Chemistry

Question 1

Atoms and the Periodic Table

Q: Define an atom and explain its structure.

Answer 1

A: An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus made up of protons and neutrons, surrounded by electrons in orbitals.

Question 2

Q: List and describe the three main subatomic particles that make up an atom.

Answer 2

A:

Protons: Positively charged particles in the nucleus.
Neutrons: Neutral particles in the nucleus.
Electrons: Negatively charged particles orbiting the nucleus.

Question 3

Q: Explain how the atomic number and mass number are determined for an element.

Answer 3

A:

Atomic Number: The number of protons in the nucleus.
Mass Number: The sum of protons and neutrons in the nucleus.

Question 4

Q: Define an isotope and provide an example.

Answer 4

A: Isotopes are variants of an element with the same number of protons but different numbers of neutrons. Example: Carbon-12 and Carbon-14.

Question 5

Q: What is the periodic table and why is it important in chemistry?

Answer 5

A: The periodic table is a tabular arrangement of elements based on their atomic number, electron configurations, and recurring chemical properties. It is important because it organizes elements in a way that reveals patterns in their properties.

Question 6

Q: Identify the key information provided for each element in the periodic table.

Answer 6

A: Atomic number, element symbol, element name, atomic mass.

Question 7

Q: Describe the arrangement of elements in the periodic table based on their properties.

Answer 7

A: Elements are arranged in order of increasing atomic number. Rows (periods) indicate the number of electron shells, and columns (groups) indicate elements with similar properties, and the number of valence electrons they have.

Question 8

Explain how elements in the periodic table are classified into groups and periods:

Answer 8

Groups: Vertical columns with elements that have similar chemical properties.
Periods: Horizontal rows that represent the energy levels of electrons.

Question 9

Give examples of elements from different groups and describe their properties:

Answer 9

Group 1 (Alkali Metals): Sodium (Na) - highly reactive, soft metals.
Group 2 (Alkaline Earth Metals)
Group 13-16 (Post transition metals and Metaloids)
Group 17 (Halogens): Chlorine (Cl) - very reactive, non-metal.
Group 18 (Noble Gases): Neon (Ne) - inert, non-reactive gases.

Question 10

Differentiate between cations and anions, providing examples of each:

Answer 10

Cations: Positively charged ions (e.g., Na⁺).
Anions: Negatively charged ions (e.g., Cl⁻).

Question 11

Define an ion and explain how ions are formed when atoms gain or lose electrons:

Answer 11

An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. Cations form when atoms lose electrons, and anions form when atoms gain electrons.

Question 12

Define ionic bonding and describe how it occurs between metal and non-metal atoms:

Answer 12

Ionic bonding is the electrostatic attraction between oppositely charged ions. It occurs when metals lose electrons to form cations and non-metals gain those electrons to form anions.

Question 13

Give examples of compounds formed by ionic bonding:

Answer 13

Sodium chloride (NaCl), magnesium oxide (MgO).

Question 14

Describe the structure of an ionic compound and explain why it has high melting and boiling points:

Answer 14

Ionic compounds form a crystal lattice structure, where each ion is surrounded by ions of the opposite charge. The strong electrostatic forces between the ions result in high melting and boiling points.

Question 15

Q: Define covalent bonding and explain how it occurs between non-metal atoms.

Answer 15

A: Covalent bonding is the sharing of electron pairs between atoms. It occurs when non-metals share electrons to achieve a full outer shell.

Question 16

Q: Describe the formation of a covalent bond through electron sharing.

Answer 16

A: In a covalent bond, each atom contributes one or more electrons to form a shared pair, creating a stable electron configuration for both atoms.

Question 17

Q: Describe the formation of metallic bonds by referring to the sea of electrons.

Answer 17

A: Metallic bonding involves a lattice of positive metal ions surrounded by a ‘sea’ of delocalized electrons. These free-moving electrons allow metals to conduct electricity and heat.

Question 18

Q: Describe why metals are conductive and malleable with reference to metallic bonding.

Answer 18

A: Metals are conductive because the delocalized electrons can move freely throughout the metal. They are malleable because the metal ions can slide past each other while remaining bonded by the sea of electrons.

