Element of LifeAtomic Structure Relative MassRelative Charge

Proton1+1

Neutron10

Electron0-1

Rutherford discovered the layout of the atom by firing alpha-particles at gold leaf particles. The number of protons is a key number, it identifies every element. It is called the atomic number. Number of Protons + Number of Neutrons = Mass. Number of Protons = Number of Electrons. Relative Atomic Mass (Ar) = Average mass of an atom compared to1/12the mass of an atom of Carbon. Number of neutrons in an element can vary, which is why we have isotopes, for example there is chlorine-35 and chlorine-37. Chlorine 37 has an atomic mass of 37, and chlorine 35 has a mass of 35. The Relative Atomic mass of chlorine is said to be 35.5, because this is an average of the isotopes. 75% of chlorine atoms are Cl-35, and the other 25% are Cl-37

Working out the number of protons and neutrons examples:

ProtonsNeutronsElectrons

79Br354435

81Br354635

35Cl171817

37Cl172017

Bromine has two isotopes. 50% of bromine is79Br, and the other 50% is81Br. Work out the average mass:

Balancing equations- Key Steps!1. List out the different atoms in the formula.2. Count the number of atoms on the left hand side, then on the right hand side.3. Note which atoms are not balanced.4. Select on atom to balance (it is usually the one that is an odd number).You can only balance by putting numbers in front of the elements!5. Update the atom count.6. If it is still unbalanced, you may need to try balancing the elements again.Groups one and two- The Alkali Metals

Weak bonds between atoms (reason for it being soft and easy to cut. Never found native in nature. Much of the ground beneath us is made out of elements from the s-block, for example magnesium and calcium. There are similarities between the groups because of their electron configuration, but differences are because of their different masses. React vigorously with water to form a metal hydroxide and hydrogen.

Metal + WaterMetal Hydroxide + HydrogenM(s)+ H2OM(OH)2+ H2Remember Squeeky pop!!

React with oxygen to form Metal Oxide. The strongest hydroxides and oxides are those closest to the bottom of the group. The elements towards the bottom of the group are more reactive, because the one outer electron is further away from the positive nucleus, so the force needed to take the electron away is comparatively less than the elements toward the top of the group. The hydroxides and oxides form alkaline solutions in water. The hydroxides and oxides can be neutralized with acid to form salts.

MO(s)+ 2HCl(aq)MCl2(s)+ H2O(l)M(OH)2(s)+ H2SO4(aq)MSO4(s)+ 2H2O(l)

The neutralizing effect used to neutralize field acidity. The general formula of group 2 carbonates is

MCO3MO(s)+ CO2

When you heat the carbonates they decompose to form the metal oxide, and carbon dioxide. The carbonates become harder to decompose as you go down the group. The thermal stability of the elements increases as you go down the groups. The solubility of the elements in hydroxides (OH-) increases as you go down the group. This is common where the negative ion has a single charge (1-) The solubility of the elements in carbonates (CO32-) decreases as you go down the group. This is common where the negative ion has a double charge (2-).

Ionisation of PotassiumNotice that as the electrons are ionised from the outside inwards, the energy required increases, this is due to the electrons being closer to the nucleus (positive charge) for each successive energy level. Every time an electron is pulled off, the charge on all the other electrons is not shielded as much.

The Periodic Table of The ElementsElements in the same block show similar behaviours. For example, all the non-metals are in the p-Block and all the reactive metals are within the s-Block. The elements in the same group show more specific similarities, for example group two contain similar properties, as was investigated previously. Horizontal rows are called periods. There are few similarities in the elements across the periods. However there are trends that are common to each period. Elements change from metallic to non-metallic across a period, and become more metallic, or more non-metallic down a group.Physical properties of the periodic table The arrangement of the periodic table is in order of atomic number.

