Crash Course Chemistry

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Anion: A negatively charged Ion, one that would attract towards an anode.

Atomic Radius This is the size of the atom and is the distance from the centre of the nucleus to the outer most electrons in a stable atom.

Avogadros number

Cation A positively charged ion that has lost electrons.

Divalent An atom that has two valence electrons (Di-Valent means two-valence).

Ductile To deform without fracture. If something is very ductile, it can be hammered into sheets without damage very easily.

Electron Affinity The amount of energy released when an electron is added to an atom to form a negatively charged ion. It is also the amount of energy required to strip an electron from a negative ion. A higher electron affinity means meaning it is harder to remove an electron.

Electronegativity The ability for an atom to attract electrons in order to covalently bond. The higher electronegativity, the more strongly it will attract them.

Ion An element that has gained or lost an electron and does no longer has the same number of electrons as protons.

Ionisation Energy The minimum amount of energy required to remove an electron from an atom in a gaseous state in order to form a positively charged ion.


Malleable Able to be hammered and pressed into shape without breaking.


Valence shell/electrons The outer most shell with electrons/outer most electrons in an atom.

Guide Words in this colour have their definitions in the table of definitions above.Atoms The number of protons in an atom determines what element it is no matter what. The number of protons is also the atomic number of the element. The mass number is the number of protons +neutrons. The number of electrons is the same as the number of protons in atoms in

The Periodic Table The periodic table is a table of elements arranged which shows all the elements arranged from the smallest to the largest. The columns in the periodic table are called Groups with the main groups from 1 to 8. The rows in the periodic table are called Periods and go from 1-7.

As seen in the picture above, it is important to know the properties of the types of elements and where they are found in the periodic table.Alkali Metals: Very Reactive. Malleable, Ductile and good conductors. One loosely bound Valence electron. Reacts violently with water. Forms cations with a 1+ charge.

Alkaline Earth Metals: Low Electron Affinities and Electronegativity Two valence electrons Smaller Atomic Radii than Alkali Metals Readily forms divalent cations with a 2+ charge.

Transition Metals: Fairly unreactive. High melting, boiling point and electrical conductivity. Have a wide range of oxidation states. Have low Ionization energy.

The Halogens: Very high electronegativitys. Seven valence electrons. Highly reactive with alkali metals and alkaline earth metals. Have low Ionization energy.

Metalloids: Have similar metal and non-metal properties. They are all solids. Found in the small step portion of the periodic table.

Noble Gases: Completely unreactive. Full valence shell. Very low electronegativitys. Low boiling points. Gases at room temperature.

The Electrons Electrons are negatively charged particles which orbit around the nucleus of an atom. They determine how the atom behaves and most of its properties.

The Bohr Model: Proposed by the scientist Niels Bohr. The Bohr Model states that electrons have set distances in which they orbit a nucleus. Each set distance is a shell and can be referred to as n. Each set distance has a fixed amount of energy with each electrons in that orbit having that amount of energy. The further distance away you get from the nucleus, the more energy is contained in the orbits.

Orbitals (sub-shells): Within each shell of an electron are orbitals. An orbital is a probability cloud and is defined as an area in space where there is a high probability of finding electrons. Each orbital can only hold a maximum of two electrons. There are s, p, d and f orbitals and each orbital has its own unique shape. Electrons fill shells from the lowest energy level to the highest. The periods in the periodic table represent which shell the electrons will go into.

s-orbital: Found in the first shell of the atom. It can hold a maximum of two electrons. Is a spherical shape. This is why the first period in our period table only has two elements.

p-orbital: Found in the second shell of the atom. The second shell is larger and can include more than just the s-orbital. It can hold a maximum of six electrons. It consists of three configurations along the 3D x-y-z axis with each one holding two electrons.

d-orbital: Found in the third shell of the atom. It can hold a maximum of ten electrons. It consists of five configurations each one holding two electrons.

f-orbital: Found in the fourth shell of the atom. It can hold a maximum of fourteen electrons. It consists of seven configurations each one holding two electrons.

