CHEMISTRY KEY WORDS

Element: A pure substance that is only made up of one type of atom

Atoms: The smallest particles of an element which can still keep the chemical properties of that element.

Molecules: A pure substance made up of two or more atoms covalently bonded.

Compound: A pure substance made up of two or more different elements chemically combined in a fixed ratio.

Mixture: made up of two or more substances that are physically combined.


KINETIC THEORY

Oxygen has a higher molecular mass than chlorine gas, hence it requires more energy for it to move and thus diffuse slower than chlorine gas.


SOLID: The particles are closely packed in a regular pattern. The particles vibrate about their fixed positions.

LIQUID: The particles are loosely packed together. The particles move at random, sliding over each other.

GAS: The particles are spread far apart. The particles move rapidly at random.


STRUCTURE AND BONDING.

MELTING POINT & BOILING POINT

Sodium chloride has a GIANT IONIC STRUCTURE that consists of strong electrostatic forces of attraction between ions. A lot of energy is needed to overcome these bonds, hence a high melting or boiling point.

Diamond has a GIANT COVALENT STRUCTURE that consists of strong covalent bonds between atoms. A lot of energy is needed to overcome these bonds, hence a high melting point or boiling point.

Oxygen has a SIMPLE COVALENT STRUCTURE that consists of weak intermolecular forces of attraction between molecules. Only little energy is needed to overcome these bonds, hence a low melting point or boiling point.

Copper has a giant metallic structure that consists of strong electrostatic forces of attraction between positive ions and a sea of free mobile valence electrons. A lot of energy is needed to overcome these bonds, hence a high melting or boiling point.

CHARGES.

NaCl & CuSO4

Sodium chloride has single charges while copper(II) sulfate has double charges. Hence copper(II) sulfate possess stronger electrostatic forces of attraction between Copper(II) ions and Sulfate ions. More energy is needed to overcome these bonds, hence a high melting point or boiling point.


ELECTRICAL CONDUCTIVITY.

Sodium chloride has a GIANT IONIC STRUCTURE that consists of sodium ions and chloride ions tightly bounded by strong electrostatic forces of attraction in fixed positions. Thus, there are no free mobile ions available for electricity.

* In an aqueous or molten state, the giant ionic structure is destroyed to release the sodium and chloride ions. These freely moving ions are able to conduct electricity as they move about in the molten liquid or aqueous solution.

Copper has a GIANT METALLIC STRUCTURE that consists of strong electrostatic forces of attraction between positive ions anda sea of free mobile valence electron. These free mobile delocalised electrons are able to carry electrical current from a negative to the positive terminal, hence giving copper the ability to conduct electricity.

Oxygen has a SIMPLE/GIANT COVALENT STRUCTURE that consists of oxygen/carbon atoms tightly bounded by strong covalent bonds. As the covalent compound is a neutral molecule, there are no free mobile ions or electrons available for conducting electricity.

*Diamond consists of a GIANT TETRAHYDRAL structure of carbon atoms where each carbon atom is covalently bonded to four other carbon atoms. As all the electrons are involved in covalent bonding, diamond cannot conduct electricity.

*Graphite consists of one carbon atom covalently bonded to three other carbon atoms in hexagonal laters of carbon atoms. One of the valence electron is not involved in covalent bonding and thus is FREE TO MOVE ABOUT to conduct electricity.

*Diamond has a giant covalent structure that consists of strong covalent bonds between atoms. A large amound of force is required to overcome these extremely strong bonds, hence it creates a lot of driction and be used as an abrasive.

*Graphite consists of hexagonal layers of carbon atoms held together by weak van der waals forces. A small amount of force applied can cause the layers of atoms to slide against each other, hence giving graphite the lubracative property.


ALLOYS AND MALLEABILITY

Copper has a giant metallic structure that consists of atoms arranged in a closely packed and orderly manner. When a considerable amount of force is applied, the layers of atoms slide over each other, allowing it to be malleable.

Addition of zinc disrupt the regular arrangement of the metal lattice due to different atomic radii of the zinc and copper atoms. Hence it is more difficult for the layers of atoms to slide against each other. Thus addition of zinc makes it stronger but less malleable.


REACTIVITY OF NOBLE GASES

Neon has already achieved a stable octet structure. It thus will have a very low tendency to gain or lose electrons as this will destroy its stable electronic configuration. Therefore, it is unreactive.


