Particles in the Atom & Atomic Radius

Comprehensive vocabulary flashcards covering atomic structure, subatomic particle properties, calculations for neutrons, and trends in atomic and ionic radii based on the lecture notes.

Atoms

The smallest parts of an element that can take place in chemical reactions; they are mostly empty space with a small, dense nucleus.

Nucleus

The center of an atom which is very small, dense, and contains protons and neutrons, giving it an overall positive charge.

Shells

Also known as energy levels, these surround the nucleus and contain negatively charged electrons.

Subatomic particles

The collective name for the protons, neutrons, and electrons that make up an atom.

Relative mass of a Proton

$$1$$

Relative charge of a Proton

$$+1$$

Relative mass of a Neutron

$$1$$

Relative charge of a Neutron

$$0$$

Relative mass of an Electron

$$\frac{1}{1836}$$

Relative charge of an Electron

$$-1$$

Charge of a single Proton

$$+1.602 \times 10^{-19}\text{ coulombs}$$

Charge of a single Electron

$$-1.602 \times 10^{-19}\text{ coulombs}$$

Electrostatic attraction

The force that holds an atom together, occurring between the positively charged nucleus and the negatively charged electrons.

Atomic number ($Z$)

Also called the proton number, it represents the number of protons in the nucleus of an atom.

Mass number ($A$)

Also called the nucleon number, it is the total number of protons and neutrons in the nucleus.

Nucleons

The collective term for protons and neutrons because they are located in the nucleus.

Calculation for number of neutrons

$$\text{Number of neutrons } = A - Z$$

Ion

Formed when an atom gains or loses electrons, resulting in an overall charge.

Cations

Positive ions formed when an atom loses electrons.

Anions

Negative ions formed when an atom gains electrons.

Atomic radius

Half the distance between the two nuclei of two covalently bonded atoms of the same type.

Trend in atomic radius across a period

Generally decreases because the atomic number ($Z$) increases (greater nuclear charge), which exerts a greater pull on the electrons in the same principal quantum shell.

Trend in atomic radius down a group

Generally increases because there is an increased number of shells, which increases shielding and weakens the nuclear pull on outer electrons.

Shielding

The process where electrons in inner shells repel electrons in the outermost shells, reducing the effective nuclear charge felt by those outer electrons.

Ionic radius of positive ions (Cations)

Generally smaller than their parent atoms because the same nuclear charge exerts a greater electrostatic force of attraction on fewer electrons.

Ionic radius of negative ions (Anions)

Generally larger than their parent atoms because extra electrons are added while the nuclear charge remains the same, leading to a weaker hold on the outermost electrons.

Behavior of Electrons in an electric field

Electrons deflect strongly toward the positive plate due to their negative charge and very small mass.

Behavior of Protons in an electric field

Protons deflect slightly toward the negative plate, confirming their positive charge and indicating they are much heavier than electrons.

Behavior of Neutrons in an electric field

Neutrons pass through without deflection because they are neutral and have no charge.