Dot-and-cross diagrams - elements

For your exam, you need to be able to draw dot-and-cross diagrams representing the covalent bonds [covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. ] in the molecules [molecules: a collection of two or more atoms held together by chemical bonds. The fundamental unit of compounds ] of some common gaseous elements [elements: All atoms of an element have the same atomic number, the same number of protons and electrons, and so the same chemical properties. ]. Remember: you only need to show the electrons in the highest energy level.

Hydrogen, H₂

Hydrogen atoms can each form one covalent bond. One pair of electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ] is shared in a hydrogen molecule (H₂).

Chlorine, Cl₂

Chlorine atoms can each form one covalent bond. One pair of electrons is shared in a chlorine molecule (Cl₂).

Oxygen, O₂

Oxygen atoms can each form two covalent bonds. Two pairs of electrons are shared in an oxygen molecule (O₂) - a double bond [double bond: A double bond is a covalent bond resulting from the sharing of four electrons (two pairs) between two atoms. ].