An ionic compound contains cations (positive ions) and anions (negative ions). The formula can be worked out from the charge on each ion since the overall charge in the compound is zero.For example, when sodium reacts with chlorine, one sodium atom loses its outermost electron and becomes a positive Na+ ion. The electron is transferred to a chlorine atom which becomes a negative chloride ion Cl-.Only one Na+ ion is needed to balance the charge on the one Cl- ion so the chemical formula is NaCl. In contrast, two Cl- ions are needed to balance the charge of an Mg2+ ion so the chemical formula is MgCl2.
Chemical Formulae
Read the text
Read the text and highlight anything you think is important. When you go on, the text is hidden and you answer from memory.
Specification: OCR Chemistry A (H032), AS-level, 2.1.2 Compounds, formulae and equations. Topic: Atoms, Ions and Compounds.
Key terms in this lesson
- Ion
- A positively or negatively charged atom or group of atoms, formed by the loss or gain of electrons.
- Cation
- A positively charged ion, formed when an atom loses one or more electrons.
- Anion
- A negatively charged ion, formed when an atom gains one or more electrons.
More in Atoms, Ions and Compounds
- Relative Isotopic Mass
- Relative Atomic Mass
- The Mass Spectrometer
- Calculating Relative Atomic Mass
- Polyatomic ions
- Chemical Equations
- Electron Shells
- Spin
All 17 lessons in Atoms, Ions and Compounds · All OCR AS-level Chemistry topics