Atoms, Bonding and Moles

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Questions and Answers

Explain how the concept of electronegativity differences between atoms dictates the type of chemical bond formed (ionic vs. polar covalent vs. nonpolar covalent). Provide examples.

Large electronegativity differences lead to ionic bonds, intermediate differences to polar covalent bonds, and negligible differences to nonpolar covalent bonds. For example, NaCl (ionic), H₂O (polar covalent), and H₂ (nonpolar covalent).

Describe how the kinetic molecular theory explains the differences in properties between solids, liquids, and gases at a molecular level.

Solids have strong intermolecular forces restricting movement. Liquids have weaker forces allowing particles to move past each other. Gases have negligible forces and particles move freely.

Explain why diamond is exceptionally hard and has a very high melting point, while graphite is soft and can conduct electricity.

Diamond has a giant covalent structure with strong covalent bonds in all directions, making it hard with a high melting point. Graphite consists of layers with strong covalent bonds but weak intermolecular forces between layers, and delocalized electrons allow it to conduct electricity.

Consider two aqueous solutions, one containing a strong acid and the other a weak acid, both at the same concentration. How would their pH, conductivity, and reactivity with a strong base differ?

The strong acid would have a lower pH, higher conductivity, and react more vigorously with a strong base compared to the weak acid. Signup and view all the answers

How does the presence of impurities affect the melting point of a substance, and why does this occur?

Impurities generally lower the melting point of a substance by disrupting the crystal lattice structure, requiring less energy to break the intermolecular forces. Signup and view all the answers

Explain the concept of 'delocalized electrons' in metallic bonding and how it contributes to the unique properties of metals (conductivity, malleability, and ductility).

Delocalized electrons are not associated with a single atom and are free to move throughout the metal lattice, allowing for electrical and thermal conductivity. The ability of atoms to slide past each other without breaking bonds contributes to malleability and ductility. Signup and view all the answers

Describe the relationship between the number of valence electrons an element possesses and its position in the periodic table, outlining how this relationship dictates its bonding behavior.

The group number corresponds to the number of valence electrons. This determines whether an element tends to gain, lose, or share electrons to achieve a stable octet, dictating its bonding behavior. Signup and view all the answers

Explain the factors affecting the strength of ionic bonds and how these factors influence the melting points and boiling points of ionic compounds.

The strength of ionic bonds is affected by the charge and size of the ions. Higher charges and smaller ionic radii lead to stronger electrostatic forces and thus higher melting and boiling points. Signup and view all the answers

Explain why increasing temperature usually increases reaction rate, but increasing the concentration of a reactant does not always increase reaction rate.

Increased temperature increases the kinetic energy of molecules, leading to more frequent and energetic collisions exceeding the activation energy. Increasing concentration only increases reaction rate if the reactant is involved in the rate-determining step. Signup and view all the answers

Describe the concept of 'percentage yield' in a chemical reaction and explain why the actual yield is often less than the theoretical yield.

Percentage yield is the ratio of actual yield to theoretical yield, expressed as a percentage. Actual yield is often less due to incomplete reactions, side reactions, loss of product during purification, or experimental errors. Signup and view all the answers

Differentiate between the terms 'atom economy' and 'percentage yield', explaining their significance in evaluating the sustainability of a chemical process.

Atom economy considers the amount of reactant atoms that become part of the desired product, while percentage yield focuses on the amount of desired product obtained relative to the theoretical maximum. High atom economy indicates a more sustainable process, minimizing waste. Signup and view all the answers

Predict the products of the electrolysis of a concentrated solution of sodium chloride (NaCl), explaining the redox reactions that occur at each electrode.

At the cathode, hydrogen gas (H₂) is produced (reduction of water). At the anode, chlorine gas (Cl₂) is produced (oxidation of chloride ions). Signup and view all the answers

Explain how a catalyst increases the rate of a chemical reaction, and illustrate this with an example.

A catalyst lowers the activation energy of a reaction by providing an alternative reaction pathway. For example, enzymes catalyze biochemical reactions in living organisms. Signup and view all the answers

Describe the difference between strong and weak acids/bases in terms of their dissociation in water, and explain how this affects the pH of their solutions.

Strong acids/bases completely dissociate in water, producing a high concentration of H⁺/OH⁻ ions, resulting in a low/high pH. Weak acids/bases only partially dissociate, resulting in a lower concentration of H⁺/OH⁻ ions and a less extreme pH. Signup and view all the answers

Explain how the reactivity series can be used to predict whether a displacement reaction will occur between a metal and a salt solution.

