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GCSE OCR CHEMISTRY > 2.1 > Flashcards

2.1 Flashcards

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1
Q

How is the term “pure” defined in chemistry?

A

In chemistry, a pure substance consists of a single element or compound with no other substances mixed in

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2
Q

What distinguishes a mixture from a pure substance in chemistry?

A

Answer: A mixture consists of two or more elements or compounds physically mixed together without chemical bonding, while a pure substance contains only one element or compound.

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3
Q

What happens to the chemical properties of substances in a mixture?

A

Answer: The chemical properties of substances in a mixture remain unchanged because they are not chemically combined.

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4
Q

: How can substances in mixtures be separated?

A

Answer: Substances in mixtures can be separated by physical means, such as filtration, distillation, or chromatography

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5
Q

what distinguishes a pure substance from a mixture?

A

A mixture, on the other hand, consists of two or more elements or compounds physically mixed together without chemical bonding.

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6
Q

How can substances in mixtures be separated, and what remains unchanged in a mixture?

A

Substances in mixtures can be separated by physical means, such as filtration or distillation. The chemical properties of the substances in a mixture remain unchanged because they are not chemically combined

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7
Q

How do melting and boiling point data help distinguish between pure substances and mixtures?

A

Pure substances melt and boil at specific and sharp temperatures, while mixtures have a range of melting and boiling points due to the presence of different substances. Melting point analysis is routinely used to assess the purity of substances, with closer measured values indicating higher purity.

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8
Q

What does a cooling curve reveal about the purity of a substance?

A

Answer: A cooling curve for a pure substance shows a sharp melting point, indicating purity. However, an impure substance produces a gradual decrease in temperature as it freezes, showing impurities present.

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9
Q

How is percentage change calculated, and why is it commonly used in purity assessments?

A

Answer: Percentage change is calculated by dividing the difference between two values by the original amount, then multiplying by 100. It is commonly used in purity assessments to quantify the degree of change in a substance’s properties due to impurities

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10
Q

Question: What is the empirical formula?

A

Answer: The empirical formula is the simplest whole number ratio of atoms of each element in a molecule.

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11
Q

Question: How does the molecular formula differ from the empirical formula?

A

Answer: The molecular formula tells you the actual number of atoms of each element in a molecule, while the empirical formula represents the simplest whole number ratio of these atoms.

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12
Q

Question: How can you deduce the empirical formula from the molecular formula?

A

Answer: From the molecular formula, the empirical formula can be deduced by finding the simplest whole number ratio of atoms of each element.

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13
Q

Can the empirical formula and molecular formula be the same?

A

Answer: Yes, sometimes the empirical formula and molecular formula are the same, such as in the case of CO2

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14
Q

Question: How can you determine the empirical formula of an ionic compound represented by a dot-and-cross diagram?

A

Answer: Count the number of atoms of each element in the diagram, as this is equal to the empirical formula of the compound

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15
Q

Question: What steps are involved in determining the empirical formula of an ionic compound represented by a 3D lattice structure?

A

Answer: Identify the ions in the lattice, write them down, and balance the charges so that the overall charge is zero. The resulting formula is the empirical formula of the compound

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16
Q

Question: How can you calculate the percentage by mass of an element in a compound?

A

Answer: The percentage by mass of an element in a compound can be calculated using the formula:
Ar x number of atoms of the element / Mr of compound x 100

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17
Q

Question: What is an alloy, and how does it differ from a pure metal?

A

Answer: An alloy is a mixture of metals, whereas a pure metal consists of a single metal element. Alloys are typically stronger and harder than pure metals due to the presence of atoms of different sizes, which disrupt the regular arrangement of atoms and prevent easy sliding of layers

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18
Q

What is a formulation, and what are some examples?

A

Answer: A formulation is a mixture designed as a useful product, typically made by following an exact recipe with carefully measured quantities of each component. Examples of formulations include paint, medicines, food, and alloys.

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19
Q

Question: Why are most metals mixed with other elements to form alloys?

A

Answer: Most metals are too soft to use on their own, so they are mixed with other elements to make them stronger and harder.

