Atomic Number, Mass Number and Configurations

• Study notes below define the key concepts in chemistry:

Atomic Number and Mass Number

• The atomic number indicates the number of protons in an atom's nucleus, defining the element and its position on the periodic table.
• The mass number is the total count of protons and neutrons in an atom's nucleus.
• Protons and neutrons, collectively known as nucleons, reside in the nucleus.

Calculations Involving Atomic Structure

• Atomic number equals the number of protons.
• In a neutral atom, the number of protons equals the number of electrons.
• Mass number minus the atomic number equals the number of neutrons.

Electron Configuration

• Electron Configuration describes the arrangement of electrons within an atom.
• The formula 2n² determines the maximum number of electrons per orbit, where n is the orbit number.
• The first shell can hold up to 2 electrons.
• Subsequent shells can hold up to 8 electrons each.
• Valence electrons are those found in the outermost shell, influencing the atom's chemical properties.

Example: Magnesium (Mg)

• Magnesium (Mg), with an atomic number of 12, has an electron configuration of (2,8,2).
• Magnesium has 2 valence electrons

Subatomic Particles

• Subatomic particles are the components that constitute an atom.
• There are three primary types: protons, neutrons, and electrons.

Protons

• Protons carry a positive charge and are located in the nucleus.
• The number of protons defines the element.

Neutrons

• Neutrons are neutral, with no charge, and are found in the nucleus.
• Neutrons contribute to nuclear stability.
• Atoms of the same element with varying neutron numbers are isotopes.

Electrons

• Electrons carry a negative charge and orbit the nucleus in energy levels or electron clouds.
• Typically, the number of electrons equals the number of protons in a neutral atom.
• Each subatomic particle has distinct properties, such as mass and charge, which collectively determine an atom's behavior.

The Periodic Table

• The periodic table organizes chemical elements by atomic number, from hydrogen (lowest) to oganesson (highest).
• Vertical columns (groups) contain elements with similar chemical properties due to the same number of outer shell electrons.
• Horizontal rows (periods) contain elements with the same number of electron shells, increasing down the table.
• Elements become less metallic moving left to right across a period.

Elements, Compounds, and Mixtures

• These are three basic forms of matter with distinct characteristics.

Elements

• Elements are pure substances made of one type of atom and can't be broken down chemically.
• Each element has unique properties and a symbol on the periodic table.

Compounds

• Compounds are made of two or more elements chemically bonded in a fixed ratio.
• Compounds have different properties than their constituent elements.
• They can be broken down into elements via chemical reactions.
• Water (H2O) and sodium chloride (NaCl) exemplifies compounds.

Mixtures

• Mixtures are combinations of physically combined substances, not chemically bonded.
• Components retain their original properties and can be separated physically.
• Mixtures can be homogeneous (uniform, like saltwater) or heterogeneous (non-uniform, like a salad).
• Elements are pure substances, compounds are chemically bonded, and mixtures are physical combinations.

Heterogeneous Mixtures

• Heterogeneous mixtures do not have uniform distribution.
• Components are visibly distinct and retain individual properties.
• Visible separation can often occur.

Homogeneous Mixtures

• Homogeneous mixtures have a uniform composition.
• Uniform composition is consistent throughout, like salt dissolved in water.
• Homogeneous mixtures appear consistent.
• Single phase is present, and components are not easily distinguishable.
• Difficult to separate

Heterogeneous Mixtures

• Heterogeneous mixtures have non-uniform composition.
• Different components are visible.

Isotopes

• Isotopes are forms of an element with the same number of protons but different numbers of neutrons, leading to varying atomic masses.
• Isotopes of the same element share the same position on the periodic table due to the number of protons.
• Isotopes have different atomic masses due to varying numbers of neutrons.
• Isotopes of an element generally exhibit similar chemical properties due to identical electron configurations.
• Isotopes have varied stability, some are stable, while others are radioactive and decay.

Carbon Isotopes:

• Carbon-12 (6 protons, 6 neutrons), Carbon-13 (6 protons, 7 neutrons), and Carbon-14 (6 protons, 8 neutrons) exist naturally.
• Carbon-14 is radioactive and used for radiocarbon dating.

Hydrogen Isotopes

• Protium (1 proton, 0 neutrons), Deuterium (1 proton, 1 neutron), and Tritium (1 proton, 2 neutrons) exist.
• Tritium is radioactive.
• Isotopes are variations of elements with identical proton numbers but differ in neutron count, affecting stability and atomic mass.