C3.2 - Atoms into ions

• A compound contains two or more elements, which are chemically combined
• Elements react together to form compounds by gaining or losing electrons or by sharing electrons
• Sharing electrons, is called covalent bonding
• Transferring electrons is called ionic bonding
• A positive sodium ion is NA+ is formed when a sodium atom loses an electron during ionic bonding

  
• A negative chlorine ion Cl- is formed when a chlorine atom gains an electron during ionic bonding

  
• The atoms of the noble gases, in Group 0, have an arrangement of electrons that make them stable and unreactive
• When sodium reacts with chlorine, each sodium atom loses an electron and each chlorine atom gains an electron. They both form stable ions. The electrostatic attraction between the oppositely charged Na+ ions and Cl- ions is called ionic bonding.

  
• Metal atoms are unstable until they lose electrons when they become stable positive ions
• An ion is an atom or group of atoms that has an electrical charge, either positive or negative
• An atom that loses electrons has more protons than electrons and so has a positive overall charge. This is called a positive ion
• An atom that gains electrons has more electrons than protons and so has a negative overall charge. This is called a negative ion
• Ionic bonding can be shown by using a dot and cross diagram