper left to the lower right through groups 13–16 in Figure \(\PageIndex{1}\) divides the elements into metals (in blue, below and to the left of the line) and nonmetals (in bronze, above and to the right of the line). Gold-colored lements that lie along the diagonal line exhibit properties intermediate between metals and nonmetals; they are called semimetals.

    The distinction between metals and nonmetals is one of the most fundamental in chemistry. Metals—such as copper or gold—are good conductors of electricity and heat; they can be pulled into wires because they are ductile; they can be hammered or pressed into thin sheets or foils because they are malleable; and most have a shiny appearance, so they are lustrous. The vast majority of the known elements are metals. Of the metals, only mercury is a liquid at room temperature and pressure; all the rest are solids.

    (Video) 2.5 The Periodic Table

    Nonmetals, in contrast, are generally poor conductors of heat and electricity and are not lustrous. Nonmetals can be gases (such as chlorine), liquids (such as bromine), or solids (such as iodine) at room temperature and pressure. Most solid nonmetals are brittle, so they break into small pieces when hit with a hammer or pulled into a wire. As expected, semimetals exhibit properties intermediate between metals and nonmetals.

    Example \(\PageIndex{1}\): Classifying Elements

    Based on its position in the periodic table, do you expect selenium to be a metal, a nonmetal, or a semimetal?

    Given: element

    Asked for: classification


    (Video) 2.5 The Periodic Table

    Find selenium in the periodic table shown in Figure \(\PageIndex{1}\) and then classify the element according to its location.


    The atomic number of selenium is 34, which places it in period 4 and group 16. In Figure \(\PageIndex{1}\), selenium lies above and to the right of the diagonal line marking the boundary between metals and nonmetals, so it should be a nonmetal. Note, however, that because selenium is close to the metal-nonmetal dividing line, it would not be surprising if selenium were similar to a semimetal in some of its properties.

    Exercise \(\PageIndex{1}\)

    Based on its location in the periodic table, do you expect indium to be a nonmetal, a metal, or a semimetal?



    (Video) The Periodic Table | OpenStax Chemistry 2e 2.5

    As previously noted, the periodic table is arranged so that elements with similar chemical behaviors are in the same group. Chemists often make general statements about the properties of the elements in a group using descriptive names with historical origins. For example, the elements of Group 1 are known as the alkali metals, Group 2 are the alkaline earth metals, Group 17 are the halogens, and Group 18 are the noble gases.

    Group 1: The Alkali Metals

    The alkali metals are lithium, sodium, potassium, rubidium, cesium, and francium. Hydrogen is unique in that it is generally placed in Group 1, but it is not a metal. The compounds of the alkali metals are common in nature and daily life. One example is table salt (sodium chloride); lithium compounds are used in greases, in batteries, and as drugs to treat patients who exhibit manic-depressive, or bipolar, behavior. Although lithium, rubidium, and cesium are relatively rare in nature, and francium is so unstable and highly radioactive that it exists in only trace amounts, sodium and potassium are the seventh and eighth most abundant elements in Earth’s crust, respectively.

    Group 2: The Alkaline Earth Metals

    The alkaline earth metals are beryllium, magnesium, calcium, strontium, barium, and radium. Beryllium, strontium, and barium are rare, and radium is unstable and highly radioactive. In contrast, calcium and magnesium are the fifth and sixth most abundant elements on Earth, respectively; they are found in huge deposits of limestone and other minerals.

    Group 17: The Halogens

    The halogens are fluorine, chlorine, bromine, iodine, and astatine. The name halogen is derived from the Greek words for “salt forming,” which reflects that all the halogens react readily with metals to form compounds, such as sodium chloride and calcium chloride (used in some areas as road salt).

