Atoms are the building blocks of matter, consisting of a surrounded by electrons. The nucleus contains protons and neutrons, while electrons orbit in shells. Understanding atomic structure is crucial for grasping chemical properties and reactions.
Isotopes are atoms with the same number of protons but different counts. This affects their mass and stability. , calculated from masses and abundances, is essential for stoichiometry and determining in chemical calculations.
Atomic Structure and the Nucleus
Structure of atoms
Atoms fundamental units of matter made up of a dense, positively charged nucleus surrounded by negatively charged electrons in shells or orbitals
Nucleus contains protons (positive charge, mass ~1 ) and neutrons (no charge, mass ~1 amu)
Electrons orbit nucleus in shells or orbitals have a negative charge and negligible mass compared to protons and neutrons
Number of electrons in an atom determines its chemical properties (reactivity, bonding)
Electrons arranged in energy levels (shells) and sublevels (orbitals) around the nucleus (, )
Atoms are electrically neutral with equal numbers of protons and electrons
Ions formed when atoms gain or lose electrons (cations are positively charged, anions are negatively charged)
Isotopes and atomic properties
Isotopes are atoms of the same element with different numbers of neutrons have the same number of protons and electrons but vary in the number of neutrons (e.g., carbon-12, carbon-13, carbon-14)
is the number of protons in an atom's nucleus defines the identity of an element (e.g., all carbon atoms have 6 protons)
All isotopes of an element have the same
is the sum of the number of protons and neutrons in an atom's nucleus differs among isotopes of the same element (e.g., carbon-12 has 6 protons and 6 neutrons, carbon-13 has 6 protons and 7 neutrons)
Represented as a superscript to the left of the element symbol (12C, 13C)
Isotopes have similar chemical properties but different physical properties (mass, )
Some isotopes are stable (non-radioactive) while others are unstable (radioactive) and undergo decay (emit particles and energy over time)
Nuclear properties and stability
is the strong attractive force between nucleons (protons and neutrons) that overcomes electrostatic repulsion between protons
is determined by the ratio of neutrons to protons in the nucleus
Stable nuclei have a specific range of neutron-to- ratios
is the energy required to break apart a nucleus into its constituent nucleons
Higher binding energy per nucleon generally indicates greater nuclear stability
Radioactivity is the spontaneous emission of particles or energy from unstable nuclei
Radioactive decay occurs when nuclei have an unfavorable neutron-to-proton ratio
Calculation of atomic weight
Atomic weight is the weighted average of the masses of an element's naturally occurring isotopes takes into account the relative abundance of each isotope
To calculate atomic weight:
Multiply the mass of each isotope by its fractional abundance (expressed as a decimal)
Sum the products of mass and fractional abundance for all isotopes
Example calculation for chlorine with two naturally occurring isotopes, 35Cl (75.77%) and 37Cl (24.23%):
Atomic weight of Cl = (34.97 amu×0.7577)+(36.97 amu×0.2423)=35.45 amu
Atomic weights are used in stoichiometry calculations and for determining the molar mass of compounds
Molar mass is the sum of the atomic weights of all atoms in a compound (g/mol)
Key Terms to Review (35)
Acetylide anion: An acetylide anion is a negatively charged ion formed when a terminal alkyne loses a proton (H+) from its carbon atom, resulting in a carbon with a negative charge. This ion is highly reactive and serves as a nucleophile in various organic synthesis reactions.
Anion: An anion is a negatively charged ion that is formed when an atom or molecule gains one or more electrons. Anions are essential in understanding both atomic structure and organic reaction mechanisms.
Antibonding MO: An antibonding molecular orbital (MO) is a type of molecular orbital that forms when atomic orbitals combine with their phases out of sync, leading to a node between the nuclei where electron density is significantly decreased. This results in repulsion and destabilization, making the molecule less stable when electrons occupy these orbitals.
Atomic mass: Atomic mass is the total weight of an atom, primarily determined by the sum of its protons and neutrons located in the nucleus. It is measured in atomic mass units (amu), where one amu is approximately equal to the mass of a single proton or neutron.
Atomic Mass Unit (amu): The atomic mass unit (amu) is a unit of mass used to express the mass of atomic and subatomic particles. It is defined as one-twelfth the mass of a carbon-12 atom at rest and in its ground state. This unit allows for the comparison of the relative masses of different atoms and molecules.
Atomic Number: The atomic number is a fundamental property of an element that represents the number of protons in the nucleus of an atom. It is a unique identifier for each element and is a crucial concept in understanding the structure and behavior of atoms.
Atomic number (Z): The atomic number is the number of protons in the nucleus of an atom, which determines the chemical element's identity and its position on the periodic table. It also influences the atom's chemical behavior in reactions.
Atomic number, Z: The atomic number, symbolized as Z, is the total number of protons found in the nucleus of an atom. It uniquely identifies the chemical element and determines its position in the periodic table.
Atomic Weight: Atomic weight, also known as atomic mass, is the average mass of an atom of a given element, taking into account the naturally occurring isotopes of that element. It is a fundamental property that characterizes the composition and behavior of atoms in chemical reactions and processes.
Binding Energy: Binding energy is the amount of energy required to remove a nucleon (proton or neutron) from the nucleus of an atom. It represents the strong nuclear force that holds the nucleus together, and it is a fundamental concept in understanding atomic structure and nuclear stability.
