The average rate of reaction is?
The change divided by the time
Relative rate of reaction is?
Particles have to collide with what for a collision to be succesful?
Enough EnergyCorrect Orientation
Collision Theory - Concentration
As concentration increases, there are more particles in the same volume. This means more collisions and thus more succesful collisions will occur. Rate will increase
Collision Theory - Surface Area
As surface area increases there are more particles available to react. More collisions and therefore more succesful collisions will occur. Rate will increase
What is the Activation Energy?
The minimum kinetic energy required by colliding particles before a reaction may occur. The energy required to form an activated complex
Why does a catalyst increase rate of reaction?
Catalyst provides an alternative reaction pathway with a lower activation energy
What is temperature?
The measure of the average kinetic energy of all the particles of a substance
Temperature and reaction rate
When the temperature is increased there is an increase in the number of particles with energy higher than the activation energy
What is a potential energy diagram?
It can be used to show the energy pathway for a reaction. Shows the enthalpy change and the activation energy for both the forward and reverse reactions
What is the enthalpy change?
ΔH (kJ mol-1) The energy difference between products and reactants
Enthalpy change in exothermic reactions?
Enthalpy change in endothermic reactions?
What is the activated complex?
An unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction
Potential Energy Diagram - EA
Activation energy for the forward reaction when a catalyst is not present
Potential Energy Diagram - Ecat
Activation energy for the forward reaction when a catalyst is present
Potential Energy Diagram - ΔH
Enthalpy change for the forward reaction
Who created the Periodic Table?
The Russian scientist Dmitri Mendeleev
How did Mendeleev create the Periodic Table?
He arranged elements in order of increasing atomic mass in conjunction with similar chemical properties, leaving gaps for elements that had not been discovered a that time
Groups 1 + 2 - Type of Bonding
Groups 1 + 2 - Structure
Groups 1 + 2 - Melting Points
Groups 3 + 4 - Type of Bonding
Groups 3 + 4 - Structure
Groups 3 + 4 - Melting Point
Groups 5,6 + 7 - Type of Bonding
Groups 5, 6 + 7 - Structure
Groups 5, 6 + 7 - Melting Points
Group 0 - Type of Bonding
Group 0 - Structure
Group 0 - Melting Points
What produces a metallic bond?
The electrostatic forces of attraction between the delocalised outer electrons and the lattice of positively charged ions
What holds the atoms of noble gases together?
Weak London dispersion forces
What forms a dipole?
The electrons in an atom or molecule being unevenly distributed
What are London dispersion forces?
The weak forces of attraction between all atoms and molecules
Relative Strength of London Dispersion Forces
Much weaker than all other types of bonding
What causes London Dispersion Forces
Electrostatic attractions between temporary and induced dipoles caused by the movement of electrons in atoms and molecules
Effect of particle size on LDF strength
The larger the atoms or molecules the greater he number of electrons and the stronger the LDFs
What is a covalent bond?
The electrostatic attraction between positively charged nuclei and negatively charged electrons which are shared between the atoms involved
Properties of Covalent molecular elements
Definite number of atoms bonded together in separate moleculesThey are discrete
Properties of Covalent networks
Have a large but indefinite number of atoms bonded together
What is covalent radius?
Half of the distance between two atoms covalently bonded together. Measures the size of an atom
Covalent radius across a period
Decreases across a period due to increasing nuclear charge and no change in the number of occupied energy levels
Covalent radius down a group
Covalent radius increases down a group due to a greater number of occupied energy levels - outer electrons are further from the nucleus
There is an increase in nuclear charge down a group however this is cancelled out by the shielding effect of the inner electrons
What is the first ionisation energy?
The energy required to remove one mole of electrons from one mole of atoms in the gaseous state
First ionisation energy across a period
Increases because the distance between the outer electrons and the nucleus decreases due to the nuclear charge increasing. Also no change in shielding effect
First Ionisation energy down a group
Decreases because the atomic size increases and the complete inner electron energy levels shield the outer electrons from the attractive force of the nucleus
What is the second ionisation energy?
The energy required to remove one mole of electrons from one mole of one plus ions in the gas state
What is electronegativity?
A measure of the attraction an atom has for the shared electrons in a covalent bond
Electronegativity across a period
Increases due to increasing nuclear charge and decreasing atomic size.
Electronegativity down a group
Decreases due to an increase in atomic radius and increase in the number of energy levels, leading to a greater screening effect
The covalent bond is a result of?
Two positive nuclei being held together by their common attraction for the shared pair of electrons
When are polar covalent bonds formed?
When the attraction of each atom for the pair of bonding electrons is different.
Polar Covalent Bonds: Differences in electronegativity
The larger the difference in electronegativity between the two atoms the more polar the bond will be
Formation of ions
If the difference in electronegativity between the two atoms is greater than 1.8 then the movement of bonding from the element of lower electronegativity to the element of higher electronegativity is complete
Spectrum with pure covalent at one end and ionic at the other. Polar covalent bonding is in the middle
Compounds formed between metals and non-metals are?
Often, but not always, Ionic
Aqueous Acids are?
Some metals can sometimes form?
Covalent bonds (e.g. SnI4)
All covalent molecules do what at a set temperature?
Boil and freeze
There are forces of attraction between covalent molecules called?
Intermolecular or Van Der Waals' forces
Hold atoms within a molecule
Intermolecular forces are?
Forces of attraction between molecules
Any 'intermolecular' forces acting between molecules are known as?
Van der Waals' forces
Types of Van der Waals' forces
London Dispersion ForcesPermanent dipole: Permanent dipole interactionsHydrogen Bonds
London Dispersion Forces are?
Forces of attraction that can occur between all atoms and molecules formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by the movement of electrons in atoms and molecules
The strength of London Dispersion Forces is related to?
The number of electrons within an atom or molecule
A molecule is described as polar if?
It has a permanent dipole
The spatial arrangement of polar covalent bonds can result in?
A molecule having a permanent dipole, therefore being polar
Permanent dipole-Permanent dipole interactions are?
Additional electrostatic forces of attraction between polar molecules
Strength of dipole-dipole interactions
Stronger than London Dispersion Forces with similar numbers of electrons
The strongest dipole-dipole interaction is?
The hydrogen bond
The hydrogen bond is found when?
Hydrogen is bonded o a strongly electrostatic element such as nitrogen, oxygen or fluorine
Hydrogen bonds are?
Intermolecular forces of attraction between molecules which contain highly polar bonds
Hydrogen Bond strength
Stronger than other forms of permanent dipole- permanent dipole interactions but weaker than a covalent bond
Melting points, boiling points and viscosity can all be explained in terms of the type and strength of?
The intermolecular forces which exist between molecules
By considering the polarity and number of electrons present in molecules it is possible to?
Make qualitative predictions of the strength of the intermolecular forces
The melting and boiling points of polar substances are greater than?
The melting and boiling points of non-polar substances with similar numbers of electrons
Melting points, boiling points, viscosity and solubility/miscibility in water are properties affected by?
The anomalous boiling points of ammonia, water and hydrogen fluoride are a result of?
Hydrogen bonding in ice results in?
An expanded structure which causes the density of ice to be less than that of water at low temperatures
Ionic compounds and polar molecular compounds tend to be soluble p in?
Polar solvents, such as water
Non-polar molecular substances tend to be soluble in?
Non-polar solvents, like heptane