Topic 1

• What is an atom?

  An atom is the smallest part of an element that can exist.
• What is an element?

  An element is a substance of only one type of atom.
• How are the elements listed and approximately how many are there?

  They are listed in the periodic table; there are approximately 100.
• Elements can be classified into two groups based on their properties; what are these groups?


  Metals and non-metals
• Elements may combine through chemical reactions to form new products; what are these new substances called?

  Compounds
• What is a compound?


  Two or more elements combined chemically in fixed proportions which can be represented by formulae.
• Do compounds have the same properties as their constituents elements?

  No, they have different properties.
• What is a mixture? Does it have the same chemical properties as its constituents materials?

  A mixture consists of two or more elements or compounds not chemically combined; it does have the same chemical properties.
• What are the methods through which mixtures can be separated (5)? Do these involve chemical reactions?

  Filtration, crystallisation, simple distillation, fractional distillation and chromatography; they do not involve chemical reactions.
• Describe and explain simple distillation?

  Simple distillation is used to separate liquid from a solution - the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.
• Describe and explain crystallisation/evaporation?

  Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H2O).

  The solution is heated until all the solvent evaporates; the solids stays in the vessel.

  Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved). Then,

  we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.
• Describe and explain fractional distillation?

  Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids have different boiling points.

  The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.

  The fractionating column contains glass beads. It helps to separate the compounds. In industry, mixtures are repeatedly condensed and vapourised. The column is hot at

  the bottom and cold at the top. The liquids will condense at different heights of the

  column.
• Describe and explain filtration?

  Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.
• Describe and explain chromatography?

  Chromatography is used to separate a mixture of substances dissolved in a solvent.

  In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with

  the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
• What is a separating funnel?

  A separatory funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form two distinct layers in the separatory funnel. We can run off the bottom layer (the liquid with greater density) to a separate vessel.
• Describe the plum-pudding model?

  The atom is a ball of positive charge with negative electrons embedded in it.
• Describe the Bohr/nuclear model and how it came about?

  The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiments.
• Later experiments led to the discovery of smaller, positive particles in the nucleus; what are these particles called?

  Protons
• What did the work of James Chadwick provide evidence for?

  The existence of neutrons in the nucleus.
• Describe the structure of an atom?

  The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons.
• State the relative masses and relative charges of the proton, neutron and electron?

  Masses: 1, 1, very small ; Charges: 1, 0 , -1 (respectively)
• Explain why atoms are electrically neutral?

  They have the same number of electrons and protons.
• What is the radius of an atom?

  0.1 nm
• What is the radius of a nucleus and what is it compared to that of the atom?

  1 x 10-14 m and 1/10000
• What name is given to the number of protons in the nucleus?

  Atomic number
• Atoms of the same element have the same number of which particle in the nucleus?

  Protons
• Where is the majority of mass of an atom?

  The nucleus
• What is the mass number?

  The total number of protons and neutrons in a nucleus.
• How does one calculate the number of neutrons using mass number and atomic number?

  Subtract the atomic number from the mass number.
• What is an isotope? Do isotopes of a certain element have the same chemical properties?

  Atoms of the same element (same proton number) that have a different number of neutrons. They have the same chemical properties as they have the same electronic structure.
• What is the relative atomic mass?

  The average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where the mass of 12C is 12.
• Give the electronic configurations of He (2), Be (4), F (9), Na (11), and Ca (20) to demonstrate how shells are occupied by electrons?

  2

  2,2

  2,7

  2,8,1

  2,8,8,2
• What are ions?


  Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons. E.g. sodium positive ion, Na+ , has an electronic configuration of 2,8 (same as Ne). An atom of sodium has lost one electron.
• Compare the properties of metals and non-metals?

  -Metals have higher boiling/melting point

  -Metals can conduct heat and electricity

  -Metals are shiny, non-metals are dull

  -Metals are malleable, non-metals brittle

  -Metals have a high density, non-metals low

  -Metals form basic oxides, non-metals form acidic oxides
• What is formed when a metal reacts with a non-metal?

  An ionic compound (made of positive and negative ions).
• What is formed when a non-metal reacts with a non-metal?

  A molecular compound containing covalently bonded atoms. Atoms share electrons, as opposed to transferring electrons between each other (cf. ionic compounds).
• Explain the following: solute, solvent, solution, miscible, immiscible, soluble, insoluble?

  A solute is a substance that is dissolved in a solvent. Together, they form a solution.

  Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix.

  Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. Insoluble substance won't dissolve in a particular solvent.
• The columns of the periodic table are called...?

  Groups
• The rows of the periodic table are called...?

  Periods
• Are elements in the same group similar or different?

  They may have similar chemical properties, as they have the same number of outer shell electrons.