What Are Chemical Elements?

Chemical elements are the basic building blocks of matter. Everything you see (and plenty of things that you don’t) – including rocks, water, living organisms, air, your computer, and even stars – is made of one or more elements. Each element is a pure substance made entirely of atoms that all have the same number of protons in their nuclei. This number, called the atomic number, uniquely identifies each element.

The Structure of an Atom

Atoms are the smallest units of elements that retain their chemical identity. Each atom consists of three main subatomic particles:

Protons are positively charged particles located in the nucleus (center) of the atom. The number of protons defines the atomic number and determines which element an atom represents. For example, all atoms with 6 protons are carbon atoms.
Neutrons are neutrally charged particles also found in the nucleus. Neutrons add mass to the atom and help stabilize the nucleus, but they don’t change the element’s identity. Atoms of the same element with different numbers of neutrons are called isotopes.
Electrons are negatively charged particles that move around the nucleus in energy levels or shells (sometimes also referred to as clouds or orbitals). Electrons are critical in chemical bonding and reactions because they are the part of the atom that interacts with other atoms.

How Do Atoms Combine?

Chemical reactions occur when atoms gain, lose, or share electrons to form chemical bonds. These interactions allow atoms to form molecules and compounds. The way an element reacts chemically depends largely on the arrangement of its electrons, particularly those in the outermost shell, called valence electrons. Find out more about how atoms combine for form molecules.

The Periodic Table: A Map of Elements

To make sense of the chemical elements and their behaviors, scientists use a powerful organizational tool called the periodic table. Created in its earliest form by Dmitri Mendeleev in the 19th century, the modern periodic table arranges elements based on their atomic number and groups elements with similar chemical properties.

Key Features of the Periodic Table

Periods (horizontal rows): Elements in the same period have the same number of electron shells.
Groups (vertical columns): Elements in the same group share similar chemical properties because they have the same number of valence electrons.
Blocks (s, p, d, f): Reflect which type of atomic orbital is being filled with electrons.

The periodic table helps us predict:

Element properties (e.g., metals vs. nonmetals)
How elements will bond with each other
Trends like electronegativity, atomic radius, and ionization energy

Categories of Elements in the Periodic Table

To further simplify and understand chemical behavior, elements are often grouped into categories based on shared characteristics. Below is a list of all known elements (as of 2025), organized by category, with atomic numbers included.

1. Alkali Metals (Group 1)

Highly reactive, soft metals, especially with water. Don’t throw a solid chunk of sodium into water unless you plan on liberating hydrogen in a violently explosive manner.

3 – Lithium (Li)
11 – Sodium (Na)
19 – Potassium (K)
37 – Rubidium (Rb)
55 – Cesium (Cs)
87 – Francium (Fr)

2. Alkaline Earth Metals (Group 2)

Reactive metals, but less so than alkali metals.

4 – Beryllium (Be)
12 – Magnesium (Mg)
20 – Calcium (Ca)
38 – Strontium (Sr)
56 – Barium (Ba)
88 – Radium (Ra)

3. Transition Metals (Groups 3–12)

Hard, dense metals with high melting points, useful in industry.

21 – Scandium (Sc)
22 – Titanium (Ti)
23 – Vanadium (V)
24 – Chromium (Cr)
25 – Manganese (Mn)
26 – Iron (Fe)
27 – Cobalt (Co)
28 – Nickel (Ni)
29 – Copper (Cu)
30 – Zinc (Zn)
39 – Yttrium (Y)
40 – Zirconium (Zr)
41 – Niobium (Nb)
42 – Molybdenum (Mo)
43 – Technetium (Tc)
44 – Ruthenium (Ru)
45 – Rhodium (Rh)
46 – Palladium (Pd)
47 – Silver (Ag)
48 – Cadmium (Cd)
72 – Hafnium (Hf)
73 – Tantalum (Ta)
74 – Tungsten (W)
75 – Rhenium (Re)
76 – Osmium (Os)
77 – Iridium (Ir)
78 – Platinum (Pt)
79 – Gold (Au)
80 – Mercury (Hg)
104 – Rutherfordium (Rf)
105 – Dubnium (Db)
106 – Seaborgium (Sg)
107 – Bohrium (Bh)
108 – Hassium (Hs)

4. Post-Transition Metals

Softer metals with mixed properties.

13 – Aluminum (Al)
31 – Gallium (Ga)
49 – Indium (In)
50 – Tin (Sn)
81 – Thallium (Tl)
82 – Lead (Pb)
83 – Bismuth (Bi)
84 – Polonium (Po)
113 – Nihonium (Nh)
114 – Flerovium (Fl)

5. Metalloids

Have properties between metals and nonmetals.

5 – Boron (B)
14 – Silicon (Si)
32 – Germanium (Ge)
33 – Arsenic (As)
51 – Antimony (Sb)
52 – Tellurium (Te)
85 – Astatine (At)

6. Nonmetals

Typically poor conductors; essential to life.

1 – Hydrogen (H)
6 – Carbon (C)
7 – Nitrogen (N)
8 – Oxygen (O)
15 – Phosphorus (P)
16 – Sulfur (S)
34 – Selenium (Se)

7. Halogens (Group 17)

Highly reactive nonmetals; often form salts.

9 – Fluorine (F)
17 – Chlorine (Cl)
35 – Bromine (Br)
53 – Iodine (I)
85 – Astatine (At)
117 – Tennessine (Ts)

8. Noble Gases (Group 18)

Inert gases with very low reactivity.

2 – Helium (He)
10 – Neon (Ne)
18 – Argon (Ar)
36 – Krypton (Kr)
54 – Xenon (Xe)
86 – Radon (Rn)
118 – Oganesson (Og)

9. Lanthanides (Period 6, f-block)

Rare earth elements; often used in electronics and magnets.

57 – Lanthanum (La)
58 – Cerium (Ce)
59 – Praseodymium (Pr)
60 – Neodymium (Nd)
61 – Promethium (Pm)
62 – Samarium (Sm)
63 – Europium (Eu)
64 – Gadolinium (Gd)
65 – Terbium (Tb)
66 – Dysprosium (Dy)
67 – Holmium (Ho)
68 – Erbium (Er)
69 – Thulium (Tm)
70 – Ytterbium (Yb)
71 – Lutetium (Lu)

10. Actinides (Period 7, f-block)

Radioactive elements, many synthetic.

89 – Actinium (Ac)
90 – Thorium (Th)
91 – Protactinium (Pa)
92 – Uranium (U)
93 – Neptunium (Np)
94 – Plutonium (Pu)
95 – Americium (Am)
96 – Curium (Cm)
97 – Berkelium (Bk)
98 – Californium (Cf)
99 – Einsteinium (Es)
100 – Fermium (Fm)
101 – Mendelevium (Md)
102 – Nobelium (No)
103 – Lawrencium (Lr)

Over time, we’ll add explanatory pages for every element to the IQ Science website, to provide you with clear insights into the ingredients that form every substance in the universe.

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