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20
Q

Question: How do alloys differ in structure from pure metals, and why are they typically harder?

A

Answer: Alloys contain atoms of different sizes, which disrupt the regular arrangement of atoms in pure metals. This distortion makes it more difficult for the layers of atoms to slide over each other, resulting in alloys that are usually much harder than pure metals.

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21
Q

Question: What is filtration, and when is it used in chemistry?

A

Answer: Filtration is a separation technique used to separate an undissolved solid from a mixture of the solid and a liquid or solution. It is commonly used, for example, to separate sand from a mixture of sand and water.

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22
Q

Question: Describe the process of filtration.

A

Answer: In filtration, a piece of filter paper is placed in a filter funnel above a beaker. The mixture of insoluble solid and liquid is poured into the filter funnel. The filter paper allows only small liquid particles to pass through as filtrate, while solid particles are too large to pass through and stay behind as a residue.

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23
Q

Question: What is crystallisation, and when is it used in chemistry?

A

Answer: Crystallisation is a separation technique used to separate a dissolved solid from a solution, particularly when the solid is much more soluble in hot solvent than in cold. It is commonly used, for example, to separate copper sulphate from a solution of copper (II) sulphate in water

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24
Q

Question: Describe the process of crystallisation.

A

Answer: In crystallisation, the solution is heated, allowing the solvent to evaporate, leaving behind a saturated solution. To test if the solution is saturated, a clean, dry, cold glass rod is dipped into the solution. If the solution is saturated, crystals will form on the glass rod. The saturated solution is then allowed to cool slowly, causing crystals to grow as solids come out of solution due to decreasing solubility. Finally, the crystals are collected by filtering the solution, washed with cold distilled water to remove impurities, and allowed to dry.

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25
Q

Question: What is simple distillation, and when is it used in chemistry?

A

Answer: Simple distillation is a separation technique used to separate a liquid and soluble solid from a solution, or to separate a pure liquid from a mixture of liquids. It is commonly used, for example, to separate water from a solution of saltwater.

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26
Q

Question: Describe the process of simple distillation.

A

Answer: In simple distillation, the solution is heated, causing the pure liquid (such as water) to evaporate and produce a vapor. This vapor rises through the neck of the round-bottomed flask and passes through a condenser, where it cools and condenses back into a pure liquid. The condensed liquid is collected in a separate container (usually a beaker). After all the liquid has evaporated from the solution, only the solid solute will be left behind in the flask

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27
Q

Question: What is fractional distillation, and when is it used in chemistry?

A

Answer: Fractional distillation is a separation technique used to separate two or more liquids that are miscible with one another, such as ethanol and water from a mixture of the two

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28
Q

Describe the process of fractional distillation

A

Answer: In fractional distillation, the solution is heated to the temperature of the substance with the lowest boiling point. This substance will rise and evaporate first, and its vapors pass through a condenser, where they cool and condense into a liquid collected in a beaker. The fractionating column contains glass beads, increasing the surface area for evaporation and condensation. This allows substances with higher boiling points to condense more readily, leaving substances with lower boiling points to evaporate out of the column and into the condenser. For example, in the fractional distillation of a mixture of ethanol and water, ethanol, with a lower boiling point, evaporates first and is collected before water, with a higher boiling point, begins to evaporate.

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29
Q

Question: When given a mixture, how do you determine which separation techniques to use?

A

Answer: To determine the appropriate separation techniques, consider the properties of the components in the mixture. Choose techniques that can effectively separate each component based on its solubility, size, or other characteristics.

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30
Q

Question: What is chromatography, and what is its purpose?

A

Answer: Chromatography is a technique used to separate substances and provide information to help identify them

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31
Q

Describe the process of paper chromatography.

A

Answer: In paper chromatography, a pencil line is drawn on chromatography paper, and spots of the sample are placed on it. The paper is then lowered into a solvent container, allowing the solvent to travel up the paper by capillary action. Different substances in the sample have different solubilities and adhesion to the paper, causing them to spread apart as they travel up the paper. Those with higher solubility travel further than others, based on their differing affinities for the mobile (solvent) and stationary (paper) phases.

