Bonding and structures

What is ionic bonding?

When a metal ion reacts with a non-meal atom electrons in the otuer shell of the metal atoms are transferred.

oppositely charged ions are held together by strong forces of attraction in ionic bonding

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Metal atoms loose electrons to become positively charged ions,

Non metals gain electrons to become negatively charged ion.

(example question)

Describe in tems of electrons the reaction between magnesium and iodine (MgI2/ ionic bonding

* Magnesium has 2 outer / valence electrons;
* It loses both outer / valence electrons (forming Mg2+ ion);
* Iodine has 7 outer / valence electrons;
* Two iodine atoms accept one electron each (forming I- ions);
* There is an electrostatic attraction between the (oppositely charged) ions and form the compound MgI2;

What is a ionic compound?

An ionic compound is a giant structure of ions.

Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.

These forces act in all directions in the lattice and this is called ionic bonding

Covalent bonding

When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong

(example question)

Describe the bonding in a molecule of ammonia NH3/covalent bond

* Nitrogen has 5 electrons in its outer shell;

Hydrogen has 1 electron in its outer shell;
* Three hydrogen atoms each share their single outer / valence electron with one nitrogen atom;
* To form three covalent bonds;
* And gain a full outer shell of electrons / noble gas structure;

Metallic bonding

Metals consist of giant structures of atoms arranged in a regular pattern.

The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure.

Properties of ionic compounds

• Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.

• These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

• When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.

Why can metals be bent and shaped ?

* Metal structure consists of layers (of particles / atoms / ions); \[
* They / particles / atoms / ions / layers) are able to / can slide (without breaking)

why is the conductivity reduced when a metal rusts?

A metal oxide compound is formed which doesnt contain any free/delocalised electrons to carry the charge.

properties of small molecules

* Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points.
* These substances have only weak forces between the molecules (intermolecular forces).
* It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.
* The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.
* These substances do not conduct electricity because the molecules do not have an overall electric charge.

polymers

Polymers have very large molecules.

The atoms in the polymer molecules are linked to other atoms by strong covalent bonds.

The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

Giant covalent structures

* Substances that consist of giant covalent structures are solids with very high melting points.
* All of the atoms in these structures are linked to other atoms by strong covalent bonds.
* These bonds must be overcome to melt or boil these substances

properties of metals and alloys

Metals have giant structures of atoms with strong metallic bonding.

This means that most metals have high melting and boiling points.

In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped.

Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder.

Why are metals good as conductors?

* metals are good conductors of electricity because the delcoalised electrons in the metal carry electrical charge through the metal.
* Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.

Diamond

In diamond each carbon forms 4 covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity.

Graphite

In graphite, each carbon atom forms 3 covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers.

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n graphite, one electron from each carbon is delocalised.

Graphene

Graphene is a single layer of graphite and has properties that make it useful in electronics and composites.

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* It is very strong due to its unbroken pattern and the strong covalent bonds between the carbon atoms
* it has free electrons which can move along its surface allowing it to **conduct electricity**
* those strong bonds between graphene’s carbon atoms are also very flexible

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Fullerenes

• Fullerenes are a group of carbon allotropes which consist of molecules that form hollow tubes or spheres

  • huge surface area and are useful for trapping catalyst molecules onto their surfaces

  • ullerenes are excellent lubricants and are starting to be used in many industrial processes

  • can be used to make nano tubes

C60