Unit 1- Chemical Changes and Structure Flashcards
What is the rate of a reaction?
The speed
What is the activation energy of a reaction?
The minimum amount of energy needed for a successful reaction.
What does the overall rate of a reaction depend on?
The frequency of the collisions between the particles
How much energy the particles collide with.
4 ways to increase the rate of a reaction:
Increase temperature
Increase concentration
Decrease particle size
Add a catalyst
What are catalysts?
Special chemicals that are added to increase the rate of a chemical reaction.
They take part in the reaction, but can be recovered unchanged and reused.
Biological catalysts are called enzymes.
Reaction rate graphs key points:
The steeper the line, the faster the reaction.
When the line becomes horizontal, the reaction has stopped.
Why is a reaction fastest at the beginning of the chemical reaction?
This is when the concentration of reactants is greatest.
Particles in an atom:
Protons, neutrons, electrons
Protons: position, relative mass and charge?
Position: nucleus
Relative mass: 1
Charge: +1
Neutrons: position, relative mass and charge?
Position: nucleus
Relative mass: 1
Charge: 0 (neutral)
Electrons: position, relative mass and charge?
Position: Orbiting nucleus
Relative mass: negligible
Charge: -1
Why are atoms electrically neutral?
Number of protons (+) = number of electrons (-)
What is the atomic number of an atom?
The number of protons in the nucleus of an atom.
What is the mass number of an atom?
The number of protons + the number of neutrons in the nucleus of an atom.
What is this called?
Mass number
X <—— (symbol)
Atomic number
Nuclide notation
How are electrons arranged in an atom?
Electrons are arranged in shells or energy levels.
How many electrons do the first 3 shells/energy levels hold?
1st shell: 2
2nd shell: 8
3rd shell: 8
What is an isotope?
Atoms which have the same atomic number but a different mass number.
Isotopes have the name number of protons but a different number of neutrons.
What is the relative atomic mass of an isotope always closer to?
The most abundant isotope.
How do atoms achieve a stable electron arrangement?
By having a full outer electron energy shell.
What is an ion?
A charged particle.
Ions are formed when atoms lose or gain electrons to obtain the stable electron arrangement of a noble gas.
Positive ions have…?
Lost electrons
Negative ions have…?
Gained electrons
To achieve a stable electron arrangement, metals…?
Lose electrons forming positive ions.
To achieve a stable electron arrangement, non-metals…?
Gain electrons forming negative ions.
How do we know the charge of an ion?
The charge of an ion is the same as its valency.
What is an ion electron equation?
An equation that shows electrons being lost or gained.
Examples:
1) Na(s) ——> Na+ + e-
2) Cl + e- ——> Cl-
3) Mg ——> Mg2+ + 2e-
4) O + 2e- ——> O2-
What is an ionic bond?
The electrostatic attraction between positive and negative ions.
Bonds between metals and non-metals.
Ionic bonding involves the transfer of electrons.
What structures do ionic bonds form?
Ionic lattice.
Lattice structures of oppositely charged ions with each positive ion surrounded by negative ions and vice versa.
Ionic lattice melting and boiling points are…?
High
Ionic lattice state at room temperature?
Solid
Do ionic compounds conduct electricity?
Only when molten or in solution as the lattice structure breaks up allowing the ions to be free to move.
What is a covalent bond?
The attraction of two nuclei for a shared pair of electrons.
In covalent bonding, electrons are shared between non-metal atoms.
This allows the non-metal atoms to achieve a stable electron arrangement.
Types of covalent structures:
Covalent molecular
Covalent network
What is covalent molecular?
Small molecules containing a certain number of atoms held together by covalent bonds. (e.g. carbon dioxide)
What is covalent network?
A giant network of non-metal atoms held together by covalent bonds. (e.g. diamond)
Covalent molecular key points:
Strong covalent bonds within the molecules and only weak attractions between the molecules.
Low melting and boiling boiling points as only weak forces of attraction between the molecules are broken when a substance changes state.
Do not conduct electricity because they don’t have charged particles which are free to move.
Covalent network key points:
Have a giant network of strong covalent bonds within one giant structure.
Have very high melting and boiling points because the network of strong covalent bonds is not easily broken.
Do not dissolve.
Covalent network melting and boiling points are…?
Very high
Covalent network state at room temperature?
Solid
Do covalent networks conduct electricity?
Never (except graphite)
Covalent molecular melting and boiling points are…?
Low
Covalent molecular state at room temperature?
Any state
Do covalent molecular bonds conduct electricity?
Never (although water is a poor conductor)
What is a diatomic molecule?
A molecule containing only two atoms.
What are the 7 diatomic elements?
Iodine
Bromine
Chlorine
Fluorine
Oxygen
Nitrogen
Hydrogen
What is a monatomic element?
One-atomed
All noble gases
Shapes of simple covalent molecules:
Linear (one bond)
Angular (two bonds)
Trigonal Pyramidal (three bonds)
Tetrahedral (four bonds)
What does it mean if a compound name ends in “ide”?
