Topic C1 - Atomic Structure and the Periodic Table

Topic C1 - Atomic Structure and the Periodic Table

1. Electronic Structure

   • The first shell always has 2 electrons and the rest have 8. In most atoms, the outer shell is not full and this makes the atom want to react to fill it.

2. Atoms

   • Contain protons, neutrons and electrons. They have a radius of about 0.1 nanometers. The nucleus is the middle of the atom and contains the protons and neutrons, it has a postive charge. The electrons move around hte nucleus in electron shells, they are negatively charged and have virtually no mass.The number of protons equals the number of electrons. The Atomic number is the bottom number and tells you how many protons there are. The mass number is the top number and tells you the total number of protons and neutrons.

3. Elements

   • Elements consist of atoms with the same atomic number. Isoptopes are the same except for extra neutrons, they have the same atomc number but different mass numbers. The realtive atomic mass of a number = the sum of (isotope amount x isotope mass number) DIVIDE the sum of amounts of all the isoptopes.

4. Compounds

   • Atoms join together to make compounds and are held toegther by chemical bonds. A metal which is formed from a metal and non-metal consists of ions. The metal atoms lose electrons to form +ve ions and the non-metal atoms gain electrons to form -ve ions. The oppsite charges means they're strongly attracted to each other, this is called ionic bonding. A compound formed from non-metals consists of molecules. Each atom sahres an electron with another atom- this is called covalent bonding. The properties of a compouns are usually totally differnet from the properties of the original elements. A formula shows what atoms are in a compound.

5. Chemical Equations

   • Chemical changes are shown using chemical equations. For example word equations. Symbol equations show the atoms on both sides and need to be balanced.

6. Mixtures and Chromatography

   • Mixtures are easily seperated because they are'nt like compounds. There is no chemical bond and the parts of the mixture can either be elements or compounds. The properties of a mixture are just a mixture of the properties of the seperate parts.
     • PRACTICAL - Paper Chromatography: 1. Draw pencil line near bottom of filter paper (pencil marks are insoluble) 2. Add a spot of ink to line and place sheet in beaker of solvent e.g. water 3. Solvent used depends on what's being tested, some compounds deissolve well in water, but sometimmes other solvemts are needed. 4. Make sure ink isn't touching solvent 5. Place lid on top of container to stop solvent evaporating. 6. solvent seeps up the apper, carrying ink with it. 7. Each dye will move up paper at a differnet rate so dyes will seperate out. Each dye will form a spot in different place. 8. If any dyes are insoluble in the solvenet you've used , they'll stay on the baseline. 9. When the solvent has nearly reached top of paper, take paper out and leave to dry. 10. The end result is a pattern of spots called a chromatogram.
   • Group 0 Elements
     • They are all inert, colourless gases. All have full outer shells. They exist as monatomic gases and are non-flammable. Thier outer shell is energertically stable.

7. More Seperation Techniques

   • PRACTICAL - filtration seperates insoluble solids from liquids, filter paper into a cone shape. There are two ways to sepreate soluble solids from solutions which are evaporation and crystallisation.

8. Distillation

   • Simple distillation is used to seperate out solutions. PRACTICAL - solution is heated, the part of the soltion that has the lowest boiling point evaporates first. The vapour is then cooled , condenses and is collected. The rest of the solution is left behind in the flask. The problem is is that it can only be used for things with very different boiling points. Fractional distillation is used to seperate a mixture of liquids. You put your mixture in a flask and stick a fractionating column on top . Then you heat it. The different liquids will all have different boiling points, so evaporate at different temperatures. The liquids with hte lowest boiling points might also start to evaporate. But the colum is cooler towards to top. So they will only get part of the way up before condensing and running back down towards the flask. When the first liquid has been collected, you raise the temperature until the next one reaches the top.

9. The History of the Atom

   • At the start of the 19th century John Dalton described atoms as solid spheres. In 1897 J J Thompson concluded from his experiments that atoms weren't solid speheres, but that an atom contained even smaller -vely charged particles. So the new theory was the 'plum pudding model', it was a ball of +ve charge with electrons stuck in it. The alpha scattering experiments in 1909 by Ernest Rutherford and Ernest Marsden was where +vely charged alpha particles were fired at an extremely thin sheet of gold. From the plum pudding model they expected the particles to pass straight through the sheet or to be slightly deflected. Whilst most of the particles did go straight through the gold sheet, more were deflected than expected, and a small number were deflected backwards. Rutherford came up with the nuclear model of the atom as the plum pudding one wasn't correct.
     • Niels Bohr's nuclear model of the atom suggested that all the electrons were contained in shells. Further experiments showed the existence of protons.

10. Development of the Periodic Table

    • In the early 1800s elements were arranged by atomic mass.Early periodic tables were not complete and some element were placed in the wrong group. This is because elements were placed in the order of relative atomic mass and did not tkae into account their properties.
      • Dmitri Mendeleev lept gaps and predicted new elements, in 1869. Medeleev put the elemts mainly in order of atomic mass, but did witch that order if the properties meant it should be changed.

11. The Modern Periodic Table

    • Elements are laid out in order of increasing atomic (proton) number. Metals are found to left and non-metals to the right. Elements with simmilar properties form columns, and are called groups. The group nimber tells you how many electrons there are in the outer shell. The rows are called periods, and each period represents another full shell of electrons.
      • Most elements are metals and they are elements that canf orm +ve ions when they react. They're towards the bottom and to the left of the periodic tale. Non-metals don't generallly form +ve ions when they react. Metals to the left on the table don't have many elctrons to remove and metals towards the bottom of the table have outer electrons which are a long way from the nucleas so feel a weaker attraction. Both of these effects means that not much energy is needed to remove the elctrons so it's feasible for the elements to react to form +ve ions with full outer shells. Non-metals have lots of electrons to remove to get a full outer shell, or towards the top - where the outer elctrons are close to the nucelaus so feel a strong attraction. It's far more feasible for them to share/gain electrons.
        • All metaks have metallic bonding which causes them to have similar basic physical properties. They are strong, but can be bent or hammered into different shapes (malleable). Thye are great at conducting heat and electricity. Thye have high boiling/metling points. Non-metals do not have metallic bonding so don't tens to exhibit the smae properties as metals. Thye tend to be dull, more brittle , aren't always solids at room temp and do not generally conduct elctricity and often have a lower density.

12. Group 1 Elements

    • Reactive, soft metals, 1 electron in outer shell so very reactive, soft and have low desnity. They form ionic compounds which non-metals A reaction with water produces hydrogen gas and react vigorously. A reaction with chlorine produces a salt and group 1 metals react with oxygen.

13. Group 7 Elements

    • The halogens are all non-metals with coured vapours, Fluorine is very reactive, poisonous yellow gas. Chloribe is fairly reactive, poisonous dense green gas, bromine is a dense, poisonous, red-brown volatile liquid, iodine is dark grey crystalline solid or a purple. They all exist as molecules which are pairs of atoms . As you go down group , the halogens beome less reactive , have higher melting/ boiling points and have higher realtive atomic masses. Halogens can form molecular compounds and form ionic bonds with metals. The more reactive halogens with displace less reactive ones.