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Pure chemistry 🧫⚗️💉 > Chapter 5: Structure and properties of materials. > Flashcards

Chapter 5: Structure and properties of materials. Flashcards

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1
Q

What is an element?

A
  • An element is a pure substance that cannot be broken down by (its) chemical means.
  • There are 118 known elements in the periodic table and each element is represented by a symbol.
  • E,g. of elements: calcium (Ca), Chlorine (cl), lead (Pb), and nitrogen (N).
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2
Q

What is a compound?

A
  • A compound is a pure substance that contains 2 or more elementa bonded chemically in a fixed ratio
  • A compound usually has an appearance and properties that are different from those of the elements it is made up of.
  • E.g. of compounds: Lead (II) chloride is a yellow solid and is made up of the elements lead (a dull and grey solid), and chlorine (a yellow and green gas)
  • A compound can be broken down into its constituent elements by its chemical means such as thermal decomposition and electrolysis (the passing of electricity through a compound).
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3
Q

What is a mixture?

A
  • A mixture is formed when 2 or more substances are mixed together without being chemically bonded.
  • The constituents of a mixture are not in a fixed ratio.
  • E.g. of mixtures: Air, sea water and cement, because they are made out of different elements and compounds.
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4
Q

What are the differences between an element, a compound and a mixture?

A
  1. Element:
    composition :
    - Made up of only 1 type ofatom
    method of separation: -
    Properties : -
    energy change: -
    melting and boiling points: Fixed
    - E.g. melting point: 0°c
    boring point: 100°c
  2. Compound:
    composition:
    - Made upof 2 or more eiements in a fixed ratio:
    Method of separation:
    - (Based on the substances’/substance’s) chemical means.
    properties:
    - Different from those of its constituent elements.
    Energy change:
    - Arises due to a chemica reaction
    melting and boiling points:
    - Fixed
  3. Mixture:
    composition:
    - 2 or more elements and or compounds in a variable ratio.
    method of separation:
    - physical means
    properties:
    - similar to those of the elements and or compounds present.
    Energy change:
    - Does not arise due to no chemicai reaction melting and bolihg points:
    - not fixed
    - Vary according to its composition and what it is made of.
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5
Q

What are ionic compounds?

A
  • Ionic compounds have melting and boiling points.
  • Ionic compounds have giant ionic crystal lattice structures.
  • The positive and negative ions in the lattice are held together by strong electrostatic forces of attraction.
  • A lot of energy is required to overcome the strong electrostatic forces.
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6
Q

What is the relationship of ionic compounds with the charge of ions, and the electrostatic forces of attraction between the ions and the melting/boiling points of compounds.

A
  • In ionic compounds, the greater the charge of the ions, the stronger the electrostatic forces of attraction between the ions and the higher the melting and boiling points of the compounds.
  • E.g. Potassium chloride consists of K+ and cl- ions while calcium oxide consists of Ca2+ and O2- ions. Since the ions in calcium oxide have a greater charge, the electrostatic forces of attraction between the ions are STRONGER and require more energy to overcome.
  • Thus, calcium oxide has a higher melting and boiling point than potassium chloride.
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7
Q

Are all ionic compounds soluble in water?

A
  • No, only most ionic compounds that are soluble in water, but insoluble in organic solvents.
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8
Q

What is the condition that ionic compounds are in the aqueous state?

A
  • Ionic compounds that are dissolved in water are in the aqueous state.
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9
Q

What are the states that ionic compounds can conduct electricity in?

A
  • Ionic compounds can conduct electricity in the molten and aqueous states.
  • Mobile charge carriers must be present to conduct electricity.
  • When an ionic compound is in the molten and aqueous state, the ions move freely and act as a mobile charger carrier. Thus, the compound can conduct electricity.
  • When an ionic compound is in a solid state, the ions are held together in a giant lattice structure and cannot move around. thus, the compound cannot conduct electricity.
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10
Q

What is a TEXTURE characteristic of an ionic compound?

A
  • An ionic compound is hard but brittle.
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11
Q

What are some characteristics and properties of simple covalent substances?

A
  • Simple covalent substances have low melting and boiling points. Thus, they are said to be volatile.
  • Simple covalent substances have simple molecular structures.
  • Weak intermolecular forces of attraction exist between the molecules of the substances.
  • A small amount of energy is needed to overcome these weak intermolecular forces.
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12
Q

What is the relationship of a simple covalent substance with the intermolecular forces and the melting/boiling points of the substances?

