Ions, Molecules, and Compounds - Grade 10 Chemistry

Ions

electrically charged atoms or groups of atoms. They form when electrons are traded between atoms of different elements.

compound

a pure substance made up of two or more elements, in which the elements are chemically combined. two main types: ionic and molecular

ionic compound

a compound that is formed from one or more positively charged ions and one or more negatively charged ions.

Ion Symbols

To write the symbol for an ion, write the symbol of the element and show the ion charge as a superscript. For example, the symbol of a calcium ion is Ca^2+. When an ion has a charge of 1^+ or 1^–, the symbol has no number in the superscript, such as for Na^+ and F^–.

multivalent element

an element that can form an ion in more than one way. Many metal elements are multivalent. The name of an ion of a multivalent element always contains a Roman numeral that indicates the ion charge.

Naming Ionic Compounds

1. Name the metal ion first. The name of the metal ion is the same as the element name. If the element can form an ion in more than one way, include a Roman numeral to indicate the charge.

2. Name the non-metal ion second. When a non-metal becomes a negative ion, the ending of its name changes to “ide.”

3. Name the ionic compound by combining the ion names.

polyatomic ion

a group of atoms, usually of different elements, that act as a single ion. For example, one atom of sulphur and four atoms of oxygen form the polyatomic ion called sulphate, or SO42–. Similar polyatomic ions are named using the suffixes “-ate” or “-ite.”

Steps for Writing Formulas for Binary Ionic Compounds

Examine the name of the compound. Identify the ions and their charges. Determine the number of each ion needed to balance the charges. Note the ratio of positive to negative ions, and write the formula. Write the chemical formula, using subscripts if needed.

molecule

a combination of two or more atoms held together by covalent bonds.

covalent bond

a connection, usually between the atoms of non-metals, in which the two atoms share a pair of electrons. The electron pair belongs to both atoms, and the attraction of the atoms for the same electron pair holds them together.

molecular element

two or more atoms, all of the same element, are joined by covalent bonds.

diatomic molecule

two or more atoms, all of the same element, are joined by covalent bonds. The formulas for diatomic molecules contain a subscript. In the

formula of a molecule. a subscript tells you the number of each atom in the molecule. ex. C^2

molecular compound

When atoms of two or more different non-metals combine, a pure substance. the atoms in molecular compounds are joined together by covalent bonds. In each bond, the atoms share a single pair of electrons.

Naming Binary Molecular Compounds

The names of binary molecular compounds that do not contain hydrogen atoms use Greek prefixes to indicate how many atoms of each element are present in a compound. ex. momo, di. Hydrogen is unique in many ways, and this is reflected in naming systems. Many compounds containing hydrogen have simply been given names.