Obviously something of a given mass is denser if it is smaller, so does this limit how small an object may be (An object of sufficient density would be a black hole would it not? In the periodic table of the elements, elements in a single column have the same number of electrons that can participate in a chemical reaction. One of the most advanced uses of radioisotopes in medicine is the positron emission tomography (PET) scanner, which detects the activity in the body of a very small injection of radioactive glucose, the simple sugar that cells use for energy.

The tiny size of the nucleus relative to the whole atom, and its tendency to sit at the center of the atom, explains why it plays a relatively minor role in chemistry. You have to get close to get the “true” size but there is a restriction on how close you can get so exact size is impossible to measure. Its shape is like that of a rural community, with expanses of uninhabited land, a few scattered farm houses, and a small village with closely packed houses at its center. The idea that something is point-like is the statement that if and when you try to break it apart or detect its finite extent by banging something into it, you fail. So, what gives an element its distinctive properties—what makes carbon so different from sodium or iron?Each element’s name can be replaced by a one- or two-letter symbol; you will become familiar with some of these during this course. The composition and the basic properties and ordening of the constituents are more important for understanding the atom casually.

An element is a pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means. PET highlights areas in the body where there is relatively high glucose use, which is characteristic of cancerous tissue. Calcium is essential to the human body; it is absorbed and used for a number of processes, including strengthening bones. Even though electrons are point-like in one sense (for instance, if you try to bounce two electrons off each other, you will find you can get them arbitrarily close together without them revealing that they have any structure), there is a way in which, when left alone, they can spread out like a wave, and fill out the entire grey area in Figure 2. Protons and neutrons contribute nearly all of an atom’s mass; the number of protons and neutrons is an element’s mass number.The re-emitted light can be detected, allowing us to “see” where the ions are, in a way somewhat analogous to how a reflection of light off a tiny but shiny diamond allows us to find it.

Just as a magnet sticks to a steel refrigerator because their opposite charges attract, the positively charged protons attract the negatively charged electrons. Singly ionized oxygen is very close to nitrogen, it will readily bind three hydrogen atoms to produce an ammonia shaped H3O+ molecule and will pair up into strongly bonded O2. So, just like Prof Strassler described, chemistry is all about the behaviour of the valence electrons (and all electrons behave according to quantum mechanics).I think it best to take a “Wittgenstein approach” and just lay everything out as you have done in the extract above. A molecule of table salt (NaCl) contains two atoms, one of sodium (Na) and one of chlorine (Cl); a molecule of water (H 2O) has two of hydrogen and one of oxygen; a molecule of table sugar (C 12H 22O 11) is made from twelve atoms of carbon, eleven of oxygen and twenty-two of hydrogen in a very particular arrangement. The human body is composed of elements, the most abundant of which are oxygen (O), carbon (C), hydrogen (H) and nitrogen (N). So, electrons in an atom are organized by energy levels, and for a given level, there is an arrangement of electrons that is the most stable. I certainly don’t have an ideal way to draw it that wouldn’t be misleading, and experts still argue about what is the best way to think about it.

The number of protons and electrons within a neutral atom are equal, thus, the atom’s overall charge is balanced. I was going to answer them later, but your point is that probably I need to bring them up — at least pose them, with links to answers — in this article directly. In other words, an atom of hydrogen is a unit of hydrogen—the smallest amount of hydrogen that can exist. Concerning the size of an electron, could you simply not mention it and merely give the mass ratio between a nucleus and an electron as some kind of measure, and cross your fingers?Although the territory that is considered part of the town may be quite large, the actual amount of area occupied by houses is very small, as is the area occupied by the village at the center of the town.