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32
Q

What are the two phases involved in paper chromatography, and what are their roles?

A

Answer: In paper chromatography, the mobile phase is the solvent (liquid) in which the sample molecules move, while the stationary phase is the chromatography paper itself. The differing affinities of substances for these phases determine the speed at which they move through the paper.

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33
Q

Question: How does thin-layer chromatography (TLC) differ from paper chromatography?

A

Answer: Thin-layer chromatography (TLC) works similarly to paper chromatography but uses a different stationary phase. Instead of paper, TLC uses a thin layer of an inert substance (e.g., silica) supported on a flat, unreactive surface

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34
Q

Question: What is the stationary phase in thin-layer chromatography (TLC), and what is its purpose?

A

Answer: In thin-layer chromatography (TLC), the stationary phase is a thin layer of an inert substance (e.g., silica) supported on a flat, unreactive surface. It provides a surface for the separation of substances based on their interactions with the mobile phase.

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35
Q

Question: What is chromatography, and what is its purpose?

A

Answer: Chromatography is a technique used to separate substances and provide information to help identify them.

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36
Q

Question: What are the two phases involved in chromatography?

A

Answer: The two phases in chromatography are the mobile phase and the stationary phase.

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37
Q

Question: What is the mobile phase in paper chromatography?

A

Answer: In paper chromatography, the mobile phase is the solvent in which the sample molecules can move, such as water or ethanol.

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38
Q

Question: How does paper chromatography work, and what are the key steps involved?

A

Answer: In paper chromatography, a pencil line is drawn on chromatography paper, and spots of the sample are placed on it. The paper is then lowered into a solvent container, allowing the solvent to travel up the paper by capillary action. Different substances in the sample have different solubilities and adhesion to the paper, causing them to spread apart as they travel up the paper. Substances with higher solubility travel further, as they spend more time in the mobile phase and are carried further up the paper.

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39
Q

Question: What are the two phases involved in chromatography?

A

Answer: The two phases in chromatography are the mobile phase and the stationary phase

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40
Q

Question: What is the mobile phase in paper chromatography?

A

Answer: In paper chromatography, the mobile phase is the solvent in which the sample molecules can move, such as water or ethanol

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41
Q

Question: What is the stationary phase in paper chromatography?

A

Answer: In paper chromatography, the stationary phase is the chromatography paper itself.

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42
Q

Question: How does thin-layer chromatography (TLC) differ from paper chromatography?

A

Answer: Thin-layer chromatography (TLC) works similarly to paper chromatography but has a different stationary phase.

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43
Q

Question: What is the stationary phase in thin-layer chromatography (TLC)?

A

Answer: In thin-layer chromatography (TLC), the stationary phase is a thin layer of an inert substance (e.g., silica) supported on a flat, unreactive surface.

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44
Q

Question: What is the mobile phase in thin-layer chromatography (TLC)?

A

Answer: In thin-layer chromatography (TLC), the mobile phase is a solvent, similar to paper chromatography

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45
Q

Question: What are Rf values used for in chromatography?

A

Answer: Rf values are used to identify the components of mixtures in chromatography.

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46
Q

How does the solvent used affect the Rf value?

A

Answer: The Rf value of a compound is dependent on the solvent used; changing the solvent changes the Rf value

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47
Q

Question: How is the Rf value calculated?

A

retention factor = distance moved by compound / distance moved by solvent

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48
Q

Question: How can chromatography be used to distinguish between pure substances and mixtures?

A

Answer: Pure substances will produce only one spot on the chromatogram, while mixtures will separate on the paper to show all the different components as separate spots.

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49
Q

Question: What does it indicate if a chromatogram has more than one spot?

A

Answer: An impure substance will produce a chromatogram with more than one spot, indicating the presence of multiple components or impurities in the sample

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50
Q

Question: What is gas chromatography used to separate?

A

Answer: Gas chromatography is used to separate a mixture of gases.

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51
Q

Question: What are the mobile and stationary phases in gas chromatography?

A

Answer: In gas chromatography, the mobile phase is an unreactive carrier gas (e.g., nitrogen), and the stationary phase is a thin layer of an unreactive liquid (e.g., silica or aluminium powder)

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52
Q

Question: Describe the process of gas chromatography.

