atomic structure and the periodic table

• An atom is the smallest part of an element that can exist
• An element is a substance of only one type of atom
• Elements are listed in the periodic table; there are approximately 100
• Elements can be classified into two groups based on their properties: metals and non-metals
• Elements may combine through chemical reactions to form new products called compounds
• A compound is two or more elements combined chemically in fixed proportions which can be represented by formulae
• Compounds do not have the same properties as their constituent elements
• A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties
• Methods to separate mixtures include: filtration, crystallisation, simple distillation, fractional distillation, and chromatography; they do not involve chemical reactions
• Simple distillation separates liquid from a solution by boiling off the liquid and condensing it in the condenser
• Crystallisation/evaporation separates a solid dissolved in a solvent by heating until the solvent evaporates, leaving the solid behind
• Fractional distillation separates a mixture of liquids based on their different boiling points using a fractionating column
• Filtration separates an insoluble solid suspended in a liquid by catching the solid in the filter paper
• Chromatography separates a mixture of substances dissolved in a solvent by allowing the solvent to rise on a piece of paper, separating the components
• A separating funnel is used to separate immiscible liquids based on their densities
• The plum-pudding model describes the atom as a ball of positive charge with negative electrons embedded in it
• The Bohr/nuclear model suggests electrons orbit the nucleus at specific distances and came about from alpha scattering experiments
• Protons are smaller, positive particles discovered in the nucleus through later experiments
• James Chadwick's work provided evidence for the existence of neutrons in the nucleus
• The structure of an atom includes a small central nucleus made up of protons and neutrons, surrounded by electrons
• Relative masses and charges of proton, neutron, and electron: Masses - 1, 1, very small; Charges - 1, 0, -1 (respectively)
• Atoms are electrically neutral because they have an equal number of protons and electrons
• The number of protons in the nucleus is called the atomic number
• Atoms of the same element have the same number of protons in the nucleus
• The majority of the mass of an atom is in the nucleus
• The mass number is the total number of protons and neutrons
• To calculate the number of neutrons, subtract the atomic number from the mass number
• An isotope is atoms of the same element with a different number of neutrons. Isotopes of the same element have the same chemical properties as they have the same electronic structure
• The relative atomic mass is the average mass value that considers the mass and abundance of isotopes of an element, based on a scale where the mass of 12C is 12
• Electronic configurations of He (2), Be (4), F (9), Na (11), and Ca (20) are:

  • He: 2
  • Be: 2,2
  • F: 2,7
  • Na: 2,8,1
  • Ca: 2,8,8,2
• Ions are charged particles formed when atoms lose electrons (positive ions) or gain electrons (negative ions)
• Properties of metals and non-metals:

  • Metals have high boiling/melting points, conductivity of heat and electricity, shiny appearance, malleability, high density, and form basic oxides
  • Non-metals have low boiling/melting points, don't conduct heat or electricity (except graphite), dull appearance, brittleness, low density, and form acidic oxides
• When a metal reacts with a non-metal, an ionic compound is formed
• When a non-metal reacts with a non-metal, a molecular compound containing covalently bonded atoms is formed
• Solute is a substance dissolved in a solvent to form a solution. Miscible substances mix, while immiscible substances do not. Soluble substances can dissolve in a solvent, while insoluble substances cannot
• The columns of the periodic table are called groups
• The rows of the periodic table are called periods
• Elements in the same group may have similar chemical properties as they have the same number of outer shell electrons
• Elements of the same period have the same number of energy levels
• Electrons occupy the lowest available energy level