Chapter 1 - Atomic Structure
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What are all substances made out of?
Atoms.
Define an element.
• A substance made from 1 type of atom.
Define an element.
• A substance made from 1 type of atom.
Define a compound.
• Substances made up of 2 or more types of atom.
State the definition of a molecule.
• A substance made up of 2 or more atoms chemically bonded together.
Describe the basic structure of the atom.
• Nucleus in the centre made up of neutrons and protons. • Surrounded by electrons orbiting in shells.
What is the Law of Conservation of Mass?
• The total mass of the products formed in the reaction = The total mass of the reactants.
Why do chemical equations need to be balanced?
• This is because atoms cannot be created or destroyed in a reaction.
Give all 4 of the state symbols used in equations.
(s) - Solid (l) - Liquid (g) - Gas (aq) - Aqueous Solution
Balance the equation: KNO3 —–> KNO2 + O2
2KNO3 ——-> 2KNO2 + O2
Balance the equation: Fe2O3 + CO ——> Fe + CO2
Fe2O3 + 3CO ——-> 2Fe + 3CO2
Define the word mixture.
• A mixture is made up of 2 or more substances not chemically combined.
Give 4 methods that can be used to separate mixtures.
• Filtration • Crystallisation • Distillation • Chromatography
Explain how a student could use distillation to obtain a pure salt and it’s solution from sea water. [4]
• Sea water is heated to evaporate the solvent. [1] • Water vapour enters liebig condenser. [1] • Hot vapour is cooled and condensed into a liquid collected in a beaker. [1] • Pure salt remains in the flask. [1]
Explain a method to carry out paper chromatography.
• Use a tube to dab a spot of the solution on a pencil line drawn at the bottom. [1] • Place the paper standing in a solvent in a beaker. [1] • Solubility of the components of the mixture determines how far up the paper it will travel. [1] • The higher the solvent has travelled, the more soluble a substance is. [1]
Describe the “Plum Pudding” model by J.J Thomson. State which sub-atomic particle he discovered.
• Sphere of positive charge with negative electrons dotted around the sphere. • Electrons.
How did Rutherford test Thomson’s plum pudding model?
• He fired positively charged alpha particles at a thin sheet of gold foil. Some particles passed through, but some bounced off in different directions and some rebounded, proving Thomson’s model wrong.
Why did Bohr challenge Rutherford’s nuclear model?
• If the nucleus was positive and the electrons in the shells were negative, the whole atom would collapse inwards, proving Rutherford’s model wrong.
How do you calculate the number of neutrons in an element?
Number of neutrons = mass number - atomic number.
State the relative charges and masses for the 3 sub-atomic particles.
Protons have +1 charge and relative mass of 1 Neutrons have 0 charge and relative mass of 1 Electrons have -1 charge and relative mass of 1/2000
What is the atomic number?
• Number of protons in each atom of an element.
What is an ion?
• A positive or negative charged atom.
What is an isotope?
• Atoms of the same element with different number of neutrons and same number of protons.
Sodium (Na) has a mass number of 23 and a atomic number of 11. Work out the number of protons, neutrons and electrons in sodium.
• 11 protons • (23-11) 12 neutrons • 11 electrons