Chemistry, 3: Atoms, elements, compounds

• In chemical changes, one or more new substances are produced

  Product has different properties to reactants
• What observable changes are seen in chemical changes?

  Colour changes

  Gas is produced

  Precipitate forms

  Bubbles of gas is produced
• In chemical reaction, mass Is conserved in all chemical reactions

  Changes in mass may occur is reactant or product is a gas
• In chemical changes, reactions can be endothermic or exothermic
• Chemical changes are difficult to reverse
• Physical changes do not create new chemical substances
• Physical changes are easy to reverse and separate
• Mixtures contains more than one substance, elements or compounds
• In mixtures, substances can be easily separated as they have not combined chemically.
• What are the properties of metals?

  • High melting point
  • Good conductor of heat and electricity
  • Malleable
  • Shiny
  • Ductile
  • Sonorous
• What are the properties of non-metals?

  • Low melting point
  • Poor conductor of heat and electricity
  • Brittle
  • Dull
• Alloys are formed when metal is mixed with other element
• In some chemical reactions, it can be reversible by changing reaction conditions
• What happens when hydrated copper (II) sulfate crystals are heated?

  White power is formed, because water is lost as steam
• What happens when you add water to anhydrous copper (II) sulfate?

  Hydrated blue copper (II) sulfate is formed again
• What is the equation for the reaction of hydrated blue copper (II) suflate?

  CuSO5H2O(s) <—> CuSO4(s) + 5H2O (l)

  Hydrated blue copper (II) sulfate crystals <—> anhydrous copper (II) sulfate + water
• What happens when you add hydrated cobalt (II) chloride crystals is heated?

  Water is lost as steam, blue anhydrous cobalt (II) cobalt is formed
• What happens when you add water to blue anhydrous cobalt (II) cobalt?

  Pink power is formed again, hydrated cobalt (II) chloride
• What is the equation for the reaction hydrated cobalt (II) chloride crystals?

  CoCl26H2O(s) <—> CoCl2(s) + 6H2O(l)

  Hydrated cobalt (II) chloride <—> anhydrous cobalt (II) chloride + water
• All matters are made out of atoms
• All atoms of a given element are identical and have the same mass
• Chemical compounds are found when different atoms combine together
• Modern theory is built upon understanding that particles that make up atoms are sub-atomic particles
• What is the relative mass and charge of protons?

  Mass: 1

  Charge: +1
• What is the relative mass and charge of neutrons?

  Mass: 1

  Charge: 0
• What is the relative mass and charge of electrons?

  Mass: 1/2000

  Charge: -1
• The nucleus is found at the center of an atom, it is made up of protons and neutrons
• Electrons form a series of shells around the nucelus
• The proton/atomic number is the number of protons in an atom
• The nucleon number is the total number of protons and neutrons
• Proton numbers are used to arrange the elements in the periodic table
• Hydrogen is the only atom with no neutron
• To find proton and electron number, do nucleon number - proton number
• Isotopes are atoms of the same elements

  Same number of protons, but different number of neutrons
• Chemical properties of an element depends on number of electrons on the outer shell

  Isotopes therefore have the same chemical properties
• Electrons are arranged in a shell around the nucleus in format 2, 8, 8, 1
• Valency electrons are the electrons in the outer shell that are involved in chemical bonding
• The number of electrons increasing in outer shell is called periodicity
• Group 1 elements have 1 elements on their outer shell

  They are highly reactive metals
• Group 1 elements are reactive as the outer electron goes further away from the nucleus, the attraction gets weaker and electrons is more easily lost