A

Answer: In gas chromatography, the mixture sample is injected into the column, and the mixture is carried by the carrier gas through the column. Different substances in the mixture will take different times to travel through the column, known as retention time, due to their attraction to the stationary phase. Substances with more attraction to the stationary phase will take longer to move through the column. As each component leaves the column, a peak is plotted against the travel time on a chromatogram generated by a computer.

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53
Q

Question: What does the number of peaks on a gas chromatogram indicate?

A

Answer: The number of peaks on a gas chromatogram indicates the number of compounds present in the mixture.

54
Q

Question: What does the number of peaks on a gas chromatogram indicate?

A

Answer: The number of peaks on a gas chromatogram indicates the number of compounds present in the mixture.

55
Q

Question: What does the height of the peak on a gas chromatogram represent?

A

Answer: The height of the peak on a gas chromatogram represents the quantity of each compound present in the mixture.

56
Q

Question: What does the position of the peak on a gas chromatogram indicate?

A

Answer: The position of the peak on a gas chromatogram indicates the retention time of each compound, which is how long it took for the compound to move through the column.

57
Q

Question: What happens to atoms of different elements in chemical reactions to achieve a full outer shell of electrons?

A

Answer: Atoms of different elements, which do not have a full outer shell of electrons, can try to achieve a full outer shell by gaining or losing electrons in chemical reactions, leading to the formation of ions

58
Q

Question: What is an ion?

A

Answer: An ion is an atom or molecule that has become charged through the loss or gain of one or more electrons.

59
Q

Question: How do metals and non-metals form ions when they react?

A

Answer: Metals will form positive ions when they react because they lose electrons, while non-metals will form negative ions because they gain electrons.

60
Q

What are metalloids or semi-metals?

A

Answer: Metalloids or semi-metals are elements that display properties of both metals and non-metals

61
Q

Question: How does the metallic character of elements change across the periodic table?

A

Answer: The metallic character of elements decreases as you move across a period on the periodic table from left to right, and it increases as you move down a group

62
Q

Question: What are positive ions called, and how can you remember this?

A

Answer: Positive ions are called cations, which can be remembered using the phrase “CATions are PAWsitive.”

63
Q

Question: What are negative ions called, and how can you remember this?

A

Answer: Negative ions are called anions, which can be remembered using the phrase “ANions are A Negative ion.”

64
Q

Metals
Property: Electron arrangement

A

1 - 3 outer shell electrons

65
Q

Metals
Property: Bonding

A

Answer: Metallic bonding due to loss of outer shell electrons

66
Q

Metals
Property: Electrical conductivity

A

Answer: Good conductors of electricity

67
Q

Metals
Property: Type of oxide

A

Answer: Basic oxides (a few are amphoteric)

68
Q

Metals
Property: Reaction with acids

A

Many react with acids

69
Q

Metals
Property: Physical characteristics

A

Usually lustrous (shiny)

Solid at room temperature (excluding mercury)
Malleable, can be bent and shaped
High melting and boiling points

70
Q

Non-metals
Property: Electron arrangement

A

4 - 7 outer shell electrons

71
Q

Non-metals
Property: Bonding

A

Covalent by sharing of outer shell electrons

72
Q

Non-metals
Property: Electrical conductivity

A

Poor conductors of electricity

73
Q

Non-metals
Property: Type of oxide

A

Acidic oxides (some are neutral)

74
Q

Non-metals
Property: Reaction with acids

A

Usually do not react with acids

75
Q

Non-metals
Property: Physical characteristics

A

Physical characteristics
Answer: - Dull, non-reflective
Different states at room temperature
Flaky, brittle
Low melting and boiling points

76
Q

Question: How does the number of outer electrons in an atom relate to its position on the Periodic Table?

A

Answer: The number of outer electrons in an atom is linked to its position in the Periodic Table. Group 1 elements have one outer shell electron, Group 2 elements have two outer shell electrons, and so on. Group 0 elements (sometimes called Group 8) have full outer shells

77
Q

Question: What happens to the attraction between the outer shell electrons and the nucleus as you descend any group on the Periodic Table?

