Althoug b tween them in reality. So, different atoms. Figure 7. This 1- ion has the sam. Two electrons are transferred from a mag transferred, typically 1 or 2 ' form Mg'' and ions. They carry an electrical charge, either positive or negative. Compounds are. Therefore in an ionic compound there must be the right number of each sort of ion, so that the total positive charge exactly cancels out the total negative charge.
Obviously, then, if you are going to work out a transferred formula, you need to know the charges on the ions. Any element in Group 6 has 6 outer electrons, and it has room to gain 2 more; this leads to a 2- ion. Similar arguments apply in the other groups shown in Table 7. The lithium atom has 1 electron in its outer shell that is easily lost, and the fluorine has space to receive one.
One electron is transferred from the lithium atom to the fluorine atom. You cannot work out the charges for some ions, you have to learn them. Ions that need to be learnt are shown in Table 7. The calcium atom 2, 8, 8, 2] has 2 electrons in its outer shell but each chlorine atom 2, 8, 7] only has room in its outer shell to take one of them. You need Table 7.
The 2 electrons are transferred from the outer shell of a calcium atom to two chlorine atoms, one to each. The formula for calcium chloride is therefore CaCl2. There is, however, also You need a simple way to work them out. You could work out a few from first covalent bonding see Chapter 8 in You will encounter other ions during the course, but these are the important principles, using their electronic structures, but that would take ages.
The ions in this list are the difficult ones - be sure to learn both would be too difficult. You need a simple, shortcut method. Any 'ide' ending means that there isn't anything complicated there. A shortcut to working out complicated formulae such as these is t o just Once you have an 'ate' ending, it means that there is oxygen and p ossibly swap over the numbers in the charges.
This is shown in Figure 7. HINT other things there as well. So, for example, copper II sulfate contains copper, Not looking carefully at word endings sulfur and oxygen. Be careful! There is no extra number in front of the charge in c1- because we do not tend to write in a 1. Why aren't ion charges shown in answer when the charges on the ions are the same. For example, the formula Oxygen is in Group 6, so the ion is 0 Actually, they can be shown. When the charges on the positive and For example, the formula for sodium negative ions are the same you can deduce that there will be 1 of each ion in To have equal numbers of positive and negative charges, you would need chloride is NaCl.
It is sometimes the formula, so there is no need to swap anything o ver. In other words, you need: make a particular point, but for most purposes the charges are left out. A lattice is a regu lar array of particles.
The lattice is held together by the strong electrostatic attractions Nitrate ions are N0 You will have to remember this. To have equal numbers of positive and negative charges, you would need two nitrate ions for each barium ion. Notice the brackets around the nitrate group. Brackets must be written That would read as 1 barium, 1 if you have more than one of these complex ions ions cont aining more nitrogen and 32 oxygens!
In any other situation, they are completely unnecessary. Alattice is a regular, repeating structure. Ionic crystals tend to be brittle. In diagrams, the ions are usually drawn in an 'exploded' view Figure 7. Each sodium ion is surrounded by 6 chloride ions.
In turn, each chloride ion is surrounded by 6 sodium ions. You have to remember that this pattern repeats itself throughout the structure over vast numbers of ions. Organic solvents include ethanol Ionic compounds tend to be insoluble in organic solvents.
If you are interested in these, you could The reasons that ionic compounds tend to be soluble in water are quite complicated. The lines in this diagram are not bonds, they negative and the hydrogen slightly positive - the molecule is called polar. This are just there to help show the arrangement of the ions. Those ions joined by lines are touching means that reasonably strong forces can be formed between water molecules and each other.
The structure of sodium chloride is described as a giant ionic lattice. We Not all ionic substances are soluble in water: magnesium oxide isn't soluble in water are using the word 'giant' here not in the sense of b ig but rather to describe because the attractions between the water molecules and the ions aren't strong HINT enough to overcome the very strong electrostatic forces of attraction between a structure where there are no individual molecules.
All the sodium ions in magnesium and oxide ions. This is really important: you must the structure attract all the chloride ions, we cannot pick out sodium chloride not talk about molecules of an ionic molecules; there are no individual molecules.