    (Video) 2.5 Lecture Video The Periodic Table

    Compounds that contain the fluoride ion are added to toothpaste and the water supply to prevent dental cavities. Fluorine is also found in Teflon coatings on kitchen utensils. Although chlorofluorocarbon propellants and refrigerants are believed to lead to the depletion of Earth’s ozone layer and contain both fluorine and chlorine, the latter is responsible for the adverse effect on the ozone layer. Bromine and iodine are less abundant than chlorine, and astatine is so radioactive that it exists in only negligible amounts in nature.

    Group 18: The Noble Gases

    The noble gases are helium, neon, argon, krypton, xenon, and radon. Because the noble gases are composed of only single atoms, they are called monatomic. At room temperature and pressure, they are unreactive gases. Because of their lack of reactivity, for many years they were called inert gases or rare gases. However, the first chemical compounds containing the noble gases were prepared in 1962. Although the noble gases are relatively minor constituents of the atmosphere, natural gas contains substantial amounts of helium. Because of its low reactivity, argon is often used as an unreactive (inert) atmosphere for welding and in light bulbs. The red light emitted by neon in a gas discharge tube is used in neon lights.

    The noble gases are unreactive at room temperature and pressure.


    The periodic table is used as a predictive tool. It arranges of the elements in order of increasing atomic number. Elements that exhibit similar chemistry appear in vertical columns called groups (numbered 1–18 from left to right); the seven horizontal rows are called periods. Some of the groups have widely-used common names, including the alkali metals (Group 1) and the alkaline earth metals (Group 2) on the far left, and the halogens (Group 17) and the noble gases (Group 18) on the far right. The elements can be broadly divided into metals, nonmetals, and semimetals. Semimetals exhibit properties intermediate between those of metals and nonmetals. Metals are located on the left of the periodic table, and nonmetals are located on the upper right. They are separated by a diagonal band of semimetals. Metals are lustrous, good conductors of electricity, and readily shaped (they are ductile and malleable), whereas solid nonmetals are generally brittle and poor electrical conductors. Other important groupings of elements in the periodic table are the main group elements, the transition metals, the lanthanides, and the actinides.


    What is the name of 2.4 element? ›

    Lanthanum | La (Element) - PubChem.

    What is 2 on the periodic table? ›

    Cambridge University's Peter Wothers telling us the tale of element number two, Helium.

    What element has 2 protons 2 neutrons and 2 electrons? ›

    One atom of Helium has 2 electrons, 2 protons and 2 neutrons.

    What element is in period 2 and 3? ›

    The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon.
    Periodic trends.
    Chemical element3
    Electron configuration[He] 2s1
    7 more columns

    How are elements named? ›

    New elements can be named after a mythological concept, a mineral, a place or country, a property or a scientist. The names have to be unique and maintain "historical and chemical consistency". This means a lot of "-iums". "They're Latinising the name," explains chemist Andrea Sella of University College London.

    What element name means emerald? ›

    The gemstones beryl and emerald are both forms of beryllium aluminium silicate, Be3Al2(SiO3)6.

    What element is 2s 2? ›


    What periodic group is 2? ›

    Group 2A (or IIA) of the periodic table are the alkaline earth metals: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). They are harder and less reactive than the alkali metals of Group 1A.

    What element is no 2? ›

    Helium (from Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element with the symbol He and atomic number 2.

    What is 2 protons 2 neutrons? ›

    Helium is the second element of the periodic table and thus is an atom with two protons in the nucleus. Most Helium atoms have two neutrons in addition to the protons.

    What do 2 protons and 2 neutrons make? ›

    The helium nucleus or α-particle, which may form a constituent of heavier nuclei, is composed of two protons and two neutrons.

    What has 2 protons and 2 neutrons atomic number? ›

    Consider the element helium. Its atomic number is 2, so it has two protons in its nucleus. Its nucleus also contains two neutrons. Since 2+2=4, we know that the mass number of the helium atom is 4.

    What element is group 2 period 4? ›

    Answer and Explanation: The symbol of the element in period 4 and group 2 is Ca. This symbol stands for the chemical element calcium, which has an atomic number of 20.

