Structures Flashcards
(46 cards)
What are the types of structure in a substance? What are they?
Giant metallic - found in metals, where metallic bonds hold together positive metals via a “sea of delocalised electrons”.
Giant ionic - found in compounds of metals with non-metals. A lattice of positive metal, and negative non-metal ions, held together by electrostatic attractions.
Giant covalent - very large covalent molecules, where atoms are joined by covalent bonds throughout the three dimensional structure.
Molecular covalent - a.k.a “covalent molecular” or “simple covalent” or simple “simple molecular”. Molecular covalent molecules have strong covalent bonds between atoms within a molecule and weak attractions between separate molecules.
What is the definition for a melting point?
Melting point: the temperature at which a solid changes into a liquid.
What is the definition for a boiling point?
Boiling point: the temperature at which a liquid changes into a gas.
What is the definition for electrical conductivity?
Electrical conductivity: the ease with which electricity passes through a substance.
What is the definition for thermal conductivity?
Thermal conductivity: the ease with which heat passes through a substance.
What is the equation for density?
Density: g/cm³ = Mass (g) / Volume (cm³)
What is the definition for hardness?
Hardness: the ability of a substance to resist being scratched.
What is the definition for strength?
Strength: how difficult it is to pull apart (tensile) or crush (compressive).
What is the definition for flexibility?
Flexibility: the ability of a substance to bend without breaking.
What is the definition for malleability?
Malleability: the ability of a substance to be hammered or beaten into flat sheets without breaking.
What is the definition for ductility?
Ductility: the ability of a substance to be pulled into long thin wires.
What is the definition for solubility in water?
Solubility in water: the maximum mass (g) of a solute that can dissolve in 100g of water at a stated temperature.
What is the definition solubility in organic solvents?
Solubility in organic solvents: the maximum mass (g) of solute that can dissolve in 100g of a solvent like tetrachloromethane at a stated temperature.
What are giant ionic bonds made up of? What are they?
A compound formed from a metal and non-metal element does so by ionic bonding. For example, when sodium reacts with chlorine, many positive sodium ions and many negative chlorine ions form. These ions are attracted to each other (because of their opposite charges) and a regular three dimensional lattice is formed - this is known as a giant ionic.
What are the general properties of a giant ionic structure? Explain.
- High melting and boiling points: Ionic bonds are very strong and they extend in three dimensions throughout the giant structure. Therefore a lot of heat energy is required to separate the ions and break the lattice, so a high temperature is required.
- Brittle: bending causes the ions to move into positions where ions of the same charge are opposite each other. This leads to repulsion between layers which then split apart.
- Electrical insulators when solid: ions held in fixed positions so cannot move to carry a current.
- Electrical conductors as molten liquids or aqueous solutions: melting the solid or dissolving it in water allows positive and negative ions to move and carry an electric current between electrodes. The ions are charge carriers.
- Usually soluble in water but insoluble in organic solvents such as tetrachloromethane
Give an example of an ionic substance.
NaCl (Sodium Chloride)
What happens when you heat NaCl?
Describe what happens if you try and crush some NaCl crystals?
Does NaCl conduct electricity.
When you add a few NaCl crystals to water what happens?
What happens when you add a few NaCl crystals to cyclohexane?
The heat has no effect - to break the strong ionic bonds of NaCl, a large temperature is required.
Ionic structures are very brittle and so the NaCl shatter easily, forming a white powder. When ions are moved slightly they come opposite ions of the same charge, they repel and then the structure shatter.
NaCl does not conduct electricity. The positive and negative ions are fixed in positions in the solid and cannot move, thus they cannot carry an electric current.
NaCl dissolves easily into a colourless solution. The ions in NaCl interact with the water molecules and move apart and occupy spaces between the water molecules in a solution.
NaCl doesn’t dissolve however in cyclohexane. The ions are not able to interact with the molecules of the organic solvent and so it does not dissolve.
What are molecular covalent substances made up of?
Molecular covalent substances are made up of small covalent molecules. The forces and attraction between molecules however is weak. The weak attraction holding the molecules together are called Van Der Waal’s forces.
The atoms themselves within each molecule are held together very strongly via strong covalent bonds.
What are the general properties of molecular covalent substances?
Very low melting and boiling points: very little heat energy is needed to break the very weak bonds between separate molecules. Hence why many molecular covalent are gases at room temperature. Remember that no covalent bonds are broken when a molecular covalent substance melts - only the Van Der Waal’s forces are broken.
They are brittle and soft if solid because of the weak forces between molecules.
Electrical insulators: their molecules are not charged.
They are insoluble in water or have a very low solubility.
Soluble in organic solvents such as tetrachloromethane, CC1₄.
Give two examples of molecular covalent substances which are solids at 20 degrees C.
Iodine and Sulphur.
Give three examples of molecular covalent substances which are liquids at 20 degrees C.
Bromine, Water and Ethanol.
Give three examples of molecular covalent substances which are gases at 20 degrees C.
Oxygen, Nitrogen and Carbon dioxide.
What happens when you heat iodine?
Describe what happens if you try and crush some iodine crystals?
Does iodine conduct electricity.
When you add a few iodine crystals to water what happens?
What happens when you add a few iodine crystals to cyclohexane?
What happens when you add a few iodine crystals to ethanol?
The dark grey solid gives off a purple coloured gas upon heating. This occurs because the neighbouring iodine molecules are only attracted to each other by weak Van Der Waal’s forces which can be easily broken causing iodine to sublime (transition directly from solid to gas).
The dark grey crystals shatter easily upon impact. The weak Van Der Waal’s forces between molecules are broken easily, causing iodine to be very brittle.
Iodine does not conduct electricity because it is made up of electrically neutral molecules which cannot carry a current.
Iodine does not dissolve in water because it has a very low solubility in water.
Iodine is however very soluble in organic solvents like cyclohexane. Iodine is also very soluble in ethanol.
What are giant covalent substances?
In giant covalent structures atoms are covalently bonded to other atoms in a regular and repeating way, producing a three dimensional lattice or “giant covalent structure”.
