### substance:

Chemical element
* All chemical elements have many isotopes
  - radionuclides
* Every chemical element yields a secondary radiation that is characteristic of that element.
* Most chemical elements consist of more than one isotope.
* Most chemical elements have isotopes
  - stable isotopes
* Some chemical elements have no stable isotopes at all and are therefore rare.
* act and react upon each other.
* are elements
  - made of atoms
  - recycled within an ecosystem
* constitute all of the ordinary matter of the universe.
* exist naturally in the environment with different concentrations.
* take different forms in the environment.
+ Radioactive decay: Nuclear physics
  * Chemical elements are made of atoms. In stable elements, the atom stays the same. In a chemical reaction, the atoms will form chemical bonds, with other atoms. Even if the bonds change during a reaction, the atoms themselves do not.

### substance | chemical element:

Cerium
* alone is too soft, so iron is used to harden it.
* gray lustrous malleable metal.
* grey, shiny or lustrous metal.
* has many uses, including as an alloying agent with iron and other metals.
* highly electropositive metal and reacts with water.
* is also an essential component of phosphors used in TV screens and fluorescent lamps
  - available in soluble forms including chlorides , nitrates and acetates
* is an element it solid metal
  - iron-gray lustrous metal
* is an iron-gray, malleable metal that oxidizes very readily at room temperature
  - soft, ductile and malleable metal
  - attacked readily by acids and alkalis
  - just one of the several rare earth metals that are important to industry
  - metallic elements
  - oxidised readily in air
  - relatively abundant in the Earth's crust
  - slightly harder than lead
  - soluble in concentrated or dilute mineral acids
* is the most abundant of the metals of the so-called rare earths
  - rare earth elements
  - only one of the rare earth metals that can be easily separated from the others
* is the second element of the lanthanide series
  - most active lanthanide after europium
* is used as the surrogate for plutonium
  - by the motion picture industry for lighting purposes
  - in making lamp mantles as incandescence is formed when burned
* malleable metal used in industrial applications.
* malleable, soft, ductile, iron-grey metal, slightly harder than lead.
* occurs chiefly in the minerals monazite and bastnaesite.
* soft, malleable, ductile, iron-grey metal with hexagonal or cubic crystalline structure.
* very reactive metal and quickly tarnishes in air.
+ Cerium, Properties: Chemical elements :: Metals
  * Cerium is a grey, shiny or lustrous metal. At room temperature Cerium is a solid. It burns in air to form a compound with one cerium atom and two oxygen atoms.

### substance:

Chemical substance
* All chemical substances can produce adverse health effects at some level of exposure.
* Any chemical substance is toxic if it is ingested or absorbed in excessive amounts.
* Every chemical substance emits a unique spectrum when it absorbs energy.
* Most chemical substances combine with it when they crystallize.
* Most chemical substances consist of chemical elements
  - different elements
  - contain atoms
* Some chemical substances are produced by candidas
  - organisms
  - secreted by animals
  - dissolve in water
  - exist as air
  - find in blood
  - induce allergies
* Some chemical substances inhibit bacterial growth
  - produce chemicals
  - release into air
  - use in food
* can be chemical elements , chemical compounds , ions or alloys
  - solids , liquids , gases, or plasma
* form part of daily life in modern societies, also in Denmark.
* have the advantage of mobility.
* increase in our blood stream.
* occur in cigarette smoke as gases or as particulates.