A
  • The larger the molecule of a simple covalent substance, the stronger the intermolecular forces of attraction and the higher the melting and boiling points of the substance.
  • E.g. Chlorine is a larger molecule than nitrogen, and it has stronger intermolecular forces of attraction which require more energy to overcome. Thus, chlorine has higher melting and boiling points than nitrogen.
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13
Q

Are all simple covalent substances insoluble in water and soluble in organic solvents?

A
  • YES, simple covalent substances are insoluble in water, but soluble in organic solvents.
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14
Q

Why are the simple covalent substances unable to conduct electricity?

A
  • Simple covalent substances are unable to conduct electricity as they do not have delocalised electrons/ions, which act as charge carriers.
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15
Q

Are covalent substances able to conduct electricity?

A
  • YES, covalent substances that dissociate in water can conduct electricity.
  • E.g. Hydrogen chloride (HCl) is soluble in water.
  • E.g. Aqueous solution can conduct electricity, due to the presence of mobile H+ and Cl- ions.
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16
Q

What are giant covalent substances?

A
  • Giant covalent substances are usually in the solid state as they consist of many atoms connected to one another by strong covalent bonds.
  • E.g. of giant covalent substances: Diamond, graphite, and silicon dioxide.
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17
Q

What are allotropes?

A
  • Allotropes are different forms of the same element with just different structural arrangements of atoms.
  • E.g. of allotropes: Diamonds and graphite.
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18
Q

What is a diamond, and does it have any melting and boiling points?

A
  • Diamond (material) has high melting and high boiling points.
  • Diamond has a giant covalent structure and each carbon atom is covalently bonded to 4 other carbon atoms in a TETRAHEDRAL ARRANGEMENT.
  • A large amount of energy is needed to break the strong covalent bonds.
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19
Q

What is a tetrahedral arrangement?

A
  • A tetrahedral arrangement is a molecular shape that occurs when there are 4 bonds / no/1 pair in the molecule’s central atom.
  • the atoms bonded to the central atom are located at the 4 corners of a tetrahedron with 109.5° angles between them.
  • This arrangement is commonly observed in molecules such as methane (CH4), and water (H2O).
  • The tetrahedral shape is formed when electrons repel one another, resulting in the tetrahedron; the shape in which all electron pairs are as far apart as possible.
20
Q

Why does diamond (material) not conduct electricity?

A

Diamond does not conduct electricity and it does not have any delocalised electrons/ions available to act as mobile charger carriers.

21
Q

Is diamond insoluble in any liquid/solvent?

A
  • Not all, but diamond is insoluble in water and organic solvents.
22
Q

What is a material property of diamond?

A
  • Diamond is strong and hard
  • The arrangement of carbon atoms in a tetrahedral structure does not allow the carbon atoms to slide over each other easily.
  • Due to its strength, and hardness, diamond is widely used as cutting tools and jewelry.
23
Q

What are the levels of melting and boiling points for graphite?

A
  • Graphite has high melting and high boiling points.
  • It has a giant covalent structure, and each carbon atom is covalently bonded to 3 other carbon atoms, thus forming a layered structure that is made up of carbon atoms in hexagonal rings.
  • A large amount of energy is needed to break the strong covalent bonds.
24
Q

Why can graphite conduct electricity?

A
  • Graphite can conduct electricity and in graphite, each carbon atom is only bonded to 3 other carbon atoms.
  • One electron in the carbon atom is not used in bonding and acts as a mobile charge carrier, allowing graphite to conduct electricity.
25
Q

Is graphite insoluble in all liquids/solvents?

A
  • No, but graphite is insoluble in water and organic solvents.
26
Q

What is a material property of graphite?

A
  • Graphite is soft and slippery.
  • There is a weak intermolecular force of attraction exists between the layers of carbon atoms in graphite.
  • A small amount of energy is needed to overcome these forces of attraction, allowing the layers to slide over each other easily.
27
Q

Why is graphite often used in pencil lead and as a lubricant?

A
  • Graphite has a soft and slippery nature, thus it is used as a lubricant or in pencil lead.
28
Q

What is the level of melting and boiling points for silicon dioxide?

