Atom: Definition

Click any underlined text below for a context-specific definition and example

• An atom is the smallest object which still has all the properties

  All atoms of any chemical element share some properties, such as the number of other atoms they bond to, or the strength of those bonds. When many atoms of an element are together their properties lead to the properties of the substance they compose.

  Example:

  Atoms of gold do not strongly attract their outermost electrons. Thus, the electrons are mobile and gold can conduct electricty

  of a chemical elementchemical element

  All atoms with the same number of protons are the same chemical element

  Example:

  All atoms of the element carbon have 6 protons

• All matter

  Anything which takes up space and has mass is matter

  Example:

  Matter includes solid objects like an orange, liquids like water and gases like steam

  is composed of atoms
• An atom is composed of a nucleus

  The nucleus is made of protons and neutrons and is the positively-charged portion of an atom

  Example:

  The nucleus of a helium atom is composed of two protons and two neutrons

  , made of protons

  Positively-charged particles which are found in the nuclei of all atoms

  Example:

  Even the smallest atom, hydrogen, has one proton in its nucleus

  (along with neutrons

  Neutrally-charged particles which are found in the nuclei of most atoms

  Example:

  There are two neutrons in the nucleus of a helium atom

  in most atoms) , and electrons

  Negatively-charged particles which move around the nucleus

  Example:

  All neutrally-charged atoms have electrons. However, charged atoms (ions) can exist without any electrons

  surrounding the nucleus
• Atoms differ from each other by their element (defined by the number of protons), their electric charge

  The electrical charge of an atom defines how strongly oppositely-charged particles attract to one another via the electromagnetic force

  Example:

  Sodium and chlorine atoms have +1 and -1 electric charges, respectively. Thus, they are attracted to one another to make table salt

  (number of electrons relative to protons

  Electrons have a negative charge (of magnitude 1) and protons have a positive charge (also of magnitude 1), so the charge of an atom is equal to the number of protons in that atom minus the number of electrons

  Example:

  A typical helium atom has 2 protons and 2 electrons. Therefore, the atom has a charge of 2 - 2 = 0. In otherwords, it is neutrally charged

  ) and isotope

  An atom which has more or fewer neutrons than other atoms of its same element

  Example:

  Carbon-14 has 8 neutrons while carbon-12 has 6 neutrons. Both are isotopes of carbon

  (number of neutrons)