Scientists Say: Atomic number | Science News for Students

Scientists Say: Atomic number

This number gives an element its place in the periodic table
Apr 17, 2017 — 7:00 am EST

This hunk of copper is element 29 on the periodic table of elements. The number refers to how many protons found in each atom of copper.


Atomic number (noun, “ah-TOM-ick number”)

This is the number of protons — positively charged particles — in a single atom. The atomic number identifies an atom as a specific element. Any atom of gold will have 79 protons, for instance. An atom with one more proton is no longer gold. It’s mercury. One less, and it’s platinum. Atomic number also determines the element’s location on the periodic table. Number one is hydrogen.

In a sentence

Scientists made four new elements by slamming smaller atoms together until their protons stuck, creating elements with the atomic numbers 113, 115, 117 and 118.

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Power Words

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atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

atomic     Having to do with atoms, the smallest possible unit that makes up a chemical element.

atomic number     The number of protons in an atomic nucleus, which determines the type of atom and how it behaves.

element     (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

mercury     Sometimes called quicksilver, mercury is an element with the atomic number 80. At room temperature, this silvery metal is a liquid. Mercury is also very toxic.

particle     A minute amount of something.

proton     A subatomic particle that is one of the basic building blocks of the atoms that make up matter. Protons belong to the family of particles known as hadrons.