Glossary

Any substance that forms aqueous solutions with a pH value less than 7.

Common acids are:

• Hydrochloric acid - HCl
• Suphuric acid - H₂S0₄
• Nitric acid - HNO₃

Acids release hydrogen ions in water which makes the solution acidic.

The different ways an element can manifest. Carbon allotropes include graphite, charcoal and diamond for example.

The different forms arise from the different ways atoms may be bonded together.

Anions are atoms or groups of atoms that have a negative electric charge. An anion has more electrons in its atomic orbitals than it has protons in its atomic nucleus. The opposite of an anion is a cation, which has a positive charge.

All simple non-metal ions (except H+, which is a proton) are anions.

The name “anion” comes from the words anode and ion. In an electrochemical cell, anions are attracted to the positively charged anode.

Anions can be monatomic, made of only one atom, or polyatomic, made of multiple atoms. Anions can exist on their own only as gases: to make a solid, ionic liquid, or solution the total electrical charge must be zero, meaning a mix of anions and cations.

Aqua regia (Royal water in Latin) is a very strong acid. It is made by mixing one part concentrated nitric acid and three parts concentrated hydrochloric acid. The acid was named by alchemists because it can dissolve the noble metals gold and platinum. Tantalum, iridium and a few other metals are not dissolved by it.

The smallest amount of an element. An atom consists of a nucleus at the centre and electrons which orbit the nucleus.

The size of an atom measured as the mean distance from the centre of the nucleus to the outermost electron.

This is the number of protons an element contains. This is equal to the number of electrons unless the substance is an ion.

The number of atoms, ions, or molecules of a substance in one mole of that substance. The value of this mathematical constant is 6.023 x 10^23.

Any substance with a pH value greater than 7. Alkalis are a subgroup of bases that are soluble in water; so a base that dissolves in water to create a solution with a pH greater than 7. Alkalis form hydroxide ions or OH- ions in water. Bases are usually hydroxides or carbonates:

• sodium hydroxide, NaOH
• calcium carbonate CaCO₃ (acids usually have hydrogen: HS())

Elements are organized into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

‘The temperature at which an element changes from a liquid to a gas. This varies depending on the environmental pressure but the figure used is based on the pressure found at sea level. The lower the pressure the lower the boiling point.’

A cation is a type of ion that has a positive electric charge. This means it has fewer electrons than protons. The opposite of a cation is an anion, which has a negative charge.

Cations can have only one atom (monatomic cations) or be made of multiple atoms together (polyatomic cations). Most metals form monatomic cations, while polyatomic cations are rarer.

Cation is pronounced “cat eye on”, not “kay shun”.

There are several different chemical bonds that can keep atoms together. Examples include covalent, ionic and metallic bonds.

Covalent bonds join two non metallic elements. In these bonds atoms which both need an extra electron can share electrons.

See also ionic and metallic bonds.

‘The CPK colouring (for Corey-Pauling-Koltun) is a popular color convention for distinguishing atoms of different chemical elements in molecular models.’

A compound contains 2 or more different elements chemically combined in fixed proportions.

They can have totally different properties from the elements they are made from.

A chemical reaction is required to separate the elements back into their original forms.

’the ratio of a substance’s mass to its volume'

Diatomic molecules consist of two atoms bonded together. In contrast, monatomic elements consist of single atoms (e.g., Ar, He). Many compounds are diatomic, such as HCl, NaCl, and KBr. Diatomic compounds consist of two different elements. Seven pure elements form diatomic molecules:

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Fluorine (F₂)
• Chlorine (Cl₂)
• Iodine (I₂)
• Bromine (Br₂)

An easy-to-remember mnemonic for the diatomic elements is: Have No Fear Of Ice Cold Beer.

‘The ability of an atom to hold electrons tightly. The trend is the same as electron affinity, bottom left to top right on the Periodic table, ignoring the noble gases. Electro negativity is important for chemical bonds.’

An electron is a tiny, negatively charged, indivisible particle that orbits the nucleus of an atom. If an electron is positively charged it is called a positron.

This tells us how much an atom wants to gain an electron. Fluorine has the highest electron affinity because its outer shell needs one electron in it’s outer, and only second shell. On the other end (left side of the periodic table) the elements have only one electron in their outer shell and want to lose them. The trend for electron affinity is from bottom left to top right (ignoring the noble gases).

aka main energy level

Electrons orbit an atom’s nucleus at fixed distances called shells. Each shell can hold up to a fixed amount of electrons. The first shell can hold up to 2 electrons.

The number of shells an element has is the same as it’s period number. Elements in the 3rd row or period have 3 shells.

Each shell is given a number (n) starting with 1 for the innermost shell. This number can be used to calculate the maximum number of electrons the shell can hold using 2n².

