Research Chemistry Unit 1 Review

Atom

The smallest unit of an element that retains the properties of that element.

Atomic Theory

A scientific theory that matter is composed of discrete units called atoms.

Democritus

An ancient Greek philosopher who proposed that matter is made of indivisible particles called atomos around 400 BCE

John Dalton's Atomic Theory

The first modern atomic theory stating that all matter is made of atoms, which combine in whole-number ratios to form compounds in 1808.

Electron

A negatively charged subatomic particle found in the electron cloud.

Proton

A positively charged subatomic particle located in the nucleus.

Neutron

A subatomic particle found in the nucleus with no charge.

Atomic Number

The number of protons in an atom that determines the element.

Mass Number

The total number of protons and neutrons in an atom.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Isotope

Atoms of the same element that have different numbers of neutrons.

Alpha Particle

A particle composed of 2 protons and 2 neutrons, equivalent to a helium nucleus.

Beta Particle

A high-energy, high-speed electron or positron emitted during beta decay.

Gamma Radiation

High-energy electromagnetic radiation with no mass and no charge.

Half-life

The amount of time required for half of a radioactive substance to decay.

Average Atomic Mass

The weighted average of the masses of an element's isotopes.

Alpha Emission

A type of radioactive decay in which an alpha particle is emitted.

Beta Emission

A type of radioactive decay in which a beta particle (electron) is emitted.

Nuclear Equation

A representation of a nuclear reaction that balances mass numbers and atomic numbers.

James Chadwick — 1932

Neutron Discovery: Physicist who discovered the neutron by bombarding beryllium with alpha particles, leading to the identification of a neutral particle with a mass similar to that of a proton, found in the nucleus of atoms.

Erwin Schrödinger — 1926

Modern Quantum Mechanical Model

model describes the behavior of electrons using wave functions. Instead of fixed orbits, it introduces the concept of electron clouds, indicating regions where an electron is likely to be found based on probabilities.

Niels Bohr — 1913

Experiment/Observation: Hydrogen Emission Spectrum

Planetary model

Developed a planetary model for the atom, proposing that electrons occupy fixed energy levels or shells around the nucleus. His work explained the discrete lines of the hydrogen emission spectrum, indicating that electrons transition between these energy levels, releasing energy in the form of light.

Ernest Rutherford — 1911

Experiment: Gold Foil Experiment

• This replaced the Plum Pudding Model.The Gold Foil Experiment demonstrated that atoms have a small, dense nucleus containing protons, leading to the conclusion that atoms are mostly empty space. This discovery was pivotal in reshaping atomic theory, replacing the previous Plum Pudding Model.

J.J. Thomson — 1897

Experiment: Cathode Ray Experiment

• conducted the Cathode Ray Experiment, observing that a beam of electrons was deflected by electric and magnetic fields, leading to the conclusion that atoms contain smaller negatively charged particles known as electrons. This challenged the idea of indivisible atoms and started the development of the Plum Pudding Model, where electrons are embedded within a positively charged sphere.