As you move along the table, the atomic radius of the elements decrease; this is because the electron shells are within the same energy level, but there re more protons as you move along the group, so the pull on the electrons is stronger, making the radius decrease. There is a periodic trend in the first ionisation energy required. The energy increases up to group eight, due to the extra protons for the same period, it then decreases as you go back to group one, because there is one extra energy level, meaning the electrons are further away from the proton, and there is more shielding of the positive charge of the nuclues. Below is the graph showing the melting point across the periods within the periodic table.Notice the peaks which correspond to the group 4 elements.This is called a periodic trend.

Periodicity GraphsThe atomic size decreases as you go across the periods. This is due to the increase in the number of protons; as the number of protons increases, the pull on the energy levels increase, so the atomic size decreases.

The first ionisation of the elements increases as you go along a period, as there are more protons acting on the energy level. It then decreases as you move onto the next period, due to the extra energy level.

The melting and boiling points increase along the period in the transition metals (due to their metallic structure) and then decrease in the gases.

Relationships between the position of an element in the periodic table and its electron structure The group in which the element is found is how many electrons are in the outer energy level. For example group one elements have one outer electron, and group seven elements have seven outer electrons. As you move along the period, the atomic number increases, therefore the number of protons and electrons increases. This means that as you move from left to right along a period an electron is added to the outer energy level. All elements within the same period have the same number of energy levels.

Ionisation Energy

The above graph shows the ionisation energies of sodium. Notice that where the jumps in the graph occur is where electrons are being taken from the next energy level. The equations for the ionisation of the electrons for sodium are:

After each successful ionisation, the following one becomes harder, this is because there is less shielding of the protons positive charge, and when electrons are being taken from the second shell, they are closer to the proton charge. The general equation for ionisation energies is:

After each ionisation, a 1+ charge is added to the ion, and there is an extra electron added to the equation.

Mass SpectrometerThe abundance of isotopes are determined using a Mass Spectrometer.

The Process1. Atoms vaporised, and sent into spectrometer.2. Heated tungsten wire produces electrons, which knock electrons from the sample, providing ions with a positive charge.3. Particles are accelerated using an electric field.4. A Magnetic field is placed 90oto the tube, the particles move; they are deflected.5. The larger particles are deflected least, and the lighter particles most.6. The number of ions hitting the detector is measured, and the magnetic field is changed so that the different isotopes can hit the detector. This gives an abundance of each separate isotope.The results The mass spectrometer is used to measure the abundances of the isotopes of an element. The results are in the form of a line graph, with the mass/charge on the x-axis, and the abundance up the y-axis.

The Graph shows the abundance of35Cl within the gas was 75%, and37Cl was 25%.

Light, Spectra and Electrons Most of our knowledge of the atomic structure has come from the area of science known as spectroscopy- the study of how light and matter interact. Chemists use two theories to describe light. The wave theory and the particle theory. Both can be used, depending on which property of light is being referred to. That is, the method which best describes the situation is chosen.

Wavelength is the measure of distance travelled by the wave in one cycle. The frequency is how many cycles the wave goes through every second. Wave a has a longer wavelength than b, but because they both travel at the speed of light; the frequency of b is twice that of a. This can be summarised as:

So if the wavelength is halved the frequency is doubled, and vice-versa.

The particle theory of light In some situations, light can be best described using the particle theory. The theory was proposed by Albert Einstein in 1905, and it regards light as a stream of energy called photons. The energy of the photons, determines whereabouts the light is in the electromagnetic spectrum. Both the wave theory and the particle theory are linked by a formula:

