1.1 AS Level

Particles in the atom and atomic radius

8 flashcards to master this topic

Key Concept Flip

Describe the distribution of mass and charge within an atom.

Answer Flip

Atoms consist of a small, dense, positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons in shells. Most of the atom's mass is concentrated in the nucleus, while most of the volume is empty space.

Definition Flip

What are the relative masses and relative charges of protons, neutrons, and electrons?

Answer Flip

Protons: relative mass = 1, relative charge = +1; Neutrons: relative mass = 1, relative charge = 0; Electrons: relative mass = 1/1840, relative charge = -1.

Definition Flip

Define atomic number and mass number.

Answer Flip

Atomic number (proton number) is the number of protons in the nucleus of an atom. Mass number (nucleon number) is the total number of protons and neutrons in the nucleus of an atom.

Key Concept Flip

How do beams of protons, neutrons, and electrons behave in an electric field?

Answer Flip

Protons (positive charge) are deflected towards the negative plate. Electrons (negative charge) are deflected towards the positive plate and to a greater extent than protons due to lower mass. Neutrons (no charge) are not deflected.

Calculation Flip

Determine the number of protons, neutrons and electrons in the ion: $^{39}K^+$

Answer Flip

Protons: 19 (atomic number of K), Neutrons: 20 (39 - 19), Electrons: 18 (19 - 1 due to +1 charge).

Key Concept Flip

Explain the trend in atomic radius across a period.

Answer Flip

Atomic radius decreases across a period due to increasing nuclear charge (more protons) which pulls the electrons closer to the nucleus, and little additional shielding.

Key Concept Flip

Explain the trend in atomic radius down a group.

Answer Flip

Atomic radius increases down a group because of the addition of electron shells. The outer electrons are further from the nucleus and are shielded by more inner electrons.

Definition Flip

What is the difference between atomic radius and ionic radius?

Answer Flip

Atomic radius refers to the size of a neutral atom, whereas ionic radius refers to the size of an ion (an atom that has gained or lost electrons). The ionic radius will differ based on whether an electron was lost (cation, smaller) or gained (anion, larger).

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1.2 Isotopes