The arrangements of electrons above the last (closed shell) noble gas.

An example for element 77, Iridium, is [Xe] 4f14 5d7 6s2. See block.

In an element all the atoms are the same. The element type is determined by the number of protons in its nucleus.

The splitting up of large and unstable nuclei into smaller nuclei. This process releases a lot of energy which is how we get energy from nuclear power stations.

Fission can occur spontaneously as a natural, unforced process or by absorbing a neutron making the nucleus even more unstable. Spontaneous fission is rare so neutrons are usually added to start the process to split the atom. This creates a chain reaction where the first fission will create more fissions and so on.

Each column of the periodic table represents a group. The elements in a group have similar properties.

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Ions are atoms that have an overall charge. This is because they’ve either lost or gained electrons. Positive ions have lost electrons and negative ions have gained electrons. An ion is denoted by plus or minus symbols: Na⁺ means the overall charge is positive and it has lost one electron. A single minus symbol means it has gained one electron.

A liquid with ions is called an electrolyte. A gas with a lot of ions is called a plasma.

When ions move, it is called electricity. For example, in a wire, the metal ions do not move, but the electrons move as electricity. A positive ion and a negative ion will move together. Two ions of the same charge will move apart. When ions move they also make magnetic fields.

Ionic bonding is a very strong bond between atoms. Salt, or sodium chloride, is an example of ionic bonding. Ionic bonds have one positively charged ion and one negatively charged ion. They are then held together by electrostatic forces.

The work between a metal and a non metal.

One or more electrons are transferred from the outer shell of metal atom to the outer shell of a non metal atom. This creates two oppositely charged ions. These are then attracted to one another by electrostatic forces. This creates an ionic compound.

Ionic compounds have very high melting and boiling points. They can conduct electricity when melted or disolved in water. See salt.

The process of creating ions.

is the energy required to remove an electron from the atom. Less is required on larger atoms because the attractive force drops off with distance and the shells of larger atoms is further from the nucleus. It’s the opposite of atomic radius. It’s very difficult to ionize helium because it only has one shell that’s close to its nucleus and that shell is full. There are multiple ionization energies for each electron removed from the atom. The second and subsequent ionization energies is always greater than the first and previous energies.

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atoms of the same element with different numbers of neutrons. These are typically defined by their mass number. The standard form of carbon is carbon-12. It has 6 protons and 6 neutrons. Carbon-13 has an extra neutron: 6 protons plus 7 neutrons makes 13.

An isotope symbol usually has the isotope number written first. Thus tritium, or hydrogen-3 would be ³H and carbon-13 is ¹³C.

The International Union of Pure and Applied Chemistry rules over naming of elements and more. For example it decided that Sulfur should be spelled with an ‘f’ rather than a ‘ph’ and aluminium should have 2 ‘i’s.

The time it takes for the number of nuclei in a radioactive isotope to halve. The half life of Bismuth is 20 billion billion years or 2 x 10¹⁹.

The halogens are a group of elements on the periodic table. It is the only element group that includes elements capable of existing in three of the four main states of matter at room temperature: solid, liquid, and gas.

The word halogen means “salt-producing,” because halogens react with metals to produce many important salts. In fact, halogens are so reactive that they do not occur as pure elements in nature. Many, however, are common in combination with other elements.

Chlorine trifluoride combines two halogens chlorine and fluorine and is the most flammable chemical ever made. This chemical is unique in being able to ignite literally anything it touches, including flame retardants. It can set fire to glass and sand, water, asbestos and Kevlar (the material from which firefighters’ suits are made).

Magic numbers are one of the key organizing principles in nuclear physics. They explain why certain nuclei are exceptionally stable, much like noble gases in atomic chemistry.

In nuclear physics, a magic number is a number of protons or neutrons that completes a nuclear shell, producing an unusually stable nucleus.

The magic numbers are 2, 8, 20, 28, 50, 82 and 126

A metallic bond is .. See covalent bond and ionic bond

The melting and boiling points are determined by the strength of the bonds holding the substance together.

‘A mixture of 2 or more elements that are not chemically combined (like a compound). These can separated physically using various methods.’

‘When metals react they lose electrons from their outer shell. This gives them the stable electronic structure of a group 0, noble gas. Because they lose electrons it means they always form positive ions.’

A standard unit of measurement in chemistry, defined as the amount of a substance that contains the same number of atoms, ions, or molecules as there are atoms in 0.012 kg of carbon 12. This number is a mathematical constant known as Avogadro’s number.

Two or more atoms that are chemically bonded. Molecules can contain multiple atoms of the same element or atoms of different elements.

Any chemically combined elements even if they’re the same element. Molecules are particles that are made from non-metals and are bonded covalently.

The opposite of diatomic

A particle in the nucleus of an atom with the same mass as a proton but with no electrical charge.