The energy contained in the photon is equal to the frequency of the radiation multiplied by Plancks constant 6.63x10-34JHz-1. For a photon of infrared ray with energy of 6x10-20J, the frequency could be worked out by dividing the energy by Plancks constant. So 6x10-20/6.63x10-34JHz-1= 9x1013Hz.Energy levels If an atom is given energy, ionisation can take place; this is where the atom loses an electron. If there is not enough energy to ionise the atom, there may be enough to shift the electrons up an energy level. This is called promotion. A promotion to another energy level requires a specific energy. When the electrons move back down a level (demotion) they emit this specific energy as light. The ionisation energy, and the promotion energy required can be worked out by the light that is emitted (the energy can be worked out by multiplying the frequency of light by Plancks constant).Spectroscopy When atoms are given energy, their electrons jump up levels. The energy that is needed to cause the electrons to jump energy levels is specific. The atoms are excited, meaning they gain energy. After the atom electrons have been promoted, they get demoted again, that is they move back down the energy levels. When being demoted, the atoms emit the specific amounts of energy. This energy is in the form of light. When the light is viewed through a spectroscope, the light emitted is split up into an emission spectrum. The spectrum consists of a series of lines; the colour of these lines is specific to the wavelength. The frequency is related to the energy:

E=hv So, we can determine the energy that the electron emits during the demotion. Elements can be identified by their light emissions. An absorption spectrum is when the light absorbed is analysed, and an emission spectrum is when the light produced is analysed.

Bohrs theory of the Hydrogen Atom Bohrs theory uses the idea of quantisation of energy. The main points of Bohrs theory were: The electron in the H atom is only allowed to exist in certain definitive energy levels. A photon of light is emitted or absorbed when an electron changes from one energy level to another. The energy of the photon is equal to the difference between the two energy levels. The frequency of the emitted or absorbed light is related to the energy energy by: E=hv. The uv emission spectrum of hydrogen can be related to the Lyman series. As the separate electrons demote, the energies are emitted. The spectrum lines become closer together the further from the nucleus. This is because the energy levels are closer together further from the n energy levels they are.

When different elements are placed in a Bunsen burner flame, the flame becomes a different colour due to the specific energy level transitions. This is the same principle in the neon lights; the electricity causes the elements to give out certain light colours.

The Different series of Spectrograms Electrons that have been demoted from a high energy level to n=1 will emit more energy than one that has been demoted to n=2. The light energy emitted by electrons moving to the n=1 is within the ultraviolet part of the spectrum, as it contains more energy, The ultraviolet emission is studied using the Lyman series. The electrons being demoted to n=2 produce visible light, that is studied using the Balmer series. The energy levels after this are within the infrared spectrum and are studied using the Paschen and Bracket series. Where all the lines on the spectrograph become one is where ionisation has taken place, and the electron is no longer restricted to specific energy values. The frequency at where the lines converged can be used to determine the ionisation energy, using E=hv.

Nuclear Fusion Fusion is an important type of reaction in which light nuclei are fused together to form heavier nuclei. High amounts of energy (millions of degrees Celsius) are required to overcome the positive charges on the two nuclei. Fusion is common within the stars, where heat energy is abundant.Examples of Fusion reactions within the sun:

The atomic numbers and mass numbers must balance within a nuclear reaction. When the universe was born, there was a lot of hydrogen. The hydrogen and dust are attracted to each other by gravity, forming huge areas of dust and gas called nebulas. The pressure in these nebulas causes extremely high temperatures. The high temperature allows the hydrogen nuclei to fuse with each forming helium. The nuclear fusion occurs fastest in the larger stars, as the temperature is greater. Most of the energy within stars is from the fusion of hydrogen to form helium; however there are other fusion reactions to form heavier elements. Small stars only convert hydrogen into helium. Medium sized stars like our sun (when hydrogen is depleted) convert helium into oxygen and carbon. Heavyweight stars convert helium into carbon and oxygen, followed by the fusion of carbon and oxygen into neon, sodium, magnesium, sulphur and silicon. Later reactions then convert these elements into calcium, iron, nickel, chromium, copper and others. In a heavyweight star; layers of elements are formed, with the denser elements closer to the centre. The element at the centre of the star is iron; this is because when iron nuclei fuse they dont produce energy, but absorb energy. Eventually the centre of the star becomes unstable, and causes the star to explode. These explosions are called supernovae, the most violent events in the universe. After the explosions, the dust and gas is attracted together and the process of the star begins again.Ionising Particles1. Some isotopes of elements are unstable. They break down spontaneously to produce ionising radiation and are described as radioactive.2. Some isotopes give off radiation very quickly, for others the process takes thousands of years.3. There are three different kinds of radiation alpha, beta and gamma.4. All three types of radiation are capable of ionising atoms, so we refer to them as ionising radiation.

