ionic and covalent bonding- Additional science

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Compounds

Compounds- substances in which atoms of two or more elements are chemically combined.

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Ionic bonding

Ionic bonding- process through which a non-metal and a metal bond by gaining or losing electrons. This is done to achieve a noble gas configuration.

IONS ARE FORMED.

POSITIVE IONS COMBINE WITH NEGATIVE IONS TO FORM IONIC COMPOUNDS

Overall charge of a compound is zero.

When atoms GAIN electrons they become NEGATIVELY CHARGED IONS

When atoms LOSE electrons they become POSITIVELY CHARGED IONS

Ionic bonding produces ions with a charge:

Group 1: Alkalis react with non-metals = +1 charge

Group 7: Hallogens- react with alkali metals = -1 charge

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Sodium chloride

Otherwise known as SALT:

Is a giant structure of ions, held together by a strong electrostatic force of attraction between oppositely charged ions. These forces act in all directions in the lattice.

Examples of ionic compounds:

Calcium Chloride

Magnesium oxide

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Structures and properties of ionic compounds:

Ionic compounds are GIANT IONIC LATTICES. These giant ionic lattices have STRONG ELECTROSTATIC FORCES in ALL DIRECTIONS which HOLD THE IONS TOGETHER. So ionic compounds have HIGH MELTING AND BOILING POINTS.

All ionic substances are:

  • Solids at room temperature
  • Conductive when liquid or MOLTEN- due to the free ions in the structure.
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Covalent bonding

A covalent bond is a shared pair of electrons, which occurs between two non-metals.

The two non-metals SHARE electrons to GAIN STABILITY AND FORM MOLECULES.

These covalent bonds are VERY STRONG

DO NOT conduct electricity because there are no ions, meaning there is no electrical charge.

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Substances with covalent bonds can be simple molec

Simple molecular substances:

Have WEAK intermolecular forces BETWEEN MOLECULES- this makes simple molecules have LOW MELTING AND BOILING POINTS because the molecules are easily overcome when the substance melts or boils.

Examples include:

CH4- Methane

H20- Water

H- Hydrogen

CL2- Chloride

HCl- Hydrochloric acid

O2- Oxygen

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Substances with covalent bonds can be giant covale

GIANT COVALENT STRUCTURES- MACROMOLECULES

  • Similar to regular ionic lattices but have NO CHARGED IONS. 

In a giant covalent structure, all the atoms are bonded to each other by STRONG COVALENT BONDS, which makes them have HIGH MELTING AND BOILING POINTS.

E.g.  

Graphite - 3 Covelnt bonds- SOFT AND SLIPPERY.

Diamond:  4 covalent bonds and is VERY HARD.

Silica 

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Graphite:

Slightly different from other giant covalent structures. Each carbon atom in it only forms 3 covalent bonds. It has WEAK INTERMOLECULAR FORCES BETWEEN ITS LAYERS, so the LAYERS are FREE TO SLIDE OVER EACH OTHER. - (this is why graphite is so soft and slippery).

Graphite is the ONLY NON-METAL which is a GOOD CONDUCTOR OF HEAT AND ELECTRICITY due to the one delocalised electron.

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Metallic bonding:

Metals:

Made of lots of atoms tightly packed together in a REGULAR PATTERN. Each atom loses its delocalised electron from its outer shell, leaving a positive ion. These delocalised electrons are FREE to move around and positive metal ions create a 'SEA OF ELECTRONS'. This creates STRONG ELECTROSTATIC ATTRACTIONS and HOLDS everything together.

Conduction in METALS:

Metals are good conductors of:

  • Heatdue to its delocalised electrons which are able to vibrate and collide therefore conduct heat
  • Electricity-  due to its delocalised electrons which are able to flow through the material to conduct electricity because they are attracted to a positive charge and therefore generate a current.
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Metals and Alloys

Metal atoms can SLIDE over each other easily due to being in NEAT COLUMNS structurally. This makes metals malleable- meaning they are easily hammered/bent into shape.

Alloy-

An alloy is a mixture of metals. The second metal is added which DISTORTS the structure of the original metal. So when the atoms are not able to slide over each other, this makes the metal HARDER AND NOT MALLEABLE.

Shape memory ALLOYS:

These alloys can be manipulated into a certain shape but when heat is applied, it will return to its original shape. E.g. Nitinol- mixture of nickel and titanium used in braces or to aid the process of healing broken bones.

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