C1 Atomic stucture/peridoic table

C1 Atomic stucture/peridoic table

1. An atom is the smallest part of an element that can exist.

   • All substances are made from tiny particles called atoms
     • Some non-metal elements exist as molecules that are made up of two atoms joined together.
   • a pure substance consists only of one element or one compound
     • a mixture consists of two or more different substances, not chemically joined together
       • Mixtures can be separated by physical processes. These processes do not involve chemical reactions, and no new substances are made.

2. ion is a charged particle formed when an atom, or a group of atoms, loses or gains electrons

3. Reactants are substances that react together in a chemical reaction. In a chemical reaction, the atoms or ions in reactants separate from one another. They join back together in a different way to form products.

4. (s) solid

   • (L) liquid
   • (G) gas
   • (aq) aqueous solution

5. The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the total mass of the products is equal to the total mass of the reactants

6. Nearly 100 years later J J Thomson carried out experiments and discovered the electron, which led him to the idea of the plum pudding model

   • In this model, the atom is a ball of positive charge with negative electrons embedded in it - like currants in a Christmas pudding.
   • John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided.

7. Gold foil expirement

   • 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil. Most alpha particles went straight through the foil. But a few were scattered in different directions.
   • evidence led Rutherford to suggest a new model for the atom, called the nuclear model
     • nucleus positivly charged
     • mostly empty space
     • protons + neutrons in nucleus
     • electrons in outer shell

8. 1932 James Chadwick found evidence for the existence of particles in the nucleus with mass but no charge. These particles are called neutrons

9. the radius of an atom is about 0.1 nm

   • the radius of a typical bacterium is 1 × 10-6 m

10. the radius of a nucleus (1 × 10-14 m)

    • the radius of a human hair is about 1 × 10-4 m.

11. Proton: Mass 1 Charge +!

    • Atomic no': number of protons
      • all atoms of a given element have the same number of protons
        • atoms of different elements have different numbers of protons
          • An atom contains equal numbers of protons and electrons. Since protons and electrons have equal and opposite charges, this means that atoms are have no overall electrical charge.

12. Neutron: Mass 1 Charge 0

13. Electron: Mass 1/2000 Charge -1

    • Mass no': number of protons + neutrons together

14. Balencing Equations

    • E.G. N2 + 3H2 → 2NH3
    • E.G. O2 +03 = O5

15. Filtration is used to separate an insoluble solid from a liquid. It is useful for separating sand from a mixture of sand and water, or excess reactant from a reaction mixture.

    • Filtration works because the filter paper has tiny holes or pores in it. These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.

16. Crystallisation is used to produce solid crystals from a solution. When the solution is warmed, some of solvent evaporates leaving crystals behind.

    • E.G. , crystallisation is used to obtain copper sulfate crystals from copper sulfate solution.
    • To obtain large, regularly shaped crystals from crystallisation: put the solution in an evaporating basin ,warm the solution by placing the evaporating basin over a boiling water bath ,stop heating when crystals begin to form around the edge of the basin. After the remaining solution has cooled down, pour the excess liquid away (or filter it). Dry the crystals using a warm oven or by patting them with filter paper.

17. Simple distillation is used to separate a solvent from a solution. It is useful for producing pure water from seawater.

    • the dissolved solute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour leaves the solution. It moves away and is cooled and condensed. The remaining solution becomes more concentrated as the amount of solvent in it decreases.
    • Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water, and for separating different fractions from crude oil.
      • Fractional distillation works because the different liquids have different boiling points. When the mixture is heated: vapours rise through a column which is hot at the bottom, and cooler at the top, vapours condense when they reach a part of the column that is below the temperature of their boiling point, each liquid is led away from the column
      • There are two ways of obtaining different liquids from the column:
        • by collecting different liquids from different parts of the column - the substance with the lowest boiling point is collected at the top of the column
        • by continuing to heat the mixture to increase the temperatures in the column - the substance with the lowest boiling point is collected first

18. Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

    • Chromatography relies on two different ‘phases’: the stationary phase, which in paper chromatography is very uniform, absorbent paper and the mobile phase is the solvent that moves through the paper, carrying different substances with it
      • The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.
        • Separation by chromatography produces a chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances:
          • a pure substance produces one spot on the chromatogram
          • an impure substance, or mixture, produces two or more spots
          • A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if: they produce the same number of spots, and these match in colour or if the spots travel the same distance up the paper

19. Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led him to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus.

    • Further experiments led to the idea that the nucleus contained small particles, called protons. Each proton has a small amount of positive charge.

