The Potential Energy Curve Bring two atoms slowly toward each other and track the potential energy of the pair. Far apart, they barely interact and the energy is near zero. As they approach, each nucleus attracts the other atom’s electrons, and the energy falls. At one specific distance the energy reaches its minimum. That distance … Read more
Why Bonds Form At All Atoms bond because the bonded arrangement has lower potential energy than the separated atoms. Electrons and nuclei arrange themselves into the configuration where attractions are maximized and repulsions are minimized, and that arrangement holds together. Every bond type in this topic is the same story told with different electron behaviour. … Read more
Why Atoms Form Ions At All An atom’s chemistry is run by its valence electrons, and the most stable arrangement an atom can reach is a full outer shell, the configuration of a noble gas. Atoms get there by the shortest route. A metal with one, two or three valence electrons loses them all: the … Read more
The One Idea Behind Every Trend Almost every periodic trend is Coulomb’s law wearing different clothes. The attraction between a nucleus and an electron grows with the charges involved and shrinks rapidly as the distance between them grows: F ∝ (q₁ × q₂) ÷ r². For a valence electron, the charge it actually feels is … Read more
What a Photoelectron Spectrum Is Photoelectron spectroscopy, PES, is an experimental technique that reads an element’s electron configuration directly. A sample is hit with high energy photons, and the photons knock electrons out of the atom. Each photon gives up its energy to free one electron. Whatever energy is left over becomes the kinetic energy … Read more
Shells, Subshells and Orbitals The electrons in an atom occupy orbitals, and each orbital holds at most two electrons. Orbitals are grouped into subshells, and subshells into shells labelled by the principal quantum number n = 1, 2, 3 and so on. Each shell contains subshells of the types s, p, d and f, appearing … Read more
Mixtures Are Not Compounds A pure substance has a fixed composition. Water is always 11.2% hydrogen by mass, and calcium carbonate is always 40.0% calcium, because their formulas fix the ratios. A mixture has no formula. It is two or more substances physically combined, and its composition depends on how much of each part went … Read more
What Percent Composition Tells You The percent composition of a compound is the percentage of its total mass that comes from each element. It is a property of the compound itself. A pure sample of water is always 11.2% hydrogen and 88.8% oxygen by mass, whether the sample is a drop or a tank of … Read more
What a Mass Spectrum Shows A mass spectrometer sorts the atoms of a sample by mass. The sample is vaporized and ionized, the ions are accelerated, and they are then separated according to their mass-to-charge ratio, written m/z. A detector records how many ions arrive at each value of m/z. The result is a mass … Read more
The Mole: Counting Particles You Cannot See Atoms and molecules are far too small to count one by one, yet chemistry constantly needs to know how many of them are reacting. The mole solves this by counting particles in bulk. One mole of any substance contains exactly 6.022 × 10²³ representative particles. This fixed number … Read more