C1 Revision

C1 Revision:

States of Matter:  States of matter depend on the forces between particles.  Solids:  There are strong forces of attraction between particles. This means they are in a fixed, vibrating position in a regular arrangement.  Particles do not move from their positions. This means that all solids keep shape and volume and do not flow.  The hotter a solid becomes, the more they vibrate.  If you heat the solid, eventually it will melt into a liquid.  Liquids:  Some forces of attraction between particles. They’re free to move past each other but they stick together.  Don’t keep a definite shape and will take the shape of any container that they are placed into. They do keep the same volume.  Particles are constantly moving with random motion. The hotter the liquid is, the faster they move.  If you cool a liquid, it will freeze to become a solid. If you boil a liquid, it evaporates.  Gases:  Almost no forces of attraction between particles. They’re free to move, travelling in straight lines and only interacting when they collide.  Don’t keep a shape or volume and will always fill any container. When the particles bounce off the walls of a container, they exert pressure.  Particles move constantly with random motion. They hotter it gets, the faster they move. Pressure increases as heat increases.  If you cool a gas, it will condense into a liquid.    Limitations of the particle model:  Lacks sizing accuracy.  Does not show space between particles.  Doesn’t show any forces between the particles or how strong they are.    How are atoms rearranged in chemical reactions?  When a substance changes matter, it’s a physical change since no new substances are made and it is reversible.  During a chemical reaction, bonds between atoms break and the atoms change places - the atoms you start off with (reactants) rearrange themselves to form different chemicals (products). These are hard to reverse. 

The History of the Atom:  Atoms are the tiny particles of matter which make up everything in the universe!  Firstly, Dalton described atoms as solid spheres and said that different spheres made up different elements.  Next, J J Thomson concluded that atoms weren’t, in fact, solid spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons! The new theory was known as they ‘plum pudding model’.  After this, Rutherford (with Geiger and Marsden) conducted the gold foil experiment. They fired positively charged alpha particles at an extremely thin sheet of gold. Using the plum pudding model, they expected most particles to pass through. However, whilst most of the particles did go straight through, some were deflected more than expects and a small number were deflected backwards! Rutherford came up with the theory of the nuclear atom. This means that there’s a tiny, positively charged nucleus at the centre, surrounded by a cloud of negative electrons. He discovered that most of the atom is empty space.  Finally, Bohr realised that clouds of electrons would cause the atom to collapse. Bohr proposed a new model in which all the atoms were contained in shells. Bohr suggested that electrons can only exist in fixed orbits or shells. Each shell has a fixed energy. His theory was supported by many.  Evidence:  These different ideas of the atomic model were accepted due to suffice amount of evidence.  As scientists did more experiments, new evidence was found and our theory of the structure of the atom was modified to fit it.  Scientists also put their ideas up for peer review, meaning that everyone gets a chance to see the new ideas, check for errors and then other scientists can use it to help to develop their own work. 

The Atom:  The atom is made up of protons, neutrons and electrons - the subatomic particles.  Protons are heavy and positively charged: mass = 1, charge = +1  Neutrons are heavy and neutral: mass = 1, charge = 0  Electrons have hardly any mass and are negatively charged: mass = 0.0005, charge = -1  The Nucleus:  The nucleus is in the middle of the atom and contains protons and neutrons.  It has a positive charge because of the protons.  Almost the whole mass of the atom is concentrated in the nucleus.  Compared to the normal size of an atom, the nucleus is tiny!  The Electrons:  Electrons move around the nucleus in electron shells and are negatively charged with virtually no mass!  They are tiny but their orbits cover a lot of space.  The volume of their shells determine the size of the atoms.  Do molecules form when atoms are bonded together?  Yes! Molecules are made up of two or more atoms. They can be made from the same element or different elements.  Simple molecules are tiny. The bonds that form between these molecules are generally a similar length to the atomic radius - 10^-10 m. 

Atoms, Ions and Isotopes:  Mass number = total number of protons and neutrons (bigger number).  Atomic number = number of protons (smaller number).  Atoms of the same element all have the same number of protons, so atoms of a different element will have different numbers of protons. To get the number of protons, just subtract the atomic number from the mass number.  Neutral atoms have no charge overall because they have the same number of protons and electrons. The charge on the electrons is the same size as the charge of the protons, but opposite so the charges cancel each other out.    Ions:  Ions have different numbers of protons and electrons. They form when atoms gain or lose electrons.  Negative ions form when atoms gain electrons - they have more electrons than protons.  Positive ions form when atoms lose electrons - they have more protons than electrons.  E.g. F- : there’s a single negative charge, so there must be one more electron than protons. F has an atomic number of 9, so has 9 protons. So F- must have 10 electrons.  Fe2+ : There’s a double positive charge, so there must be two more protons than electrons. Fe has an atomic number of 26, so have 26 protons. So Fe2+ must have 24 electrons.    Isotopes:  Isotopes have a different number of neutrons. They have the same atomic number but a different mass number. If they had different atomic numbers, they would be a different element!  E.g. Carbon-12: 6 protons, 6 electrons, 6 neutrons… Carbon-13: 6 protons, 6 electrons, 7 neutrons… Carbon-11: 6 protons, 6 electrons, 5 neutrons etc.  Relative Atomic Mass = sum of (isotope abundance x isotope mass number)/sum of abundances of all the the isotopes