Atomic structure and periodic table

• 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.
• Into what two groups can elements be classified based on their properties?

  Elements can be classified into metals and non-metals.
• What are the new substances called that are formed when elements combine through chemical reactions?

  They are called compounds.
• What is a compound?

  A compound is two or more elements combined chemically in fixed proportions which can be represented by formulae.
• Do compounds have the same properties as their constituent elements?

  No, they have different properties.
• What is a mixture?

  A mixture consists of two or more elements or compounds not chemically combined together.
• Does a mixture have the same chemical properties as its constituent materials?

  Yes, it does have the same chemical properties.
• What are the five methods through which mixtures can be separated?

  Filtration, crystallisation, simple distillation, fractional distillation, and chromatography.
• Do the methods of separating mixtures involve chemical reactions?

  No, 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.
• What does the thermometer read during simple distillation?

  The thermometer will read the boiling point of the pure liquid.
• How does simple distillation differ from evaporation?

  In simple distillation, we get to keep the liquid, while evaporation only removes the solvent.
• Describe and explain evaporation.

  Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent.
• What is crystallisation?

  Crystallisation is similar to evaporation, but we only remove some of the solvent to form a saturated solution.
• What happens when we cool down a saturated solution during crystallisation?

  The solid starts to crystallise as it becomes less soluble at lower temperatures.
• How are crystals collected after crystallisation?

  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 with different boiling points.
• What is the role of the fractionating column in fractional distillation?

  The fractionating column helps to separate the compounds by allowing repeated condensation and vaporisation.
• How does the temperature gradient in the fractionating column affect the separation of liquids?

  The column is hot at the bottom and cold at the top, allowing liquids to condense at different heights.
• Describe and explain filtration.

  Filtration is used to separate an insoluble solid suspended in a liquid.
• What is the residue in filtration?

  The residue is the insoluble solid that gets caught in the filter paper.
• What is the filtrate in filtration?

  The filtrate is the substance that comes through the filter paper.
• Describe and explain chromatography.

  Chromatography is used to separate a mixture of substances dissolved in a solvent.
• How does paper chromatography work?

  In paper chromatography, a piece of paper with a spot containing a mixture is placed in a beaker with some solvent.
• What happens to the solvent level in paper chromatography?

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

  A separatory funnel is an apparatus for separating immiscible liquids.
• How do immiscible liquids behave in a separating funnel?

  Two immiscible liquids of different densities will form two distinct layers in the separatory funnel.
• Describe the plum-pudding model of the atom.

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

  The nuclear model suggests that electrons orbit the nucleus at specific distances (shells).
• How did the Bohr/nuclear model come about?

  It came about from the alpha scattering experiments.
• What are the smaller positive particles discovered in the nucleus called?

  They are called protons.
• What did the work of James Chadwick provide evidence for?

  It provided 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.
• What are the relative masses and charges of the proton, neutron, and electron?

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

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

  The radius of an atom is 0.1 nm.
• What is the radius of a nucleus compared to that of an atom?

  The radius of a nucleus is $1 \times 10^{-14} \text{ m}$ and is approximately 1/10000 of the radius of an atom.
• What name is given to the number of protons in the nucleus?

  The name given to the number of protons in the nucleus is atomic number.