Kinetic Particle Theory
Describe the change in arrangement and motion for water at -5 °C and 5°C.
Arrangement: particles in water change from very closely packed in an orderly manner to less closely packed in a disorderly manner.
Motion: particles in water change from vibrating about their fixed positions to sliding over each other.
Describe the change in arrangement and motion for water at 5 °C and 105°C.
Arrangement: particles in water change from closely packed in a disorderly manner to very far apart in a disorderly manner.
Motion: particles in water change from sliding over each other to moving randomly at high speeds in all directions.
Elements, Compounds and Mixtures
State differences between elements and compounds.
Elements cannot be broken down into simpler substances by chemical means but compounds can.
Elements consist of only one type of atoms but compounds consist of two or more elements that are chemical combined.
State differences between compounds and mixtures.
Compounds can only be separated using chemical methods while mixtures can be separated using physical methods.
Compounds have different physical and chemical properties from their constituent elements while mixtures have the same chemical properties from its components.
The elements in a compound are always combined in a fixed proportion but the components of a mixture can be mixed in any proportion.
There is little or no energy change when a mixture is formed but there is an energy change when compounds are formed.
Separation and Purification
Why must the starting line be drawn in pencil?
Pencil lead (graphite) is insoluble in the solvent hence it will not be separate and contaminate the chromatogram.
Why must the starting line not be drawn in pen?
Pen ink is soluble in the solvent hence it will be separated and contaminate the chromatogram.
Why must the starting line be above the solvent?
To prevent the samples tested from dissolving directly into the solvent
Why must the starting spots be as small?
To prevent the spots from spreading sideways or overlap with one another as the solvent moves up.
How can we ensure that a substance is pure?
For solids: measure melting point. Pure solids melt at a fixed and exact temperature. Impure solids melt over a range of temperature at lower temperatures than the pure solid.
For liquids: measure boiling point. Pure liquids boil at a fixed and exact temperature. Impure liquids boil over a range of temperature at higher temperatures than the pure liquid.
Atomic Structure
Define isotopes
Atoms of the same element with same number of protons but different number of neutrons.
Ionic Bonding
Why does sodium chloride (or any ionic compound) have a high melting point and boiling point?
Why does sodium chloride (or any ionic compound) exist as a solid at room temperature?
Sodium chloride has a giant ionic lattice structure.
A lot of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged ions (sodium cations and chloride anions).
Why does sodium chloride (or any ionic compound) not conduct electricity in the solid state?
Why does sodium chloride (or any ionic compound) conduct electricity in the liquid or aqueous state?
In the solid state, the ions are held in fixed positions by strong electrostatic forces of attraction. Hence, there are no free mobile ions to carry charge.
In molten/ aqueous state, the electrostatic forces of attraction between the ions have been overcome. Hence there are free mobile ions to carry charge.
Covalent bonding
Why does carbon dioxide (or any simple covalent compound) have low melting and boiling pts?
Carbon dioxide has a simple molecular structure. Little energy is needed to overcome the weak intermolecular forces of attraction between CO2 molecules.
Why does (carbon dioxide) not conduct electricity in any state?
Carbon dioxide has a simple molecular structure with no mobile electrons or ions to carry the electrical charge.
Why does diamond/ graphite/ silicon dioxide have a high melting point and boiling point?
Diamond/ graphite/ silicon dioxide has a giant molecular structure. A lot of energy is needed to break the network of strong covalent bonds between atoms.
Why is diamond hard?
Diamond has a giant molecular structure. Each carbon atom is joined to four other carbons by strong covalent bonds in a tetrahedral structure. A lot of energy is needed to break the network of strong covalent bonds.
Why is silicon dioxide hard?
Silicon dioxide has a giant molecular structure. Each silicon atom is covalently bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms. A lot of energy is needed to break the network of strong covalent bonds.
Why is graphite soft and slippery?
Graphite has a giant molecular structure with 2D layers of carbon atoms. The layers of carbon atoms are held together by weak intermolecular forces of attraction. Little energy is needed to overcome these forces.
Why can’t diamond/ silicon dioxide conduct electricity?
Diamond/ silicon dioxide has a giant molecular structure where there are no mobile electrons to carry electrical charge.
Why can graphite conduct electricity?
In graphite, each carbon atom is bonded to three other carbon atoms. Hence, only 3 valence electrons in each carbon atom are used for covalent bonding and there is one free mobile electron to carry the electrical charge.
Metallic bonding
Why does magnesium (or any metal) have a high melting point and boiling point?
Why does magnesium (or any metal) exist as a solid at room temperature?
Metals have giant metallic lattice structure.
A lot of energy is required to overcome the strong electrostatic forces of attraction between the metal cations and sea of delocalised electrons.
Why do metals conduct electricity?
In metals, the sea of delocalised (mobile) electrons can serve as charge carriers.
Why do metals conduct heat?
In metals, the sea of delocalised (mobile) electrons can serve as heat/ energy carriers.
Why are metals malleable/ ductile?
Due to the sea of delocalised (mobile) electrons, the layers of metal atoms can slide over one another without disrupting the metallic bond.
Acids, Bases and Salts
What is a strong/ weak acid/ alkali?
A strong acid ionises/ dissociates fully in water to give hydrogen ions.
A weak acid ionises/ dissociates partially in water to give hydrogen ions.
A strong alkali ionises/ dissociates fully in water to give hydroxide ions.
A weak alkali ionises/ dissociates partially in water to give hydroxide ions.
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