Dot-and-cross diagrams - compounds

You will also 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 compounds [compounds: Substances formed by the chemical union (involving bond formation) of two or more elements. ]:

Hydrogen chloride, HCl

Hydrogen atoms and chlorine 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 chloride molecule (HCl).

Water, H₂O

Hydrogen atoms can each form one covalent bond, while oxygen atoms can each form two covalent bonds. Two pairs of electrons are shared in a water molecule (H₂O).

Ammonia, NH₃

Hydrogen atoms can each form one covalent bond, while and nitrogen atoms can each form three covalent bonds. Three pairs of electrons are shared in an ammonia molecule (NH₃).

Methane, CH₄

Hydrogen atoms can each form one covalent bond, while carbon atoms can each form four covalent bonds. Four pairs of electrons are shared in a methane molecule (CH₄).

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