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Man gave names to all the elements

Hydrogen - from the Greek for water forming. Helium - from the Greek helios , the sun, where it was first detected spectroscopically. Lithium - from the Greek lithos , a stone Beryllium - from the Greek beryllo , which was their name for the mineral beryl. Boron - a combination of borax+carbon. Humphry Davy coined the name; the element came from the mineral borax and shared some properties of carbon. Carbon - from the Latin carbo for charcoal. Nitrogen - nitre forming. Nitre is an old name for potassium nitrate. Nitrogen was once called choke-damp in England. Oxygen - from the Greek for acid forming. Fluorine - from the Latin fluere to flow, after the tendency of the mineral fluorspar to melt in a flame. Neon - from the Greek neos new. Sodium - devised by its discoverer, Humpry Davy, from soda (sodium carbonate) which was named after the Latin sodanum , meaning headache remedy. The symbol Na comes from natrum , Latin for soda. Magnesium - named after Magnesia, a region of Greec...
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How to do calculations in science

\(\require{mhchem}\) Example 1. Speed, distance, and time Problem How long does it take a bee flying at 20 m/s to cover a distance of 100 m? List what you know $$s = 20~\ce{m/s}, d = 100~\ce{m}, t = ?$$ Write out the equation speed = distance / time, $$s=\frac{d}{t}$$ Substitute in your values $$20=\frac{100}{t}$$ Rearrange if necessary Multiply both sides by t. $$20t = 100$$ Divide both sides by 20. $$t = \frac{100}{20}$$ Calculate your answer $$t = 5$$ Check and format the answer, showing units. Is your answer sensible? $$t = 5~\ce{s}$$ (no requirements in the question for decimal places or significant figures). Sensible = yes. Check by backwards calculation. $$s=\frac{100}{5}=20~\ce{m/s}$$ Correct. Example 2. Concentration, volume, and number of moles Problem ...
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What is oxidation?

\(\require{mhchem}\) Oxidation for the chemist can be defined in lots of ways. The most obvious is: addition of oxygen . If we burn magnesium in oxygen... $$\ce{magnesium + oxygen -> magnesium~oxide}$$ $$\begin{equation} \ce{2Mg(s) + O2(g) -> MgO(s)} \end{equation}$$ The magnesium gains oxygen and is oxidised. Students are often taught the mnemonic OILRIG, which tells us Oxidation Is Loss. This refers to electrons. So our second definition is oxidation is loss of electrons . If we look at what happens to magnesium atoms in that same reaction, we can see that they are oxidised by losing electrons to form positive ions. $$\begin{equation} \ce{Mg -> Mg^2+ + 2e-} \end{equation}$$ Another definition of oxidation is removal of hydrogen . In organic chemistry an alcohol can be oxidised to an aldehyde, and in this reaction hydrogens atoms are removed. $$\begin{equation} \ce{CH3CH2OH +[O] -> CH3CHO + H2O } \end{equation}$$ where [O] represents an oxidising agent. Finally we ...
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The mole

\(\require{mhchem}\) In English we have lots of names for a number of items: a pair is 2, a dozen is 12, a score is 20, and a gross is 144. In chemistry the mole is also a number of items, but a much larger number. The mole is a convenient way for chemists to count particles (atoms, molecules, ions, or electrons) so that we can think about them in manageable numbers. If I say that 4 g of He gas contains 602 214 07 000 000 000 000 000 atoms of helium, that becomes painful to think about and is hard to write down. If I write the number in standard form, as \(6.022 \times 10^{23}\), it becomes easier to write but is still tricky to imagine. If instead I give that amount of substance a short and friendly name (“mole”), chemical reactions become easier to talk about. One mole of oxygen reacts with two moles of hydrogen to make two moles of water. Mole really just means “a standard number of particles”. $$\ce{hydrogen + oxygen -> water}$$ $$\begin{equation} \ce{2H2(g) + O2(g) -> 2H2...
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Ammonium nitrate and the Beirut explosion, 4 August 2020

\(\require{mhchem}\) On 4 August 2020 a massive explosion devastated the city of Beirut, Lebanon. It is thought a fire amongst a shipment of fireworks ignited a warehouse containing 2,750 tons of ammonium nitrate that had been stored at the docks. More than 130 people died and 4,000 were injured. Ammonium nitrate is used as a fertilizer and in explosives for mining and construction. In its pure form it is not highly explosive, but when mixed with something to act as a fuel, explosive. The mixture of 94% ammonium nitrate and 6% number 2 fuel oil is commonly used as an explosive and this is given the name ANFO. (Number 2 fuel oil comes from fractional distillation of crude oil; this fraction is used as heating oil and its carbon chains are 14 to 20 long.) In Beirut, the ammonium nitrate fertilizer had been impounded from a shipment in 2014 and stored since then. Ammonium nitrate is made industrially by reacting concentrated nitric acid with ammonia (an \(\ce{acid-base}\) reaction...
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Tests for negative ions

\(\require{mhchem}\) The tests for negative ions we need to know about for GCSE are: halides (chloride \(\ce{Cl-}\), bromide \(\ce{Br-}\), iodide \(\ce{I-}\)), carbonate \(\ce{CO_3^2-}\), and sulfate \(\ce{SO_4^2-}\). The simplest test is for carbonate so let's start with that. Carbonate ions The basis for this test is that: $$\ce{acid + carbonate -> salt + water + carbon\ dioxide}$$ If we add acid to a substance and find that it produces \(\ce{CO2}\), we know we have a carbonate. We test for \(\ce{CO2}\) by bubbling the gas through our old friend limewater; if the limewater turns milky, the gas was \(\ce{CO2}\). So, by putting acid in our solution to be identified, and testing any gas produced with limewater, we can tell whether carbonate ions are present. (We can also use this reaction to test for an acid, by adding some carbonate and seeing if \(\ce{CO2}\) is produced. Examiners sometimes ask the question that way round.) If we used hydrochloric acid and potassium ca...
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Separations

\(\require{mhchem}\) Chemists are always being asked how to separate mixtures of things. A mixture is two or more substances put together but not chemically combined. We use different properties of the two substances to achieve separation. Example: you are given a mixture of dry salt and sand. How can we separate them? If you had enough time, a microscope, and a very fine pair of tweezers, you could examined the grains one by one. The cubic grains would be salt, and you could (in theory) sort those out from the others. That would take a dreadfully long time, but this technique of hand picking can occasionally be useful. Louis Pasteur (inventor of Pasteurisation) used it to separate left- and right-handed crystals. In hand picking we are using a physical property of the substances—their appearance—to separate the two substances. An easier way is to use a different property: solubility. If we add water to our mixture, the salt dissolves and the sand doesn't. We can then use...
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