Na Atomic Structure What do those numbers mean? Atoms are made up of smaller particles called protons, neutrons and electrons. Electrons (which have a negative charge) travel in orbits called shells around the nucleus. The nucleus contains protons (which have a positive charge) and neutrons (which have no charge) 1. Can you think why atoms always have the same amount of electrons as protons? Each element is made up of different sized atoms. Large atoms e.g. iron atoms have lots of protons, neutrons and electrons. 2. Explain why hydrogen is a light gas but iron is a heavy solid. What do those numbers mean? On the periodic table there are some numbers next to every element. These are important as they tell us how large the atom is. The mass number is the number of protons + neutrons in the atom. The atomic number is the number of protons (or electrons) in the atom. 23 Na 11 The atoms of which element have: a) 19 protons b) 35 electrons c) 2 neutrons d)201 particles in the nucleus?

How to draw atoms It has 3 electron shells. Shell 1 can only hold up to 2 electrons. Once that is full up you move onto… Shell2 which can hold up to 8 electrons. Once that is full up you move onto… Shell 3 which can also hold 8 electrons but as there is only one left in sodium so it sits all alone on shell 3. This is a sodium atom (Na). It has 11 protons and 12 neutrons in the nucleus. Na 11p 12n 4. Now try drawing the following atoms in your books: a) Hydrogen b) Lithium c) Oxygen d) Neon e) Calcium f) Chlorine Questions to make you think! (Hints are at the bottom of the page) Electrical current is the flow of electrons through a conductor. Using atomic structure explain why calcium is a good conductor and oxygen is a poor conductor. Elements can react together to form compounds (the salt you use on your chips is a compound of sodium (a metal) and chlorine (a non-metal)). When a metal reacts it gives away electrons. When non-metals react they take electrons. The more reactive an atom is the more easily it can give these electrons away or steal them from another atom. Explain why the more reactive metals are found near the bottom of the periodic table whilst the more reactive non-metals are found at the top of the table. 7. Elements react together because they like to have a full outer shell of electrons. Explain why group 8 in the periodic table (last column on the right) is full of very un-reactive elements. If you could do number 6 you should have no problems here!. Opposites attract! Think magnets - this attraction decreases with distance For the electrons to flow they have to become detached from the atoms.