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Y3 Chemistry > CH5: STRUCTURE AND PROPERTIES OF MATERIALS > Flashcards

CH5: STRUCTURE AND PROPERTIES OF MATERIALS Flashcards

1
Q

What is an element?

A
  • a pure substance
  • cannot be broken down into simpler substances
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2
Q

What is a compound?

A
  • a pure substance
  • 2 or more elements that are chemically combined
  • in a fixed ratio
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3
Q

How can compounds be separated into their constituents?

A
  1. thermal decomposition
  2. electrolysis
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4
Q

What is thermal decomposition?

A

When a compound BREAKS DOWN/DECOMPOSES into its own constituents when HEATED.

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5
Q

What is electrolysis?

A

Passing electric current through the compound for it to break down into its constituents.

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6
Q

What are mixtures?

A
  • 2 or more elements and/or compounds
  • not chemically combined
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7
Q

Characteristics of compounds.

A
  1. Do not have the same CHEMICAL PROPERTIES as their constituent elements
  2. Constituent elements are
    combined in a FIXED PROPORTION by MASS.
  3. Can only be separated through chemical separation such as ELECTROLYSIS and THERMAL DECOMPOSITION
  4. FIXED melting and boiling point
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8
Q

Characteristics of mixtures.

A
  1. Have the same properties as its components
  2. No fixed composition
  3. Can be separated through physical separation techniques
  4. Range of melting and boiling points
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9
Q

What are alloys?

A

A MIXTURE of 2 or more metals

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10
Q

Examples of alloys

A

Steel, brass, bronze

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11
Q

What are the structural properties of ionic compounds?

A
  • ALTERNATING +ive and -ive ions
  • closely packed and arranged in an orderly manner
  • held together by strong ELECTROSTATIC forces of attraction
  • form a GIANT IONIC LATTICE STRUCTURE
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12
Q

What are the chemical properties of ionic compounds?

A
  1. high melting and boiling point
  2. hard but brittle
  3. soluble in water but not in organic solvent
  4. electrical conductor
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13
Q

Why do ionic compounds have high melting and boiling points?

A
  • Ionic compounds form a giant ionic crystal lattice structure
  • LARGE amount of THERMAL ENERGY is required to OVERCOME the STRONG IONIC BONDS between oppositely charged ions.
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14
Q

Why are ionic compounds hard but brittle?

A

Strong forces of attraction between oppositely charged ions > resistant to deforming.

When a strong force is applied, ions move away from their lattice positions and ions of the same charge approach each other. Ions with like charges repel each other, causing the loss of the lattice structure.

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15
Q

Why are ionic compounds soluble in water but insoluble in organic substances?

A
  • Water is polar molecule.
  • The partial +ive charge from the H ends of the water molecule will be attracted to anions
  • the partial -ive charge at the O ends of the water molecules will be attracted to cations.
  • Water molecules will pull the ions away from the crystal lattice into the solution and the ionic compound will eventually dissolve into the solution.
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16
Q

Can ionic compounds conduct electricity in a solid state? Why/why not?

A

No.
Ionic compounds have giant ionic lattice structures > oppositely-charged ions are held in fixed positions by strong electrostatic forces of attraction > ions are not mobile
For a substance to be an electrical conductor > mobile charged particles (ions/electrons) must be present

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17
Q

explain why ionic compounds in molten/aqueous state can conduct electricity

A

The strong electrostatic forces of attraction between the oppositely-charged ions have been overcome. The ions are now mobile.

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18
Q

What are the structural properties of simple covalent molecules?

A

The atoms within simple covalent
molecules are held together by strong covalent bonds.

The simple covalent molecules are
held together by weak intermolecular forces of attraction.

In a solid state, they form a lattice structure.

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19
Q

What are the properties of simple covalent molecules?

A
  1. Low melting and boiling points
  2. non-conductor of electricity
  3. insoluble in water but soluble in organic solvents
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20
Q

Why do simple covalent molecules have low melting and boiling points?

A

A small amount of energy is required to overcome the weak intermolecular forces of attraction between the simple covalent molecules.

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21
Q

Why are simple covalent molecules not a conductor of electricity?

A

There are no delocalised valence electrons available to conduct electricity.

22
Q

Why are simple covalent molecules insoluble in water?

A

Simple covalent molecules do not have negative or positive charges, so they are not electrostatically attracted to the water molecules.

23
Q

What are the structural properties of giant covalent structure?

