Yr 9 Topic 1 Chemistry Summary Notes PDF

TOPIC 1: RADIOACTIVITY (CHEMISTRY) Sub-topic: Periodic Table, Atoms, Ions Atoms  Atoms are the basic building blocks of matter  Made up of a small, dense nucleus surrounded by orbiting electrons  All everyday matter has mass and is made up of atoms. Structure of Atom (atomic...

TOPIC 1: RADIOACTIVITY (CHEMISTRY) Sub-topic: Periodic Table, Atoms, Ions Atoms  Atoms are the basic building blocks of matter  Made up of a small, dense nucleus surrounded by orbiting electrons  All everyday matter has mass and is made up of atoms. Structure of Atom (atomic structure)  Protons have a positive electric charge, are inside the nucleus and have a relative mass of 1.  Neutrons are neutral (no charge), are inside the nucleus and have a relative mass of 1.  Electrons have a negative electric charge, orbit around the nucleus in ‘electron shells’ and have a very small mass (1/1840 of the mass of a proton)  Useful video: https://www.youtube.com/watch?v=pNroKeV2fgk Elements  Element: A pure substance made up of only one type of atom  Element also refers to: a type of atom (with a particular number of protons)  Listed on the periodic table Atomic Number and Mass Number  Atomic Number = The number of protons (also determines the number of electrons in a neutral atom)  Mass Number = Number of protons + Number of neutrons (since electrons have very little mass)  Useful video: https://www.youtube.com/watch?v=4PU-2TWEp5E Compounds  Compound: A substance made up of two or more elements (types of atoms) combined in a fixed ratio/proportion  E.g. Water H20, sodium chloride NaCl (table salt), Iron Sulfide FeS, Copper sulfate CuS04  Can be broken down into elements by a chemical reaction Molecule  Two or more atoms bonded (joined) together in a small group  Elements OR compounds can form molecules  E.g. Nitrogen gas N2, Oxygen Gas 02, Water H20, carbon dioxide C02 Electron Configuration Diagram  Electrons are arranged in shells or orbits of different energy around the nucleus  Useful video: https://www.youtube.com/watch?app=desktop&v=hSkJzE2Vz_w  Neutral atoms have the same total number of electrons as protons (atomic number)  Electrons exist in shells around the nucleus o Electrons fill up the closest available shell to the nucleus first (lowest energy shells first) o 1st shell holds maximum 2 electrons o 2nd shell holds maximum 8 electrons o 3rd shell holds maximum 8 electrons Writing Electron Configuration  Number of electrons in each shells separated by commas,  For example: o Calcium has an electron configuration 2,8,8,2  2 electrons in 1st shell  8 electrons in 2nd shell  8 electrons in 3rd shell  2 electrons in 4th shell  (20 electrons overall – same as atomic number) Valence Shell  The outermost occupied shell of an atom is called the valence shell.  The electrons in the outmost shell are called valence electrons.  It is the transferring or sharing of valence elections that causes chemical bonds between atoms. Valency  The valency of an element is equal to the number of electrons that each atom needs to gain or lose (or share) to fill its outer shell. o Atoms want to gain or lose electrons to get a full outer shell (like Nobel gases) o Having a full outer shell is more stable The Periodic Table  Rows are called PERIODS  Columns are called GROUPS – elements in the same group have similar properties o Some groups have special names:  Group 1A = Alkali metals  Group 7A = Halogens  Group 8A = Nobel Gases  Metals are on the left of the zig-zag line o Shiny, malleable, conductors of electricity and heat, usually solid at room temperature  Non-metals are on the right of the zig-zag line o Can be solid, liquid or gas as room temperature, solid non-metals are dull, brittle, poor conductors of electricity and heat (insulators),  Semi-metals/metalloids near the zig-zag line o Some elements like Silicon and Germanium have properties of both metals and non-metals. Periodic table and electron configuration  The period an element is in tells you the number of electron shells it has.  The group an element is in tells you the number of valence electrons (number of electrons in outermost (valence) shell)  Useful video: https://www.youtube.com/watch?v=-qwDLW6fq8Q ‘Special’ Groups  Group 1A: Alkali metals: only one outer shell (valence) electron o Soft metals, they are very reactive (since they easily lose their one valence electron to have a full outer shell), react strongly with Halogens.  Group 2A: Alkali Earth metals: two valence electrons o Similar to Alkali metals, but slightly less reactive.  Group 7A: Halogens: seven valence electrons o Reactive non-metals (since they only need one electron to gain a full outer shell), brightly colours gases, liquids and solids. React strongly with Alkali metals.  