A pair of electrons shared between two atoms. Each of the positively charged nuclei is attracted to the same negatively charged pair of electrons.
Covalent bonds are shown using 'dot and cross' diagrams.
Covalent bonds between two hydrogen atoms are very strong.
Whenever a bond is formed, energy is released which makes the atoms involved more stable.
Covalent bonding causes each atom to have a full outer shell of electrons, therefore, noble gases cannot covalently bond.
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Ionic Bonding
One atom is more attracted to a pair of electrons more strongly than the other atom. The electron pair is pulled very close to that atom and away from the other.
X loses control of its electron and becomes positively charged (a CATION). Y gains that electron and becomes negatively charged (an ANION).
An ion is a charged particle.
Ionic bonding is bonding in which there has been a transfer of eletrons from one atom to another to produce ions. The substance is held together by strong electrical attractions between positive and negative ions.
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Metallic Bonding
Most metals are hard and have high melting points, suggesting that the forces holding the particles together are very strong.
The electrons are no longer attatched to atoms and flow around the whole metal; they are delocalised.
Metallic bonding is an array of positive ions in a 'sea of electrons'.
The strength of the bonds depends on how many electrons there are in the outer shell of the atom. The bigger the number, the stronger the bonds.
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