A

nswer: As you descend any group on the Periodic Table, the outer shell electrons become further away from the nucleus due to increasing atomic size as more shells of electrons are present. This weakens the attraction between the outer shell electrons and the nucleus.

78
Q

Question: How does the position of a metallic element on the Periodic Table affect its reactivity?

A

Answer: The further down the group a metallic element is, the more easily it can react by losing its outer electron(s).

79
Q

Question: How does the position of a non-metallic element on the Periodic Table affect its reactivity?

A

Answer: The further down the group a non-metallic element is, the harder it is to react as it is more difficult to attract extra electrons and therefore gain electrons to obtain a full outer shell.

80
Q

Question: What is the arrangement of elements on the Periodic Table based on?

A

Answer: The arrangement of elements on the Periodic Table is based on increasing atomic number.

81
Q

Question: What is the significance of periods on the Periodic Table?

A

Answer: Periods, the horizontal rows on the Periodic Table, indicate the number of electron shells an atom has. Each period corresponds to the number of electron shells present in the atoms of the elements in that row

82
Q

Question: What is the significance of groups on the Periodic Table?

A

Answer: Groups, the vertical columns on the Periodic Table, indicate the number of outer electrons each atom has. Each group corresponds to the number of electrons in the outermost shell of the atoms of the elements in that column

83
Q

Question: What is the outermost shell of an atom called, and why is it important?

A

Answer: The outermost shell of an atom is called the valence shell. It is important because atoms are more stable if they can completely fill this shell with electrons.

84
Q

Question: How do atoms react with other atoms to achieve a full outer shell of electrons?

A

Answer: Atoms can gain electrons to complete their existing outer shell, forming anions (for non-metals). They can also lose electrons to empty their outer shell, forming cations (for metals). Additionally, atoms can share electrons to gain full outer shells, forming covalent bonds.

85
Q

Question: How is the electron configuration of an atom represented using number notation?

A

Answer: The electron configuration of an atom is represented by writing down the number of electrons in each shell, separated by commas or full stops. This notation starts with the innermost shell closest to the nucleus

86
Q

Question: What is the significance of the number of shells present in the electron configuration notation?

A

Answer: The number of shells represented in the electron configuration notation indicates the period or row the element is in on the Periodic Table.

87
Q

Question: How does the number notation for electron configuration relate to the group number of an element?

A

Answer: Elements in the same group have the same number of outer shell electrons. Therefore, the last number in the electron configuration notation indicates the number of outer shell electrons and corresponds to the group number of the element.

88
Q

How can the electron configuration of an element be determined using number notation?

A

Answer: The number notation for electron configuration provides information about the number of shells and the number of electrons in the outermost shell, which can be used to determine the position of the element in the Periodic Table and its chemical properties

89
Q

Question: What does the electron configuration notation “2.8.2” represent?

A

Answer: The electron configuration notation “2.8.2” indicates an element in Period 3 (since there are 3 notations) and Group 2 (since the last notation is “2”), with a total of 12 electrons distributed across the shells

90
Q

Question: What is an ion?

A

Answer: An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons

91
Q

What is the purpose of ion formation?

A

Answer: Ions are formed to obtain a full outer shell of electrons, which increases the stability of the atom or group of atoms

92
Q

Question: How do negative ions form, and what are they called?

A

Answer: Negative ions, called anions, form when atoms gain electrons, resulting in more electrons than protons.

93
Q

How do positive ions form, and what are they called?

A

Answer: Positive ions, called cations, form when atoms lose electrons, resulting in fewer electrons than protons.

94
Q

What is the relationship between the number of electrons gained or lost and the charge of an ion?

A

Answer: The number of electrons gained or lost by an atom equals the charge of the resulting ion. For example, if a magnesium atom loses 2 electrons, the resulting charge is 2+.

95
Q

Question: What holds positively and negatively charged ions together in an ionic bond?

A

Answer: Positively and negatively charged ions are held together by the strong electrostatic forces of attraction between the oppositely charged ions.