Bohr Model: The Bohr model is a representation of the atom developed by Danish physicist Niels Bohr in 1913. It depicts the atom as having a central nucleus surrounded by electrons that orbit in discrete circular paths, or shells, around the nucleus. This model helps explain the behavior of electrons within an atom and provides insights into atomic structure.
Bonding MO: A bonding MO is formed when atomic orbitals overlap constructively, leading to a decrease in energy and an increase in stability of the system. It allows electrons to be shared between atoms, facilitating chemical bonding.
Cation: A cation is a positively charged ion that is formed when an atom loses one or more of its valence electrons. Cations are an essential component in understanding both atomic structure and organic reaction mechanisms.
Cation radical: A cation radical is a molecule that has lost an electron, resulting in a positively charged species with an unpaired electron. It is often formed during the ionization process in mass spectrometry, specifically within the context of analyzing small molecules using magnetic-sector instruments.
Condensed structures: Condensed structures are simplified representations of molecules in organic chemistry that show the arrangement of atoms without explicitly drawing all bond lines between them. They list each central atom along with the atoms connected to it, typically omitting single bonds and using subscripts for multiple identical groups or atoms.
Electron: An electron is a subatomic particle that carries a negative electric charge and is found in all atoms, orbiting the nucleus. Electrons are fundamental to the structure and behavior of atoms and play a crucial role in chemical bonding and the flow of electrical current.
Electron shell: An electron shell is a group of atomic orbitals with the same principal quantum number, n, indicating its distance and energy level relative to the nucleus in an atom. These shells define the distribution of electrons around an atom's nucleus and are crucial for determining how atoms interact in chemical bonding.
Ion: An ion is an atom or molecule that has gained or lost one or more electrons, giving it a net positive or negative charge. Ions are fundamental to the understanding of atomic structure and the behavior of matter at the atomic level.
Isotope: Isotopes are atoms of the same element that have the same number of protons in their nucleus but a different number of neutrons. This results in atoms of the same element having slightly different atomic masses.
Mass Number: The mass number, also known as the nucleon number, is the total number of protons and neutrons in the nucleus of an atom. It is a fundamental property that represents the overall mass of an atom and is an important characteristic in understanding the structure and behavior of atoms.
Mass number (A): The mass number (A) is the total number of protons and neutrons in an atom's nucleus. It gives the atomic mass unit (amu) of the atom, which is crucial for understanding the atom's overall stability and reactivity.
Molar Mass: Molar mass is the mass of one mole of a substance, which is the amount of a substance that contains the same number of particles (atoms, molecules, or ions) as there are atoms in 12 grams of carbon-12. It is a fundamental concept in chemistry that relates the mass of a substance to the number of particles it contains.
Molecular orbital (MO): A molecular orbital is a region in a molecule where an electron has the highest probability of being found. It is formed by the overlap of atomic orbitals from different atoms during bond formation.
Molecular orbital (MO) theory: Molecular Orbital Theory is a method in chemistry for describing the electronic structure of molecules using quantum mechanics. It explains how atomic orbitals combine to form molecular orbitals, which are then occupied by electrons.
Neutron: A neutron is a subatomic particle that has no electric charge and is found in the nucleus of an atom. It plays a crucial role in the stability and composition of atomic nuclei, contributing to the overall structure and properties of elements.
Nuclear Force: The nuclear force, also known as the strong force, is a fundamental force in nature that holds the nucleus of an atom together. It is one of the four fundamental forces in the universe, along with gravity, electromagnetism, and the weak nuclear force.
Nuclear Stability: Nuclear stability refers to the ability of a nucleus to maintain its structure and resist undergoing radioactive decay. It is a fundamental concept in atomic structure that describes the factors determining the likelihood of a nucleus to remain intact or undergo transformation.
Nucleus: The nucleus is the central and most important part of an atom, containing the protons and neutrons that make up the atom's dense, positively charged core. It is the defining feature of atomic structure and is essential for understanding the behavior and properties of atoms.
Orbital: An orbital is a mathematical function that describes the wave-like behavior of an electron in an atom. It defines the probability distribution of an electron around the nucleus of an atom, and is a fundamental concept in quantum mechanics and atomic structure.
Organophosphate: Organophosphates are a class of organic compounds containing phosphorus, characterized by their structure which includes a direct bond between a phosphorus atom and carbon atoms. They are widely recognized for their use in pesticides, nerve agents, and various industrial applications.
Proton: A proton is a subatomic particle that is found in the nucleus of an atom. It has a positive electric charge and is one of the fundamental building blocks of all matter in the universe.
Quantum Mechanical Model: The quantum mechanical model is a fundamental theory in physics that describes the behavior of matter and energy on the atomic and subatomic scale. It provides a probabilistic interpretation of the properties and interactions of particles, challenging the classical, deterministic view of the physical world.
Radioactivity: Radioactivity is the spontaneous emission of radiation, such as alpha particles, beta particles, or gamma rays, from the unstable nuclei of certain atoms. This phenomenon occurs as the nucleus of a radioactive atom attempts to achieve a more stable configuration by undergoing transformations that release energy in the form of these radiations.
Shell: The shell of an atom refers to the distinct energy levels or regions surrounding the nucleus where electrons are found. Electrons are organized into shells based on their energy levels, with the innermost shell being the lowest energy level and the outermost shells representing higher energy levels.
Skeletal structures: Skeletal structures are simplified diagrams used in organic chemistry to represent the framework of molecular bonds in organic compounds, primarily focusing on carbon atoms and their connections. These structures omit symbols for carbon atoms at the vertices and do not always show hydrogen atoms, making complex molecules easier to visualize and draw.