Ionic, Covalent and Metallic Structures
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Ionic, Covalent and Metallic Structures. IONIC. COVALENT. eg sodium chloride (salt). PURE substances have different STRUCTURES depending on the type of BONDING they have. METALLIC eg copper. SIMPLE eg carbon dioxide, water. GIANT eg diamond, graphite.

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Ionic covalent and metallic structures

IONIC

COVALENT

eg sodium chloride (salt)

PURE substances have different STRUCTURES depending on the type of BONDING they have

METALLIC

eg copper

SIMPLE

eg carbon dioxide, water

GIANT eg diamond, graphite

The structure of a substance decides what its PHYSICAL PROPERTIES will be.


Ionic covalent and metallic structures

IONIC

Positive sodium ion Na+

Negative chloride ion Cl-

Ionic substances are compounds of metals and non-metals (eg sodium chloride, copper oxide, magnesium sulphide etc)

They are made of IONS: atoms which have lost or gained electrons giving them a positive or negative CHARGE

The + ions and – ions STRONGLY ATTRACT each other to make a regular crystal structure


Ionic covalent and metallic structures

Strong ionic bond

Because of the very STRONG BONDS between the IONS, ionic compounds have HIGH MELTING & BOILING POINTS

Sodium chloride melts at over 800°C


Ionic covalent and metallic structures

H2O

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DISSOLVE

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As ionic compounds are made of CHARGED IONS, they can CONDUCT ELECTRICITY but ONLY if the ions can MOVE.

If it is MOLTEN the ions can move

If it is DISSOLVED the ions can move

800°C

20°C


Ionic covalent and metallic structures

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MOLTEN IONIC COMPOUND

MOLTEN ionic compounds CONDUCT ELECTRICITY


Ionic covalent and metallic structures

H20 molecule

Ions free to move around

When salt is put in water, H2O molecules pull the ions apart to make a solution. This lets the ions move around.


Ionic covalent and metallic structures

PURE WATER

SOLID SALT

SALT SOLUTION

DISSOLVED ionic compounds also CONDUCT ELECTRICITY


Ionic covalent and metallic structures

  • Ionic Bonding Questions

  • List two compounds that contain ionic bonds. (Grade D)

  • Describe three properties of ionic compounds. (Grade C)

  • Explain why ionic compounds often form giant structures – maybe draw a diagram (Grade B)


Ionic covalent and metallic structures

H atom

O atom

Whole thing

= H2O molecule

SIMPLE MOLECULAR SUBSTANCES

These are substances like carbon dioxide CO2, water H2O and methane CH4 which are always made of simple molecules whether they are SOLIDS, LIQUIDS OR GASES


Ionic covalent and metallic structures

MOLECULES ONLY WEAKLY ATTRACT EACH OTHER

VERY STRONG bonds BETWEEN ATOMS

(so molecule is very hard to break up)

WEAK bonds BETWEEN MOLECULES

(so molecules are easy to separate)


Ionic covalent and metallic structures

This means simple molecular substances have LOW melting and boiling points

Liquid oxygen boiling at -183°C

Solid oxygen at -240°C


Ionic covalent and metallic structures

As the bonds between the molecules are weak, simple molecular substances are weak and soft when solid.

As the molecules are NOT CHARGED simple molecular substances DON’T CONDUCT ELECTRICITY when solids, liquids or gases.


Ionic covalent and metallic structures

Carbon atom molecular substances are weak and soft when solid.

Only STRONG bonds

GIANT MOLECULAR SUBSTANCES

In these materials strong covalent bonds join atoms together with other atoms of the same type to make giant structures, rather than little groups.

Every C atom joined to 4 others

DIAMOND

(this is only part of the structure - the same pattern carries on in every direction)


Ionic covalent and metallic structures

SILICA (Silicon dioxide SiO molecular substances are weak and soft when solid.2) has a similar structure to diamond

Every Si atom joined to 4 O atoms

Silica is the main substance in ROCKS. Pure silica is called QUARTZ


Ionic covalent and metallic structures

Because all the atoms in Giant Structures are UNCHARGED, they will not conduct electricity.


Ionic covalent and metallic structures

GRAPHITE – a special case STRONG BONDS they:

WEAK BONDS

STRONG BONDS

Common form of carbon found in soot, charcoal, pencil leads etc

Carbon atoms each joined to 3 others with STRONG bonds to make hexagonal sheets of atoms

The sheets of atoms are joined to other sheets by WEAK bonds


Ionic covalent and metallic structures

As the bonds between the layers of atoms are weak, they can easily slide over each other

As the C atoms are only bonded to 3 others, the extra electrons form clouds of ‘free electrons’ between the layers


Ionic covalent and metallic structures

GRAPHITE - Properties easily slide over each other

The STRONG BONDS between the ATOMS mean it has HIGH MELTING and BOILING POINTS

The WEAK BONDS between the LAYERS mean it is SOFT and SLIPPERY as the layers SLIDE over each other easily (used in pencils and as a solid lubricant)

The FREE ELECTRONS between the layers mean that graphite CONDUCTS ELECTRICITY (used as sliding contacts in electric motors)


Ionic covalent and metallic structures

  • Covalent Bonding Questions easily slide over each other

  • List one covalent compound that has a simple structure and one that has a giant structure. (Grade C)

  • Describe two properties of simple covalent compounds and two properties of giant covalent compounds. (Grade B)

  • Explain why graphite and diamond have different properties (Grade A)


Ionic covalent and metallic structures

METALS easily slide over each other

In a metal the atoms are held together by strong bonds in regular structures.

This means most metals have high melting and boiling points and are hard and strong


Ionic covalent and metallic structures

As they have LOST a few electrons, the atoms become POSITIVE IONS

Free (“delocalised”) electrons

In a metal the atoms LOSE SEVERAL OF THEIR OUTER ELECTRONS which drift around between the metal ions as FREE ELECTRONS.


Ionic covalent and metallic structures

The large number of free electrons makes all metals are GOOD CONDUCTORS of electricity AND heat.

The regular structure means the layers of atoms can fairly easily slide over each other without breaking the bonds (though not as easily as graphite) and so metals are MALLEABLE (bend rather than snap)


Ionic covalent and metallic structures

  • Metallic Bonding Questions CONDUCTORS of electricity AND heat.

  • List two elements that contain metallic bonding. (Grade D)

  • Describe three properties elements that contain metallic bonding. (Grade C)

  • Explain why metallic structures conduct electricity OR are malleable (Grade B)


Ionic covalent and metallic structures

SUMMARY - Descriptions CONDUCTORS of electricity AND heat.

METALLIC

Strong malleable solids

Don’t dissolve

eg copper

IONS ONLY

IONIC

Crystals

Dissolve in water

eg sodium chloride (salt)

IONS +

FREE ELECTRONS

SIMPLE Covalent

Usually Gases

eg CO2, H2O

ATOMS joined into GIANT MOLECULES

GIANT Covalent

Hard strong solids

Don’t dissolve

eg diamond

(graphite – special case)

MOLECULES ONLY


Ionic covalent and metallic structures

SUMMARY - PROPERTIES CONDUCTORS of electricity AND heat.