Understanding the Physical and Chemical Properties of Matter

Physical Properties of Matter

A physical property is a feature that can be studied using the senses or by measuring with a specific instrument. These properties manifest themselves primarily in physical processes such as state changes, temperature changes, pressure changes, etc.

• Examples include color, hardness, density, boiling point, and melting point.

Physical properties are categorized as:

• General Properties: A single value can be applied to different substances, such as mass, volume, color, and texture.
• Specific Properties: Each substance has a particular value, such as density, specific gravity, boiling point, and melting point.

Chemical Properties of Matter

Chemical properties are distinctive characteristics of substances observed when they combine with others, resulting in processes that often change the original substances into new ones.

• Some chemical properties of matter include reactivity, heating value, and acidity.

Extensive and Intensive Properties

Extensive properties relate to the external chemical structure, which can be measured easily and depend on the amount and form of matter. Examples include weight, volume, length, potential energy, and heat.

In contrast, intensive properties are related to the internal chemical structure of matter, such as temperature, melting point, boiling point, specific heat, and refractive index. Intensive properties can be used to identify and characterize a pure substance, such as water, which is composed solely of water molecules (H₂O).

Rutherford's Model

Rutherford: Based on the results of his work, which demonstrated the existence of the atomic nucleus, Rutherford argued that almost the entire mass of the atom is concentrated in a tiny core with a positive electric charge. Electrons orbit the nucleus in circular paths, possessing negligible mass and a negative electrical charge. The electrical charges of the nucleus and electrons neutralize each other, resulting in an electrically neutral atom.

• The atom has a nucleus containing its mass and positive charge.
• The rest of the atom is mostly empty, with electrons forming a ring around the nucleus.
• The atom is neutral because the total positive charge in the nucleus is balanced by the number of electrons surrounding it.
• When electrons are forced out, a positively charged structure remains.
• The atom is stable because electrons maintain a spin around the nucleus, generating a centrifugal force that balances the electrical force of attraction from the nucleus, allowing them to stay in orbit.
• The energy contained in a photon depends on the type of radiation (the wavelength). As the wavelength decreases, the energy increases.
• The visible spectrum ranges from approximately 4.3 x 10^-14 to 7.5 x 10¹⁴ Hz, including purple, blue, green, yellow, and red.
• In regions of increased frequency (decreased wavelength), the energy content of photons is significantly higher.
• Ultraviolet (UV) radiation is not visible to the naked eye, but its high energy content acts as a catalyst in many chemical processes.

Bohr's Model

Bohr: Postulated that electrons spin at high speeds around the atomic nucleus. Electrons are arranged in various circular orbits, which determine different energy levels. An electron can access a higher energy level by absorbing energy. To return to its original energy level, the electron must emit the absorbed energy.

• An electron has a definite and characteristic energy level based on its orbit. An electron in the K shell (closest to the nucleus) has the lowest possible energy. As the distance from the nucleus increases, so does the radius of the level and the electron's energy level.
• An electron in the layer closest to the nucleus (K layer) has the lowest energy or is in a ground state. When atoms are heated, they absorb energy and move to higher energy levels, becoming excited.
• When an electron returns to a lower level, it emits a specific amount of energy in the form of a quantum of light, which has characteristic wavelength and frequency, producing a spectral line.
• The wavelength and frequency of a photon produced by an electron transitioning from a higher to a lower energy level in a hydrogen atom are defined by specific equations.
• According to Bohr, an atom can only exist in a limited number of stationary states, each with a defined energy level.
• Energy can only change through discrete jumps, each corresponding to a transition from one state to another.

Dalton's Atomic Theory

Dalton: Introduced the idea of the discontinuity of matter, proposing that matter is composed of indivisible and unchangeable particles called atoms. This was the first scientific theory to support the concept of atoms, apart from ancient philosophers like Democritus and Leucippus, whose claims lacked rigorous experimental support.

• All atoms of the same element are identical (having equal mass and properties).
• Atoms of the same element can exist as isotopes, which have different masses.
• Atoms of different elements have different masses and properties.
• Compounds are formed when atoms join together in fixed ratios.

Thomson's Model

Thomson: Proposed that electrons are uniformly distributed throughout the atom, known as the