‘The central part of an atom comprising of protons and neutrons.’

The shape of the orbit of an electron.

Organic chemistry is the study of chemical compounds that contain carbon. Carbon has the ability to form a chemical bond with a wide variety of chemical elements and other carbon atoms because of its 4 valence, or outermost, electrons. This allows a nearly unlimited number of combinations, called organic compounds.

The subject of carbon compounds is called organic chemistry because all known organisms, or living things, are made up of water and carbon compounds. Organic chemistry largely involves the synthesis, or formation, of organic products by chemical reaction using different reactants and reagents, the substances used up during a reaction. Several different areas of chemistry expand on the concepts and principles of organic chemistry, including biochemistry, microbiology, organometallic chemistry and medicine.

The study of hydrocarbons is a very large part of organic chemistry. Hydrocarbons are molecules containing only the elements carbon and hydrogen in the form of chains.

These are the numbers we would have on an atom if it was in its ionized form.

The oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms are fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. Beside nearly-pure ionic bonding, many covalent bonds exhibit a strong ionicity, making oxidation state a useful predictor of charge.

See the full list of oxidation states on Wikipedia.

When metals and non-metals react with oxygen they make compounds called oxides.

All oxides are compounds, and contain a single element bonded with oxygen. Examples include magnesium oxide MgO, sodium oxide Na₂O and aluminium oxide Al₂O₃.

Metal oxides act as bases. This means they can neutralise an acid.

Non-metal oxides usually dissolve in water to make acidic solutions.

A row of the periodic table, which contains the elements that successively fill up a specific electron shell with electrons. The first element in each period has one electron in its outer shell, making it relatively unstable, while the last element in each period has a full outer shell, making it relatively stable.

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An electron that has a positve charge. These are found in antimatter where the protons have a negative charge.

The positively charged particle in the nucleus of an atom.

Some isotopes have an unstable nucleus. To become stable the nucleus gives out radiation. This is called radioactive decay. This is a completely random process.

Activity is the rate at which a source of unstable nuclei decay, This is measured in becquerel or bq. 1bq = 1 decay per second.

Here are 4 types of radioactive decay:

1. alpha particles - a helium nucleus, that is 2 protons and 2 neutrons. These can travel about 5cm in air before they collide with air particles and stop. Can be stopped by a piece of paper or skin. Poses a threat when inhaled, ingested or injected. Very strongly ionising.
2. beta particles are electrons or positrons ejected from the nucleus at very high speed. These are formed inside the nucleus when a neutron changes into a proton and an electron. These can travel around 15cm in air before stopping. Main threats to health are again when inhaled, ingested or injected. Can be stopped by several mm of aluminium. Quite strongly ionizing.
3. electromagnetic radiation from the nucleus in the form of gamma rays x-rays or ultraviolet rays. Gamma rays can travel several metres in air before stopping. They can be stopped by several centimetres of 1ead. Weakly ionizing.
4. neutron - a neutron is ejected by the nucleus.

Ionizing radiation is a type where the particles or waves ejected can ionize other atoms they interact with. Something that produces ionizing radiation is said to be radioactive.

These not the only types of radioactive decay.

A radioisotope is a radioactive isotope, also known as a radionuclide, or radioactive nuclide. It is any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.

More than 1,800 radioactive isotopes of the various elements are known. Some of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products. Each “parent” radioactive isotope eventually decays into one or at most a few stable isotope “daughters” specific to that parent.

A material that is chemically changed in the course of a chemical reactions.

A chemical present at the start of a reaction. Reactants appear on the left of a chemical equation, before the arrow →.

The number of protons and neutrons. Where there are multiple isotope the average is calculated but this is a weighted average based on the abundance of each isotope.This is known as the relative atomic mass. The symbol for relative atomic mass is Ar.

The units are based upon Carbon 12 atoms. Carbon 12 atoms are said to have a mass of 12 exactly so other atomic masses are derived from this. 1 atomic mass unit (amu) is 1/12 x of a carbon 12 atom.

Note that the mass number is not the same. This is simply the number protons plus the number of neutrons. There is no weighted average of the different isotopes.

In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions and negatively charged ions, which results in a compound with no net electric charge. The constituent ions are held together by electrostatic forces termed ionic bonds.

When an acid and an alkali are combined in a neutralization reaction a salt is produced along with water.

The name of a salt takes the first part of the alkali, the metal name, and the second from the acid. Nitric acid makes salts ending with nitrate. Sulfuric acid makes salts ending in sulfate and hydrochloric acid makes salts ending with chloride.

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An element symbol is related to the name of the element. However some may relate to the element’s name in another language

The outermost electron shell (or energy level). The number of electrons here is also the group number of the element.

The van der Waals radius, rw, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the van der Waals equation of state. - Wikipedia