    How many elements are in period 2 and 3? ›

    Period 1 has 2 elements while period 2 and period 3 have 8 elements each.

    What are period 3 elements called? ›

    > The third period elements are called typical elements or representative elements because they represent the properties of their own group without anomalies. The third period consists of eight elements which are: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon.

    Which element is named after a goddess? ›

    Vanadium owes its name to these colours: it was named for the Scandinavian goddess of beauty and fertility, Vanadís (Freyja) because those names were originally given to several of the delightful colours adopted by vanadium-containing compounds.

    What element is named after Earth? ›

    Tellurium is named after the Latin word tellus, meaning "earth".

    Can I name my child emerald? ›

    Emerald is a girl-given name of English origin, meaning “green gemstone.” A precious rock on your fingers, baby Emerald, will soon become your most treasured possession. This gorgeous number holds equal power and beauty to Emily, Emma, and Emilia, but with a uniqueness to help baby Emerald forge their own fate.

    What elements are named after gods? ›

    Also, mythological entities have had a significant impact on the naming of elements. Helium, titanium, selenium, palladium, promethium, cerium, europium, mercury, thorium, uranium, neptunium and plutonium are all given names connected to mythological characters.

    What element is named after a Greek god? ›

    About the Display: Promethium is a radioactive element, therefore, the box contains items that represent the element and the Greek god Prometheus, for whom the element is named after. Prometheus was known to be an intelligent trickster who stole fire from Zeus to give to mortals, resulting in his subsequent punishment.

    What does 2s mean in chemistry? ›

    1 is first shell, 2 is second shell etc. The letter tells you which orbital it is, eg s, p, d or f. The superscript number tells you how many electrons are in that orbital. 1s^2 means 2 electrons are in the 1s orbital. 1s^2 2s^2 2p^6 means 2 electrons in the 1s orbital, 2 electrons in the 2s orbital.

    What does 2s 2p mean in chemistry? ›

    That means that the 2s orbital will fill with electrons before the 2p orbitals. All the 2p orbitals have exactly the same energy. Example 1: The electronic structure of hydrogen. Hydrogen only has one electron and that will go into the orbital with the lowest energy - the 1s orbital.

    How many electrons are in 2s? ›

    The 2s subshell holds a maximum of 2 electrons, and the 2p subshell holds a maximum of 6 electrons.

    Why group 2 elements are called? ›

    The elements of group - 2 are called alkaline earth metals because because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth's crust.

    What atom atomic number is 2? ›

    Consider the element helium. Its atomic number is 2, so it has two protons in its nucleus.

    What is the use of group 2? ›

    Group 2 elements are used for both everyday and chemical applications. They are used in antacids as magnesium oxide. Barium is used to track the movement of meals on x-rays in the field of gastroenterology. Calcium oxide and calcium carbonate are used to remove sulfur gas from reactions of fossil fuels.

    What element is 2.8 2? ›

    Magnesium with atomic number 12, has the electronic configuration 2, 8, 2.

    What elements have a little 2? ›

    The elements with a 2 in their formula are hydrogen, nitrogen and oxygen, plus the elements in group 7 (IUPAC group 17).

    Which atom has 2 protons? ›

    A helium nucleus has two protons and two neutrons.

    What has 2 protons? ›

    An atom with two protons is always a helium atom.

    Is 2 protons and 2 neutrons alpha or beta? ›

    Alpha particles (α) are positively charged and made up of two protons and two neutrons from the atom's nucleus.

    Which has 2 neutrons? ›

    Deuterium an isotope of hydrogen has two neutrons in its nucleus.

    What is 1 proton and 2 neutrons? ›

    Tritium is an isotope of hydrogen that is composed of one proton, two neutrons, and one electron. The symbol for tritium is 3H. The atomic number of tritium is 1 and the atomic mass of tritium is 3.

    What elements has 2 protons and 2 electrons? ›

    Helium is the second most abundant element in the universe. Helium is composed of two electrons, two protons, and usually two neutrons. It is a colorless, odorless, inert gas.