The b onding in a giant ionic Hexane is non-polar and does not form strong enough attractions to the ions to compound. This will be marked wrong break apart the ionic lattice. There is no limit to in the exam and you could lose all the the number of particles present, all we know is that there must be the same marks for a question!
It has exactly the same structure as sodium chloride. The only difference electricity when they are molten have melted or if they are dissolved in water been melted - it is a liquid.
This happens because the ions then become free to move attraction. It is really important that you use the correct words when explaining this. In sodium chloride, the electrostatic attractions are weaker because they are Do not use the word 'electrons'. You must talk about the ions being free to move. A lot of ii lithium bonds with oxygen to make lithium oxide energy has to be supplied to break the strong electrostatic forces of attraction iii magnesium bonds with fluorine to make magnesium fluoride.
Ionic compounds tend to be crystalline. Sometimes the crystals are too small to be seen except a potassium combines with fluorine under powerful microscopes. In any bond, particles are held together by electrostatic attractions between something positively charged and something negatively charged. What holds the atoms together is the strong electrostatic attraction between the nuclei positively charged of the atoms that make up the bond, and the shared pair of electrons negatively charged.
In most of the simple examples you. The more bonds In chemistry, we talk about things electron to the shared pair of electrons. That doesn't have to be the case.
Both electrons may come from the same atom. The H2 molecule is much more stable than two separate hydrogen atoms. Generally, the lower the energy something has, the more stable it is. By sharing 1 electron with go of the book, it will fall to the floor, a hydrogen atom, both atoms will have t he same number of electrons as the Covalent bonds are often shown using dot-and-cross diagrams.
If you look at the arrangement of electrons around HINT therefore it becomes more stable. Remember that, although the electrons the chlorine atom in the covalently bonded molecule of HCI Figure 8. That is the same as an electrons. Similarly, the hydrogen now has 2 electrons in its outer shell - the them in reality; the dots and the same as helium. In fact, the inner electrons are often left out of bonding diagrams.
But be careful! In an exam, only leave out the inner Hydrogen atoms form diatomic molecules with the formula H 2. The atoms in electrons if the question tells you to. Another way of representing the covalent an H2 molecule are joined together by a covalent bond.
The covalent bond bonding in HCI is shown in Figure 8. We also use lines to represent the covalent bonds between atoms, but be Molecules contain a certain fixed number of atoms, which are joined together careful, the diagram shown in Figure 8. Hydrogen molecules are said to be diatomic because they contain two atoms. In H2 , each hydrogen atom has only one electron to share, so it can only form covalent one covalent bond.
The shared pair of electrons is in the outer shell of both, bond therefore each atom has the same number of electrons as a noble gas atom helium in this case. Some people talk shell they have the same number of about the 'octet rule', referring to this 8.
Remember, we are counting shared electrons as a noble gas atom - they electrons as belonging to the outer shells of both atoms. When there is one atom in the middle and other atoms are joined to it as in C H4 or PCl:i the outer atoms will virtually always have 8 electrons in their outer shell or 2 if they are H. In fact, it is very difficult to think of an example w here the outer atoms do not have 8 electrons. There are some molecules where the central atom does not have 8 electrons in the outer shell, and we will look at a couple of examples of those later on.
A Figure 8. By sharing 1 electron with There are also four pairs of electrons around the each of 4 hydrogen atoms the C will have 8 electrons in its outer shell and central atom in water: two of these are pairs of each H will have 2 electrons in its outer shell.
Therefore C forms 4 covalent electrons involved in covalent bonds and two are pairs bonds, 1 w ith each H atom. H molecule is polar has a slightly negative and a slightly positive end and that a stream of water can be bent by an electrically charged object.
In ammonia, a nitrogen atom Ethane has the formula C 2 H 6. The bonding is similar to methane Figure 8. This is called an organic compound. You will leam more about molecules such as this in Unit 4. HINT When drawing molecules containing carbon and hydrogen it is useful to remember that carbon always forms A Figure 8.
