Notes, summaries, assignments, exams, and problems for Chemistry

Basic Atomic Structure

• Proton: A particle with a positive charge located in the nucleus. Mass = 1 AMU.
• Neutron: An atomic particle with no charge and a mass approximately equal to a proton. It is a structural component of the atomic nucleus. Mass = 1 AMU.
• Electron: A particle with a negative charge that orbits the nucleus.
• Nucleus: The positively charged center of an atom.
• Atom: The basic unit of a chemical element.
• Atomic Mass Unit (AMU): Used to express atomic and molecular weight.
• Atomic Number: The number of protons in an atom of a chemical element.
• Isotope: Atoms of an element containing an equal number of protons but a different number of neutrons in their nuclei.

Isotopes

• All atoms of an element do not weigh the same amount.
• The number of neutrons

Properties of Metals:

Shiny, lustrous, can be polished, strong, and solid.

Nonmetals:

Dull, not lustrous, cannot be polished, weak, half are gases.

18 Families or Groups, 18 Periods:

Elements in the same group have common characteristics. Horizontal is period, vertical is family or group.

Periodic Law:

The PT is organized by atomic number Z. Elements with similar properties are in the same family.

Properties of Metalloids:

Have characteristics of metals and nonmetals. Located between metals and nonmetals.

Johann Dobereiner (1829):

Classified elements into groups of three, called triads.

John Newlands (1838-1898):

Law of Octaves (1863) suggested arranging elements in octaves.

Dmitri Mendeleev (1834-1907):

Published a table of elements organized by increasing... Continue reading "Evolution of the Periodic Table: From Triads to Actinides" »

Thermal Energy and Particle Motion

Thermal energy is intrinsically linked to temperature, which reflects the movement of particles within matter. This concept is a cornerstone of the Kinetic Theory of Matter, stating that all matter is composed of tiny particles in constant, random motion.

Changes in Matter: Physical vs. Chemical

When we observe the world around us, we identify two distinct types of transformations that matter undergoes:

Physical Changes

A physical change is a process where the fundamental nature or chemical composition of a substance remains unaltered. The original substance does not transform into a new, chemically different substance. Examples include:

• Changes of State: Such as ice melting into water, or water boiling into steam.

Mixtures and Compounds

A mixture is a material system made up of two or more different substances which are mixed but not combined chemically.

Types of Mixtures

• Heterogeneous: The components are visibly diverse.
• Homogeneous: The components are uniformly distributed, appearing as a single substance.

Basic Chemical Concepts

• Phase: A physically distinct form of matter, such as a solid, liquid, or gas.
• Element: A substance that is made up of only one type of atom.

Changes of State

• Melting Point: The temperature at which a solid melts. The particles gain energy, vibrate faster, and eventually move around, becoming a liquid.
• Boiling Point: The temperature at which a liquid boils. The particles gain energy, move faster, break free, and become a gas.

Tests for

Understanding Temperature

What is Temperature?

Temperature is the measurement of a substance's thermal energy.

Measuring Temperature

Mercury Thermometer

A mercury thermometer consists of a bulb containing liquid mercury and a thin tube. The liquid expands due to thermal expansion and rises up the tube, allowing the temperature to be read on a calibrated scale.

Digital Thermometer

A digital thermometer uses a microprocessor that measures the temperature and displays it on a liquid crystal display (LCD).

Temperature Scales

Common temperature scales include Celsius (ºC) and Kelvin (ºK).

• Celsius to Kelvin: K = C + 273.15
• Kelvin to Celsius: C = K - 273.15

Heat Transfer Mechanisms

Conduction

Conduction is the transfer of heat energy primarily from solid to solid... Continue reading "Science Essentials: Temperature, Heat, Reactions, Environment" »

An Arrhenius acid is a substance that dissociates in water to form hydrogen ions or protons. In other words, it increases the number of H⁺ ions in the water. In contrast, an Arrhenius base dissociates in water to form hydroxide ions, OH^-.

A Bronsted-Lowry acid is a solution that donates protons and is known as a proton donor. The Bronsted-Lowry base, on the other hand, is a solution that accepts protons and is known as a proton acceptor. Going back to a Bronsted-Lowry acid, in general, it must contain a hydrogen ion that it can give up.

Defining Matter

Matter is defined as anything that has mass and takes up space.

Pure Substances

Pure substances possess constant physical properties (e.g., odor, hardness, density, boiling points). They can be classified as either elements or compounds.

Elements

Elements consist of only one kind of atom and cannot be broken down into a simpler type of matter by either physical or chemical means. Elements are found in the periodic table and are categorized as:

• Metals: Tend to lose electrons, resulting in a positive charge (cations).
• Nonmetals: Tend to gain electrons, resulting in a negative charge (anions).
• Metalloids.

Compounds

Compounds are formed when atoms of two or more different elements are chemically bound together. They can be broken down into... Continue reading "Classification of Matter: Elements, Compounds, and Separation Techniques" »

Atomic Nucleus and the Nature of Radioactivity

The nucleus is the small central core of an atom, containing a positive electric charge and the majority of the atom's mass. It is made up of nucleons (protons and neutrons) bound together by the strong nuclear force. This force is stronger than the electromagnetic force between the nucleus and electrons, but it only works over very short distances. The nucleus does not intervene in chemical changes.

Radioactive Decay and Radioisotopes

Some atoms, whether naturally occurring or artificial elements, have particular combinations of protons and neutrons that make them unstable. These atoms decompose by emitting energetic radiation and changing the nucleus. This process is known as radioactive decay,... Continue reading "Atomic Nuclei, Radioactivity, and Chemical Bonding" »

Advanced Materials Science Concepts

High Entropy Alloys (HEAs)

What Materials Are Named ‘High Entropy Alloys’?

Substances constructed with equal or nearly equal quantities of five or more metals. They exhibit a higher degree of fracture resistance, tensile strength, as well as corrosion and oxidation resistance compared to conventional alloys.

What Conditions Must Be Satisfied to Obtain HEA from a Number of Chemical Elements?

Gibb’s phase rule applies: F=C-P+2.

Graphene and Graphene-Like Materials

Differences Between Graphene and Silicene

Silicene is not flat; it is stronger than graphene. Silicene’s hydrogenation reaction is more exothermic than graphene’s.

Three Examples of Graphene-Like Materials

• Layered van der Waals materials
• Graphene-like