Atoms, Molecules, and Ions – General Chemistry 1 (AdDU-SHS)

Q&A flashcards covering evolution of atomic theory, basic laws of matter, Dalton’s postulates and revisions, discovery of subatomic particles, atomic and mass numbers, isotopes, molecules, allotropes, ions, and key equations from the Grade 12 General Chemistry 1 lecture.

What does the Greek word “atomos” mean?

Uncut or indivisible

Which three basic laws of matter laid the foundation for Dalton’s Atomic Theory?

Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions

State the Law of Conservation of Mass.

In a chemical reaction, total mass of reactants equals total mass of products; matter is neither created nor destroyed.

Who formulated the Law of Conservation of Mass?

Antoine Lavoisier (1743-1794)

State the Law of Definite Proportions.

A pure compound always contains the same elements combined in the same proportions by mass, regardless of source or quantity.

Who proposed the Law of Definite Proportions?

Joseph Proust (1754-1826)

State the Law of Multiple Proportions.

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

Give an example pair illustrating the Law of Multiple Proportions.

Carbon monoxide (CO) and carbon dioxide (CO₂)

Who is called the father of modern atomic theory?

John Dalton (1766-1844)

Dalton Postulate 1

All matter is composed of tiny, indivisible particles called atoms.

Dalton Postulate 2

All atoms of an element are identical in mass and chemical properties; atoms of different elements differ in these properties.

Dalton Postulate 3

A chemical compound always contains the same atoms in the same ratio.

Dalton Postulate 4

In chemical reactions atoms rearrange to form new compounds; atoms are not changed into other elements.

One revision to Dalton’s theory regarding atom divisibility

Under certain circumstances atoms can be split into smaller particles.

Experiment that discovered the electron

J. J. Thomson’s cathode-ray tube experiment

Key evidence from Thomson’s cathode-ray experiment

Cathode rays are negatively charged particles (electrons) present in all atoms.

Thomson’s atomic model nickname

Plum-pudding (or raisin-bread) model

Experiment that led to the nuclear model of the atom

Ernest Rutherford’s gold-foil (alpha-particle scattering) experiment

Main conclusion of Rutherford’s experiment

Atom is mostly empty space with a tiny, dense, positively charged nucleus containing most of the mass.

Who discovered the neutron?

James Chadwick

Relative charge and mass of proton

+1 charge; relative mass 1

Relative charge and mass of neutron

0 charge; relative mass 1 (slightly heavier than proton)

Relative charge and mass of electron

–1 charge; relative mass ≈0.0006

Define atomic number (Z).

Number of protons in the nucleus; identifies the element.

Define mass number (A).

Total number of protons plus neutrons (nucleons) in the nucleus.

Formula to find number of neutrons

Neutrons = Mass number – Atomic number (A – Z)

Write the isotopic symbol format.

A (mass number) over Z (atomic number) next to the element symbol, e.g., ₂₃¹¹Na

What are isotopes?

Atoms with the same atomic number but different mass numbers (same protons, different neutrons).

Why do isotopes have identical chemical behavior?

They contain the same number of protons and electrons, which determine chemical properties.

Most abundant isotope of carbon

Carbon-12

Define allotrope.

Different structural forms of the same element with distinct physical/chemical properties (e.g., graphite, diamond, fullerene).

Define molecule.

Smallest particle of an element or compound that retains its chemical identity; composed of atoms bonded together; electrically neutral.

Define ion.

An atom or group of atoms that bears an electric charge due to unequal numbers of protons and electrons.

Distinguish cation vs. anion.

Cation: positively charged ion (more protons than electrons). Anion: negatively charged ion (more electrons than protons).

Formula for charge of a monatomic ion

Charge = # protons – # electrons

How many electrons are in ₂₇¹³Al³⁺ ?

10 electrons (13 protons – 3 + charge)

Chemical notation for a phosphorus ion with 15 protons and 18 electrons

³¹₁₅P³⁻

Explain why mass of an atom is concentrated in the nucleus.

Protons and neutrons (almost all the mass) reside in the small nucleus, while electrons have negligible mass and occupy the atom’s volume.