It will therefore share 2 other sharing 1 electron. The hydrogen electrons to have 8 electrons in its outer shell. In water, an oxygen atom forms atoms always go on the outside, never 2 covalent bonds - 1 with each H atom. The formula of water is H There are therefore two shared pairs of A Figure 8. Pairs of electrons in the outer shell of the central atom repel each other and will therefore tend to get as far o,o apart as possible. For example, in a methane molecule there are four double pairs of electrons around the central C atom and for these to be as far covalent away from each other as possible, they must be arranged in a tetrahedral bond.
Therefore, we know that Br will form have 8 electrons in its outer shell. When you d raw a dot-and-cross diagram for CH3Br you electrons between the nitrogen atom s; this is called a triple covalent b ond or, H will only be asked to show the outer electrons Figure 8.
When drawing chloroethene, remember that C will form 4 covalent clarity, you do not need to use different bonds, H will form 1 and Cl will form 1. Nitrogen gas consists of n itrogen molecules bond ed like this.
The triple bond from the sharing of three pairs of electrons between the two nitrogen atoms is very strong and needs a lot of energy to break. That is why nitrogen is. It does not matter where you put the H showing the covalent bonds. This is not, and Cl atoms relative to the C, and you do not have to use different colours.
An oxygen atom has 6 electrons in its outer shell and a carbon atom has 4. Each F will share 1. This m eans that B only has a total of 6 electrons in its outer shell. C2H4 atoms attached to each carbon atom and a double bond between the carbon You will find out more about this in Unit 4. The central at om is S and the outer atom s are 0. So the S atom shares 2 electrons with each of the O atoms to form two double bonds.
Atoms in Periods 3 and below 4, 5, 6, 7 can have more than 8 electrons A sulfur atom originally had 6 electrons in its outer shell and so now, if it shares in their outer shells. The maximum 4 electrons, it has 1 0 electrons in its outer shell.
Bromomethane has the formula CH 3Br: the 3 H atoms and the B r atom are atom in a molecule can share is equal to the number of electrons in its outer :oisio: joined to the central C atom.
Br has 35 electrons and we have not learnt how shell. So, sulfur can form up to 6 bonds A Figure 8. The boiling points It is not always the case that melting Molecules contain fixed numbers of atoms joined by strong covalent bonds.
If increase down this group, which means we have to put in more energy to and boiling points increase as the M, we look closely at liquid water, there are individual water molecules, where the increases and really the rule only applies break the intermolecular forces as the relative molecular mass increases. This H and O atoms are joined together with strong covalent bonds. But there must to sets of very similar substances, such means that the intermolecular forces of attraction must become stronger as also be some forces between water molecules which keep them in the liquid as the halogens or the alkanes see relative molecular mass increases.
These forces are intermolecular forces. Chapter This is discussed further in Chapter This is because the molecules don't have any overall electrical charge there are no ions and We are using the term covalent These intermolecular forces between molecules are much weaker than molecular compounds to mean all the electrons are held tightly in the atoms or in covalent bonds an d so are covalent bonds. When we boil water it is only these weak intermolecular forces covalent compounds with a simple not able to move from molecule to molecule.
Looking at Figure molecular structure. Covalent molecular substances tend to be insoluble in water. There are some 8. The covalent bonds between the H and O atoms in the molecules have and HCI that react with water as they dissolve. All that has changed in gaseous water is that there are no intermolecular forces, they have been broken.
Covalent molecular substances are often soluble in organic solvents. When a substance consists of molecules with intermolecular forces of attraction between them, we say that it has a simple molecular structure. Virtually all the compounds you w ill encounter that have Diamond is a form of pure carbon.
Each carbon atom has four electrons in its outer shell and it therefore forms Substances with simple molecular structures tend to be gases or liquids or four covalent bonds. In diamond, each carbon bonds strongly to four other solids with low melting points and boiling points.
The reason for this is that not A tetrahedron is a triangular-based carbon atoms in a tetrahedral arrangement. Figure 8. In a tetrahedral arrangement, structure to see what is happening. Look carefully at the top five atoms in Figure 8. In Figure 8.