A metal will displace another metal from its salt solution if it is higher in the reactivity series (more reactive). This is because the more reactive metal has a greater tendency to lose electrons. Signup and view all the answers

Describe the process of extracting aluminum from its ore (bauxite) via electrolysis, including the role of cryolite and the reactions at the anode and cathode.

Bauxite is dissolved in molten cryolite to lower its melting point for electrolysis. At the cathode, aluminum ions are reduced to form aluminum metal. At the anode, oxide ions are oxidized to form oxygen gas, which reacts with the carbon anode to form carbon dioxide. Signup and view all the answers

Explain the principles behind titration, including the use of a standard solution, an indicator, and the concept of the equivalence point.

Titration involves reacting a solution of unknown concentration with a standard solution (known concentration) until the reaction is complete, indicated by a color change from an indicator. The equivalence point is when the moles of acid and base are equal. Signup and view all the answers

Describe the process of metallic bonding and explain how the structure contributes to properties such as malleability and electrical conductivity.

Metallic bonding consists of a lattice of positive ions surrounded by a 'sea' of delocalized electrons. The delocalized electrons allow for electrical and thermal conductivity, while the ability of atoms to slide past each other without breaking bonds allows for malleability and ductility. Signup and view all the answers

Explain why graphite can conduct electricity but diamond cannot, despite both being made of carbon atoms.

Graphite has delocalized electrons between layers which are mobile and can carry charge, while diamond has all its electrons involved in strong covalent bonds, with no free electrons to conduct electricity. Signup and view all the answers

What are the implications of the law of conservation of mass for writing and balancing chemical equations?

The law of conservation of mass means that the number of atoms of each element must be the same on both sides of a chemical equation, requiring the equation to be balanced. Signup and view all the answers

Outline the principles of the Haber process. Include the equation, catalysts used, conditions, and why these specific conditions are used.

The Haber process combines nitrogen and hydrogen to form ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Iron catalyst, 450°C, and 200 atm pressure are used. High pressure favors ammonia formation. Moderate temperature gives acceptable rate and yield. Signup and view all the answers

Explain how to determine the limiting reactant in a chemical reaction given the masses of two reactants and a balanced equation. Why is identifying the limiting reactant important?

Convert masses to moles using molar masses. Use mole ratios from the balanced equation to determine which reactant would produce less product. That one is the limiting reactant. It's important because it dictates the maximum product yield. Signup and view all the answers

What is relative formula mass `Mr`? Explain using an example compound such as $CO_2$. What is its significance in stoichiometric calculations?

Mr is the sum of the Ar values of all atoms in a formula. For CO₂, Mr = Ar(C) + 2Ar(O) = 12 + 216 = 44. It's used to convert between mass and moles in stoichiometry. Signup and view all the answers

Explain why metals are typically malleable and ductile, while ionic compounds are brittle. Relate this to their structure and bonding.

Metals have layers of atoms that can slide due to the delocalized electrons. Ionic compounds break when layers shift, bringing like charges together, causing repulsion. Signup and view all the answers

Describe the trend in reactivity of Group 1 metals with water and explain the reasons behind this trend.

Reactivity increases down the group. This is because the outer electron is further from the nucleus, making it easier to lose, forming a positive ion. Signup and view all the answers

Explain, at a molecular level, how a buffer solution resists changes in pH when small amounts of acid or base are added.

A buffer contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Added acid reacts with the conjugate base; added base reacts with the weak acid, minimizing pH change. Signup and view all the answers

How does the structure of a simple molecular substance like water ($H_2O$) affect its properties, such as boiling point and surface tension?

Water's bent shape leads to polarity, resulting in hydrogen bonds (strong intermolecular forces). These bonds give it a relatively high boiling point and high surface tension. Signup and view all the answers

Describe the differences in properties between giant ionic structures and giant covalent structures. Relate this to their structure and bonding.

Giant ionic structures have high melting and boiling points, are brittle and conduct electricity when molten or dissolved. Giant covalent structures have very high melting points and do not conduct electricity (except for graphite), and are very hard. Signup and view all the answers

Describe what happens during electrolysis, explaining oxidation, reduction, anode, cathode, and electrolyte using an example such as electrolysis of copper sulfate solution using inert electrodes.

