Chemistry

  • Created by: kitkatz04
  • Created on: 05-05-19 10:38

Ionic Bonding

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions.

  • Ionic compounds have regular structures, called giant ionic lattices. In a giant ionic lattice, there are strong electrostatic forces of attraction acting in all directions between the oppositely charged ions.
  • As the ionic lattice contains such a large number of ions, a lot of energy is needed to overcome this ionic bonding so ionic compounds have high melting and boiling points.
  • The strength of the ionic bonds depends on the charge on the ions. Ions with higher charge will have stronger forces between them, so will need more energy in order to overcome these forces.
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Mole Calculations

  • One mole of atoms contains 6 x 1023 atoms, no matter what element it is.
  • This number is used in chemistry because if you could count out this many carbon atoms, the total mass of carbon you would have is 12 g. On the other hand, weighing out 12 g of carbon allows you to know how many atoms you have.
  • EXAMPLE:
  • One mole of carbon atoms has a mass of exactly 12g. Because magnesium atoms each have twice the mass of carbon atoms (24Mg compared with 12C), one mole of magnesium has a mass of 24g. In fact, one mole of any element has a mass in grams that is equal to its relative atomic mass.

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Metallic Bonding

Metallic bonding is a type of chemical bonding that rises from the electrostatic attractive force between delocalised electrons and positively charged metal ions.

Instead of the delocalised electrons orbiting their respective metal ions, they form a "sea" of themselves that surrounds the positively charged metal ions. 

The metal ions are arranged in a metallic lattice structure. This lattice has layers of the metal ions. 

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Properties of Metal

Metals have many properties. Many metals share the same properties, not all, however. 

Typical physical properties of metal: 

high melting point

good conductor of heat

good conductor of electricity

high density

malleable (bendable)

ductile (can be drawn into wires/thin sheets without breaking)

Exceptions:

mercury has a low melting point and exists as a liquid at room temperature

elements in group one have low melting points, but also low densities, for example, sodium is less dense than water and so it floats

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Covalent Bonding

A covalent bond is formed when two atoms share a pair of electrons. Covalent bonding occurs in most non-metal elements, and in compounds formed between non-metals.

These shared electrons are found in the outer shells of the atoms. Usually, each atom contributes one electron to the shared pair of electrons.

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Crude Oil

Hydrocarbons are substances that are only made from hydrogen and carbon. Crude oil is a complex mixture of hydrocarbons. 

It is the remains of organisms that lived and died millions of years ago - mainly plankton which was buried in mud.

The different fractions of crude oil have many domestic and industrial uses.

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Fractional Distiliation

Fractional distillation separates a mixture into a number of different parts, called fractions.

Crude oil is a mixture of hydrocarbons.

A tall fractionating column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.

The crude oil is evaporatedand its vapours condense at different temperatures in the fractionating column.

The higher up the column, the lower the boiling point, lower viscosity (flow more easily), and higher flammability

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Isomers

Isomers are molecules with the same molecular formula but a different structural formula.

They are usually represented by 'displayed formula' which are the diagrams with the lines and chemical symbols. Isomers are unique and a good way to check it is to rotate it, etc. and see if it is still unique to your others. Example:

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Combustion

Combustion is a rapid reaction between oxygen and a substance that releases heat and light energy. 

A fuel is a substance that reacts with oxygen to release useful energy. 

Complete Combustion of Hydrocarbons

Plenty of oxygen needed for this. An example is the blue flame on a gas hob. 

- hydrocarbon + oxygen ---> carbon dioxide + water

Complete Combustion of Butane

- Butane is used in lighters. 

- butane + oxygen ---> carbon dioxide + water

If there is a shortage of oxygen in combustion reactions, incomplete combustion takes place. 

Instead of producing carbon dioxide and water, it produces carbon monoxide and carbon (soot). Also produces less energy.

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Empirical Formula

The empirical formula of a compound is the simplest whole number ratio of atoms of each element in the compound. It is determined using data from experiments and therefore empirical. 

For example, the molecular formula of glucose is C6H12O6 but the empirical formula is CH2O. This is because we can divide each number in C6H12O6 by 6 to make a simpler whole number ratio.

For empirical calculations, you have to use the relative atomic mass (Ar).

To work out empirical formula:

Step 1: Write the element symbols

Step 2: Write the masses

Step 3: Write the relative atomic mass values

Step 4: Divide the masses by the relative atomic masses

Step 5: Divide all by the smallest number

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