Electron Configuration: Electron configurations are a way of writing down where each electron is located within an atom. It involves three main parts written down to form an equation. In order to write the electron configuration of an atom, we write:1. The number of the shell.2. The letter of the orbital.3. The number of electrons in that orbital.

Electrons fill orbitals in a certain order, from the lowest energy to the highest. A trick we can use to write this is to memorise the following diagram and draw diagonal lines to determine the order in which orbitals will be filled in.

From this diagram, we know that electrons will fill in the following order: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 and so on.

Just by looking at the above equation, we know: This atom has a total of 30 electrons. (Total number of electrons in each orbital. We can determine that this is an atom of Zinc. (Assuming it isnt an ion)

Write the electron configuration for Chromium.

1. Chromium is in the second period of the periodic table.2. It is the 24th element, meaning it has a total of 24 electrons in its natural state.3. We know how many electrons each orbital can hold.4. All we need to do now is look at the diagram and start filling in all 24 electrons for Chromium in the order of the diagram.5. Therefore Chromium has the following electron configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d4

Ionization Energy: Ionization energy is the amount of energy required to remove an electron from an atom to create a positively charged Ion. When an electron is removed from an atom, it forms a positively charged ion called a cation. This is because before the electron was removed there were an equal number of protons and electrons and hence the overall charge was neutral. Now that the electron is removed, there are more protons than electrons and hence the overall charge is positive. The outer most electrons have the most energy and hence require the least energy to be removed so they are the first to be removed. The closer an electron is to its nucleus, the more energy required to remove the electron. When all of the electrons in the outer most shell are removed, there is a jump in energy required to start removing electrons in the next outer most shell. This makes sense as electrons are being attracted towards the protons in the nucleus and the closer they are, the stronger the force of attraction and hence the more energy required to remove the electron. Energy is also required when adding electrons to form negatively charged ions called anions. This energy is called the electron affinity. The orbitals are also on periodic table as shown below with the number of elements for each row of the orbitals corresponding to the number of electrons the orbital can hold, for example all the s-orbitals in green have only two elements in each row.

Stoichiometry Stoichiometry is the science of measuring chemicals that go into and out of reactions. It allows us to count atoms and molecules by weighing them.

Atomic Mass: The atomic mass of an element is the average number of all the isotopes of that element and their abundance on earth. Atomic mass is measured in atomic mass units (amu). We can calculate atomic mass by adding the number of protons and neutrons in an element. We can also calculate it if given the isotopes and their abundances by using the following steps. Convert the abundance of each isotope of the element from a percentage to decimal. Multiply the abundance of each isotope by its mass. Add the final results of each isotope together.

Relative Atomic Mass: The ratio of the average mass of an atom to 1/12th of the mass of an atom of carbon-12. 1 amu = 1/12th the mass of a carbon-12 (12C) atom which is 1.99264648 x 10-23.

Gallium has two stable isotopes: Galium-69 (60.11% abundant) and Galium-71 (39.89% abundant). Their atomic masses are 68.926 and 70.925 respectively. Calculate the average atomic mass of Gallium.

1. Convert the percentages to decimals.2. 60.11*(1/100) = 0.6011 and 39.89*(1/100) = 0.39893. Multiply the isotopes masses by their abundance.4. Add the results together.5. (0.6011*68.926) + (0.3989*70.925) 6. = 69.72 amu

If you have a look at the periodic table for the mass of Gallium, you will notice it is 69.72 amu.

Moles: A mole is one of the most important units in chemistry. It allows us to express a chemicals atomic mass in terms of grams. A mole is equivalent of the amount of atoms in 12 grams of Carbon-12 which is 6.022 x 1023. This number is known as Avogadros number. A mole of anything means 6.022 x 1023 of that object, so a mole of rice would mean 6.022 x 1023 grains of rice. For example, a mole of oxygen would mean 6.022 x 1023 atoms of oxyg