Atomic Models: From Plum Pudding to Nuclear

Atomic Models

• Scientific models can be revised or replaced with new experimental evidence.
• Atoms were initially thought to be indivisible, tiny spheres.
• The discovery of the electron led to the plum pudding model.
• The plum pudding model: an atom is a ball of positive charge with negative electrons embedded within.
• Alpha particle scattering experiments led to the nuclear model.
• Nuclear model: the mass of an atom is concentrated in a charged, central nucleus; this replaced the plum pudding model.
• Niels Bohr adapted the nuclear model.
• Bohrs model: electrons orbit the nucleus at specific distances.
• Bohr's theoretical calculations aligned with experimental observations.
• Further experiments revealed that the positive charge of a nucleus can be subdivided into smaller particles.
• Each particle has the same amount of positive charge; these particles are protons.
• James Chadwick's work confirmed the existence of neutrons within the nucleus.
• This discovery occurred about 20 years after the nucleus was accepted as a scientific concept.

Elements, Compounds, and Mixtures

• Elements, compounds, and mixtures can all be distinguished from each other.

Separation and Purification

• Separation and purification methods: filtration, crystallization, simple distillation, fractional distillation.
• It is possible to select suitable separation and purification techniques based on information about the substances.

Measurement

• Common lab equipment: stopwatches, thermometers, balances, measuring cylinders.
• These are to measure time, temperature, mass, and volume, respectively.
• It's possible to argue the advantages and disadvantages of experimental methods and apparatus.

Atomic Structure

• The atom contains a central nucleus with neutrons and protons.
• The nucleus is surrounded by electrons in shells.

Subatomic Particles

• Protons, neutrons, and electrons have distinct relative charges and masses.

Atomic Number

• Proton number/atomic number refers to the amount of protons in the nucleus of an atom.

Mass Number

• Mass number/nucleon number refers to the total amount of protons and neutrons in the nucleus of an atom

Electronic Configuration

• Electronic configuration can be determined for elements and their ions with proton numbers 1 to 20.
• Example: 2,8,3.

Isotopes

• Isotopes are different atoms of the same element.
• Isotopes have the same number of protons but different numbers of neutrons.

Periodic Table

• The Periodic Table arranges elements into periods and groups.
• The elements are arranged in the order of the increasing proton number/atomic number.
• The position of an element in the Periodic Table indicates its properties.
• Elements in the same group of the Periodic Table have similar chemical properties.
• This is based on their electronic configuration.

Group 1 and Group 0

• Group I alkali metals (lithium, sodium, potassium) are relatively soft metals.
• Down the group: melting point decreases, density increases, and reactivity increases.
• Properties of other elements in Group I can be predicted given information about the elements.
• Group VIII noble gases have a full outer shell
• The number of outer shell electrons equals the group number for Groups I to VII.
• The number of occupied electron shells equals the period number.
• Character changes from metallic to non-metallic across a period.

Competencies

• Physical and chemical changes are distinct, with different characteristics.