C1 Atomic structure and periodic table

• Atoms

  • Atoms are the smallest unit of matter that can undergo chemical change
  • Atoms of each element are represented by a chemical symbol
• Elements

  • There are approximately a hundred different elements
  • Elements can be found in the periodic table
• Compounds formation

  1. Compounds are formed from elements by a chemical reaction

  2. Chemical reactions involve the formation of one or more substances and often involve a detectable change in energy
• Compound

  • Contains two or more elements chemically combined in fixed proportions
  • Can be represented by a formula using the symbols of the atoms from which they are formed
• Compound

  • Magnesium oxide
• Separation of compounds

  Compounds can only be separated by chemical reactions
• Chemical reactions representation

  Chemical reactions can be represented using word equations or balanced chemical equations using symbols
• Students should be able to use the names and symbols of the first 20 elements in the periodic table
• Mixtures consist of two or more elements or compounds that are not chemically combined together
• Mixtures

  • Chemical properties of each substance in the mixture are unchanged
  • Mixtures can be separated using physical processes
• Filtration

  Separates a soluble substance in a solution and an insoluble substance
• Crystallization

  Removes water from a salt solution by heating and evaporating to form crystals
• Simple distillation

  Separates substances based on differences in boiling points
• Fractional distillation

  Separates a complex mixture by boiling points, used for crude oil separation
• Distillation

  Alkanes enter the condenser, rise until they reach their boiling point, then condense. Large molecules with high boiling points are collected at the bottom, while shorter alkanes with lower boiling points are collected at the top
• Chromatography

  A process where a spot of pigment or dye is placed on filter paper, water is allowed to run up the paper carrying the pigment with it, resulting in separation of substances
• New experimental evidence has led to changes in scientific models over time
• Before the discovery of the electron, atoms were believed to be indivisible spheres
• JJ Thompson theorized atoms as plum pudding, with electrons (plums) and positive charge (pudding)
• Rutherford's alpha scattering experiment led to the discovery of the nucleus in the atom
• The nuclear model of the atom includes electrons orbiting the nucleus
• Niels Bohr suggested electrons orbit in specific energy levels around the nucleus
• The nucleus of an atom consists of protons and neutrons
• Alpha scattering experiment

  Refined the atomic model from plum pudding to nucleus with positive charge concentrated in a tiny space at the center
• Plum pudding model vs. Bohr model

  In plum pudding model, electrons are randomly scattered, while in Bohr model, they orbit in discrete energy shells
• Number of electrons in an atom is equal to the number of protons
• Atoms have no o
• Atoms

  Have discrete energy shells
• Number of electrons is equal to the number of protons in an atom
• Protons

  Have a positive one charge
• Electrons

  Have a negative one charge
• Atoms have no overall charge as they must have an equal number of protons and electrons
• The number of protons in an atom defines its element
• Atoms are incredibly small, approximately 0.1 nanometers
• The radius of the nucleus is much smaller, occupying only 1/10,000 of the size of the atom
• Protons have a mass of one relative to neutrons
• Neutrons have a mass of one relative to protons
• Electrons have a very small mass, approximately 1/1860 of a proton
• The sum of protons and neutrons in an atom is called the mass number
• Atoms of the same element can have different numbers of neutrons, known as isotopes