If you continue with chemistry you will We are only showing a small part of the learn that there are different types of You can see from Table 8. The structure continues intermolecular forces. You will come as the relative molecular mass increases. Each of the lines in this diagram hydrogen bonds. There is a special It is not a molecule because the number of atoms joined up in a real diamond type of intermolecular force between water molecules called hydrogen bonds.
Molecules always contain fixed numbers of atoms joined by covalent bonds. This is because of the very strong carbon-carbon covalent bonds, which extend throughout the for example the solid form ice is less chlorine er, 71 whole crystal in three dimensions. A lot of energy has to be supplied to break dense than the liquid form.
It is important to realise how this is d ifferent from the simple iodine , molecular structures that we saw above. Although the forces holding the atoms together in diamond there are no intermolecular forces it has a giant structure, there are each layer are very strong, the attractions between the layers are much weaker Actually, the reason that the layers slide no molecules.
Covalent bonds, which are very strong, must be broken in order and not much energy is needed to overcome them. Layers slide over each over each other fairly easily is more to melt or boil it. In general, all substances with giant covalent structures are solids with high not a lubricant in a vacuum. Graphite Graphite mixed with clay to make it harder is used in pencils.
When you write being a lubricant relies on water with a pencil, you are leaving a trail of graphite layers behind on the paper. Other substances does not happen in a vacuum. Graphite has high melting and boiling points. Again, a lot of energy has to be supplied to break the including the covalent bonds.
That needs very large amounts of energy strong covalent bonds in the giant structure. Drill bits can be tipped with because the covalent bonds are so strong. Graphite conducts electricity. If you look back at Figure 8. All t he electrons in the outer shells of the each carbon atom is joined to only three others. Each carbon atom uses three carbon atoms are tightly held in covalent bonds between the atoms.
None are of its outer shell electrons to form three single covalent bonds. The fourth free to move around. The movement of these delocalised Diamond doesn't dissolve in water or in any other solvent.
This is again because of the electrons allows graphite to conduct electricity. If the diamond dissolved, these bonds would have to be broken. As one end of the Some other properties of graphite are: crystal is heated the atoms vibrate more.
The strong bonds throughout the giant. The distance between the graphite layers is more than twice the distance GRAPHITE Graphite is also a form of carbon, but the atoms are arranged differently, between atoms in each layer. In a sense, a graphite crystal contains a lot of wasted although it still has a giant structure.
Graphite has a layer structure, rather space, which isn't there in a diamond crystal. In a pack of cards, each card is strong but the individual cards are easily separated. The same is true in graphite. Allotropes are different forms of the same element. Another allotrope of carbon is C00 fullerene. Diamond and graph ite both have giant structures but C 00 fullerene has a sim ple molecular structure. In solid or liquid C 00 fullerene there are C 00 molecules with weak inter molecular forces between them.
The fact that C 60 has a simple molecular structure has a big influence on its physical properties. C60 fullerene has lower melting and boiling points than diamond and graphite.
This does not require as much energy as breaking. Some forces of attraction between layers have been shown. These are not bonds and could have been drawn anywhere between the layers.
This is why we include the C60 in the name. It does not take as much energy to. ANALYSIS 7 The table below gives details of the boiling temperatures of some break the intermolecular forces of attraction in C 00 fullerene compared to substances made of covalent molecules.
Arrange these substances in Unlike diamond and graphite C60 breaking the strong covalent bonds in d iamond. C 00 fullerene does not conduct electricity. Although all the carbon atoms in intermolecular forces of attraction have C 00 only form three bonds, the fourth electron on each atom can only move to be broken for it to dissolve.
How does this bond hold two atoms water together? It is a liquid at room temperature. J 6 Explain the following in terms of structure and bonding: a diamond is harder than graphite b C 00 fullerene has a lower melting point than graphite c graphite conducts electricity d diamond does not conduct electricity. This holds the structure together. A Figure 9. When they come to write the symbol Metals have giant structures.
There are no individual molecules and all the for a metal such as sodium in positive ions in the lattice attract all the delocalised electrons. You write it as atoms, as Na. The metal as a whole carries no charge. Most metals are hard and have high melting points.
