atoms, elements and compounds

• What is the smallest part of an element that can exist?

  An atom
• What are the tiny particles that make up all substances called?

  Atoms
• How are atoms of each element represented?

  By their own chemical symbol
• What does a chemical symbol consist of?

  One or two letters
• How does a chemical symbol start?

  With a capital letter
• What does the symbol 'O' represent?

  An atom of oxygen
• What is the correct chemical symbol for sodium?

  Na
• Why must sodium be written as Na and not NA, na, or nA?

  Because chemical symbols must start with a capital letter and any other letter in lower case
• What is a chemical formula used for?

  To represent an element or compound in balanced chemical equations
• What is the formula for most elements?

  Its chemical symbol
• What is the chemical symbol for helium?

  He
• What is the chemical symbol for carbon?

  C
• Which elements exist as molecules made up of two atoms joined together?

  Non-metal elements
• How are the formulae of diatomic non-metal elements represented?

  By the element's symbol followed by a subscripted '2'
• What is the chemical formula for iodine?

  I2
• What mnemonic can be used to remember certain diatomic elements?

  IBring Clay For Our New House
• What is a compound?

  A substance that contains two or more elements that are chemically combined
• How are the elements in a compound present?

  In fixed proportions
• What is the chemical formula for carbon dioxide?

  CO2
• What does a chemical formula show about a compound?

  The symbols for each element and the number of atoms of each element
• What is the formula for magnesium oxide?

  MgO
• What does the subscript number in a formula indicate?

  If there is more than one atom of an element
• What are some examples of compounds and their formulae?

  • Sodium chloride: NaCl
  • Potassium bromide: KBr
  • Magnesium iodide: MgI2
  • Carbon dioxide: CO2
  • Carbon monoxide: CO
  • Sulfur trioxide: SO3
  • Water: H2O
  • Ammonia: NH3
  • Methane: CH4
• How can compounds be formed?

  From their elements in chemical reactions
• What is an ion?

  A charged particle formed when an atom or group of atoms loses or gains electrons
• How are the electrical charges of ions shown?

  In superscript text
• What are the names and formulae of some common ions?

  • Sodium: Na+ (One positive)
  • Magnesium: Mg2+ (Two positive)
  • Chloride: Cl- (One negative)
  • Oxide: O2- (Two negative)
• How can the formula of an ionic compound be predicted?

  Using the formulae of its ions
• What must the numbers of ions in a formula provide?

  An equal number of positive and negative charges
• What is the format of a word equation?

  • Reactants → Products
  • A + sign separates two or more reactants or products
• What are reactants in a chemical reaction?

  Substances that react together
• What happens to atoms or ions in reactants during a chemical reaction?

  They separate and join back together in a different way
• What is the word equation for the reaction of potassium hydroxide with sulfuric acid?

  Potassium hydroxide + Sulfuric acid → Potassium sulfate + Water
• What does the arrow in a chemical equation represent?

  It means 'reacts to make'
• What is a balanced chemical equation?

  It represents a chemical reaction using the formulae of the reactants and products
• What do state symbols in balanced chemical equations indicate?

  The physical state of that substance
• What are the state symbols and their meanings?

  • (s): Solid
  • (l): Liquid
  • (g): Gas
  • (aq): Aqueous solution
• What does the law of conservation of mass state?

  No atoms are lost or made during a chemical reaction
• What must a balanced symbol equation have?

  The same number of atoms of each element on both sides of the arrow
• How do you balance a chemical equation?

  Add numbers to the left of one or more formulae