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# 3.5 Chapter summary

## 3.5 Chapter summary (ESBMK)

Presentation: 23PV

• A chemical bond is the physical process that causes atoms to be attracted together and to be bound in new compounds.

• The noble gases have a full valence shell. Atoms bond to try fill their outer valence shell.

• There are three forces that act between atoms: attractive forces between the positive nucleus of one atom and the negative electrons of another; repulsive forces between like-charged electrons, and repulsion between like-charged nuclei.

• The energy of a system of two atoms is at a minimum when the attractive and repulsive forces are balanced.

• Lewis diagrams are one way of representing molecular structure. In a Lewis diagram, dots or crosses are used to represent the valence electrons around the central atom.

• A covalent bond is a form of chemical bond where pairs of electrons are shared between two atoms.

• A single bond occurs if there is one electron pair that is shared between the same two atoms.

• A double bond occurs if there are two electron pairs that are shared between the same two atoms.

• A triple bond occurs if there are three electron pairs that are shared between the same two atoms.

• A dative covalent bond is a description of covalent bonding that occurs between two atoms in which both electrons shared in the bond come from the same atom.

• Dative covalent bonds occur between atoms of elements with a lone pair and atoms of elements with no electrons. Examples include the hydronium ion ($$\text{H}_{3}\text{O}^{+}$$) and the ammonium ion ($$\text{NH}_{4}^{+}$$).

• The shape of molecules can be predicted using the VSEPR theory.

• Valence shell electron pair repulsion (VSEPR) theory is a model in chemistry, which is used to predict the shape of individual molecules. VSEPR is based upon minimising the extent of the electron-pair repulsion around the central atom being considered.

• Electronegativity is a chemical property which describes the power of an atom to attract electrons towards itself in a chemical.

• Electronegativity can be used to explain the difference between two types of covalent bonds: polar covalent bonds (between non-identical atoms) and non-polar covalent bonds (between identical atoms or atoms with the same electronegativity).

• A polar molecule is one that has one end with a slightly positive charge, and one end with a slightly negative charge. Examples include water, ammonia and hydrogen chloride.

• A non-polar molecule is one where the charge is equally spread across the molecule or a symmetrical molecule with polar bonds.

• Bond length is the distance between the nuclei of two atoms when they bond.

• Bond energy is the amount of energy that must be added to the system to break the bond that has formed.

• Bond strength means how strongly one atom attracts and is held to another atom. Bond strength depends on the length of the bond, the size of the atoms and the number of bonds between the two atoms.

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