chemistry A*

• Matter is anything that has mass and occupies space
• There are 3 states of matter: solids, liquids, and gases
• Solids:

  • Particles are packed closely together
  • Forces between particles are strong, so particles can only vibrate
  • Solids have a stable, definite shape and volume
  • In crystalline solids, particles are packed in a regularly ordered pattern
  • Solids can change into liquids by melting and into gases by sublimation
• Liquids:

  • Nearly incompressible fluid
  • Conforms to the shape of its container
  • Retains a nearly constant volume
  • Shape is determined by its container
  • Liquids are formed when solids are heated above their melting point
• Gases:

  • Compressible fluid
  • Conforms to the shape of its container and expands to fill it
  • Molecules have enough kinetic energy for minimal forces effect
  • No definite shape or volume, occupies the entire container
  • Liquids can be converted to gases by heating to the boiling point
• The Kinetic Theory of Matter states:

  • All matter is made up of tiny moving particles
  • Particles are in continuous movement
  • Speed of movement depends on mass, temperature, and other factors
  • Kinetic energy means movement energy
• Physical changes are changes in which no new substance is formed

  • Examples include melting and dissolving
  • Physical changes are reversible
  • Changing the state of matter is a physical change done by heating or cooling
• Melting:

  • Change of state from solid to liquid
  • Temperature at which a solid melts is the melting point
• Evaporation:

  • Change of state from liquid to gas
  • Temperature at which a liquid evaporates is the boiling point
• Sublimation:

  • Some substances change directly from solid to gas
  • Occurs when heating a solid gives particles more kinetic energy to break forces of attraction
• Diffusion:

  • Random movement of liquid or gas particles to fill space evenly
  • Rate depends on mass, temperature, presence of other substances, and intermolecular spaces
• Separating Solid/Solid Mixtures:

  • By Magnet: used when one solid is magnetic
  • By Sublimation: heating to separate solids with one undergoing sublimation
  • By Solvent Extraction: used when one solid is water-soluble
• Separating Solid/Liquid Mixtures:

  • Solubility: maximum amount of solute that can dissolve in a solvent
  • Saturated Solution: very concentrated solution with maximum solute dissolved
  • Solubility increases with temperature
  • By Evaporation: heating to evaporate liquid leaving solute behind
  • By Crystallization: forming crystals by evaporating a solution
• Crystallization method for soluble solid/liquid solutions:

  • Put solution in a beaker
  • Set up the apparatus with a tripod, gauze, and Bunsen burner
  • Insert a glass rod in the beaker
  • Turn on the Bunsen burner and continuously dip the glass rod in the solution
  • When crystals of the solute start to form on the glass rod, turn off the Bunsen burner (crystallization point)
  • Leave the solution to cool
  • Filter the solution to collect the crystals (residue)
  • Wash the crystals with distilled water and dry them between filter papers
• Simple distillation method for soluble solid/liquid solutions:

  • Set up the apparatus as shown in the diagram
  • Turn on the Bunsen burner
  • The solvent evaporates and rises as vapor into the condenser
  • The cold water in the condenser makes the vapor condense into liquid
  • The solvent is collected in the tube or beaker on the other side of the condenser (distillate)
  • The solute is collected in the flask as powder
  • Use a thermometer to measure the boiling point of the solvent
• Filtration method for insoluble solid/liquid mixtures:

  • Set up the apparatus
  • Pour the mixture into the filter funnel
  • The solvent goes through and is collected in the beaker (filtrate)
  • The insoluble solid is collected from the funnel (residue)
• Decantation method for insoluble solid/liquid mixtures:

  • Let the insoluble solid settle at the bottom of the beaker
  • Pour the liquid into another beaker, leaving the solid behind
• Centrifugation method for insoluble solid/liquid mixtures:

  • Put the mixture in a test tube
  • Place the test tube in the centrifugation machine
  • Start the machine to separate the mixture into two layers: liquid at the top and solid at the bottom
  • Separate the layers by decantation
• Separating funnel method for immiscible liquids:

  • Immiscible liquids like oil and water settle in layers
  • Pour the mixture into the separating funnel
  • Let the denser liquid settle at the bottom
  • Open the tap to collect the denser liquid, then close it and collect the lighter liquid
• Fractional distillation method for miscible liquids:

