S1.2 The nuclear atom Notes

Atom

The fundamental building block of matter.

Subatomic particles

Particles that are smaller than an atom, including protons, neutrons, and electrons.

Proton

A positively charged subatomic particle found in the nucleus of an atom.

Neutron

A neutral subatomic particle found in the nucleus of an atom.

Electron

A negatively charged subatomic particle that orbits around the nucleus of an atom.

Nucleus

The dense, positively charged core of an atom, containing protons and neutrons.

Atomic number (Z)

The number of protons in the nucleus of an atom, which defines the element.

Mass number (A)

The total number of protons and neutrons in an atom's nucleus.

Ion

An atom or group of atoms that has gained or lost electrons, resulting in a net electrical charge.

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 the same number of protons but different numbers of neutrons.

Relative atomic mass

A weighted average of the masses of an element's isotopes based on their natural abundances.

Relative abundance

The percentage of a specific isotope of an element present in a naturally occurring sample.

Probability of finding an electron

The likelihood of locating an electron in a specific region of an atom, defined by orbitals.

Chemical symbol

A notation used to represent a chemical element, such as 'Au' for gold.

Nucleons

The collective term for protons and neutrons in an atomic nucleus.

Isotopic abundance

The occurrence of a particular isotope in a sample compared to others.

Chlorine-35

An isotope of chlorine with 17 protons and 18 neutrons.

Chlorine-37

An isotope of chlorine with 17 protons and 20 neutrons.

Gas centrifugation

A method used to separate isotopes based on their mass differences.

Density

Mass per unit volume of a substance, which can differ among isotopes.

Melting point

The temperature at which a substance changes from solid to liquid.

Boiling point

The temperature at which a substance changes from liquid to gas.

Protium (H-1)

The most common hydrogen isotope, with 1 proton and no neutrons.

Deuterium (H-2)

A heavier isotope of hydrogen, with 1 proton and 1 neutron.

Tritium (H-3)

A radioactive hydrogen isotope, with 1 proton and 2 neutrons.

Uranium-235

An isotope of uranium that is used in nuclear reactors and weapons.

Uranium-238

A more abundant isotope of uranium, less useful for nuclear reactions.

Relative mass of electron

Negligibly small compared to protons and neutrons.

Isotopes and chemical properties

Isotopes have nearly identical chemical properties because they have the same number of electrons.

Nuclear symbol

A notation that indicates the number of protons and neutrons in an atom.

Atomic mass

The mass of an element as reflected in its atomic weight on the periodic table.

Neutrons and stability

Neutrons help stabilize the nucleus by offsetting the repulsion between protons.

Indivisible atoms

Atoms are not indivisible; they can be broken down into subatomic particles.

Element identity

Determined by the number of protons in the nucleus.

Example of an ion

A magnesium ion has 12 protons and 10 electrons.

Example of a neutral atom

A chlorine atom has 17 protons and 17 electrons.

Mass number formula

Mass number (A) = Number of protons + Number of neutrons.

Nuclear symbol format

Written as: A/Z Chemical symbol, where A = mass number and Z = atomic number.

Relative masses summary

Isotopes have different masses due to varying neutron numbers.

Calculation of relative atomic mass

Based on the weighted average of isotopes' masses and abundances.

Natural abundance

The relative amount of each isotope present in nature.

Comparison of isotopes

Similar to comparing coins with the same face value but different weights.

Ionization

The process of gaining or losing electrons to form ions.

Stability of isotopes

Some isotopes are more stable than others due to neutron-proton ratios.

Centrifugation

A technique used to isolate different isotopes based on their mass differences.

Physical properties of isotopes

These may vary due to differences in mass, but chemical properties do not.

Nuclear reactions

Processes in which isotopes may behave differently based on their stability.