This suggests that the electrostatic forces of attraction between the positive ions and the delocalised electrons are strong. In the case of sodium, only one electron per atom is delocalised, leaving ions with only one positive charge on them. The bonding in sodium is quite weak, as metals go, which is why sodium is fairly soft, with a low melting point for a metal. This means that the bonding is stronger in magnesium and the melting point is higher.
Explain typical physical properties of metals, including electrical conductivity and malleability. Imagine what happens if a piece of metal is attached to an electrical power source.
Sodium is a metal. These electrons solution because the ions are free to move. Ionic substances do not. When a sodium the ions are not free to move. It is more electrons flow along important not to confuse this: this end by t he positive the wire from the negative ionic substances: ions move terminal of the power terminal of the power source and then flow source to replace those metals: electrons move away along t he wire moving away in the metal.
This does not affect the bonding in the. This means that they can be drawn out into wires. The explanation is the same as why they are malleable. State the electronic configuration of a magnesium atom and use it to explain what this phrase means. Sodium, magnesium and aluminium are three consecutive elements in the Periodic Table.
Explain these values in terms of the electronic configurations of the elements and metallic bonding. In these chapters you have met the following types of structure and bonding: giant metallic structure giant covalent structure giant ionic structure covalent molecular structure Some information about some substances is given below.
In each case state what type of structure and bonding it has. It doesn't conduct electricity even when it is molten. It is insoluble in water. It doesn't conduct electricity and it is insoluble in water.
Before we continue, we need to remind ourselves about why things do or don't It dissolves freely in water to give an orange solution. In order for things to conduct electricity, there must be e Substance Eis a pink-brown flexible solid.
It conducts electricity. The charged particles will be either electrons or ions; it is important that you are clear which one you are talking about. It is used in overhead power cables. Metals conduct electricity because the delocalised electrons are free to move. They do, however, conduct electricity when they are molten have melted or if they are dissolved in water in aqueous solution. This happens because the ions then become free to move around.
The power supply can be a 6 volt battery or a power pack. It doesn't matter which. Figure Then: methane CH4 and carbon dioxide CO,. These do not conduct electricity in any state or in solution. Ammonia solution conducts electricity because there are ions which are free to move. The solid consists of a giant structure Hydrogen chloride gas dissolves in water to form hydrochloric acid HCl aq. Hydrogen chloride ionises in water: The ions are locked tightly in the lattice and aren't free to move.
The solid HCl aq As soon as the solid melts, the. This electrode means that there are extra electrons at the right-hand electrode, so it is negative. When metals conduct electricity you will not notice anything happening, except perhaps that the metal gets hotter.
The positive lead II ions in the molten lead II bromide are an ionic compound, either molten or in solution, a chemical reaction occurs. When they get there, each Electrolysis is a chemical change caused by passing an electric current through a compound which is either molten or in solution. These fall to the bottom of the container as molten lead. This can be represented by a half-equation. Electrolytes all contain ions. The movement of the ions is responsible for both the The power source pumps new electrons along the wire to replace the electrons conduction of electricity and the chemical changes that take place.
The electricity is passed into and out of the electrolyte through two Bromide ions are attracted to the positive electrode, the anode Figure Carbon is frequently used for electrodes because it conducts When they get to the positive electrode, the extra electron which makes the electricity and is chemically fairly inert this means that it does not react with bromide ion negatively charged moves onto the electrode.
Platinum is also fairly inert and can be used instead of carbon. Various electrode is short of electrons. Half-equations show either oxidation HINT other metals are sometimes used as well. The loss of the extra electron converts each bromide ion into a bromine atom: Remember PANiC : positive anode, The positive electrode is called the anode.
The negative electrode is called the Electrons are shown as e- in half- Br Br atom to form a covalent bond. Sodium ions are reduced to sodium atoms. Chloride ions are oxidised to chlorine molecules.
KEY POINT These half-equations must always balance in terms of the number of atoms on each side, but also in terms of the charges; the total charge must be the same It is really important to use the correct on both sides.
This is why we need 2 electrons in the second half-equation but terms when talking about the reactions positive electrode only 1 in the first. Bromide ions are electrons transfer attracted to the anode, where they lose from the bromide Let us look at another example, the electrolysis of molten aluminium oxide electrons to form bromine molecules. We get aluminium at the cathode and oxygen at the anode. Aluminium Do not confuse bromide and bromine.
