IBDP Chemistry 2025: Structure 2.2 Simplified

Let's explore the fundamental building blocks of atoms: protons, neutrons, and electrons.Protons have a positive charge and a mass of one atomic mass unit. Neutrons have no charge and the same mass, while electrons have a negative charge but are much lighter.These particles are arranged in a specific way to form atoms. The nucleus contains protons and neutrons.Electrons orbit the nucleus in energy levels, or shells. Each shell can hold a specific number of electrons.The atomic number of an element is determined by the number of protons in its nucleus.The mass number is the total number of protons and neutrons in the nucleus.Electrons are constantly moving around the nucleus in their shells, while protons and neutrons stay within the nucleus.The scale of these particles is remarkable. The nucleus is about one hundred thousand times smaller than the entire atom.Now that we understand the basic particles and structure of atoms, we can explore how electrons are arranged in more detail.Electrons are arranged in energy levels around the nucleus, with each level having a maximum capacity.The maximum number of electrons in each energy level follows the two n squared rule, where n is the energy level number.Each energy level contains sublevels, labeled s, p, d, and f, each with different electron capacities.The aufbau principle shows us the order in which electron orbitals are filled.Let's look at sodium, with atomic number 11. Its electrons fill the orbitals in order.Notice how sodium has one electron in its outer three s orbital, making it highly reactive.Chlorine, with 17 electrons, follows the same pattern but needs one more electron to complete its outer shell.The arrangement of electrons in the outer shell largely determines an element's chemical properties and reactivity.Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei.For example, chlorine has two naturally occurring isotopes: chlorine-35 with 18 neutrons, and chlorine-37 with 20 neutrons. Both have 17 protons, making them chlorine atoms.The mass number of an isotope is calculated by adding the number of protons and neutrons together.To calculate the relative atomic mass of an element, we need to consider the abundance of each isotope.Let's calculate the relative atomic mass of chlorine. Chlorine-35 has an abundance of 75.77 percent, while chlorine-37 makes up 24.23 percent.We multiply each isotopic mass by its abundance as a decimal, then add the results.This gives us twenty-six point fifty-two plus eight point ninety-seven.The final relative atomic mass of chlorine is thirty-five point forty-nine atomic mass units.Isotopes have numerous important applications in modern science and medicine.They are used in medical diagnosis with technetium-99m, cancer treatment using cobalt-60, archaeological dating with carbon-14, and nuclear power generation with uranium-235.Now that we understand isotopes and mass numbers, let's move on to our next topic.Ionization energy is a crucial measure of how strongly an atom holds onto its electrons.For example, when we remove an electron from sodium, it requires 496 kilojoules per mole of energy.Looking at trends across the periodic table, ionization energy generally increases from left to right across a period.And decreases as we move down a group.Across a period, the increasing nuclear charge leads to stronger attraction between the nucleus and electrons.Down a group, additional electron shells and increased shielding result in weaker attraction to outer electrons.Let's examine successive ionization energies using magnesium as an example.Looking at magnesium's electron configuration helps explain the large jump in energy after removing two electrons.This dramatic increase occurs because we're now removing electrons from a stable, filled inner shell.Let's explore two important atomic properties: electron affinity and atomic radius.Electron affinity measures the energy change when an atom gains an electron. Negative values indicate energy release.Looking at our periodic table, we can see how electron affinity varies.Electron affinity generally becomes more negative as we move across a period, showing increased tendency to gain electrons.Now let's examine atomic radius, which is half the distance between the nuclei of two bonded atoms.Atomic radius shows clear trends across the periodic table. It decreases from left to right across a period.And increases as we move down a group, due to additional electron shells.These trends are caused by changes in nuclear charge and electron shielding effects.These atomic properties are crucial for understanding chemical behavior and predicting reactivity.Thanks for exploring atomic properties with Spark.E!