96
Q

What types of elements typically form ionic bonds?
Answer

A

: Ionic bonds typically occur between a metal and a non-metal.

97
Q

How can ionic bonds be represented diagrammatically?

A

Answer: Ionic bonds can be represented using dot and cross diagrams, where solid dots and crosses represent electrons from each atom, and large square brackets encompass each atom with the charge shown as a superscript outside the brackets

98
Q

n a dot and cross diagram for an ionic bond, which electrons are typically represented?

A

Answer: In dot and cross diagrams for ionic bonds, only the valence shell (outer shell) electrons are typically represented.

99
Q

What is the purpose of using dot and cross diagrams to represent ionic bonds?

A

Answer: Dot and cross diagrams provide a simple and quick visual representation of the formation of an ionic compound, illustrating the transfer of electrons from one atom to another to achieve stability through the formation of ions.

100
Q

Question: Describe the formation of sodium chloride (NaCl) through ionic bonding.

A

Answer: Sodium, a Group 1 metal, loses its one outer electron to form a positively charged sodium ion (Na+), while chlorine, a Group 7 non-metal, gains this electron to form a negatively charged chloride ion (Cl-). The resulting oppositely charged ions are then attracted to each other by strong electrostatic forces, forming the ionic compound sodium chloride (NaCl).

101
Q

Question: What happens to the electron configuration of sodium and chlorine during the formation of sodium chloride?

A

Answer: Sodium loses its one outer electron to achieve a full outer shell, while chlorine gains this electron to also achieve a full outer shell.

102
Q

What is the charge of the sodium ion and the chloride ion in sodium chloride?

A

Answer: The sodium ion (Na+) has a positive charge of 1+, and the chloride ion (Cl-) has a negative charge of 1-.

103
Q

Question: What is the formula of the ionic compound formed by sodium and chlorine?

A

Answer: The formula of the ionic compound formed by sodium and chlorine is NaCl, indicating a 1:1 ratio of sodium ions to chloride ions.

104
Q

Question: What type of bonding holds the sodium and chloride ions together in sodium chloride?

A

Answer: The sodium and chloride ions are held together by strong electrostatic forces of attraction, characteristic of ionic bonding.

105
Q

Question: Describe the formation of magnesium oxide (MgO) through ionic bonding.

Front

A

Answer: Magnesium, a Group 2 metal, loses two outer electrons to form a positively charged magnesium ion (Mg2+), while oxygen, a Group 6 non-metal, gains these electrons to form negatively charged oxide ions (O2-). The resulting oppositely charged ions are then attracted to each other by strong electrostatic forces, forming the ionic compound magnesium oxide (MgO).

106
Q

What happens to the electron configuration of magnesium and oxygen during the formation of magnesium oxide?

A

Answer: Magnesium loses two outer electrons to achieve a full outer shell, while oxygen gains these electrons to also achieve a full outer shell

107
Q

What is the charge of the magnesium ion and the oxide ion in magnesium oxide?

Front

A

Answer: The magnesium ion (Mg2+) has a positive charge of 2+, and the oxide ion (O2-) has a negative charge of 2-.

108
Q

What is the formula of the ionic compound formed by magnesium and oxygen?

A

Answer: The formula of the ionic compound formed by magnesium and oxygen is MgO, indicating a 1:1 ratio of magnesium ions to oxide ions

109
Q

Question: What type of bonding holds the magnesium and oxide ions together in magnesium oxide?

A

Answer: The magnesium and oxide ions are held together by strong electrostatic forces of attraction, characteristic of ionic bonding

110
Q

Question: What are the advantages of using dot and cross diagrams to represent ionic compounds?

A

Answer: Dot and cross diagrams are useful for illustrating the transfer of electrons and indicate from which atom the bonding electrons originate

111
Q

Question: What are the disadvantages of dot and cross diagrams in representing ionic compounds?

A

Answer: Dot and cross diagrams fail to illustrate the three-dimensional arrangements of the atoms and electron shells, and they do not indicate the relative sizes of the atoms involved

112
Q

Question: What are the advantages of using ball and stick models to represent ionic compounds?

