Atomic Structure and the Periodic Table of Elements
Atomic Structure
Atomic Number (Z)
The number of protons in an atom’s nucleus defines the element. This is called the atomic number (Z).
Mass Number (A)
The sum of protons and neutrons in the nucleus is the mass number (A).
Isotopes
Isotopes are atoms of the same element with the same atomic number but different mass numbers due to varying numbers of neutrons.
Chemical Element
A pure substance composed of atoms with the same atomic number.
Rutherford’s Experiment (1910)
Ernest Rutherford’s experiment revealed the distribution of electrons and protons within the atom.
Nucleus
The nucleus occupies a small fraction of the atom’s total volume and contains the positively charged protons.
Electron Cloud
Electrons revolve around the nucleus in the electron cloud, occupying most of the atom’s volume.
Bohr Atomic Model
Niels Bohr proposed a model where electrons revolve in stationary circular orbits around the nucleus without losing energy.
- These orbits have specific energy levels (N), with higher energy levels further from the nucleus.
- Electrons can jump between energy levels.
Corrections to the Bohr Model
- Sommerfeld (1915): Proposed elliptical electron orbits.
- Zeeman (1916): Observed that elliptical orbits could have different orientations.
- Uhlenbeck and Goudsmit (1925): Discovered that electrons spin on their axis, creating a magnetic field.
Quantum Numbers
- Principal Quantum Number (n): Represents the main energy level.
- Azimuthal Quantum Number (l): Describes the shape of the orbital (s: 0, p: 1, d: 2, f: 3).
- Magnetic Quantum Number (ml): Specifies the orientation of the orbital in space.
- Spin Quantum Number (ms): Indicates the spin of the electron (+1/2 or -1/2).
Maximum number of electrons in each subshell: s2 p6 d10 f14.
Periodic Table
The periodic table organizes 117 known elements based on their atomic number.
- Elements in the same vertical group share similar properties.
- Properties change progressively across a period (horizontal row).
- Metals are located on the left and center, while nonmetals are on the right (except for hydrogen).
Electron Affinity
Electron affinity is the energy change when an electron is added to a neutral gaseous atom, measured in kJ/mol.
Types of Chemical Bonds
- Ionic Bond: Formed between ions with opposite charges.
- Covalent Bond: Formed by sharing valence electrons between atoms.
- Metallic Bond: Valence electrons are delocalized and move freely throughout the metal lattice.
Energy Resources
Renewable Energy Sources
Renewable energy sources are sustainable and replenishable.
Geothermal Energy
Utilizes heat from the Earth’s interior to generate electricity. Drilling at great depths can be challenging and expensive.
Hydropower
Harnesses the energy of waterfalls and rivers to rotate turbines. Can lead to the displacement of communities and requires safety measures to prevent dam failures.
Solar Energy
Converts sunlight into heat or electricity. Efficiency depends on the number of daylight hours.
Wind Energy
Uses wind turbines to generate electricity. Can be noisy and visually impact landscapes.
Tidal Energy
Captures energy from the rise and fall of tides. Requires large infrastructure and can have a significant environmental impact.
Biofuels
Derived from plant and animal waste. Large-scale cultivation can contribute to deforestation.
Non-Renewable Energy Sources
Non-renewable sources are finite and take millions of years to form. They are also major contributors to pollution.
Fossil Fuels
Formed from the remains of ancient organisms. Limited supplies and combustion releases carbon dioxide, contributing to global warming.
Nuclear Energy
Transforms nuclear energy into electricity or heat. Requires high safety standards and the construction of nuclear power plants is expensive.
Nature and Constitution of Matter
Mixtures
Mixtures are combinations of two or more substances that can be separated by physical methods such as evaporation, filtration, decantation, distillation, and crystallization.
Heterogeneous Mixtures
Components are visibly distinguishable and have different properties at different points in the mixture. Examples: water and oil, sand and water, granite.
Homogeneous Mixtures (Solutions)
Components are uniformly distributed and indistinguishable to the naked eye. Properties are the same throughout the mixture. Examples: air, blood, saltwater.
Pure Substances
Pure substances have a fixed composition and defined properties. They cannot be separated into simpler substances by physical methods.
Elements
Pure substances that cannot be broken down into simpler substances by chemical methods. Examples: oxygen (O2), nitrogen (N2), iron (Fe).
Compounds
Pure substances formed by the chemical combination of two or more elements. Can be separated into their constituent elements by chemical methods. Example: water (H2O) can be decomposed into hydrogen and oxygen by electrolysis.
Basic Properties of Matter
General Properties
Properties common to all matter, including mass and volume.
Specific Properties
Properties that depend on the type of substance.
Mass
The amount of matter in a body. Measured in kilograms (kg) using a balance.
Volume
The amount of space occupied by a substance.
Boiling Point
The temperature at which a liquid changes into a gas.
Melting Point
The temperature at which a solid changes into a liquid.
Density
The mass per unit volume of a substance.
Specific Heat
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MASS: is amount of matter that has a body.
• The unit of mass in the international system is the kilogram (kg)
·The instrument used to measure mass balance is
· Other units used to measure the mass are: