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Tuesday, 20 June 2017


Edition 004

Chemistry revision: Some of the useful keywords and things to remember about Atoms, elements and compounds.
By: Daniella Nasser 9D
I wrote this article to help students understand and enjoy chemistry as much as I do.
 Free vector graphic: Key, Art, Vintage, Keys, Antique - Free Image ...File:Atom.svg - Wikimedia Commons
Key words:
Ions: charged particles, formed when electrons are gained or given up.
  • Positive ions: lost electrons.
  • Negative ions: gained electrons.

Elements: Are made up of one type of atom only.

Compounds: Are made up of more than one kind of atom chemically bonded together in fixed proportions.

Proton number (atomic number): Number of protons in the nucleus of an atom. In the periodic table the elements are arranged in ascending order of proton number.

Nucleon number (mass number): Number of protons and neutrons in the nucleus of an atom.

  • Important things to remember:
  • Atoms have a neutral overall electrical charge, this is because the number of electrons in an atom is the same as the number of protons in its nucleus.
  • Atoms may be identified by their proton number.

Isotopes: atoms of the same element (consequently same atomic number) but with different numbers of neutrons (dissimilar nucleon number).

Example: Isotopes of hydrogen.

1 - 1 = 0
2 - 1 = 1
3 - 1 = 2

Uses of radioisotopes:
  • Industrial check for leaks in pipes
  • Medical use of cobalt-60 is to treat cancer.

Ionic Bonding
Atoms join together (form bonds) in order to achieve the stable electron arrangement of noble gases.

Ionic bond: electrostatic attraction between oppositely charged ions.  It is a type of bonding between metal atoms and non-metal atoms.   

The metal atom gives up the electrons in its outermost shell and gives them to the non-metal. When a metal atom has lost its electrons in the outermost shell it turns into a cation (a positive ion).
  • The charge on the cation is determined by the number of electrons lost.

When a non-metal atom obtains electrons it turns into an anion (a negative ion).
  • The charge on the anion is determined by the number of electrons gained.

  • Ions form a lattice, a regular arrangement of alternating positive and negative ions.

Properties of ionic compounds:
  • High melting points and boiling points due to the strong electrostatic force between the ions.
  • Conduct electricity only when dissolved in water or melted because the ions become free to move.
  • They are normally soluble in water.


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