A

Answer: Ball and stick models are useful for illustrating the arrangement of atoms or ions in three-dimensional space, making them especially useful for visualizing the shape of an ionic compound.

113
Q

Question: What are the disadvantages of ball and stick models in representing ionic compounds?

A

Answer: Ball and stick models fail to indicate the movement of electrons, inaccurately represent the distances between ions, do not accurately depict ion sizes, do not show the charges on ions, and do not accurately represent the electrostatic forces of attraction between ions

114
Q

Question: What is a covalent bond?

A

Answer: A covalent bond is a type of chemical bond formed between non-metal atoms when they share pairs of electrons to achieve a full outer shell of electrons.

115
Q

Question: What are shared electrons in a covalent bond called?

A

Answer: Shared electrons in a covalent bond are called bonding electrons

116
Q

What are the properties of covalently bonded substances?

A

Answer: Covalently bonded substances may consist of small molecules or giant structures. They have very strong covalent bonds within molecules but weak intermolecular forces between molecules

117
Q

Question: What are simple covalent molecules?

A

Answer: Simple covalent molecules are small molecular structures formed by covalent bonds between non-metal atoms. Examples include Cl2, H2O, and CO2.

118
Q

Question: How can simple covalent molecules be represented?

A

Answer: Simple covalent molecules can be represented using dot-and-cross diagrams, which show the arrangement of electrons and the sharing of electron pairs between atoms.

119
Q

Question: Provide examples of simple covalent molecules and their dot-and-cross diagrams.

A

Answer: Examples include hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2), hydrogen chloride (HCl), water (H2O), ammonia (NH3), and methane (CH4

120
Q

Question: What are the limitations of dot-and-cross diagrams for representing simple covalent molecules?

A

Answer: Dot-and-cross diagrams fail to illustrate the 3D arrangements of the atoms and electron shells, and they do not indicate the relative sizes of the atoms.

121
Q

Question: What are the advantages of dot-and-cross diagrams?

A

Answer: Dot-and-cross diagrams are useful for illustrating the transfer of electrons and indicating from which atom the bonding electrons come from.

122
Q

Question: What are the advantages of ball-and-stick models for representing molecules?

A

Answer: Ball-and-stick models are useful for illustrating the arrangement of atoms in 3D space and visualizing the shape of a molecule.

123
Q

What are the disadvantages of ball-and-stick models?

A

Answer: Ball-and-stick models fail to indicate the movement of electrons, and the atoms are placed far apart from each other, which does not accurately represent the closer proximity of atoms in reality.

124
Q

Question: What are the advantages of 2D representations of molecules?

A

Answer: Displayed formulae are 2D representations that provide simpler versions of the ball-and-stick model, adequately indicating the atoms in a molecule and their connections

125
Q

Question: What are the disadvantages of 2D representations of molecules?

A

Answer: 2D representations fail to illustrate the relative sizes of atoms and bonds, and they cannot provide an idea of the molecule’s shape in 3D space.

126
Q

Question: What are giant covalent structures?

A

Answer: Giant covalent structures are large, variable networks of non-metal atoms bonded to each other via strong covalent bonds, resulting in substances that are usually solid at room temperature.

127
Q

Question: What distinguishes giant covalent structures from small molecules?

A

Answer: Unlike small molecules, giant covalent structures contain no weak intermolecular forces between molecules, only covalent bonds

128
Q

Question: What are some properties of giant covalent structures?

A

Answer: Giant covalent structures have high melting and boiling points due to many strong covalent bonds. Most cannot conduct electricity, although there are exceptions such as graphite and graphene

129
Q

Give examples of giant covalent structures and their special characteristics.

A

Answer: Diamond is transparent and the hardest naturally occurring substance. Graphite is a grey-black solid with good electrical conductivity. Silicon dioxide is a semiconductor and very strong

130
Q

Question: What are polymers?

A

Answer: Polymers are very large covalent molecules made by linking together large numbers of smaller molecules called monomers.

131
Q

Question: What are some examples of common polymers?

A

Answer: Common polymers include polythene (used in plastic bags) and polyvinyl chloride (PVC, used in water pipes).

GCSE OCR CHEMISTRY (7 decks)

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