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Chemistry (P1 & P2)
Key Concepts in Chemistry
| Question | Answer |
|---|---|
| What was Dalton's model of an atom? (3) | - All substances are made of atoms, they are small particles that cannot be created, divided or destroyed - Atoms of the same element are exactly alike - Atoms join with other atoms to make new substances |
| What did J.J Thomson do that proved Dalton wrong? | Cathode-ray tube for an experiment and discovered atoms can be divided in to smaller parts. |
| How did Thomson know the particles were negatively charged? | The beam moved from the negatively charged plate to the positively charged plate |
| What was Thomsons plum-pudding model? | Atom model in which negative electrons are scattered throughout soft blobs of positively charged material. |
| What did Rutherford do in his experiment and what happened? | Shot beam of positively charged particles into a sheet of gold foil, some particles continued in a straight line, some bounced back and some went to the sides |
| What did Rutherford's new model of the atom say? | Most of the atom's mass is found in a region in the centre called the nucleus |
| What is in Rutherford's model? | The atom is mostly empty space and electrons travel in random paths around the nucleus |
| Describe the structure of an atom. | A nucleus containing protons and neutrons surrounded by electrons in shells |
| What is the relative charge of a proton, neutron and electron? | +1, 0 and -1 |
| What is the relative mass of a proton, neutron and electron? | 1, 1 and negligible |
| Explain why atoms contain an equal number of protons and electrons. | Atoms are neutral and charge on proton is +1 and electron -1, so charges cancel |
| Describe the nucleus of an atom. | Very small compared to the overall size of the atom |
| Where is most of the mass of an atom concentrated in? | The Nucleus |
| What are isotopes? | Different atoms of the same element with the same number of protons but different number of neutrons in their nuclei |
| How do you calculate RAM? | (Percentage x Mass number) + (Percentage x Mass number) / 100 |
| How did Mendeleev arrange elements in the periodic table? | Ordered his table in order of atomic mass, and left gaps for elements he thought hadn't been discovered yet |
| Describe how Mendeleev used his table to predict the existence and properties of some elements not then discovered. | He realised elements with similar properties belonged in the same groups, elements with properties predicted by mendeleev were later discovered and filled the gaps |
| Why was Mendeleev's order not true? | Because of isotopes of the same element |
| How is the periodic table set up in terms of atomic number? | Elements arranged in order of atomic number and so that elements with similar properties are in columns (groups) |
| Why do elements in the same group have similar properties? | They have the same amount of electrons in the outer shell |
| What are rows called in the periodic table and how are they ordered? | Periods, increasing atomic number |
| What are metals in the periodic table? | Elements that react to form positive ions (most elements to the left) |
| What are non-metals in the periodic table? | Elements that do not form positive ions (small amount on the right) |
| Explain how the electronic configuration of an element is related to its position in the periodic table. | Elements in groups represent how many electrons in outer shell (eg. group 2, 2 electrons), Elements in periods represent the last shell the element has (eg. Period 3 has its outer shell in the 3rd) |
| How does ionic bonding work with metals and non-metals? | Electrons in the outer shell of the metal atom are transferred |
| What are positively charged atoms called? | Cations |
| What are negatively charged atoms called? | Anions |
| What is an ion? | An atom or group of atoms with a positive or negative charge |
| How do we work out number of electrons in an ion? | Work out what it would've been first and then subtract electrons lost or add electrons gained |
| Explain the formation of ions in ionic compounds from their atoms, limited to compounds of elements in groups 1, 2, 6 and 7 | Ions produced by metals in Group 1 and 2 and by non-metals in 6 and 7 have the electronic structure of a noble gas (group 0) |
| What does "ide" mean at the end of a compound? | Negatively charged and has 2 elements, one nonmetal |
| What does "ate" mean at the end of a compound? | Negatively charged and has 3 elements, one of which oxygen |
| What doe "oxide" involve? | O (2-) |
| What does "hydroxide" involve? | OH(-) |
| What does "halide" involve? | -1 halide ion |
| What doe "Nitrate" involve? | NO3 (1-) |
| What doe "Carbonate" involve? | CO3 (2-) |
| What doe "Sulfate" involve? | SO4(2-) |
| Explain the structure of an ionic compound. | Lattice structure, consisting of a regular arrangement of ions held by strong electrostatic forces between oppositely-charged ions |
| How is a covalent bond formed? | When 2 atoms share a pair of electrons |
| What does covalent bonding result in? | The formation of molecules |
| Recall the typical size (order of magnitude) of atoms and small molecules | Simple molecular substances consist of molecules in which the atoms are joined by strong covalent bonds, therefore atoms are smaller than small molecules |
| Describe the melting and boiling points of ionic compounds. | High because a lot of energy is required to break the strong bonds |
| What happens when ionic compounds are melted or dissolved in water? | They conduct electricity because the ions are free to move and carry current |
| Describe the melting and boiling points of simple molecular compounds. | Low, made of non-metals |
| What happens when simple molecular compounds are melted or dissolved in water? | The weak intermolecular forces are broken, not covalent |
| How is the electricity in these? | They don't conduct it, although some breakdown in water to form ions which do |
| What are giant covalent structures made from and how is the melting point? | Nonmetal elements and solids with very high melting point |
| Can they conduct electricity and what is required to melt them? | Some can and the covalent bonds have to be overcome |
| What do metals consist of? | Giant structures of atoms arranged regularly, the electrons in the outer shell are delocalised |
| What allows metals to be bent and shaped? | The layers of atoms being able to slide over each other |
| For ionic compounds what do strong electrostatic forces allow? | High melting and boiling points |
| For ionic compounds what do movable ions allow? | Ability to conduct electricity when molten/dissolved |
| For ionic compounds what do fixed ions not allow? | Electricity when solid |
| What are graphite and diamond? (2) | Different forms of carbon and they are giant covalent substances |
| Explain the structure of diamond. | Each carbon is joined to 4 other carbons covalently, Very hard, high melting point and doesn't conduct electricity |
| Explain the structure of graphite. |
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