RadiationType of RadiationMass (AMU)ChargeShielding material

AlphaParticle4+2Paper, skin, clothes

BetaParticle1/1836-1Plastic, glass, light metals

GammaElectromagnetic Wave00Dense metal, concrete, Earth

The atoms all want to be within the stable isotopes area, which is near to where n/p=1 for small particles and n/p=1.5 for larger ones. Radiation occurs in the isotopes to allow them to get into the stable area.

Nuclear Equations1. Nuclear equations are used to summarise the processes which produce alpha and beta particles. They include the mass number, the atomic number, the charge and the chemical symbol for each particle involved.

Alpha Decay1. Alpha decay is most common in elements with a mass number that is larger than 83, The isotope produced from alpha decay will have a mass number four units lower and a nuclear charge that is 2 units lower.

23892U23490Th+42He

Beta Decay1. During beta decay, the mass number remains constant, but the proton number increases by one unit, because a neutron is converted into a proton and an electron.

146C147N +0-1eGamma Decay1. Gamma decay is the emission of energy from the nucleus which is changing from a high energy level to a lower one. Gamma rays are a high frequency radiation.

Half-lives1. Unstable isotopes never stop emitting radiation.2. Each different isotope decays at a different rate, and is not affected by temperature or pressure.3. Radioactive decay depends on how much material there is; the amount of radiation is proportional to the mass of the element.4. The half-life is unique to every isotope, and it is the amount of time it takes for half of the element to be decayed. The half life is always the same.

Chemical BondingIonic Bonding Most metal atoms have three or fewer outer electrons. A noble gas configuration is reached if these are lost to form positively charged ions (cations).

Most non-metal atoms have more than three outer shell electrons. To become stable, they must become negatively charged ions (anions).

There are limits to how many electrons an atom can pick up. If one electron is gained, the atom becomes an anion with a negative charge. This will repel any more electrons wanting to join the energy level, and so atoms gaining two or three electrons are rare.

It is also hard to remove three or more electrons from an atom, as the ionisation energy increases after each electron is removed.

When metals bond with non-metals, electrons are transferred from the metal atoms to the non-metal atoms. The metal atoms become cations with a positive charge, and the non metals become anions with a negative charge. Opposites attract, and the atoms are held together by an electrostatic attraction.

Electron dot cross diagrams are used to represent the way the atoms bond together.Example:

Each sodium atom loses one electron and each chlorine atom gains an electron. The formula for sodium chloride is NaCl, however this doesn't mean that sodium and chlorine are only found in pairs; they are found in lattices.

The electrostatic force is spread evenly around each sodium cation and chlorine anion. A sodium cation will therefore be able to attract chlorine anions in all directions, and vice-versa.

The chloride cation can attract six sodium anions, therefore the structure formed is a lattice.

Any sodium ion within the structure will be surrounded by 6 chloride ions. It will be repelled by the other sodium ions, and so the layers will form with alternating sodium and chloride ions.Covalent bonding Non-metallic elements bond with each other by sharing electrons. This is called covalent bonding. Shared electrons count as the outer electron for both elements.

In this case the Hydrogen is found in pairs, as there are no charges involved in holding the atoms together, so there is no interaction with the other hydrogen atoms.

Electron pairs which form covalent bonds are called bonding pairs.

Electrons not involved are called lone pairs.

When one pair of electrons form a covalent bond, it is called a single covalent bond.

When two pairs of electrons form a covalent bond, it is called a double bond, for example when carbon dioxide is formed.

When three pairs of electrons form the bond, it is called a triple covalent bond.

Two of the bonds in the COare formed by atoms contributing an electron to the shared pair. In the third bond, both of the electrons come from oxygen, this is called a dative bond.Polar and non-polar bonds The atoms in a covalent bond are held together by the nuclei which are exerting a pull on the shared pair of electrons, which are located between the two atoms.