A
  • Silicon dioxide has high melting and boiling points.
  • Silicon dioxide has a giant covalent structure, and each silicon atom is surrounded by 4 oxygen atoms and each oxygen atom is bonded to 2 silicon atoms in a tetrahedral arrangement.
  • A large amount of energy is needed to break the strong covalent bonds.
29
Q

Why does silicon dioxide do not conduct any electricity?

A
  • Silicon dioxide does not conduct electricity, and it does not have any delocalised electrons/ions available to act as mobile charger carriers.
30
Q

is silicon dioxide insoluble in all liquids/solvents?

A
  • No, but silicon dioxide is insoluble in water and organic solvents.
31
Q

What is a material property of silicon dioxide?

A
  • Silicon dioxide is strong and hard, and the arrangements of the silicon and oxygen atoms in a tetrahedral structure do not allow the atoms to slide over each other easily.
  • Due to its strength and hardness, silicon dioxide is widely used in the production of concrete and glass.
32
Q

What are macromolecules?

A
  • macromolecules are another type of covalent substances besides simple and giant covalent substances.
33
Q

What is one example of a macromolecule? (What are polymers?)

A
  • Polymers are macromolecules and they are made up of many covalent molecules joined together in long chains.
34
Q

Why do polymers not have fixed melting and boiling points?

A
  • Polymers do not have fixed melting and boiling points, instead, they have macromolecular structures, polymer molecules are held together by intermolecular forces of attraction.
  • The strength of the intermolecular forces depends on the size of the polymer molecules.
35
Q

Why does macromolecules not conduct electricity?

A
  • Macromolecules do not conduct electricity, and there are no electrons/ions available to act as mobile charger carriers.
36
Q

Are all macromolecules insoluble in liquids/solvents?

A
  • No, but most macromolecules are insoluble in water and soluble in organic solvents.
37
Q

What is the level of melting and boiling points for metals?

A
  • Metals have high melting and high boiling points.
  • Metals have giant metallic lattice structures.
  • Strong electrostatic forces of attraction exist between the cations and the “sea of delocalised electrons” in the metallic lattice structures.
  • A large amount of energy is needed to overcome these forces of attraction.
38
Q

Are metals good or bad conductors of electricity and heat?

A
  • Metals are good conductors of electricity and heat.
  • The delocalised valence electrons allow efficient transfer of thermal energy throughout the metallic lattice structure.
  • the “sea of delocalised electrons” in the metallic lattice structure can move around and hence act as charge carriers and this allows the metal to conduct electricity.
39
Q

Are metals malleable and ductile?

A
  • Yes, metals are malleable (can be bent/flattened) and ductile (can be drawn into wires –> long).
  • The atoms of metals are arranged in an orderly, and regular manner.
  • When a force is applied (on an object/structure), the layers of atoms can slide over each other easily.
  • The ions in the metallic lattice structure are kept together by delocalised valence electrons provided that the applied force is not too large.
40
Q

What is an alloy made out of?

A
  • An alloy is a mixture of a metal and one/more than one other element.
41
Q

What is the composition of common alloys and their uses?

A
  1. Low carbon steel
    Composition:
    - Carbon (0.25%)
    - Iron
    Properties:
    - Soft
    - Easily-shaped
    Uses:
    - Car bodies
    - Machineries
  2. High carbon steel
    Composition:
    - Carbon (1.5%)
    - Iron
    Properties:
    - Strong
    - Brittle
    Uses:
    - Knives
    - Cutting tools
  3. Stainless steel
    Composition:
    - Iron
    - Chromium
    - Nickel
    - Carbon
    Properties:
    - Resistant to corrosion
    - Shiny
    Uses:
    - Cutlery
    - Surgical instruments
42
Q

Why are alloys harder than pure metals?

A
  • Alloys are harder than pure metals because the lattice structure of an alloy is not regular as it contains different atoms of different sizes.
  • This prevents the atoms from sliding over one another easily when a force is applied.
43
Q

Why do alloys melt over a range of temperatures?

A
  • Alloys melt over a range of temperatures because they are mixtures.
44
Q

Are alloys poor or good conductors of heat and electricity?

A
  • Like metals, alloys are good conductors of heat and electricity.
45
Q

How is the identity, structure and bonding of a substance deduced from its properties?

A

The mind map can be seen on page 55 of Chemistry Revision Guide.

Pure chemistry 🧫⚗️💉 (12 decks)

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