    What particle has 2 protons and 2 electrons? ›

    Therefore, the atom of the element that has two protons and two electrons is helium.

    What elements are in group 2 period? ›

    The elements in the group include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

    What is Period 5 periodic table? ›

    The period 5 transition metals are yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), and cadmium (Cd).

    What element is in period 7 group 2? ›

    Period 7
    Atomic # Name87 Fr88 Ra

    What is group 2 period 2? ›

    The element present in the second period and the second group is Beryllium. Beryllium has an atomic number 4 and is an alkaline earth metal.

    How many elements are there? ›

    Today, with 118 known elements, it is widely regarded as one of the most significant achievements in science.

    How many elements are in period 4? ›

    Hence, there are 18 elements in period 4 of the periodic table.

    Is period 3 a metal? ›

    The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine and argon.
    Electron configuration[Ne] 3s2 3p1
    7 more columns

    Is period 3 all metals? ›

    There are only 2 gaseous elements in period 3; chlorine and argon. These are definitely non-metals since metals DO NOT exist as gases at room temperature and pressure.

    What element has the same name as one of our coins? ›

    It was named nickel after one of its ores, a reddish material that German miners called kupfernickel - St Nicholas's copper. '

    Which element is named after the name of a planet? ›

    Scientists named the elements uranium, neptunium, and plutonium after planets. In 1789, they named element 92, uranium, after Uranus, discovered in 1781.

    What are the basic rules for naming elements? ›

    (i) The names should be short and obviously related to the atomic numbers of the elements. (ii) The names should end in 'ium' whether the element was expected to be a metal or otherwise. (iii) The symbols for the systematically named elements should consist of three letters.

    What is the rarest element you can buy? ›

    Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements.
    Appearanceunknown, probably metallic
    Mass number[210]
    Astatine in the periodic table
    27 more rows

    Is element a diamond? ›

    In short, the answer is no. The statement 'diamond is an element' is misleading as carbon itself is an element. While a diamond is composed of 100% of carbon with no other elements involved, it is not an element but simply an allotrope of the element carbon.

    What elements make gold? ›

    Usually gold is created from platinum, which has one less proton than gold, or from mercury, which has one more proton than gold. Bombarding a platinum or mercury nucleus with neutrons can knock off an neutron or add on a neutron, which through natural radioactive decay can lead to gold.

    Which element is named after a god? ›

    About the Display: Promethium is a radioactive element, therefore, the box contains items that represent the element and the Greek god Prometheus, for whom the element is named after.

    What element is named after Sun God? ›

    Etymology: Helium comes from the Greek word for sun, helios.

    What is a yellow element that stinks when burned? ›

    Answer and Explanation: Sulfur is the name of the element that stinks and has a yellow color.

    What are the newest elements? ›

    Their names are Nihonium, Moscovium and Tennessine. The fourth element is named Oganesson. It was named after a Russian nuclear physicist named Yuri Oganessian.

    How many elements are named after? ›

    This list of chemical elements named after people includes elements named for people both directly and indirectly. Of the 118 elements, 19 are connected with the names of 20 people. 15 elements were named to honor 16 scientists (as curium honours both Marie and Pierre Curie).

    What are 3 elements named after countries? ›

    Elements which are named after currently existing countries and cities are as:
    • Polonium, named after Poland.
    • Francium and gallium, both named after France.
    • Nihonium, named after Japan.
    • Germanium was named for Germany.


    1. 2.5 Intro to the Periodic Table
    (Ken Schenck)
    2. The periodic table explained in 2.5 minutes
    (Sla Apzak)
    3. 2.5 Introduction to the Periodic Table
    (Kelly Davis)
    4. The genius of Mendeleev's periodic table - Lou Serico
    5. Sections 2.4 and 2.5 - The Periodic Table, Molecules and Ions
    (Chemistry with Buck)
    6. Chapter 2.5 - Periodic Trends
    (Dr. Scott Witherow)


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