MYP Integrated Sciences Atoms and Space Key Definitions

The smallest unit of an element that retains the element’s chemical properties; it consists of a nucleus (protons and neutrons) with electrons around it.

The ionizing radiation we are exposed to all the time from natural and human-made sources in our environment.

A model of the universe in which space has been expanding from a very hot, very dense early state, leading to the cooler, structured universe observed today.

A chain reaction is a self-sustaining sequence of nuclear fission events caused by neutrons released from previous fissions.

A constellation is a recognized pattern of stars as seen from Earth.

Electromagnetic radiation filling space, observed today mainly as microwaves, interpreted as cooled and stretched light released when the early universe became transparent.

The Doppler effect is the change in observed wavelength or frequency of a wave due to relative motion between the source and the observer.

A solar-system object that orbits the Sun and is nearly round due to its own gravity, but has not cleared the neighborhood around its orbit.

A property of matter that can be positive or negative and causes electrical interactions (attraction or repulsion) between objects.

A fundamental particle with a negative electric charge of $-1.6\times 10^{-19}\,\text{C}$ and a very small mass of $9.1\times 10^{-31}\,\text{kg}$.

A force of attraction or repulsion between electric charges.

In a geocentric model, a small circular motion of a planet whose center itself moves on a larger circle around Earth, used to reproduce observed planetary motions.

An exoplanet is a planet that orbits a star outside the Solar System.

A galaxy is a vast system of stars and matter held together by gravity.

A model of the solar system in which Earth is at the center and the Sun, Moon, planets, and stars move around Earth.

The half-life of a radioactive substance is the time taken for half of the unstable nuclei in a sample to decay.

A model of the solar system in which the Sun is central and the planets (including Earth) orbit the Sun.

Hubble’s law states that the speed at which a galaxy moves away from us is proportional to its distance from us.

An ion is a charged atom formed by the gain or loss of electrons.

Radiation that can remove electrons from atoms or molecules, creating ions.

A lunar eclipse occurs when the Earth is between the Sun and the Moon.

A mutation is a random change in DNA that introduces new genetic variants (alleles).

A particle in the nucleus with no net charge and a mass about $1.67\times 10^{-27}\,\text{kg}$.

Nuclear fission is the splitting of a heavy atomic nucleus into smaller nuclei, releasing energy and neutrons.