Complete Chemistry Study Guide: Atoms, Radiation, Reactions, and Bonding

Comprehensive vocabulary flashcards covering subatomic particles, isotopes, radioactive decay, nuclear energy, stoichiometry, thermochemistry, acids and bases, and ionic bonding.

Subatomic particles

The three constituent parts of an atom: protons (charge of $+1$, relative mass of $1$, in the nucleus), neutrons (neutral charge of $0$, relative mass of $1$, in the nucleus), and electrons (charge of $-1$, relative mass of $\frac{1}{1840}$, orbiting the nucleus in shells).

Atom

The smallest part of an element that still behaves as that element, composed of protons, neutrons, and electrons, and consisting mostly of empty space.

Nucleus

The dense core of an atom composed of protons and neutrons; it carries an overall positive charge because neutrons have no electric charge.

Atomic number

The number of protons in an atom, which determines the element's identity and position on the periodic table.

Mass number

The sum of the number of protons and neutrons present within an atom's nucleus.

Element

A substance made of atoms that all possess the exact same number of protons (atomic number), though their mass numbers may vary.

Number of neutrons calculation

The formula used to determine neutron count: $\text{Neutrons} = \text{mass number} - \text{atomic number}$.

Electron configuration

The arrangement of electrons in shells (energy levels) around an atom's nucleus, which fill from innermost shell outward and hold up to $2, 8, 8$ electrons for the first $20$ elements.

Valence shell

The outermost electron shell of an atom; having this shell completely filled makes an atom chemically stable and significantly less reactive.

Octet rule

The principle stating that for elements $1$ to $20$, a stable, full valence shell consists of $8$ electrons (with the exception of helium, which is full with $2$).

Ion

An atom that carries an overall positive or negative electrical charge as a result of losing or gaining electrons.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Net charge

The resultant electrical charge of an atom or ion, determined by: $\text{Charge} = \text{number of protons} - \text{number of electrons}$.

Isotope

Atoms of the same element containing the same number of protons but a different number of neutrons, resulting in different mass numbers.

Radioisotope

An unstable isotope that releases nuclear radiation as it spontaneously decays to reach a more stable state.

Radiation

The release of energy in the form of electromagnetic waves or high-speed particles, commonly associated with nuclear changes.

Radioactive decay

The process by which an unstable atomic nucleus loses energy by emitting radiation (alpha, beta, or gamma) to transition into a more stable state.

Daughter isotope

The resulting isotope formed after a parent radioisotope undergoes radioactive decay.

Alpha decay

Decay occurring in high-mass nuclei with excessive protons, emitting an alpha particle ($2$ protons and $2$ neutrons), reducing the mass number by $4$ and atomic number by $2$.

Beta decay

Decay occurring in nuclei with too many neutrons, wherein a neutron converts into a proton and an electron, ejecting the electron (beta particle) and increasing the atomic number by $1$ while leaving the mass number unchanged.

Gamma decay

The emission of pure electromagnetic energy from an excited nucleus following alpha or beta decay; proton and neutron counts remain unchanged, creating no new element.

Alpha particle ($\alpha$)

A radiation particle consisting of $2$ protons and $2$ neutrons (identical to a helium nucleus); stopped by paper, travels approximately $10\,\text{cm}$ in air, cannot penetrate skin, but is hazardous if swallowed.

Beta particle ($\beta$)

A high-speed electron emitted from a decaying nucleus; stopped by aluminium or layers of fabric, travels up to a few metres in air, and can cause skin burns or internal damage if inhaled or ingested.

Gamma radiation ($\gamma$)

Pure electromagnetic energy that penetrates deeply into matter, requiring several centimetres of lead to stop; travels large distances in air and causes cell burns, cancer, and DNA damage.

Radioactivity

The spontaneous emission of high-energy particles (alpha, beta) or electromagnetic waves (gamma rays, X-rays) from an unstable atomic nucleus.

Radiation imaging

The diagnostic or industrial technique of passing radiation (typically gamma rays or X-rays) through an object or body to detect internal structures or flaws based on differential absorption rates.

Radiotherapy

A medical treatment for cancer that uses targeted doses of ionising radiation (such as caesium-137 gamma rays or targeted X-rays) to kill or inhibit the growth of malignant cells.

Half-life

The time required for half of the radioactive nuclei present in a given sample to decay.

