The Smallest Unit of Matter: Atom

All food and cooking processes are built upon atoms and molecules. All living systems (animals, microbes, and smaller life forms) are composed of atoms and molecules. These atoms and molecules form the chemistry of life through how they organize, interact, and undergo reactions. To understand cooking and baking at the molecular level, it’s important to know how atoms and compounds come together and function.

Atom: The Fundamental Building Block of Matter

An atom consists of three main subatomic particles:

• Proton: Positively charged particles located at the center of the atom. An atom’s identity is determined by its proton count, which is used to arrange elements in the periodic table based on their atomic number.
• Neutron: Neutral particles found at the center of the atom.
• Electron: Negatively charged particles located around the atom. Electrons have negligible mass but carry a negative electric charge.

Isotopes

Atoms of the same element can have the same number of protons but different numbers of neutrons. These atoms are called isotopes. Isotopes have the same chemical properties but different physical properties.

For example, carbon-12 and carbon-13 have the same number of protons (6 protons), but carbon-12 has 6 neutrons, while carbon-13 has 7 neutrons. Thus, carbon-12 and carbon-13 are isotopes with the same chemical properties but different mass numbers.

Another example is the three isotopes of hydrogen:

• Protium (H-1): 1 proton, 0 neutrons.
• Deuterium (H-2): 1 proton, 1 neutron.
• Tritium (H-3): 1 proton, 2 neutrons.

Allotropes

Substances with the same chemical properties but different physical properties are called allotropes. For example, diamond, graphite, and amorphous carbon are made of only carbon (C), but their arrangement in space and the strength of their bonds differ. Similarly, O₂ (oxygen) and O₃ (ozone) gases are allotropes of each other.

Atomic Number and Mass Number

• Atomic Number (Z): Refers to the number of protons in an atom of an element. It also determines the number of electrons in the atom.
• Mass Number (A): The sum of the protons and neutrons in an atom’s nucleus. The mass number is calculated as:

For example, the boron atom has a mass number of 12 and an atomic number of 5. Therefore, the boron atom has 5 protons and 7 neutrons in its nucleus (12 – 5 = 7).

Atomic Number

The atomic number of an element is the number of protons in its atom. Since protons are positively charged, this number is also called the “nuclear charge.”

Radioactivity

Radioactive materials, like those in elements such as uranium, emit alpha (α), beta (β), and gamma (γ) radiation during their decay process. These radiations are high-energy rays that can pass through materials, darken photographic films, and cause certain substances to emit fluorescent light.

• Alpha (α) Radiation: Consists of positively charged particles and is deflected by positive metal plates.
• Beta (β) Radiation: Consists of negatively charged electrons and is deflected by negative plates.
• Gamma (γ) Radiation: Neutral, high-energy rays that are unaffected by electric or magnetic fields.

Molecule and Compound Concepts

Molecule

A molecule is the smallest chemical unit formed by the chemical bonding of two or more atoms. Molecules are typically formed by covalent bonds between atoms. For example, water (H₂O) is a molecule made up of two hydrogen atoms and one oxygen atom. Molecules can also be formed by atoms of the same element. For example, the oxygen molecule (O₂) is formed by two oxygen atoms bonding together.

Compound

A compound is a substance composed of two or more different elements. Compounds form through ionic or covalent bonds between atoms. Compounds are created by the combination of elements with different physical and chemical properties. For example, water (H₂O) and salt (NaCl) are compounds. While all molecules are compounds, not all compounds are molecules, because some compounds may not form molecular structures but instead possess crystalline forms.

Types of Chemical Compounds and Formulas

Chemical compounds are substances formed by the chemical bonding of two or more elements. The formulas of compounds are written using the symbols of the elements that compose them, and this notation is known as the chemical formula. Chemical formulas show the type of elements in a compound and the relative number of atoms of each element.

The formulas of compounds provide important information about the components of the compound:

• Type of Elements in the Compound: Indicates which elements are present.
• Relative Numbers of Elements: Shows the number and proportion of atoms of each element in the compound.

Compounds are generally divided into two main categories: ionic compounds and molecular compounds.

Types of Chemical Compounds

1. Ionic Compounds

Ionic compounds are formed through the transfer of electrons between metal and nonmetal elements. In these compounds, one atom loses electrons while the other gains them. This results in the formation of positively charged cations (atoms that lose electrons) and negatively charged anions (atoms that gain electrons). The electrostatic attraction between these ions holds the compound together.

Example: Sodium Chloride (NaCl)

• Sodium (Na) loses an electron to form the Na⁺ cation.
• Chlorine (Cl) gains an electron to form the Cl⁻ anion.
• The electrostatic attraction between Na⁺ and Cl⁻ forms the sodium chloride compound.

General Properties of Ionic Compounds:

• Typically have high melting and boiling points.
• Conduct electricity when dissolved in water (in ionized form).
• Are hard and brittle.

2. Molecular Compounds

Molecular compounds form through the sharing of electrons between nonmetal atoms. In these compounds, atoms share electrons to create covalent bonds. There are no ions in molecular compounds; instead, the atoms are bonded together.

Example: Water (H₂O)

• Water is formed by covalent bonds between two hydrogen (H) atoms and one oxygen (O) atom.
• The hydrogen atoms share electrons with the oxygen atom.

General Properties of Molecular Compounds:

• Typically have low melting and boiling points.
• Do not conduct electricity when dissolved in water (do not ionize).
• Usually exist as gases, liquids, or soft solids.

Law of Conservation of Mass

The Law of Conservation of Mass is a fundamental principle in chemistry that states that matter cannot be created or destroyed, only transformed from one form to another. This law applies to both chemical and physical processes. In chemical reactions, the total mass of the reactants is equal to the total mass of the products.

The conservation of mass also holds true in physical processes such as melting, boiling, dissolving, etc.

Example: Aluminum and Hydrochloric Acid Reaction

When a piece of aluminum reacts with hydrochloric acid, aluminum chloride and hydrogen gas are produced.

Given:

• Mass of Hydrochloric Acid: 50 g
• Mass of Aluminum Chloride: 65 g
• Mass of Hydrogen Gas: 5 g

According to the Law of Conservation of Mass:

Formulating:

Aluminum Mass + 50 g = 65 g + 5 g
Aluminum Mass + 50 = 70
Aluminum Mass = 70 – 50
Aluminum Mass = 20 g

Result: The mass of the aluminum used is 20 g.

Law of Definite Proportions

The Law of Definite Proportions, discovered by Joseph Proust in 1799, states that elements combine to form compounds in fixed proportions by mass. According to this law, no matter how a compound is formed, the ratio of the masses of the elements in the compound remains constant.

For example, in water (H₂O), the ratio of oxygen to hydrogen is always 16 grams of oxygen to 2 grams of hydrogen for every 18 grams of water. This ratio does not change regardless of how the water is obtained.

Example: Water (H₂O) Compound

• In 18 grams of water, there are 16 grams of oxygen and 2 grams of hydrogen.
• In 9 grams of water, there are 8 grams of oxygen and 1 gram of hydrogen.

This ratio remains constant, regardless of the method used to obtain the water.