ACIDS, BASES & SALTS

STRONG AND WEAK ACIDS.

A strong acid is a substance which ionises completely in water to form a concentration of hydrogen ions.

A weak acid is a substance which ionises partially in water to form a low concentration of hydrogen ions.

A strong acid would react faster and cause a more vigorous reaction due to its higher concentration of hudrogen ions.

STRONG AND WEAK ALKALIS.

A strong alkali is a substance which ionises completely in water to form a high concentration of hydroxide ions.

A weak alkali is a substance which ionises partially in water to form a low concentration of hydroxide ions.

SALTS are compounds formed by the displaacement of hydrogen ions of an acid by a reactive metal.


REDOX REACTION

OXIDATION STATES

The oxidation state of X increased from -2 in XY to 0 in XZ, thus stating an oxidation reaction.
The oxidation state of Y decreased from 0 in XY to -2 in ZY, thus stating a reduction reaction.
Thus having both oxidation and reduction reactions, this is a redox reaction.

ELECTRON TRANSFER

An atom X gains/loses 5 electrons to form B. Reduction/Oxidation occurs.

REDUCING AGENT

X undergoes oxidation when the oxidation state of X increased from -2 in XY to 0 in XZ.

OXIDISING AGENT.

X undergoes reduction when the oxidation state of X decreased from 2 in XY to 0 in XZ


ENERGY CHANGES

The energy absorbed by the breaking of N Moles of X bonds and N moles of Y bonds is __kJ greater/lesser than the energy released by the forming of N Moles of X bonds and N moles of Y bonds, hence making it an exothermic/endothermic reaction


RATE OF REACTION

CATALYST

A catalyst is a substance which speeds up a reaction without itself being changed chemically and the mass remains the same before and after the reaction.

A catalyst speeds up the rate of reaction by offering an alternative reaction pathway that requies lower activation energy.

INCREASING TEMPERATURE

When the temperature increases, the X and Y molecules gain kinetic energy and move at higher speeds, this increases the frequency of effective collision between them. Thus the rate of reaction increases.

INCREASING PRESSURE

When the pressure increases, the X and Y molecules move at higher speeds and occur more unit volume. This increases the frequency of effective collisions between them. Thus the rate of reaction increases.

INCREASING CONCENTRATION

When the concentration increases, the amount of X and Y molecules per unit volume increases. This increases the frequency of effective collisions between them, thus the rate of reaction increases.

USING POWDERED REACTANTS OR CATALYST

This increases the surface area to volume ratio of the X and Y molecules available for reaction. The catalyst lowers the activation energy required for reaction to occur. This increases the frequency of effective collisions, thus the rate of reaction increases.


AIR

Carbon Monoxide: reacts more readily than oxygen with haemoglobin in red blood cells to form carboxyhaemoglobin, a stable compound. This inhibits the transportation of oxygen around the body, leading to dizziness or even death.

Acid Rain: Oxides of nitrogen/ Sulfer dioxide oxidises in air and dissolves in rainwater to form acid rain. It corrodes buildings and destroys vegetations.

Ozone Depletion: CFCs(chlorofluocarbons) destroy the ozone molecules, hence depleting the ozone layer, which prevents the penetration of harmful UV rays, which on prolonged exposure causes skin cancer.

How is nitrogen monoxide formed?
-In car engines where temperature is high, this provides energy for the bonds between nitrogen atoms to break and thus reacts with oxygen in the air to form nitrogen monoxide.

Global warming: increase in the volume of greenhouse gases causing heat to be absorbed by the greenhouse gases and trapped in the earth's atmosphere. Thus causes global warming which melts ice bergs, causing flooding in lowlands.


HABER PROCESS

Source of Hydrogen : cracking of crude oil fractions
Source of Nitrogen : Fractional distillation of liquidified air


REACTION CONDITIONS.

Haber Process: Fine Iron, 450C, 250 atm

Cracking of Hydrocarbon: Aluminium oxide/Silicon dioxide, 600C

Substitutions of Alkanes by Cl/Br: UV Light

Addition of HYdrogen to Alkenes to form Alkanes: Nickel, 200C

Addition of Steam to Alkenes to form Alcohols: Phosphoric (V) Acid, 300C, 60atm

Dehydration from Alcohols to Alkenes: Conc Sulfuric Acid, Warm

Formation of Ester: Conc Sulfuric Acid, Warm

Formation of Addition Polymers: 200C, 1000atm