Carbon dating

A scientific dating technique that measures the ratio of unstable carbon-14 (half-life of approximately $5730$ years) to stable carbon-12 to calculate the age of organic specimens up to about $60000$ years old.

Nuclear fission

The process of splitting a heavy, unstable atomic nucleus into smaller nuclei via neutron bombardment, releasing excess neutrons, lighter radioisotopes, and thermal energy.

Nuclear fusion

The nuclear reaction in which two light atomic nuclei combine to produce a single heavier nucleus, liberating vast quantities of heat and light as observed in the Sun.

Mass-energy equivalence ($E = mc^2$)

Einstein's principle demonstrating that mass and energy are interconvertible, where $E$ is energy at rest, $m$ is mass, and $c^2 = 9 \times 10^{16}\,\text{J/kg}$ ($\text{speed of light}^2$).

Law of conservation of mass

The scientific law formulated by Antoine Lavoisier stating that the total mass of matter remains constant during a chemical reaction, as atoms are rearranged rather than created or destroyed.

Reactants

The original chemical substances present at the start of a reaction whose bonds break during the process.

Products

The newly formed chemical substances produced at the end of a reaction with newly established chemical bonds.

Chemical bond

The electrostatic force of attraction holding atoms together in compounds or molecules.

Closed system

An experimental apparatus sealed so that gaseous substances cannot enter or escape, enabling accurate measurements to verify mass conservation.

Coefficient

A whole number placed directly before a chemical formula in an equation denoting how many molecules or formula units are involved.

Subscript

A small number positioned directly after an element's symbol indicating the exact count of atoms of that element within a single molecule or formula unit.

Molecule

A distinct chemical entity consisting of two or more atoms held together by chemical bonds.

Balancing chemical equations

The method of altering coefficients (without altering subscripts) in a chemical equation to ensure that equal quantities of each atomic species exist on both reactant and product sides.

Exothermic reaction

A chemical reaction that releases thermal energy into the surrounding environment, resulting in products that possess less chemical energy than the original reactants.

Endothermic reaction

A chemical reaction that absorbs thermal energy from the environment, causing the surroundings to cool and resulting in products with greater stored chemical energy than the reactants.

Energy profile diagram

A graphical representation plotting chemical potential energy against reaction progress to depict the net absorption (endothermic) or liberation (exothermic) of energy.

Photosynthesis

An endothermic biological reaction occurring inside chloroplasts in which plants absorb radiant light energy to convert water and carbon dioxide into glucose and oxygen.

Cellular respiration

An exothermic metabolic reaction taking place inside mitochondria that oxidises glucose into carbon dioxide and water, releasing heat and ATP energy to support bodily functions near $37\,^\circ\text{C}$.

Combustion

An exothermic chemical reaction wherein a fuel rapidly reacts with oxygen gas, emitting heat and light and producing carbon dioxide and water when burning fossil fuels.

Acid

A chemical compound typically dissolved in water that tastes sour, can be corrosive, and displays a pH value strictly below $7$.

Base

The chemical opposite of an acid; a substance that feels slippery or soapy, tastes bitter, can be corrosive, has a pH above $7$, and is termed an alkali when dissolved in aqueous solution.

Neutralisation

An exothermic chemical reaction between an acid and a base moving the system toward a neutral pH of $7$, following the general word equation: $\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}$.

pH scale

A logarithmic measure of acidity or basicity ranging around $7$ (neutral), where values below $7$ represent acids and values above $7$ represent bases, with each whole unit change signifying a $10$-fold variation in acidity.

Metal carbonate

A basic, typically white solid compound formed by a metal cation bound to a carbonate ion ($\text{CO}_3^{2-}$, composed of one carbon and three oxygen atoms).

Acid + metal reaction

An exothermic chemical pathway yielding a dissolved salt and flammable hydrogen gas: $\text{acid} + \text{metal} \rightarrow \text{salt} + \text{H}_2$.

Acid + metal carbonate reaction

A chemical reaction producing a salt, carbon dioxide gas, and water: $\text{acid} + \text{metal carbonate} \rightarrow \text{salt} + \text{CO}_2 + \text{H}_2\text{O}$.

Ionic bond

A chemical bond established by the electrostatic attraction between oppositely charged ions, formed when a metal atom transfers valence electrons to a non-metal atom.

Ionic compound

A neutral chemical substance composed of cations and anions held together by ionic bonds in ratios such that total positive charge balances total negative charge.