Question 19

Chemical Reactions

Q: Define a chemical reaction and provide an example.

Answer 19

A: A chemical reaction is a process where substances (reactants) are transformed into new substances (products). Example: 2H₂ + O₂ → 2H₂O.

Question 20

Q: List and explain the five main types of chemical reactions.

Answer 20

A:

Synthesis: Two or more simple substances combine to form a more complex substance (A + B → AB).
Decomposition: A complex substance breaks down into simpler substances (AB → A + B).
Combustion: A substance reacts with oxygen, often producing heat and light (hydrocarbon + O₂ → CO₂ + H₂O).
Single Replacement: One element replaces another in a compound (A + BC → AC + B).
Double Replacement: The ions of two compounds exchange places in an aqueous solution to form two new compounds (AB + CD → AD + CB).

Question 21

Q: Discuss properties of ionic compounds formed in precipitation (double replacement) reactions using the solubility table.

Answer 21

A: Precipitation reactions occur when two aqueous solutions react to form an insoluble solid (precipitate). Solubility tables help predict whether a precipitate will form based on the solubility of the products.

Question 22

Q: Describe the conservation of mass and energy in a chemical reaction.

Answer 22

A: The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.
The law of conservation of energy states that energy is neither created nor destroyed, only transferred or transformed.

Question 23

Q: Identify the reactants and products in a given chemical equation.

Answer 23

A: Reactants are the starting substances in a chemical reaction, and products are the substances formed. Example: In the reaction 2H₂ + O₂ → 2H₂O, H₂ and O₂ are reactants, and H₂O is the product.

Question 24

Q: Balance a chemical equation to satisfy the law of conservation of mass.

Answer 24

A: Ensure the number of atoms of each element is the same on both sides of the equation.

Question 25

Q: What are exothermic and endothermic reactions? Provide examples of each.

Answer 25

Exothermic: Reactions that release energy (e.g., combustion of methane).
Endothermic: Reactions that absorb energy (e.g., photosynthesis).

Question 26

Q: Identify the products of the reaction between acids and metals, acids and bases, and acids and carbonates.

Answer 26

1. Acids and Metals
   When acids react with metals, the products are typically a salt and hydrogen gas. The general reaction can be represented as:
   Acid+Metal→Salt+HydrogenGas

Example:
Hydrochloric acid (HCl) reacting with zinc (Zn):
2HCl+Zn→ ZnCl2+H2

2. Acids and Bases
   When acids react with bases, the products are typically a salt and water. This is a neutralization reaction. The general reaction can be represented as:
   Acid+Base→Salt+Water

Example:
Hydrochloric acid (HCl) reacting with sodium hydroxide (NaOH):
HCl+NaOH→NaCl+H2

3. Acids and Carbonates
   When acids react with carbonates, the products are typically a salt, water, and carbon dioxide gas. The general reaction can be represented as:
   Acid+Carbonate→Salt+Water+CarbonDioxide

Example:
Hydrochloric acid (HCl) reacting with calcium carbonate (CaCO₃):
2HCl+CaCO3→CaCl 2+H2O+CO2

A M: Salt + Hydrogen Gas
A B: Salt + Water
A C: Salt + Water + Co2

Question 27

Q: Understand the particle theory and use it to explain how the rate of a chemical reaction can be increased.

Answer 27

A: The particle theory states that matter is made up of tiny particles in constant motion. Reaction rates increase with higher temperature, concentration, agitation, surface area, and the presence of catalysts.

Question 28

Q: Describe the factors that can influence the rate of a chemical reaction.

Answer 28

Temperature: Higher temperature increases particle movement, leading to more collisions.
Concentration: Higher concentration increases the number of particles, leading to more collisions.
Agitation: Stirring increases particle collisions.
Surface area: Smaller particles expose more surface area for reactions.
Catalysts and enzymes: Speed up reactions by lowering the activation energy.

Question 29

Q: Discuss the importance of chemical reactions in everyday life.

Answer 29

A: Chemical reactions are essential for processes like digestion, respiration, cooking, and manufacturing.