Definitions
Atom
The smallest unit of ordinary matter that forms a chemical element, consisting of a nucleus and one or more electrons.
Proton
A subatomic particle found in the nucleus of every atom with a positive electric charge.
Neutron
A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.
Electron
A subatomic particle with a negative charge, found in all atoms and acting as the primary carrier of electricity in solids.
Atomic Number (Z)
The number of protons in the nucleus of an atom, which determines the element's position in the periodic table.
Mass Number (A)
The total number of protons and neutrons in an atom's nucleus.
Atoms consist of a dense nucleus surrounded by a cloud of negatively charged electrons. The nucleus contains two types of subatomic particles: protons, with a positive charge, and neutrons, which have no charge. Together, protons and neutrons are known as nucleons. The number of protons in the nucleus defines the atomic number of an element and determines its chemical properties.
Electrons are extremely light compared to protons and neutrons, residing in electron shells around the nucleus. Protons and neutrons are almost equal in mass, significantly heavier than electrons, and reside in the atom's nucleus. The charge of protons is balanced by the negative charge of electrons, making atoms electrically neutral overall.
The atomic number (symbol Z) is equivalent to the number of protons in an atom’s nucleus and defines which element it is. The mass number (symbol A), the sum of protons and neutrons, indicates the mass of the atomic nucleus. An element’s isotope is defined by its mass number since isotopes have equal numbers of protons but different numbers of neutrons.
Electron configuration involves the distribution of electrons across the various shells and subshells of an atom. For the first 20 elements, electrons fill the shell in a specific order defined by quantum mechanical rules (e.g., 2, 8, 8, 2 for the first three levels). Recognizing these patterns is key to understanding chemical reactivity and bonding.
Simple ions form through the gain or loss of electrons, achieving a full outer shell. Metals tend to lose electrons forming cations, whereas non-metals gain electrons to form anions. For example, Na becomes Na⁺ after losing one electron, while Cl becomes Cl⁻ after gaining one.
Ions form when atoms gain or lose electrons, resulting in a net positive or negative charge. The tendency of an atom to become an ion relates to its position in the periodic table: group I and II form cations, whereas groups VI and VII form anions. The charge and ionization reflect the orbital structure and energy levels.
Simple ions and polyatomic ions combine to produce neutral compounds. The formula of an ionic compound reflects the balance of the total positive and negative charges. Polyatomic ions, like sulfate (SO₄²⁻) and nitrate (NO₃⁻), participate in forming compounds through ionic bonds, where total charges must be balanced.
The formula of an ionic compound reveals the ions involved. Naming involves stating the cation followed by the anion. Common polyatomic ions include sulfate (SO₄²⁻), nitrate (NO₃⁻), and carbonate (CO₃²⁻). Examples include sodium nitrate (NaNO₃), calcium sulfate (CaSO₄), and magnesium carbonate (MgCO₃).
Balancing equations ensures the law of conservation of mass is obeyed, with equal numbers of each type of atom on both sides of the equation. To balance, adjust the coefficients—not the subscripts—of the reactants and products. Example: H₂ + O₂ → H₂O becomes 2H₂ + O₂ → 2H₂O after balancing.
To remember :
Atoms form the building blocks of matter, comprising a nucleus of protons and neutrons, surrounded by electrons. Atomic number defines element identity, while mass number considers total nucleons. Electron configurations guide chemical behavior, and ions form through electron transfer, matching periodic table trends. Ionic compounds result from cation-anion interactions, with formulas that require careful charge balance. Names derive from recognizable patterns of constituent ions, and chemical reactions must reflect mass conservation through balanced equations.