Made up of two types of elements.
What does it mean if a compound name ends in “ite” or “ate”?
Made up of three types of elements, one which is oxygen.
Definition of valency?
A term used to describe the combining power of an atom.
What does “SVSDF” stand for?
Symbol
Valency
Swap
Divide (if possible)
Formula
Roman numerals from 1-6?
1- I
2- II
3- III
4- IV
5- V
6- VI
What is a group ion?
Group ions contain two or more atoms.
Most group ions have a negative charge.
How can we determine the valency of a group ion?
Use the number of charges.
What do we do when a formula contains more than one group ion?
The group ion must be written in brackets.
Prefixes from 1-6?
1- Mono
2- Di
3- Tri
4- Tetra
5- Penta
6- Hexa
Prefix rule:
If you see a prefix DO NOT use the SVSDF system.
What does the ionic formulae include?
The charges present on each of the ions. (Charges are the same as the valency of the element.)
Charge on an ionic compound?
Neutral
The mole key points:
A mole is a unit of measurement.
For most elements, 1 mole is the relative atomic mass (RAM) in grams.
However, for the 7 diatomic elements, 1 mole is twice the RAM in grams.
The Gram Formula Mass (GFM) is the mass of 1 mole.
Method on how to do calculations from balanced chemical equations:
1) Write a balanced chemical equation, unless already given.
2) Identify the two chemicals referred to in the question and write the mole ratio.
3) Gather information from the question.
4) Calculate the number of moles.
5) Use the mole ratio to calculate the number of moles of the substance you are trying to find.
6) Calculate the mass.
How is a solution formed?
When a soluble substance is dissolved in a solvent.
What does the concentration of a substance depend on?
How much of a substance is dissolved in it.
What do we need to do to the volume if it’s in cm^3?
Divide by 1000 to make it into litres.
Concentration, number of moles, volume, mass and GFM units:
Concentration: moles per litre (mol l^-1)
Number of moles: no units
Volume: litres (l)
Mass: grams (g)
GFM: grams (g)
What numbers do acids show up as on the pH scale?
1-6
What numbers do alkalis show up as on the pH scale?
8-14
What number is a neutral solution on the pH scale?
7
Hydrogen ion symbol?
H+
Hydroxide ion symbol?
OH-
What breaks down into hydrogen ions and hydroxide ions?
Water molecules
H2O <—> H+ (aq) + OH- (aq)
(Reversible reaction)
Only a few molecules are dissociated into free ions.
An acidic solution has a greater concentration of…?
H+ ions
An alkaline solution has a greater concentration of…?
OH- ions
A neutral concentration has…?
An equal concentration of H+ and OH-
Why is water a poor conductor of electricity?
It is mainly made of molecules and contains only a few ions.
What happens when you dilute an acidic solution with water?
It will decrease the concentration of H+ ions and the pH will increase towards 7.
What happens when you dilute an alkaline solution with water?
It will decrease the concentration of OH- ions and the pH will decrease towards 7.
What forms an acidic solution?
Soluble non-metal oxides dissolving in water.
What forms an alkaline solution?
Soluble metal oxides dissolving in water.
What is the name of a substance that neutralises acids?
A base
What is a base that dissolves in water called?
An alkali
What happens in a neutralisation reaction?
An acid reacts with a base, causing the pH to move towards 7.
Metal oxide + acid ——>
Salt + water
Metal hydroxide + acid ——>
Salt + water
Metal carbonate + acid ——>
Salt + water + carbon dioxide
What type of salt does hydrochloric acid make?
Chloride
What type of salt does sulfuric acid make?
Sulfate
What type of salt does nitric acid make?
Nitrate
How to name a salt?
1st part: first name of the base
2nd part: depends on the acid
Example:
Calcium carbonate + sulfuric acid ——> Calcium sulfate + water + carbon dioxide
What is a precipitation reaction?
When two solutions are mixed together and one of the products is insoluble.
How can we remove the insoluble solid (precipitate) from the liquid.
Filtration
What does the precipitate take its name from?
The positive metal ion from one reactant and the negative ion from the other.
What is the name of ions that are present in a reaction mixture but don’t take part?
Spectator ions
They appear unchanged on both sides of the chemical equation.
As a result, they are often left out (omitted) in the chemical equation.
Why do we use an indicator in titrations?
To show the endpoint of the reaction.
What piece of equipment should be used to accurately measure the volume of a liquid?
A burette/pipette
What is the name of a solution of accurately known concentration?
Standard solution
How to perform a titration with accuracy?
The conical flask should be sitting on a white tile. This will help you to observe colour changes more accurately.
All of the burette readings should be taken at eye level.
The titration should be repeated until two concordant results (within 0.2cm^3 of each other) are obtained.
Titration calculations rule:
When using the results from a table for calculations, always ignore the rough titration result and calculate the average of the two concordant results.