When both atoms that have bonded are the same, the pull on the electrons is the same, so the electron pair is exactly in between the two of the atoms. These are known as non-polar bonds.

Different atoms can attract the electrons unequally, so the electron pair will be closer to one atom than the other.

The atom with the greatest proton pull will have the electrons closer to it. The amount of protons and the distance from the proton will affect the force of attraction. These sort of bonds are called polar bonds.

The electron pulling power of an atom is known as its electronegativity. Atoms with strong forces of attraction for the shared pair of electrons are said to have a high electronegativity.

The lower down the group you go; the less the electronegativity is, and the further along the period you go; the higher the electronegatvity the atom has. The electronegativity trend is the same as the first ionisation energy.

We can use the difference in electronegativity values to predict how polar a covalent bond will be. In a Carbon-Fluorine bond; fluorine has a electronegativity of 4, and carbon has an electronegativity of 2.6, so the pair of electrons will be closer to the fluorine atom.

This can be written as:Cd+-- Fd- The fluorine has got a slightly negative charge, as the electrons are closer, and carbon has a slightly positive charge, as the electrons are further away.

If the electronegativity is high enough, the electron will be taken fully by the element with the highest electronegativity resulting in ionic bonding.Metallic Bonding

The strong forces which act between the separate atoms within a metal are known as metallic bonds.

The diagram below explains why metals act as they do:

The positive ions are arranged in a regular spaced lattice shape. The outer shell electrons move freely through this lattice. The free electrons are often described as a cloud or sea of electrons.

Each positively charged ion is attracted to the sea of negative electrons.

The electrostatic attraction binds the entire structure together as one unit.

In the model above, a particular electron does not belong to one of the positive ions, but is attracted to all of them. These electrons are described as delocalised.

The strength of the metallic bonding depeneds upon the number of electrons. Therefore magnesium (two outer electrons) has stronger metallic bonding than sodium (one outer electron).

This strong electrostatic attraction is why metals have high boiling/melting points, and are dense strong materials.

They are good conductors of electricity due to the delocalised electrons that are mobile.hapes of Molecules Dot and cross diagrams can be used to describe the layout of molecules. However it has its limitations as it only shows the two dimensional layout of the atoms, and not the three dimensional shape. All electrons have a negative charge; like charges repel, so the electrons are arranged so that they are as far away as possible from each other. This is what determines the shape of molecules. It is not only the shared electrons that affect the shape of the molecule, but the lone pairs also affect the shape, in fact they have a greater effect as their negative charge is stronger than that of the shared electrons. Balloons can be used to represent the layout of different molecules:

The various shapes of the molecules are as follows: Triangular Planar. Tetrahedral. V-shaped. Linear. Pyramidal.Triangular Planar Boron tri-fluoride (BH3) has a dot and cross diagram as below:

The bonding electron pairs around the central Boron atom have the same repulsion, and so an equilateral triangle is formed around the central Boron molecule. This means that the angle between the fluorine molecules is 120o.Tetrahedral Methane (CH4) has a dot and cross diagram as below:

The four bonding electron pairs around the central carbon atom in this molecule have the same negative repulsion, and so they are formed so that they are as far apart as possible. The angle found between the molecules in 109.5o.V-shaped Water (H2O) has a dot and cross diagram as below:

In this molecule around the central oxygen atom, the shared pair of electrons repel each other, but the two lone electrons also repel the two shared pairs and so a v-shape is formed, with an angle of 104.4oin between the atoms.Linear Beryllium chloride (BeCl2) has a dot and cross diagram as below:

As there are only two bonding pairs of electrons, they are found directly opposite each other.Pyramidal Ammonia (NH3) has a dot and cross diagram as below:

The lone pair of electrons around the central Nitrogen atom repel the three bonding electron pairs forming a pyramid shape, with an angle of 107obetween each atom.