You may remember from Chapter 7 that this means that The new electrons on the electrode flow back into the power source. This happens either by giving pack, the bulb and the electrodes.
You will learn more about oxidation and reduction reactions in Chapter Oxidation and reduction are words used to describe what is happening to things When we electrolyse molten aluminium oxide, the half-equation for the reaction in certain chemical reactions.
This is an oxidation reaction. Oxidation If we look again at the electrode equations in the electrolysis of lead II equation. Check the charges to make Is sure you have the same total charge When molten zinc II chloride is electrolysed, zinc is obtained at the cathode bromide, we see that the lead II ions gain electrons at the cathode: Loss of electrons on both sides.
Zn reduction Gain of electrons is reduction. The lead II ions are reduced to lead atoms. Gain of electrons anode: 2c Loss of electrons is oxidation. In the reactions going on at the electrodes anode. You can probably see now t hat positive ions are known as cations because reduction, and so we call these half-equations.
Both these reactions involve they are attracted to the cathode negative electrode. Negative ions are known ions and so, in the exam, you may be asked to write ionic half-equations as anions because they are attracted to the anode positive electrode. Not all ionic compounds can be electrolysed when they are molten. Some break up into simpler substances before their melting point.
It is impossible to melt it. When you electrolyse sodium chloride solution you do not get the same products as when you electrolyse molten sodium chloride. The hydrogen at the cathode comes from the water. It ionises very slightly to give hydrogen ions Safety Note: Wear eye protection.
Once chlorine is detected We can investigate the electrolysis of an aqueous solution such as the current must be switched off. Whenever you have water present, you have to consider these ions as well as water again. However, sodium is a very reactive metal. Hydrogen is less reactive than sodium so The more reactive something is, the it is easier to add an electron to a hydrogen ion to form a hydrogen atom. The reactivity series is discussed in Each time a water molecule ionises, it also produces a hydroxide ion.
There is a build-up of these in the solution around the cathode. These hydroxide ions battery Chapter The glass tube, rubber bung and electrodes together are sometimes called an electrolytic cell. We can see if something is happening by looking for bubbles of gas or a There is an alternative way of looking at this cathode reaction, starting from KEY POINT metal forming at the electrodes.
Any gases can be tested. HINT from the cathode: volume of hydrogen as chlorine. When the However, in reality we appear to obtain less chlorine than expected because it I? Either should be You can see more easily why the solution becomes alkaline using this half- L athode and chlorine forms at the positive electrode anode.
There are, however, many, many If the sodium chloride solution is dilute, more chloride ions present in the solution, and so it is mainly these that are In this case, the only positive ions arriving at the cathode are hydrogen ions you get noticeable amounts of oxygen oxidised at the anode: from the acid and the water. These are discharged to give hydrogen gas: produced as well as chlorine.
This comes from the hydroxide ions: 2c1- aq For every 4 electrons that flow around the circuit, you would get 1 solution remaining at the end will be. The ions in the solution were: molecule of oxygen. But 4 electrons would produce 2 molecules of hydrogen. You get twice the number of molecules of hydrogen as of oxygen. What we sometimes do to stop this happening is to carry out the electrolysis experiment for a few minutes first in order to saturate the water with oxygen and then start to collect the gases; this gives much better results.
Copper is below hydrogen in the reactivity series, which means that it gases produced. Cu s reduction This experiment could be used sulfate Sulfate ions and hydroxide ions from the water w ill be attracted to the anode. Instead, you get oxygen from the oxidation water is H You may come across either half-equation in the exam.
What is left in the solution? The ions originally present were: reactive metal such as zinc, for bromine or iodine at the anode. Reasonably concentrated With other common negative ions copper. In between, you will get obtain oxygen at the anode.
If you use Copper ions and hydroxide ions are d ischarged at the electrodes. How can I download Pearson chemistry book. I need this book. But I cannot download. Please help me. Save my name, email, and website in this browser for the next time I comment. Privacy Policy About us Contact us.
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