In this chapter Fundamentals of Chemistry, students will be able to identify and provide examples of different branches of chemistry, understand how these branches differ, and distinguish between matter and specific substances. They will define key concepts such as ions, molecular ions, formula units, free radicals, atomic number, atomic mass, and atomic mass unit. Students will also differentiate among elements, compounds, and mixtures, define relative atomic mass based on the C-12 scale, and recognize the differences between empirical and molecular formulas, as well as atoms and ions. Additionally, they will classify chemical species from given examples, identify representative particles of elements and compounds, and relate gram atomic mass, gram molecular mass, and gram formula mass to the concept of a mole. Understanding how Avogadro’s number relates to a mole, differentiating various mass terms, and converting atomic, molecular, and formula masses into their respective gram forms will also be key outcomes of their learning.

BRANCHES OF CHEMISTRY

Physical Chemistry looks at how the makeup of matter affects its physical properties and how these properties change. It explores things like atom structure, how molecules form, and how gases, liquids, and solids behave. It also studies the impact of temperature and radiation on matter.

Organic Chemistry focuses on compounds made mainly of carbon and hydrogen, known as hydrocarbons, and their derivatives. These compounds can occur naturally or be made in labs. Organic chemists investigate the structure and qualities of both natural and synthetic compounds, which are important for industries such as oil, chemicals, and medicine.

Inorganic Chemistry studies all elements and their compounds, except those that are just carbon and hydrogen. It has many applications in various industries, including glass, cement, ceramics, and metallurgy, which is the process of extracting metals from ores.

Biochemistry examines the structure, composition, and chemical reactions of substances found in living organisms.

BASIC DEFINITIONS

Matter is anything that has mass and takes up space, including our bodies and everything around us. In chemistry, we study matter in three physical states: solid, liquid, and gas. A pure piece of matter is called a substance, which has a fixed composition and specific properties. On the other hand, impure matter is known as a mixture, which can be either homogeneous (uniform) or heterogeneous (not uniform).

Every substance has both physical and chemical properties. Physical properties relate to the state of the substance, such as color, smell, taste, hardness, shape, solubility, and melting or boiling points. For example, when ice is heated, it melts into water, and when water is further heated, it boils to become steam. Throughout these changes, the chemical composition of water remains the same.

Chemical properties depend on the substance’s composition. When a substance undergoes a chemical change, its composition changes, resulting in new substances. For instance, when water breaks down into hydrogen and oxygen gases, that’s a chemical change. All materials can be classified as either a substance or a mixture.

Elements

In ancient times, only nine elements were known: carbon, gold, silver, tin, mercury, lead, copper, iron, and sulfur. Back then, elements were thought to be substances that couldn’t be broken down into simpler parts through ordinary chemical processes. By the end of the 19th century, 63 elements had been discovered, and today there are 118 elements, with 92 occurring naturally.

An element is now defined as a substance made up of the same type of atoms, all having the same atomic number, and cannot be broken down into simpler substances by regular chemical means. These elements can be found in nature either on their own or combined with other elements, and they exist in varying amounts in the Earth’s crust, oceans, and atmosphere.

Elements can be solids, liquids, or gases. Most are solids, like sodium and copper, while only a few, such as mercury and bromine, are liquids. There are also gaseous elements, including nitrogen, oxygen, chlorine, and hydrogen.

Elements are grouped into three categories based on their properties: metals, non-metals, and metalloids. About 80% of elements are metals. Each element is represented by a symbol, usually derived from its name in English, Latin, Greek, or German. For instance, H stands for hydrogen, N for nitrogen, and Ca for calcium. If the symbol has two letters, only the first one is capitalized, like Na for sodium.

A key property of an element is its valency, which indicates how it combines with other elements. This depends on the number of electrons in its outer shell. In simple covalent compounds, valency is the number of hydrogen atoms that can bond with one atom of that element. For example, chlorine has a valency of 1, oxygen has 2, nitrogen has 3, and carbon has 4.

In ionic compounds, valency reflects how many electrons an atom gains or loses to achieve a stable electron configuration. Elements with fewer than four electrons tend to lose them, like sodium (Na), magnesium (Mg), and aluminum (Al), which have valencies of 1, 2, and 3, respectively. In contrast, elements with five or more electrons tend to gain electrons to complete their outer shell, such as nitrogen (N), oxygen (O), and chlorine (Cl), which have valencies of 3, 2, and 1, respectively. A radical is a group of atoms that carries a charge.

Compounds

A compound is a substance made of two or more elements that are chemically combined in a fixed ratio by mass. When elements combine, they lose their individual properties and form new substances with entirely different characteristics. Compounds cannot be broken down into their original elements using simple physical methods. For example, carbon dioxide is formed when carbon and oxygen combine in a mass ratio of 12:32 (or 3:8), while water is created from the chemical combination of hydrogen and oxygen in a ratio of 1:8.

Compounds can be classified as ionic or covalent. Ionic compounds do not exist as independent molecules; instead, they form a three-dimensional crystal structure where each ion is surrounded by oppositely charged ions, resulting in strong attractions. This gives ionic compounds high melting and boiling points, and they are represented by formula units like NaCl (sodium chloride) or KBr (potassium bromide).

Covalent compounds, on the other hand, usually exist as molecules, which are the true representatives of these compounds. Their formulas are called molecular formulas, such as H₂O (water), HCl (hydrochloric acid), and C₂H₄ (ethylene).

Mixtures

A mixture is formed when two or more elements or compounds are physically combined without a fixed ratio. In a mixture, the individual substances retain their own chemical identities and properties. Mixtures can be separated back into their components using physical methods like distillation, filtration, evaporation, crystallization, or magnetization.

Mixtures can be homogeneous, meaning they have a uniform composition throughout (like air or ice cream), or heterogeneous, where the composition is not uniform (like soil or wood).

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