A

Atoms form a network of strong covalent bonds that extend through the structure.

24
Q

What are allotropes?

A

Different forms of the same element with different structural arrangement of atoms.

25
Diamond and graphite are _______ of carbon
allotropes
26
Compare and contrast the chemical properties of diamond and graphite:
similarities: - high melting point - insoluble in water but soluble in organic solvents differences: Diamond > electrical insulator Graphite > electrical conductor Diamond > hard Graphite > soft and slippery
27
Describe the structure of diamond:
- giant covalent structure - each carbon atom is covalently bonded to 4 other carbon atoms - in a TETRAHEDRAL arrangement
28
Why doe giant covalent structures have high melting points?
A large amount of energy is required to break the strong covalent bonds between the atoms throughout the structure
29
Why is diamond not an electrical conductor?
- has giant covalent structure - all 4 valence electrons of each carbon atom are used for covalent bonding - no delocalised valence electrons present to conduct electricity
30
Why is diamond hard?
All carbon atoms are held together by strong covalent bonds throughout the structure.
31
Describe the structure of graphite
- giant covalent structure - made of many layers of HEXAGONAL RINGS of carbon atoms - each carbon atom forms **strong covalent bonds** with 3 other carbon atoms - each layer is held together by **weak intermolecular forces** of attraction
32
Why is graphite an electrical conductor?
- Each carbon atom only uses 3 out of 4 valence electrons in bonding - The valance electrons not used in bonding are delocalised to conduct electricity.
33
Why is graphite soft and slippery?
- has a giant covalent structure - layers of carbon atoms in graphite are held together by weak intermolecular forces of attraction - layers are able to slide over one another when a force is applied
34
Structure of silicon dioxide:
- giant covalent structure - silicon and oxygen atoms linked to each other via strong covalent bonds. - ratio of silicon atoms to oxygen atoms is always 1 : 2.
35
What are polymers?
- macromolecules - consist of many covalent molecules joined into chains of much larger molecules. - exist as discrete molecules
36
Properties of polymers:
- no fixed melting and boiling points - solid at room temperature - insoluble in water and soluble in organic solvents - cannot conduct electricity in any states due to the absence of mobile ions and electrons.
37
Why do polymers have no fixed melting/boiling points?
- may be formed by molecules of a range of sizes. - typically soften over a range of temperatures when the weak intermolecular forces of attraction are overcome by the molecular vibrations with higher K.E
38
What are the properties of metals?
- high melting point - conductor of heat + electrical conductor in all states - insoluble in water but soluble in organic solvents - ductile and malleable
39
Why do metals have high melting points?
A large amt of energy is needed to overcome the strong electrostatic forces of attraction between the positive ions and the 'sea' of delocalised valence electrons.
40
Define 'ductile' and 'malleable'
ductile - can be stretched without breaking malleable - can be hammered without breaking
41
Why are metals ductile and mealleable?
- have giant covalent structures - cations are arranged in orderly layers - when a force is applied, the layers of metal ions can slide over one another
42
What is an alloy?
A mixture of a metal with one or more elements
43
Examples of alloys:
- bronze - brass - solder - stainless steel
44
Why are alloys stronger than pure metals?
1. Pure metals have a giant metallic lattice structure - If enough force is applied, the layers of cations can slide over one another over the sea of delocalised valence electrons. 2. Since the regular lattice arrangement is disrupted by atoms of different sizes, a larger force is needed for the layers slide over each other. - Alloys tend to be less malleable and less ductile than the pure metals
45
Why do alloys have a lower melting point than pure metals?
In pure metals, a large amt of energy is needed to overcome the strong electrostatic forces of attraction between the cations and the 'sea' of delocalised valence electrons. In alloys, the regular lattice arrangement is disrupted by atoms of different sizes. Hence, their arrangement is less orderly and which disrupts the bonds between the ions. Less energy is required to overcome the electrostatic attraction and bonds between the cations.
46
If a substance can be separated by physical means, it is a ____.
mixture
47
If a substance has a high melting or boiling point, it is a ____.
Metal Giant covalent compounds Ionic compounds
48
If a substance can conduct electricity (molten/liquid state and aqueous state only), it is _______.
Ionic compound
49
If a substance can conduct electricity (in any state) it is ______.
Metals and graphite
50
If a substance is soft and slippery, it is?
Graphite

Y3 Chemistry (5 decks)

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