Answer key

Prepared by: learnloophq@gmail.com

Last edited 25 days ago by Learn LoopHQ.

Chapter: 03. Elements And Compounds

⁠

Differentiate between molecules of elements and molecules of compounds, providing examples and explaining atomicity.

Molecules of elements are formed when two or more atoms of the same element combine chemically, whereas molecules of compounds are formed when atoms of two or more different elements combine chemically. For example, an oxygen molecule (O_2) consists of two oxygen atoms, making it a molecule of an element. In contrast, a water molecule (H_2O) consists of two hydrogen atoms and one oxygen atom, making it a molecule of a compound. Atomicity refers to the number of atoms present in a molecule of an element, classifying them as monoatomic (e.g., Helium), diatomic (e.g., Nitrogen), triatomic (e.g., Ozone), or polyatomic (e.g., Sulphur).

Discuss the various practical applications of elements in daily life, citing examples.

Elements play crucial roles in daily life due to their diverse properties. Copper and aluminium are used extensively in electrical wires and cooking utensils because they are excellent conductors of heat and electricity. Gold, silver, and platinum are prized for jewellery due to their lustrous appearance. Iron’s strength makes it ideal for heavy tools and machines, while its alloys like brass (copper + zinc) and bronze (copper + tin) are used for statues and machine parts. Extremely hard diamonds serve as gems and for cutting glass. Graphite is essential for pencil leads, and inert gases like argon and neon fill electric bulbs to protect the filament.

List and explain the important physical properties of metals, including exceptions.

Metals typically exhibit several distinct physical properties. They are generally solid at room temperature, with mercury being a notable exception as a liquid. Most metals are hard and strong, though sodium and potassium are soft enough to be cut with a knife. They are lustrous, possessing a shiny appearance, and are both malleable (can be hammered into sheets) and ductile (can be drawn into wires). Furthermore, metals are excellent conductors of heat and electricity, have high melting and boiling points (except sodium and potassium), and are sonorous, producing a ringing sound when struck.

Explain the chemical classification of matter with examples.

Matter is chemically classified into pure substances and impure substances, also known as mixtures. Pure substances contain only one kind of particles, such as sugar which has similar particles throughout. In contrast, impure substances or mixtures consist of two or more pure substances physically mixed in any proportion, like soil which contains various particles such as clay and gravel. This fundamental classification helps distinguish between substances with definite compositions and those with varied compositions.

List and explain the important physical properties of non-metals, including exceptions.

Non-metals exhibit properties contrasting with metals. They can be solids (like sulphur) or gases (like oxygen) at room temperature, with bromine being the sole liquid non-metal. Generally, they are soft, though diamond is an exceptionally hard non-metal. Non-metals are non-lustrous and typically brittle, meaning they cannot be hammered into sheets or drawn into wires. They are poor conductors of heat and electricity, with graphite being the only exception for electrical conductivity. Lastly, non-metals have low melting and boiling points (except diamond and graphite) and are non-sonorous, meaning they do not produce a ringing sound.

Define what a compound is and elaborate on its characteristic properties.

A compound is a pure substance formed when two or more elements chemically combine in a fixed proportion by mass. One key property is its homogeneous and pure nature. The constituent elements cannot be separated by physical methods, only by chemical means, such as electrolysis of water. Crucially, a compound’s physical and chemical properties are entirely distinct from its individual constituent elements; for instance, flammable hydrogen and oxygen combine to form water, which extinguishes fire. Furthermore, energy is always absorbed or released during a compound’s formation, and all molecules of a specific compound are identical and possess unique properties.

Discuss the significance of chemical formulae and the information they convey.

Chemical formulae are a concise and universally accepted way to represent molecules of elements or compounds, saving time, space, and energy in scientific communication. They provide crucial information about the composition of a substance. A formula clearly indicates which elements are present in the compound. For instance, CO_2 shows carbon and oxygen. It also specifies the exact number of atoms of each kind within one molecule and their precise ratio, like one carbon atom to two oxygen atoms in CO_2. Finally, a chemical formula enables the calculation of the mass of one molecule of the compound by summing the masses of its constituent atoms.

Define elements and explain how they are classified based on their properties, providing examples for each type.

An element is a pure substance made up of only one kind of atoms that cannot be broken down into simpler substances by any physical or chemical method. Based on their properties, elements are broadly classified into four groups. Metals, like gold and copper, are generally lustrous, malleable, and good conductors. Non-metals, such as oxygen and carbon, are typically dull, brittle, and poor conductors. Metalloids, including silicon and arsenic, exhibit properties of both metals and non-metals. Lastly, noble gases like helium and neon are gaseous elements that are unreactive.

Describe the key properties that define pure substances.

Pure substances possess several distinguishing properties. They have a definite chemical composition and exhibit uniform composition throughout. This uniformity results in definite physical and chemical properties, including fixed melting and boiling points. For instance, pure water consistently freezes at 0°C and boils at 100°C. Additionally, pure substances have a characteristic color, odor, and taste, and importantly, they cannot be split into simpler substances by any physical method.

Explain how symbols for elements originated and the rules for modern symbol representation.

The representation of elements has evolved over time. Early alchemists used specific signs and symbols, often with mythological origins, to denote elements. John Dalton later introduced a more systematic approach, representing atoms with circles containing different markings. However, modern symbols follow standardized rules for simplicity and universality. Many symbols are derived from the first letter of their English name (e.g., O for Oxygen). If the first letter is already taken, a second significant letter is added, with the first capitalized and the second lowercase (e.g., Ca for Calcium). Some symbols are derived from their Latin names (e.g., Fe for Iron from Ferrum).

Want to print your doc?
This is not the way.

Try clicking the ⋯ next to your doc name or using a keyboard shortcut (

CtrlP

) instead.