Group 8A: Nobel Gases: have a full outer shell o All gases, very inert (non-reactive). Patterns in the periodic table  elements in the same group have similar properties, because they have the same number of outer shell (valence) electrons  Atomic radius is a measure of the size of an atom. o The smallest elements/atoms are at the top and large towards the bottom (more electron shells down a group) o Atomic radius decreases across a period (row) because the number of protons and electrons increases across a period, but the number of electron shells is the same. Therefore as you move across a period there is more electrostatic attraction between the positive nucleus and the orbiting electrons, making the atom smaller. Ions  Ions: Ions are atoms (or groups of atoms) that have lost or gained electrons, and therefore are positively or negatively charged  Atoms lose or gain electrons to get a full valence (outer) electron shell (becoming more stable)  Ions are written with the charge in the top right corner (1’s are not written) o E.g. sodium ion 𝑁𝑎+ , Calcium ion 𝐶𝑎2+ , Aluminium ion 𝐴𝑙 3+ , chloride ion 𝐶𝑙 − , oxide ion 𝑂2− , phosphide ion 𝑃3− o Use the valency table in an exam!!  Useful video https://www.youtube.com/watch?v=PCZtnbxtXqE (first 2:00 min only) Cation  An atom that has lost electrons is called a cation and has a positive charge (because it has more positive protons than negative electrons)  Example: A neutral Calcium atom (2,8,8,2) loses two electrons to get a full outer shell to form a calcium ion 𝐶𝑎2+ Anion  An atom that has gained electrons is called an anion and has a negative charge (because it has more negative electrons than positive protons)  Example: A neutral Chlorine atom (2,8,7) gains one electron to get a full outer shell to form a chloride ion 𝐶𝑙 − Ionic Bonding  Metal and non-metals often react, with electrons transferring from the metal to the non-metal to form cations and anions.  There is a force of electrostatic attraction between oppositely charged ions – this is called an ionic bond  Compounds formed from oppositely charged ions bonding together are called ionic compounds  https://www.youtube.com/watch?v=zpaHPXVR8WU Naming Anions in Ionic Compounds  Naming Anions – the last part of the element name is remove and replaced with “ide” o E.g. chlorine atom 𝐶𝑙 → chloride ion 𝐶𝑙 − o Fluorine atom 𝐹 → fluoride ion 𝐹 − o Sulfur atom 𝑆 → sulfide ion 𝑆 2− o Oxygen atom 𝑂 → oxide ion 𝑂2− o Nitrogen atom 𝑁 → nitride ion 𝑁 3− o Phosphate atom 𝑃 → phosphide ion 𝑃3− Sub-topic: Nuclear Radiation Isotopes  Isotope: An atom of a particular element that has a different number of neutrons (but same number of protons)  Useful video: https://www.youtube.com/watch?v=EboWeWmh5Pg  Isotope notation (below) Radioisotope  Radioisotope: A radioactive isotope with an unstable nucleus that will decay (give out radiation) to become more stable  A radioisotope usually has too many neutrons or too few neutrons.  Instability is due to an imbalance between the electrostatic repulsion between positive protons and the strong nuclear force holding the particles in the nucleus together.  Useful video: https://www.youtube.com/watch?v=IVtwfSBSLtI Radioactive decay  The process of an unstable nucleus releasing radiation.  Releasing radiation makes the atom’s nucleus more stable  For alpha and beta decay, the element changes into a new element (since the number of protons in the nucleus changes) Types of Nuclear Radiation (alpha, beta, gamma)  Useful video: https://www.youtube.com/watch?v=VeXpMijpazE Alpha Particles Beta Particles Gamma Rays What is it? (composition) A Helium nucleus A high energy electron Very short wavelength electromagnetic wave (2 protons and 2 neutrons) (electromagnetic radiation) Charge +2 -1 Zero Mass High (Mass number of 4) Small Zero Ionisation ability (how Comparatively High Medium Comparatively Low easily does it remove electrons from other matter?) Penetrating Power (how Low Medium High easily can it pass through materials) Half-life  Half life: The time taken for half the radioactive atoms in a sample to decay  Useful video: https://www.youtube.com/watch?v=IDkNlU7zKYU  The more unstable the nucleus of an atom is, the shorter the half-life. The more unstable a nucleus is, the more likely it is to decay. o Example, carbon-14 has a half-life of 5700 years. o If you had a 1 kg lump of carbon-14, after one half life of time, i.e. after 5700 years had passed, only 500 g would still be carbon-14. (The other 500 g would have decayed to form the stable isotope nitrogen-14) o After 11 400 years, or two half-lives of time, you would have only 250 g of carbon-14 and after 16 100 years only 125 g of the carbon-14 would be left (see below)  In the graph below, we can see the half-life of the radioactive element is 2 days, because it takes 2 days for the level of radiation to reduce to half the original value. (which means only half the sample has the original radioactive substance) Ionising radiation  Ionising radiation: radiation that can knock electrons off atoms, turning them into ions.  Alpha particles, beta particles, Gamma rays (also Ultraviolet waves & X-Rays) are types of ionising radiation  Ionising living tissue, especially the DNA inside cells, can lead to cancer / mutations in cells  People need to limit exposure to ionising radiation Background Radiation  A constant very low-level of ionising radiation that surrounds us and is harmless  Sources include the Sun, cosmic rays, radioisotopes in the air you breathe, rocks, bricks/granite in houses, certain elements in food e.g. radioactive potassium in bananas PERIODIC TABLE – this is the version you will get in an exam