Electrolysis uses electricity to decompose a compound. At the anode (positive electrode), oxidation (loss of electrons) occurs. At the cathode (negative electrode), reduction (gain of electrons) occurs. The electrolyte contains ions that conduct electricity. In copper sulfate, copper ions go to the cathode and are reduced to copper. Hydroxide ions go to the anode and are oxidized to oxygen. Signup and view all the answers

Explain the difference between acids and alkalis in terms of proton ($H^+$) and hydroxide ($OH^-$) ion concentration. What is neutralisation?

Acids have a higher concentration of $H^+$ ions than $OH^-$ ions. Alkalis have a higher concentration of $OH^-$ ions than $H^+$ ions. Neutralisation is the reaction between an acid and an alkali to form a salt and water, where $H^+$ and $OH^-$ ions combine to form water. Signup and view all the answers

How can you calculate the concentration of a solution in $g/dm^3$ and $mol/dm^3$? How are these related?

Concentration in $g/dm^3$ is mass (g) divided by volume ($dm^3$). Concentration in $mol/dm^3$ is moles divided by volume ($dm^3$). To convert from $g/dm^3$ to $mol/dm^3$, divide by the molar mass in $g/mol$. Signup and view all the answers

Describe, using an example, how to balance a chemical equation. Explain why it is important.

For example, $H_2 + O_2 \rightarrow H_2O$. Balanced, it becomes $2H_2 + O_2 \rightarrow 2H_2O$. Balancing ensures the number of atoms of each element is the same on both sides, obeying the conservation of mass. Signup and view all the answers

Explain how the oxidation state of an element changes during oxidation and reduction. Provide example half-equations.

During oxidation, the oxidation state increases (loss of electrons). During reduction, the oxidation state decreases (gain of electrons). For example, $Fe^{2+} \rightarrow Fe^{3+} + e^-$ (oxidation) and $Cu^{2+} + 2e^- \rightarrow Cu$ (reduction). Signup and view all the answers

Describe how a catalyst works, including the concept of activation energy. Explain why a catalyst does not appear in the overall balanced equation.

A catalyst lowers the activation energy of a reaction by providing an alternative reaction pathway. It is not consumed in the reaction, so it is regenerated and doesn't appear in the overall equation. Signup and view all the answers

Explain the relationship between the structure and properties of metals, giant ionic compounds, and simple molecular substances, focusing on electrical conductivity, melting point, and brittleness.

Metals: Conduct electricity due to delocalized electrons, malleable due to layers sliding. High melting points due to strong metallic bonds. Giant ionic compounds: Don't conduct as solids, brittle due to ion repulsion when layers shift. High melting points due to strong electrostatic forces. Simple molecular: Low melting/boiling points due to weak intermolecular forces, do not conduct. Signup and view all the answers

Explain how the differences in electron configurations and nuclear charge contribute to the differing chemical behaviors of sodium and chlorine.

Sodium has one valence electron it readily loses to achieve a stable configuration, forming a +1 ion. Chlorine has seven valence electrons and readily gains one to achieve a stable configuration, forming a -1 ion. Their differing electronegativities cause them to form ionic bonds. Signup and view all the answers

Describe the process of extracting a metal from its ore through reduction with carbon. Include an example, limitations, and why this method is used for certain metals.

Metal oxides are heated with carbon, which removes oxygen to form the metal and carbon dioxide. Eg. iron oxide is reduced to iron. It's limited to metals less reactive than carbon and is used as it's a cheap and effective method for moderately reactive metals. Signup and view all the answers

Describe how to determine the empirical formula of a compound from percentage composition data. Explain why the empirical formula may not be the same as the molecular formula.

Convert percentages to masses, then to moles. Divide by the smallest number of moles to get the simplest whole-number ratio, giving the empirical formula. The molecular formula is a multiple of the empirical formula, if the Mr is different. Signup and view all the answers

Explain the difference between intramolecular and intermolecular forces. How do these forces affect the physical properties of substances?

Intramolecular forces are within molecules (e.g., covalent bonds), holding atoms together. Intermolecular forces are between molecules (e.g., hydrogen bonds), affecting boiling point, etc. Stronger intermolecular forces mean higher melting/boiling points. Signup and view all the answers

What are isotopes? Explain how isotopes of the same element can have different physical properties but almost identical chemical properties.

Isotopes are atoms of the same element with different numbers of neutrons. They have different masses, affecting physical properties like density. Chemical properties are similar as they have the same electron configuration. Signup and view all the answers

Flashcards

Atoms

Fundamental building blocks of matter, composed of protons, neutrons, and electrons.

Protons

Positively charged particles located in the nucleus of an atom.