20. Atoms of the same element with different numbers of neutrons are called isotopes.

    • isotopes have the same atomic number but a different mass number than it's counterparts
      • All hydrogen atoms contain one proton (and one electron), but they can contain different numbers of neutrons. Hydrogen-1 is the most abundant (most common) isotope of hydrogen.
        • All three isotopes of hydrogen have identical chemical properties. This is because the number of electrons determines chemical properties, and all three isotopes have one electron in their atoms.
          • The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes. It takes account of the abundance of each of the isotopes of the element.
            • E.G. Hydrogen would be 1
            • relative atomic mass= total mass of atoms/total number of atoms

21. The atomic weight of an element is equivalent to what we now call its relative atomic mass

    • Early periodic tables were incomplete, since many elements were unknown. Also, some elements were placed in groups with elements that were not similar to them.
      • Dmitri Mendeleev was a Russian chemist.
        • He published his first periodic table of the elements in 1869. In it, he arranged the elements in order of increasing atomic weights. He also took into account the properties of the elements and their compounds.
          • His table had gaps in it and showed elements with similar chemical properties lined up in groups
            • However, from their atomic weights, some pairs of elements next to each other were in the wrong order.
              • Mendeleev left gaps in his table for elements not known at the time. By looking at the properties of the elements next to a gap, he could also predict the properties of these undiscovered elements. For example, Mendeleev predicted the existence of 'eka-silicon', which would fit into a gap below silicon.
              • Another scientist later discovered the missing element, germanium. Its properties were found to be similar to the predicted ones and confirmed Mendeleev's periodic table.
        • Mendeleev did not know about isotopes, but their existence explains pair reversals. The positions of iodine and tellurium were reversed in Mendeleev's table because: iodine has one naturally occurring isotope, iodine-127 and the most abundant tellurium isotopes are tellurium-128 and tellurium-130

22. Model Perdoic Table

    • elements are arranged in rows, called periods, in order of increasing atomic number
    • elements with similar properties are placed in vertical columns, called groups
    • The 1st electron shell contains a max of 2 electrons
      • The electronic structure of an element is linked to its position on the periodic table.
        • no' of shells: period number
        • no' of electrons in outermost shell: group number
        • numbers added together: atomic number
    • All other shells can have a max of 8 electrons
    • Elements in group 1 and group 2 are metals. Atoms of group 1 elements have one electron in their outer shell, and atoms of group 2 elements have two electrons in their outer shell.
      • Elements in groups 6, 7 and 0 are non-metals. Atoms of group 7 elements have seven electrons in their outer shell, and atoms of group 0 elements (the noble gases), except helium, have eight electrons in their outer shell.
      • Atoms of metal elements give away electrons in their reactions to form positive ions. The ions formed have a full outer electron shell, so are very stable.
        • Atoms of non-metal elements gain electrons in some of their reactions to form negative ions. The ions formed have a full outer electron shell, so are very stable.
    • Noble gases all have complete outer shells (except helium), low boiling points and boiling point increases going down the group
      • the atoms become larger as they go down the group
        • the intermolecular forces between the atoms become stronger
          • More energy is needed in order to break these bonds
      • they are extremely unreactive and do not take part in chemical reactions because they have no tendency to lose, gain, or share electrons.
      • The elements in group 1 are called the alkali metals.
        • there soft
        • relatively low melting points
        • relatively low densities
        • When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged ions.
          • The alkali metals react with water to produce a metal hydroxide and hydrogen
            • Sodium hydroxide is an alkali. It is a base that dissolves in water to form an alkaline solution.
              • This has a higher pH than 7
              • turns universal indicator solution blue or purple
              • the reactivity of these metals increases going down the group.
        • The group 1 elements react with oxygen from the air to make metal oxides.
          • At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.
            • The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.
              • At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions.
          • going down in group 1
            • the atoms become larger
            • the outer electron becomes further from the nucleus
            • the force of attraction between the nucleus and the outer electron decreases
            • the outer electron is lost more easily
        • group 7 are called halogens and are non-metals
          • The halogens exist as simple molecules. Each molecule is made up of a pair of halogen atoms joined by a single covalent bond.
            • In all groups of the periodic table, the further down the group an element is, the higher its relative molecular mass.
          • In group 7, the further down the group an element is, the higher its melting point and boiling point. This is because
            • the molecules become larger
            • the intermolecular forces become stronger
            • more energy is needed to overcome these forces
          • When a group 7 element takes part in a reaction, its atoms each gain one electron. These atoms form negatively charged ions.
            • The halogens react with metals to produce salts. The salts are made up of ions, which are held together by ionic bonds.
            • In group 7, the reactivity of the elements decreases down the group.
              • The halogens react with non-metals such as hydrogen. When a halogen reacts with hydrogen, the product is a compound called a hydrogen halide.
                • The hydrogen halides are gases at room temperature. They dissolve in water to produce acidic solutions. Hydrogen chloride dissolves in water to produce hydrochloric acid, HCl(aq).
              • going down the group
                • atoms larger
                • the outer shell becomes further from the nucleus
                • an outer electron is gained less easily
                • the force of attraction between the nucleus and the outer shell decreases

23. Most elements are metals. In their chemical reactions, metal atoms lose electrons to form positive ions.

    • E.G. when magnesium burns in air, each atom loses two electrons to form a Mg2+ ion
    • Elements that do not form positive ions in their chemical reaction are non-metals.
    • Metal and non-metal elements have different physical properties:
      • Metal
        • high melting and boiling points
        • good conductor of heat/electric
        • Shiny
        • high density
        • Malleable
        • ductile: able to be drawn out into a thin wire.
      • Non-Metal
        • low melting and boiling points
        • poor conductor of heat/electric
        • Dull
        • low density
        • brittle

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