chem 1010
Atomic Structure
Proton and Atomic Number
Hydrogen has one proton in its nucleus.
Atomic number of hydrogen is 1.
Definition: Atomic number is the number of protons inside the nucleus of an atom.
The atomic number determines the name of the atom.
Mass Number
Definition: Mass number is the summation of the number of protons and neutrons inside the nucleus.
Example:
For hydrogen: Atomic number = 1, Mass number = 1 (no neutrons).
For helium: Atomic number = 2, Mass number = 4 (2 protons and 2 neutrons).
Standard Notation for Atoms
Atoms are presented in standard notation as follows:
Atomic symbol: Represents the element (e.g., H for hydrogen, C for carbon).
Superscript: Mass number (e.g., $_{A}^Z$ where A is the mass number).
Subscript: Atomic number (e.g., $_{6}^{12}$ for carbon).
Important:
Atomic number is denoted as Z.
Mass number is denoted as A.
Atomic number: count of protons.
Mass number: count of protons and neutrons (A = Z + N, where N = number of neutrons).
Counting Neutrons
The number of neutrons can be calculated as:
Carbon Example
Carbon has 6 protons and 6 neutrons.
In standard notation: $_{6}^{12}C$.
Neutral carbon: 6 electrons (protons = electrons).
Isotopes
Definition: Isotopes are atoms that have the same number of protons (same element) but a different number of neutrons.
Example: Carbon has three isotopes:
Carbon-12 ($_{6}^{12}C$): 6 protons, 6 neutrons.
Carbon-13 ($_{6}^{13}C$): 6 protons, 7 neutrons.
Carbon-14 ($_{6}^{14}C$): 6 protons, 8 neutrons, slightly radioactive.
Oxygen Example
Oxygen has 8 protons and 8 neutrons.
In standard notation: $_{8}^{16}O$ (mass number = 16).
Subatomic Particles
Electrons: Negatively charged with a relative charge of -1; very small mass compared to protons and neutrons.
Protons: Positively charged with a relative charge of +1; mass = 1 AMU.
Neutrons: No charge; mass = 1 AMU.
Atomic Mass Unit (AMU)
Definition: 1 AMU is defined as 1/12 of the mass of a carbon-12 atom.
Practical Masses:
Mass of a proton: 1 AMU.
Mass of a neutron: 1 AMU.
Mass of an electron: Approximately , significantly less than that of protons and neutrons (approx. ).
Electron Properties
Electrons move quickly around the nucleus, in shells, and have wave properties at relativistic speeds.
Speed of electrons can be up to 0.7% of the speed of light (where ).
Stability of Atoms
In neutral atoms, the number of protons = number of electrons.
The attractive force between protons (in nucleus) and electrons (in shells) creates a stable configuration, counterbalanced by repellent forces between electrons in different shells.
Atomic Model Interaction
Interactive models can visualize how adding/removing protons or electrons alters atom identity and charge.
Adding neutrons does not change charge or identity but can stabilize the atom.
Ions and Charges
Cations: Formed when electrons are removed, resulting in a positively charged ion.
Example: Carbon becomes a cation when it loses one electron (from 6 to 5 electrons), yielding a charge of +1. Notation: .
Anions: Formed when electrons are added, resulting in a negatively charged ion.
Example: Fluorine becomes an anion when it gains an electron, yielding a charge of -1: .
Periodic Table and Atomic Calculations
To determine protons, neutrons, and electrons in elements:
Use a periodic table to identify atomic numbers for protons and electrons.
Calculate neutrons as: , with A as mass number.
Example Problem
For a neutral calcium atom (Ca, atomic number 20):
Protons = 20, Electrons = 20.
Elements and Compounds
Elements can exist as single atoms or in compounds where atoms form chemical bonds.
Allotropes: Different structural forms of the same element. Examples in carbon:
Graphite: Layered structure, soft, used in pencils.
Diamond: Tetrahedral bonding, very hard.
Buckminsterfullerene: Spherical arrangement, e.g., Buckyballs in soot.
Metal Extraction
Metals in nature are usually in mineral compounds, not elemental.
Example extraction methods include smelting (e.g., copper oxide to copper).
Chemical Changes during Extraction
For copper extraction:
.
Indicates both physical changes (solid to liquid) and chemical changes (reactants to products).
Silicon and Electronics
Silicon has semiconductor properties and is essential in electronics. Purification reaches up to 12 n (99.999999% pure for microchips).
Crystalline vs Amorphous:
Crystalline: Ordered structure (e.g., quartz).
Amorphous: Disordered structure (e.g., glass).
Sustainability in Materials Science
Sustainability balances environmental protection, social well-being, and economic development:
Mindful resource usage and pollution minimization is critical for future generations.
Cradle-to-cradle recycling aims to ensure recovered materials retain quality for future production, unlike typical recycling processes that degrade quality.