  • Set up the apparatus as shown in the diagram
  • Heat the mixture
  • The liquid with the lowest boiling point condenses first
  • The glass beads provide a surface for condensation
  • Collect different liquids at different boiling points
• Chromatography:

  • Used to separate and identify substances in a mixture
  • Solubility of substances determines separation
  • Can be used to test purity of substances
  • Rf Value is calculated to identify substances
  • Different spots indicate different components in the sample
• Atomic structure:

  • Atoms consist of protons, neutrons, and electrons
  • Nucleus contains protons and neutrons, surrounded by energy shells with electrons
  • Protons have a positive charge, neutrons have no charge, electrons have a negative charge
  • Atomic number = number of protons = number of electrons
  • Mass number = protons + neutrons
  • Isotopes have different number of neutrons
  • Relative atomic mass is the average mass of isotopes compared to Carbon-12
• Periodic table:

  • Elements arranged in ascending order of atomic number
  • Groups have the same number of valence electrons
  • Periods have the same number of energy shells
  • Metals and non-metals have different properties
  • Metallic properties decrease from left to right in the table
• Malleability:

  • If a metal is malleable, it can be hammered into shapes without being broken
• Ductility:

  • If a metal is ductile, it can be pulled into wires
• Sonority:

  • If a metal is sonorous, it makes a pleasant sound when struck
• Metals have either 1, 2, or 3 valence electrons

  Non-metals have either 4, 5, 6, 7, or 8 valence electrons, except helium which has 2
• Metals lose electrons forming positive ions

  Non-metals gain electrons forming negative ions
• Metals are reducing agents

  Non-metals are oxidizing agents
• Metals form basic or amphoteric compounds

  Non-metals form acidic or neutral compounds
• Metals form ionic compounds with non-metals

  Non-metals form either ionic compounds with metals, or covalent compounds with other non-metals
• Alkali Metals (Group 1):

  • Lithium, Sodium, Potassium, Rubidium, Caesium, and Francium (radioactive)
  • Good conductors of heat and electricity
  • Soft metals, with lithium being the hardest and potassium the softest
  • Extremely reactive, need to be stored away from air or water
  • Low densities and melting points
  • React with oxygen to form metal oxides
  • React with water to form metal hydroxide and hydrogen gas
  • React with halogens to form metal halides
• Halogens (Group 7):

  • Fluorine, Chlorine, Bromine, Iodine, Astatine
  • Colored elements, color gets darker going down the group
  • Exist as diatomic molecules
  • React with hydrogen to form hydrogen halide
  • React with metals to form metal halides
  • Reactivity decreases going down the group, with chlorine being most reactive
• Transition Elements:

  • Harder and stronger than metals of groups 1 & 2
  • Higher densities and melting points
  • Less reactive than metals of groups 1 & 2
  • Excellent conductors of heat and electricity
  • Show catalytic activity
  • React slowly with oxygen and water
  • Form simple ions with several oxidation states and complicated ions with high oxidation states
• Noble Gases (Group 8):

  • Colorless gases
  • Extremely unreactive due to full outer energy shells
  • Used in various applications, e.g., argon in light bulbs and neon in advertising
• Ionic Bonding:

  • Based on electrostatic force of attraction between ions in the molecule
  • Formed between metals and non-metals
  • Formulae of ionic compounds are determined by valency
• Covalent Bonding:

  • Occurs between non-metals
  • Atoms share electrons to achieve full outer energy shells
  • Types of covalent bonds include single and double covalent bonds
• Allotropes of Carbon:

  • Diamond: 3D tetrahedral structure, very hard, doesn't conduct electricity, insoluble in water
  • Graphite: Layers of linked hexagons, soft and slippery, conducts electricity
• Metallic Structures:

  • Positive ions surrounded by a sea of delocalized electrons
  • Malleable and ductile, conducts electricity, high melting and boiling points
• Alloys:

  • Mixtures of metals or metals and non-metals
  • Harder and more resistant to corrosion than pure metals
  • Examples include brass, bronze, steel, and stainless steel